SuzukiSavage.com - Loud afterfire on decel from 50 to 30; tuning Q's

Dave

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Re: Loud afterfire on decel from 50 to 30; tuning
Reply #15 - 06/11/19 at 03:32:41

The proper sized pilot jet should provide the "best" idle with the fuel screw turned out around 2 - 2.5 turns. If you need more than that the pilot jet is too small......fewer turns means the pilot jet is too big (especially if the engine still runs smoothly with the screw turned all the way in).

You should be jetting your carb for what the engine does when it is running - not for what it does when you close the throttle. When you close the throttle completely, it closes the butterfly and creates a very high vacuum situation - a lot of air can be pulled past the butterfly by the high vacuum and the only fuel that flows comes out of the idle fuel circuit (and some from the TEV). This creates a lean condition and the fuel/air mixture is so weak the spark plug cannot ignite it......but it can be ignited in the exhaust system - this is what creates the popping explosions in the exhaust. The TEV valve is supposed to add fuel when the throttle is closed and reduce the noise - but even a proper working TEV valve provides marginal help......I believe it was sized when we all used gasoline with no ethanol in it, and it is not providing enough fuel to stop the banging/popping. Some folks fool with the spring - but I don't think the problem is "when" it comes on - I believe the problem is that it just doesn't provide enough fuel and some way needs to be found to change the jets to provide more fuel from the TEV. (When I can find some time I will study a carb and see if I can see what contrils the fuel/air mix added by the TEV).

What muffler do you have on the bike? The more open the muffler the worse the noise is going to be. And....this problem is not unique to the Savage - every day you can hear the V-Twin Harleys with loud mufflers popping and backfiring when they let off the throttle (but they seem to love the noise).

My advice is to jet the bike for how it runs when you are "on" the throttle or are riding at a steady speed - and learn to use throttle control to lessen the noise. When you shift gears you can slowly roll off the throttle as you shift - but don't let the throttle slam completely closed....leave it open a slight amount. Same thing for your deceleration from 50 - 30 mph.......don't close the throttle completely and just roll on enough throttle to stop the noise. You don't need to add so much throttle that the bike is accelerating - just 1/8th open so the engine gets some fuel and the lean condition in the carb goes away and the bike runs smoothly. The Savage is a primitive bike with a primitive fuel system.....it is not fuel injected.....and you can learn to work with the bike and become a "rider"! After you do this for a little while it will become second nature and you won't have to think about it.....most engines really don't like you to "crack or slam" the throttle open or closed instantly, and respond better to having the throttle rolled on or off. My Cafe' bike has a round slide Mikuni and it does not have a TEV valve, and if I close the throttle completely while decelerating I can pop and bang with the best Harley.......or I can use a slight bit of throttle and the bike runs nice and smooth while slowing down- it is all in the wrist!

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VortecCPI

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Re: Loud afterfire on decel from 50 to 30; tuning
Reply #16 - 06/11/19 at 04:04:11

Dave wrote on 06/11/19 at 03:32:41:

The proper sized pilot jet should provide the "best" idle with the fuel screw turned out around 2 - 2.5 turns. If you need more than that the pilot jet is too small......fewer turns means the pilot jet is too big (especially if the engine still runs smoothly with the screw turned all the way in).

When my wife's bike was stock best/fastest idle was attained with the screw 2.5-3.0 turns out so I went up one size. This also helped part-throttle leanness just a little bit. A lot of dirt bike guys run a slightly-rich slow/pilot to aid engine cooling.

As mentioned earlier every carb is different so each must be treated on its own. However each should run pretty good with a starting baseline. In the dirt bike forums when the baseline jetting does not work the issue is always fuel/float level.

The only time my wife's bike backfires is if you slam the throttle closed with a lot of engine speed. If you roll it back slowly (i.e., not all the way closed) it does not backfire.

My 1986 Yamaha SRX600 single with SuperTrapp system never backfires, nor did my Twin-Cam HD with V&H Pro Pipe or the two Honda XL/XR 600s I have spent a lot of time on top of.

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ohiomoto

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Re: Loud afterfire on decel from 50 to 30; tuning
Reply #17 - 06/11/19 at 05:36:56

My point to all of this is that a) we shouldn't be handing out jet sizes like prescriptions (suggestions are good but users need to test) and b) everyone always suggests jetting on the richer side, but that MIGHT not always be the case.

BTW, I'm 6'3" 250 lbs and I honestly don't want to go much over 70 mph on this bike so I'm happy to shut down at 80 mph. I think it will probably go another 5 mph, maybe 10 going downhill.

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batman

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Re: Loud afterfire on decel from 50 to 30; tuning
Reply #18 - 06/11/19 at 06:47:32

It seemed obvious to me that his bike was lean in the pilot circuit and running rich in mid range , and that a smaller pilot and only 2 washers on the needle seemed just the reverse of what was needed to make the bike run a bit better, but I think at this point being sure the air mix screw is in fact stock, would be the better starting point. Yes my bike does 90, but I use that as a tuning guide ,I don't ride at that speed ,I'm a 5mph over the limit rider , 80% of the time riding 2 up (245lbs) I am much more concerned with safety, than with speed , being retired I enjoy miles of smiles, and have all day to get there.

