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Message started by IslandRoad on 02/01/17 at 23:33:42

Title: What else causes surging?
Post by IslandRoad on 02/01/17 at 23:33:42

Hi guys,

I've hit a bit of a dead-end with troubleshooting a surging issue with my S40. I was wondering if anyone could shed some light or point me in the right direction. I'm working through the basic mods on the site but just can't nail this surging thing. The bike is a couple of years old and has done 4800 km (2990 miles)

I installed a Dyna muffler and experimented with the jets until I settled on 52.5/152.5 and spacer at 50% (2 brass washers). I had a spell of about a week where it ran really well - smooth and strong all the way through the throttle, and impressive top speed. It was a joy to ride.

Then one day I ran the fuel too low and had to switch to reserve (on the stock petcock). I had a raptor on order at the time because my vac line was leaking fuel. When I filled her up and took off, the surging started again. I have since installed the raptor. The bike no longer smells like fuel when stationary but the surging continues at low speeds in low gears.

In desperation, I upped the pilot jet to 55 and reduced the spacer to 25% in an attempt to resolve the problem. The surging continued and the performance dropped at the wide end of the throttle, and I couldn't hit the same top speed. It also felt like it was running rich, especially at open throttle. So I think I've hit the limit of the jets and will return to 52.5/152.5 and 50% spacer.

A couple of things that might be relevant:

1: I am running the stock air filter

2: Whenever I take the bottom of the carb off there is a tiny amount of black "dust" settled in the lowest point of the float bowl.

3: The washers I used for the spacers where originally too big on the outside diameter. I filed them down to fit. They now actually have a smaller OD than the original spacer.

Any ideas on what might be going on?

Title: Re: What else causes surging?
Post by Dave on 02/02/17 at 04:02:20

You could have an air leak somewhere. At the bottom of your page it shows the bike is a 2014, and that is a bit too new for the intake boot to be cracked and brittle - but an air leak in that area can cause the mixture to go lean and cause surging. Is the rubber plug you put on the vacuum cap in good shape?

Have you checked your float level?

Black goo could be an indication your fuel line is decomposing.....and that can plug a pilot jet up really quickly. Or the place you buy gasoline is selling you contaminated fuel.

Title: Re: What else causes surging?
Post by Ruttly on 02/02/17 at 04:17:44

Lean mixture or a vaccuum leak

Title: Re: What else causes surging?
Post by Steve H on 02/02/17 at 04:19:32

The tiny little o-ring is still on the needle?

Title: Re: What else causes surging?
Post by Dave on 02/02/17 at 04:58:08

302B72717077757A430 wrote:

The tiny little o-ring is still on the needle?

Idle fuel mixture screw............

Title: Re: What else causes surging?
Post by Gary_in_NJ on 02/02/17 at 05:10:41

If you suspect a vac leak, with the engine running you can spray the carb and carb boot a listen for a change in rpm. if the rpm increases you have found the source of the leak.

You mention some black crud at the bottom of the fuel bowl. You may have a clogged jet or passage in the carb. Also, if you are running a fuel filter, have a look at it to ensure that it hasn't become a restriction. When you swap out the fuel valve for the Rapter unit, pour the fuel into a clear container our pour it through a coffee filter to see if there is something floating in your tank that could be causing a restriction.

Title: Re: What else causes surging?
Post by stewmills on 02/02/17 at 06:36:29

Also, if you fiddled with the plunger that holds the needle (and you had to in order to adjust the needle) you need to make sure that:

a) you put the metal tab back in there properly with the holes lined up and if I recall correctly, the little dimple down. You should be able to see directly through the bottom through the two little holes once it is screwed in.

b) you didn't damage the plunger. If you cleaned it with anything caustic it could be the little debris that you see floating in the bowl, but I doubt it as I am not sure how that kid of debris could get down in the bowl.

c) make sure your plunger didn't get marred on the sides. If you put it in a vise or something like that to hold it wile you worked on it, that is a bad idea as any little marring will create a catch point and not allow the slide to "slide" smoothly. If it can't slide up properly when you nail the throttle, it isn't letting enough fuel in.

d) as others noted, make sure you don't have crap in your tank or failing fuel line, etc. If you never get to reserve you may never be getting down to the bottom of the tank and getting any of the debris that may be settled down there and when you hit reserve recently you picked some of it up.