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Majorfatboy

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Re: Loud afterfire on decel from 50 to 30; tuning
Reply #19 - 06/11/19 at 17:19:21

@Batman:
Thanks for the OEM numbers, looking at part pictures now, will pull My current mix screw later and compare to make sure, but there may be some slight differences between the two at the needle point. Still not entirely convinced it's the problem, as My problem is while I'm at speed, not at idle, but it couldn't hurt to try. Cost's insane though, most places so far want about nine bucks for the screw, and several bucks S&H. And I'm quite magnificently broke at the moment, lol.
Didn't have time to get to the bike today, and They're talking rain again tomorrow, but the TEV's on the list for re-exam, along with the header and carb mounts.

@Ohiomoto
Brother, I agree 100%, but here's the thing: Anyone who so much as mention's this bike's name on the internet gets shoved over here. "Oh, an S40/savage? They have a website for that, You should ask Your questions there. Now scram". So here We all are, and everyone here will push two things: A new petcock (rightfully so, the stock one's crap), and re-jetting and modding the carb. So a newjack's going to do what the "experts" tell them. Any dialog here slams to a halt until You do these two things with this crowd.
"Hey guys I'm having X problem."
"Did You do the slide mod and rejet?"
"Well, no..."
"Well obviously that's Your problem!"
Yee haw.
I've been lurking Thumpertalk, as they seem to have great heaping gobs of info on things You can do with this style of carb, but there's no point in Me posting there, as They'll just send Me here. The S40's not an off-roader either, so yeah.

@Dave:
I'm not chopping the throttle, not even close. The decel kabooms I'm getting are from Me already doing what You are recommending; Slow, steady roll off of the throttle.
Example 1: I'm cruising at just over 40 with traffic. Traffic starts to slow down gradually. Equally gradually I roll off the throttle, matching speed. KABOOM.
Example 2: I'm cruising at just over 50 on an empty stretch (no one behind or directly ahead of Me). I see a traffic light far ahead turn yellow. Time to decelerate. There's no rush though, given My current speed and range to said traffic light. I ever so slowly roll off the throttle. KABOOM.
That's why I'm working on this. This isn't from hard/sloppy riding, as I said the bike didn't do this in it's stock config before it broke down. Originally it just ran like crap and did a bunch of small rapid-fire pops when engine braking in second. I am, as You put it, "jetting your carb for what the engine does when it is running - not for what it does when you close the throttle".
most engines really don't like you to "crack or slam" the throttle open or closed instantly, and respond better to having the throttle rolled on or off.
You're not actually reading what I've been posting, are You? At no point have I stated anything to this nature. I know how to operate a bike, I don't beat the thing like it owes Me money. Especially on this bike, it's to temperamental to treat harshly. Now those Harley Street 500's I was on at the MSF course a few years ago, those bikes could take some abuse. Newer tech though.
and you can learn to work with the bike and become a "rider"!
Really dude? And what do You think I am now?
The muffler's stock, by the way. Everything is, accept for the Raptor petcock and carb mods, both of which are religiously pushed by this very website.

Will probably tinker with it over the weekend, considering putting it back to stock (white spacer, 145 main) just to see what happens.

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ohiomoto

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Re: Loud afterfire on decel from 50 to 30; tuning
Reply #20 - 06/11/19 at 20:25:58

First, I think Dave might have been backing me up as much or more than he was instructing you.

Second, I think you have this under control. You are pretty much going in the right direction, but let me point out a few things that might make sense.

You seemed to have solved the issue that left you stranded (let's assume the petcock or cleaning the carb solved the issue). But you did a lot of tuning while you were in there based on what is commonly recommended by many on this site. (I'll add that most of the people giving you said advise are really smart and know their crap. I'm sure their bikes run well.)

While I think it's reasonable for someone to want to kill two birds with one stone, I'm not a fan of changing anything until after you solve the issue that was leaving you stranded. The reason I don't like it is because the issue that left you stranded could have been the issue that was causing your bike to run like crap before it left you stranded. But you don't now for sure because you changed a bunch of other stuff. Now you're chasing your tail. I'm not picking on you, it happens all the time around here and I've been there and done that too.

I would have recommended testing after the petcock replacement before taking the carb apart at all. If it still ran terrible, I would have taken the carb apart to see what's inside. If I found stock jetting, I would have checked the float level, cleaned it up and put the stock jets back in. A completely stock bike should run decently well if there are no issues. If it's running terrible, then you still have bigger issues than jetting.

Moving on to where you stand now...

I might be the only one on here who actually thinks that it's is possible that our bikes are actually too rich off the bottom end from the factory. If you read through my posts, you'll see that my bike runs great at very low temperatures with almost no warm up. Lean running bikes don't do that. Oh, it doesn't backfire either...interesting. (It will crackle and pop if I rev the piss out of it and chop the throttle closed.) See where I'm going here?