Good luck!

Title: Re: What else causes surging?
Post by justin_o_guy2 on 02/02/17 at 08:58:54

installed a Dyna muffler and experimented with the jets until I settled on 52.5/152.5 and spacer at 50% (2 brass washers). I had a spell of about a week where it ran really well - smooth and strong all the way through the throttle, and impressive top speed. It was a joy to ride.

How does running out of gas, hitting a tree, dropping the bike, Change your air/fuel ratio?
If it Ran Good with the Wrong Jets in it for a week, can you explain Why?
If it's Running Right for a week, and something happens, and now the jetting is wrong, only something that changed how much gas per unit of air passes through could have done that.

I'd put the jets in that gave you good performance. As stated, the fuel line may be disintegrating,
Surging Is a subjective word. What speed, what throttle setting, what gear, so the carb geniuses will know what circuits in the carb are agrieving you.

The petcock can shad rubber, fuel line, too.
The Raptor and a new fuel line, put the jets back that gave you good results.
The washers are a smaller diameter.
How much smaller?
Did it run good with them in the carb?
If so, why would that change?

Title: Re: What else causes surging?
Post by IslandRoad on 02/02/17 at 12:53:08

Thanks heaps for the responses guys. There are a couple of avenues in there that sound promising.

Dave, I'll check the air intake. The vac cap is brand new and fits very snug. The fuel line idea is really interesting. The dust in the carb is definitely black. I reckon it could be little bits of black rubber from the fuel line.

Ruttly, I'm pretty sure about the fuel mix in terms of the jets. So that does lean it toward an issue with air.

Dave, I didn't know there was an o-ring on the idle mix screw. I've never had it all the way out before. I'll keep that in mind.

Gary, I've already changed to the raptor. I didn't inspect the fuel thoroughly, but it was fresh fuel and I have a pretty fine filter on the funnel I use when filling the bike. However I'll check the fuel as part of the torubleshooting. When you say "spray the carb", what do you mean? What do I spray it with?

Stew, that's a really good point about the diaphragm tube. I didn't damage it, but due to my inexperience, I didn't clean particularly carefully. I didn't even realise unti now that that tube slides up and down. I'll take care of that. As for the diaphragm itself, I wass very careful in getting that out (and in putting it back in). I also made sure the rubber was seated properly between the top of the carb and the carb body. That piece goes in and out very easily.

Justin, Yeah, I was thinking the same as you. The jets were working well for a week. It went off again after I ran on reserve. I figured it probably wasn't the jets but just wanted to try something (I had been meaning to test higher jets anyway, as part of my learning). As I mentioned I hit the upper level and started to drop the performance. So at least I know where the limit of the jets is now :)

Yes, 'surging' is subjective. It comes on in second and third gear in the 1/8 - 1/4 throttle range. Everything else runs great. It feels they way it feels when I'm riding into a moderate swirling headwind. The bike feels like it's being held up ever so slightly in short irregular bursts. Based on all my reading on here, that points to the spacer mod (which I have done, and had working). I think you're correct - it's something else.

As for the washer OD size, I haven't measured them but they are definitely smaller than the spacer, and slightly irregular circumference. I thought maybe that was creating some sideways play in the needle.

Title: Re: What else causes surging?
Post by IslandRoad on 02/02/17 at 13:02:04

One more question, There's a plastic tube with a lip on it that guides the large spring in the carb diaphragm. I'm almost certain when I first opened the carb, the plastic tube was in the bottom of the diaphragm tube, with the lip at the bottom. However when I'm reassembling it, it looks to me as though it should be at the top so that the lip on the plastic tube is pressing up onto the lid of the carb, and the spring is seated in the bottom of the diaphragm.

In short, which way does this white tube go in the carb? Lip down, into the tube with spring over it, or spring in first then the tube down the middle with the lip on top?

Title: Re: What else causes surging?
Post by Gary_in_NJ on 02/02/17 at 13:33:19

5268777A757F49747A7F1B0 wrote:
Gary When you say "spray the carb", what do you mean? What do I spray it with?

Use a standard carb cleaner. In the US we have a product called Gum-Out

Title: Re: What else causes surging?
Post by IslandRoad on 02/02/17 at 13:35:54

Thanks :)

Title: Re: What else causes surging?
Post by Dave on 02/02/17 at 13:36:24

I don't know what "white tube" you are talking about?

http://i64.tinypic.com/ws4l53.jpg

Title: Re: What else causes surging?
Post by IslandRoad on 02/02/17 at 13:51:15

Hi Dave, The photo I posted is cut off at the bottom. If you scroll it up you can see the spring and the tube. Or click the link to see the full sized version.

I had previously checked the image you posted and couldn't find the tube either.

Title: Re: What else causes surging?
Post by Dave on 02/02/17 at 14:02:45

I have never seen that tube in any carb I have worked on....must be a non-US thingy.

I would most likely mount it at the top of the spring so that it is stationary - if you mounted it at the bottom it would move up/down with the slide.

Title: Re: What else causes surging?
Post by stewmills on 02/02/17 at 14:11:15

Yeah, that white tube is odd. One would think that it the white tube is inside the slide that it is extra weight trying to raise up, and I would also say that it should be up top.

Now since it is all under spring pressure you might think that where it is will have no effect on the slide being able to raise up, but it doesn't take much of a vacuum to raise the slide and IMHO every little once counts.

Title: Re: What else causes surging?
Post by IslandRoad on 02/02/17 at 14:11:32

That's what I was thinking. Also, when placed at the bottom it wobbles on the heads of the screws. It seats nicely into the underside of the cap.

Interesting that you've never seen one. Maybe it is an Aus thing. If all else fails, I'll try leaving it out and see if it changes anything.

I've never seen one in any videos of carb cleaning/rebuilding etc.

Title: Re: What else causes surging?
Post by IslandRoad on 02/02/17 at 14:14:55

Hi Stew,

I was just replying to Dave when I saw your reply. I thought the same thing. It just looks like weight to me.

I don't know enough about how the vac carb works to make an educated guess, but intuitively, it seems to me that if it's adding a little bit of weight then that might affect the slide at low throttle, if that requires a very small lift in the slide - I'm just guessing though.

66617062787C797966150 wrote:

Title: Re: What else causes surging?
Post by IslandRoad on 02/02/17 at 14:16:13

I think I'm gonna do that first - spray the carb, leave out the plastic tube and see what I get.

Title: Re: What else causes surging?
Post by stewmills on 02/02/17 at 14:27:20

I bet you will be doing this by tomorrow ; 8-)

Title: Re: What else causes surging?
Post by IslandRoad on 02/02/17 at 14:49:40

Haha ... never!

Title: Re: What else causes surging?
Post by Kris01 on 02/02/17 at 16:42:38

I'll 2nd that. I've never seen that tube either.

Would the bike surge with a bad petcock? Maybe the float can't keep up or the petcock is slightly plugged? Just throwing out ideas.

Title: Re: What else causes surging?
Post by IslandRoad on 02/02/17 at 16:52:12

I thought the same and, on inspection, the stock petcock was leaking fuel into the vac line. I swapped it out for a Raptor the other day. Bike still surges, but at least I know the Petcock is stable.

053C273D7E7F4E0 wrote:

I'll 2nd that. I've never seen that tube either.

Would the bike surge with a bad petcock? Maybe the float can't keep up or the petcock is slightly plugged? Just throwing out ideas.

Title: Re: What else causes surging?
Post by Dave on 02/02/17 at 17:57:35

6B6C7D6F757174746B180 wrote:

I bet you will be doing this by tomorrow ; 8-)

I bet I won't be doing that tomorrow.....or any other day! :o

Title: Re: What else causes surging?
Post by batman on 02/02/17 at 18:09:42

I'm wondering if this isn't an attempt to limit the slide from opening fully,(a governor ?) I'd reassemble the carb with and without the tube an check the travel on the slide if it is shorter with the tube I'd toss it! believe us we've never seen anything inside the spring in our carbs,this is a first!