I have a 47.5 pilot, a 3/4 spacer and 147 main. (I'm thinking I could run a stock white spacer with a 150 main, but I'm too lazy to bother since I'm satisfied with how the bike runs now.)

My gut tells me that the stock jetting is actually a tad rich off the bottom, pretty close in the middle and a little lean on top. I think that the slow bottom end throttle response and backfires on deceleration could be attributed to a rich condition just off idle.

If you clean up the bottom end, you may be able to fatten up the main to get that smoother, longer pulling power you like. Then you can adjust the needle as needed and even revisit the pilot again if needed.

Lastly, I think that the condition of the slide can not be overlooked. If it's sticking it will cause all kinds of dead spots in your power delivery. I was chasing a dead spot in the middle with my bike until I replaced my slide. The black coating was worn pretty good. I tried cleaning it, but when I realized that I had that dead spot no matter what jets I had it was time to get a new one. $125 later, my dead spot was gone. Best money I spent on that bike to date.

I'm not claiming I know anything more than the rest of the guys and gals on here. I'm simply sharing my ideas and experience. You need to find out what works best for you. And please share your findings with us so we can all learn from them.

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VortecCPI Full Member Offline SuzukiSavage.com Rocks! Posts: 127	Re: Loud afterfire on decel from 50 to 30; tuning Reply #21 - 06/12/19 at 03:37:43 ohiomoto wrote on 06/11/19 at 20:25:58: I have a 47.5 pilot, a 3/4 spacer and 147 main. (I'm thinking I could run a stock white spacer with a 150 main, but I'm too lazy to bother since I'm satisfied with how the bike runs now.) What is your elevation in Ohio?
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Dave

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Re: Loud afterfire on decel from 50 to 30; tuning
Reply #22 - 06/12/19 at 03:40:50

What does the TEV diaphragm look like - is it soft and pliable.....or stiff?

When they get aged and stiff, the TEV valve won't open when it should and could contribute to the popping and banging. They don't last forever, and I had to replace the one in the 2002 that I worked on.

You can find aftermarket replacements on eBay pretty cheaply....it is a diaphragm used on other carbs as well.

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« Last Edit: 06/12/19 at 05:51:17 by Dave »

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Re: Loud afterfire on decel from 50 to 30; tuning
Reply #23 - 06/12/19 at 03:53:06

VortecCPI wrote on 06/12/19 at 03:45:13:

With respect to ThumperTalk...

I am a pretty big contributor, especially around Honda CRF230F.

Dyno testing has shown conclusively that a 120 main is THE main to use with stock carb and stock engine uncorked at sea level.

Dyno testing has shown conclusively that a 110 main is THE main to use with stock carb and stock engine uncorked at sea level with exhaust baffle internals removed and replaced with a pack of ten 4-inch SuperTrapp discs. More flow equates to more pressure drop and more signal across the main, hence it becomes smaller. Also included in this mix is less dilution of the incoming charge due to spent exhaust gas in the chamber. All this data is available from Frank Nye at Engines Only and this is a subject all of its own...

Extensive testing has shown conclusively that a 45/48* slow/pilot is what to use use with stock carb and stock engine uncorked at sea level.

Extensive testing has shown conclusively that #4 on the needle is what to use use with stock carb and stock engine uncorked at sea level.

For elevation and/or temperature changes we use data from charts sourced from Honda and extrapolated by me to determine main jet size multipliers.

Surely we can find the same for the stock Mikuni on stock engine at sea level...

The #1 cause of jetting issues is improper fuel/float level. Too low and the carb meters lean. Too high and the carb meters rich.

* I have jetted many and we have found the majority like #45 but some, like mine, like #48.

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Re: Loud afterfire on decel from 50 to 30; tuning
Reply #24 - 06/12/19 at 16:30:08

Majorfatboy , sorry about your budget ,but the truth is you can't afford to not buy a new stock air screw. just as your valves in your head need to be ground to MATCH the seats in the head so must the air mix screw match the seat in the carb body. even the float level valve in the bowl is sold only as an assembly -matching valve and seat . It's that important, if you can't regulate the fuel/air mix in the pilot system ,your chance of stopping the backfires is very poor.

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« Last Edit: 06/13/19 at 08:18:51 by batman »

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ohiomoto Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 2778	Re: Loud afterfire on decel from 50 to 30; tuning Reply #25 - 06/13/19 at 06:11:41 Batman is correct, the proper screw should be used. That said, the screw does so little in the grand scheme of things that it shouldn't prevent you from getting the bike running reasonably well. @ Vortec...600-1100 feet in my area.
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Re: Loud afterfire on decel from 50 to 30; tuning
Reply #26 - 06/15/19 at 04:46:54

ohiomoto wrote on 06/13/19 at 06:11:41:

@ Vortec...600-1100 feet in my area.

About the same here in CLT. Interesting that you are not lean on the needle and I am. I have checked for proper fuel/float level so the only thing left is needle height.

Other than slight part-throttle leanness the engine runs VERY strong from idle to top. The extra slide hole also helped a lot.

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