Title: Re: What else causes surging?
Post by Kris01 on 02/02/17 at 18:28:23

If it works without the tube in the northern hemisphere then I'd assume it would work the same way south of the equator. ;)

Title: Re: What else causes surging?
Post by twhitus on 02/03/17 at 05:42:11

ive seen those tubes before on scooters which have similar carbs. They are used as a way to limit how much the slide can move and sort of a hp/throttle/speed limiter. first thing we did was remove them.

Title: Re: What else causes surging?
Post by Dave on 02/03/17 at 05:55:31

16150A0B161711620 wrote:

Some countries have controls on size/HP for certain tax classes....I wonder if this tube restricts how far the slide can open in order to limit the HP or top speed of the bike?

Put the spacer in the carb, then use your finger to open the slide and see how far it will rise in the venturi. If it won't go all the way up.....get rid of it!

Title: Re: What else causes surging?
Post by stewmills on 02/03/17 at 08:46:50

I'll 3rd, or 4th that. I'd say scrap the tube (it tests go well) as it does sound like just a HP limiter that would restrict the slide. Maybe you can use it to make a kaleidoscope for your kids or something ;D?

Title: Re: What else causes surging?
Post by justin_o_guy2 on 02/03/17 at 12:26:43

Are you Hunting for a throttle setting that you can feel a surge in or, in the Normal course of riding, you're bothered by a noticeable surging?

Title: Re: What else causes surging?
Post by verslagen1 on 02/03/17 at 12:38:54

It may be a 'lerner' type thing. I'd say toss it.

seated on the bottom, it's just extra weight and may slow the response a little.
seated at the top, it'll reduce the diaphragm area (although open around the spring) and will reduce the amount/speed that it goes up.
Or it may just be long enough to keep from fully opening.

Title: Re: What else causes surging?
Post by justin_o_guy2 on 02/03/17 at 12:48:48

And it could be allowing the spring to catch on the tube, causing the slide to pause, then pop loose and jump.

Title: Re: What else causes surging?
Post by IslandRoad on 02/03/17 at 18:59:03

You might be onto something guys,

In Australia we have a classification called Learner Approved Motorcycles (LAMS). New riders have to ride a LAMS bike for the first three years. The specs for LAMS include; no bigger than a 660cc, and a certain power/weight ratio. Sometimes, manufacturers restrict the throttle to come in under the specs. The S40 is classified as LAMS.

It's a beautiful sunny Saturday afternoon here, so I'm going to spend a couple of hours experimenting with the carb setup. I'll begin by removing the tube and see how she rides :)

0E35382F3E32292F343C312E5D0 wrote:

[quote author=16150A0B161711620 link=1486020822/15#26 date=1486129331]ive seen those tubes before on scooters which have similar carbs. They are used as a way to limit how much the slide can move and sort of a hp/throttle/speed limiter. first thing we did was remove them.

Title: Re: What else causes surging?
Post by IslandRoad on 02/03/17 at 19:55:46

Justin, I'm bothered by the surging in normal riding. It affects the way I 'read' the bike. Normally when the surging gets my attention, I at first think the road surface has changed, then I think about my fuel level (am I getting low?), are my wheels loose?, then I realise it's the bike surging. It's very distracting.

Having said that, when I'm tuning and test-riding, I pay close attention, looking for the exact conditions that correlate to the problem. If I get close to a solution, I forget about tuning for a while and run the bike as per my normal riding. I find out soon enough if it's been sorted out.

4C5355524F4879497941535F14260 wrote:

Are you Hunting for a throttle setting that you can feel a surge in or, in the Normal course of riding, you're bothered by a noticeable surging?

Title: Re: What else causes surging?
Post by justin_o_guy2 on 02/03/17 at 20:05:36

If it's like that, yeah, worth hunting down.. wish you luck.

Title: Re: What else causes surging?
Post by IslandRoad on 02/04/17 at 00:17:24

Well, it's been an interesting afternoon!

I tested the bike without that plastic tube inside the large spring in the carb slide.

I reckon that tube is a limiter, as some of you have suggested. And I reckon it's there to get the bike into the LAMS classification here in Australia.

Without the tube in there the bike had considerably stronger acceleration on full throttle, and it added about 10 kph to the top speed the bike could hit. Having the tach installed was handy. I reckon the bike was able to rev higher as well. (I had to hang on a little more when I opened up the throttle).

I reckon that limiter would mess with road testing for the main jet, because it prevents the bike from reaching full open throttle. I'm speculating a bit there.

As for the tuning, I did two things. I would have done them one at a time so I knew what was going on, but I've had the tank off that many times in the last couple of weeks so I just wanted to get done.

1. I had the bottom and top of the carb off while the carb was still in the bike. I doused what ever I could reach with carb cleaner. I hate to confess this, but as a newbie, I had previously done the spacer mod and re-jetting without realising the need to ensure everything was really clean after handling the needle, slide etc.

2. I sourced some stainless steel washers with an outside diameter that fits nicely down the hole where the spacer sits. Previously, I was using modified brass washers which left a bit of play on the sides. I wondered if that play may have caused the needle to not sit exactly vertical while lifting.

One of those two things, or both of them, sorted out the surging at low throttle [ch9786].

Title: Re: What else causes surging?
Post by IslandRoad on 02/04/17 at 01:32:36

Thanks again for all the suggestions. It's terrific to have all this combined experience to draw on [ch9786]

Title: Re: What else causes surging?
Post by Kenny G on 02/04/17 at 06:56:59

Island Road,

It is always good to hear stories with a happy ending.

Kenny G

Title: Re: What else causes surging?
Post by justin_o_guy2 on 02/04/17 at 12:44:42

0238272A252F19242A2F4B0 wrote:

Thanks again for all the suggestions. It's terrific to have all this combined experience to draw on [ch9786]

The Professional Mechanics at the dealership rarely have a good working knowledge of these bikes. I remember one person commenting on finding a dealership with a mechanic who knew enough to be considered Knowledgeable. The combined knowledge and experience found here is mindbogling.

Title: Re: What else causes surging?
Post by IslandRoad on 02/04/17 at 13:13:14

I can't imagine the time, money, and frustration that would be involved in trying to work through this stuff with a local mechanic.

That's not to question the ability of the local guys, just saying the bike has many little nuances. And when you want to tune it just the way you want it, you need experienced backup [ch9786]

637C7A7D60675666566E7C703B090 wrote:

[quote author=0238272A252F19242A2F4B0 link=1486020822/30#36 date=1486200756]Thanks again for all the suggestions. It's terrific to have all this combined experience to draw on [ch9786]

Title: Re: What else causes surging?
Post by IslandRoad on 02/04/17 at 22:12:43

For the sake of completeness I'll add a final anecdotal observation to this thread.

With that plastic tube sitting in the carb, the bike could accelerate strongly, and in 5th gear it peaked at about 5500 rpm and 140 km/h (87 mph).

With the tube removed it peaked at about 6000 rpm and 150 km/h (93 mph).

That's just off a one-off test so it's not exactly scientific data (I was kind of busy holding on while reading the tach). And I'm not gonna do the testing required, at that level, to provide more substantial data. But, there it is, for what it's worth 8-)

Title: Re: What else causes surging?
Post by eau de sauvage on 02/06/17 at 15:31:55

The LAMS power to weight ratio is 150kW per 1000kg then you have to add a further 80kg for the rider and 10kg for petrol, so that would put the S40 at 173kg plus 90kg = 263kg

So that's 3.8 times the power of the bike which is 23kW gives the S40 87kW per tonne, which is so far inside the requirement of 150kW/tonne that it does not make sense that it would be their to make it fit under the LAMS scheme.

In fact it still comes in under the LAMS limit without the extra 90kg!

Title: Re: What else causes surging?
Post by IslandRoad on 02/06/17 at 17:21:04

Thanks for doing the sums [ch9786]. I was wondering how they stacked up. So now I'm really curious what it's there for.

I did put it back in until I work out what it is. As I said earlier, my testing has been anecdotal, while I was testing other things.

When I first took it out, on the first test ride, I lost all throttle response above 1/4 turn on the throttle. I assumed I hadn't seated the spring properly in the carb cap (fitting it while still in the bike is a bit fiddly). I took the cap off and refitted while really making sure the spring was seated properly - and being very careful with the diaphragm ). The power gain at open throttle was noticeable.

I'm going to pull the carb when I have time to see if it limits the range of the lifter.

The other thing I thought it might do is guide the large spring. But it's interesting that no-one else on here seems to have seen it in the S40/savage before.

If you do the spacer mod it would be interesting to know if there's one in your carb, given that you are also in Australia.

7D6F7B786F696B0E0 wrote:

Title: Re: What else causes surging?
Post by eau de sauvage on 02/06/17 at 20:01:46

I'll be hopefully fitting the dyna next week, (as well as a k&n) and I will have the carb apart. I'm also curious to see what tube is about. My guess is that it will be there. FFIW, our S40 had bad surging when we got it (almost new 800kms), but a bit of pilot screw fiddling sorted it out that was with the standard pilot jet and three turns out; the bigger pilot allowed 1 3/4 turns out but the surging stopped either way. That's all it may be just a bit of fiddling with the pilot screw! I don't know how many turns out it is at the moment, but maybe turn it out another 1/2 turn and see what that does, easy and fast to do.

Title: Re: What else causes surging?
Post by justin_o_guy2 on 02/06/17 at 20:09:00

Before fiddling, gently close it, count turns, write it down. That way you will always be able to get back to Square One, and you will know if you're getting it out far enough to
A: risk vibrating loose
Or
2: require a jetting change.

Title: Re: What else causes surging?
Post by IslandRoad on 02/06/17 at 23:24:15

I was wondering if you had had the Dyna installed yet. Let us know how it goes. :)

7F6D797A6D6B690C0 wrote:

Title: Re: What else causes surging?
Post by IslandRoad on 02/06/17 at 23:33:53

Thanks for the advice Justin.

I tried a larger pilot jet amongst all the 'plastic tube drama'. I had the idle mix screw opened up quite a bit and I think it vibrated itself substantially CCW. Then I was also adjusting the idle speed screw with gloves on, at an intersection. Pretty sure I put it all out of whack. The bike ran like crap (The exhaust sounded aweful) and when I got back home the idling was drastically horrible .. the bike was blowing smoke and sounded awful. It scared the hell out of me. I had been testing the top speed and thought I had blown something.

I had a cup of coffee, reset the idle mix screw and the idle speed. Everything went back to a recognisable state. Absolutely scared the hell out of me.

I take your point about writing down the turns and doing it properly.

Also, I think I have somewhat overlooked the effect of the idle mix screw, while doing all this tuning (I was just thinking that last night). I have some time to tinker tomorrow, so I'll do some experimenting.

203F393E23241525152D3F33784A0 wrote:

Title: Re: What else causes surging?
Post by justin_o_guy2 on 02/07/17 at 06:25:17

If the idle speed is set properly it's hard to hear what the idle air mix screw is doing. Drop your idle speed to get that adjusted. I took a ride with a screwdriver in my shirt pocket and adjusted at the lights. That way it was only parked,idling every now and then and only for a couple of minutes, AND I was riding.. And it w a s not on the sidestand.

Title: Re: What else causes surging?
Post by IslandRoad on 02/08/17 at 00:38:28

I had some time to work on the bike today so I pulled the carb to check out that plastic tube. And to see if it is actually a limiter.

This is the tube as it sits in the carb:

Title: Re: What else causes surging?
Post by IslandRoad on 02/08/17 at 00:39:10

Here's a closer look:

Title: Re: What else causes surging?
Post by IslandRoad on 02/08/17 at 00:40:17

The image on the left shows how high the lifter can rise with the tube in place. The image on the right shows the same with the tube removed:

Title: Re: What else causes surging?
Post by IslandRoad on 02/08/17 at 00:58:25

I'm gonna go ahead and say yeah, it's a rev limiter.

I did two solid test rides on a warmed up bike, with a newly-cleaned and tuned carb:

1. with the tube in, and
2. with the tube out

(no other changes).

Today's test confirmed my initial test from the other day (when I had other things going on, so I wasn't confident about the accuracy of the test).

The difference is significant. With the tube removed I can feel an increase in 'pull' while accelerating hard up through the gears. I could feel it in the suspension as the bike leaned back at full throttle. The bike was able to rev a bit higher (by about 500 - 700 rpm) and the top speed increased by somewhere around 12 - 15 km/h (7.5 - 9 mph). It also reached top speed more easily.

I think the bike probably had a bit more to give if I wound it out further, but I'd pushed it hard enough to confirm my earlier conclusions, and then backed it off and enjoyed a casual ride home ... with a big smile on my face ;D

Title: Re: What else causes surging?
Post by eau de sauvage on 02/08/17 at 05:23:39

@IslandRoad, thanks for the photos, I'll definitely be removing the tube if I find one. I assumed that you would already be aware of the pilot mix screw turnout. Anyhoo, are you saying the surging is now solved? And what pilot jet size and how many turns out have you settled on. I'll have the dyna in mid next week.

Title: Re: What else causes surging?
Post by IslandRoad on 02/08/17 at 05:56:36

Yeah, the surging is resolved :). I still have pretty regular backfiring, nothing serious though.

I knew about the idle mix screw but kind of forgot about it once I got onto the spacer and main jet.

At the minute I'm on 52.5/152.5 with a 50% spacer. I finally found some stainless steel washers that fit nicely - 6 of them equal the height of the spacer. I'm using 3. I've turned the idle mix screw out close to 2 turns.

I had a hell of a time troubleshooting the tuning due to a leaking vac line on the petcock, and admittedly I didn't realise how important it was to wear gloves and clean up really carefully with carb cleaner when handling the inner parts of the carb (newbie mistake).

I only ditched that white tube today and all went well. It really does open up the top end of the throttle, as you can imagine. Puts a smile on your face.

Once I cleaned the carb (I flushed whatever I could reach with spray carb cleaner) and replaced the petcock, the tuning came together in line with what I've been reading on this forum.

In a couple of days I may try out a 55 pilot just to see if it stops the backfiring, but I'm not too concerned about it. The bike is running great.

Keep in mind I'm also using this as a learning exercise so I'm happy to keep going until I prove to myself there's no further to go :)

697B6F6C7B7D7F1A0 wrote:

Title: Re: What else causes surging?
Post by Dave on 02/08/17 at 11:18:17

If your backfire issues occur when you close the throttle to shift gears, or when you close the throttle to slow down.....that is normal and occurs even on a well jetted carb - you should be jetting for how the bike runs when you are accelerating.....not for what it does when the throttle is closed. If you install a larger pilot jet to "fatten" up the mixture when the throttle is closed....your engine will be running too rich at low throttle settings, and this can carbon up the engine and spark plug, hurt fuel mileage, and also cause premature wear of the piston/rings/cylinder.

When you are decelerating or accelerating and shifting - you don't want to snap the throttle all the way closed.....or you will get a backfire (or a lot of them). Just roll the throttle toward the closed position part way, and there will be little or no backfire. When you allow the throttle to close completely the only fuel to the engine is coming from the idle circuit, and the mixture goes very lean....and the exhaust gets noisy. You can easily control this by just opening the throttle up a tiny bit.......that is what the TEV valve on the stock CV carb is supposed to do - it just doesn't seem to provide enough extra fuel to solve the problem completely - so you just have to do it manually by rolling on a tiny bit of throttle. If you want noisy while you are decelerating you just close the throttle....if you want to be more peaceful you just open up a bit of throttle until the noise goes away......after a bit of riding with this method it all becomes instinct and is part of the fun of riding this big, primitive single.

Modern fuel injected engines don't have to be treated this way - but the Savage engine does. It is all part of what it takes to be a good rider on the Savage.

Title: Re: What else causes surging?
Post by IslandRoad on 02/08/17 at 11:51:24

Thanks for the advice Dave [ch9786]

Title: Re: What else causes surging?
Post by eau de sauvage on 02/08/17 at 14:44:15

@IslandRoad, you will find this article relevant, I saw bits of it quoted around the web and I eventually tracked down the full original post. tl;dr scroll down to 'Burn Baby Burn'

http://www.vtxoa.com/forums/73-how-step-step/21714-air-fuel-motors-missives-article-updated-1-3-06-a.html

Title: Re: What else causes surging?
Post by IslandRoad on 02/08/17 at 15:41:25

Thanks heaps. Really informative article :)

5F4D595A4D4B492C0 wrote: