SuzukiSavage.com - Print Page

SuzukiSavage.com
/cgi-bin/YaBB.pl
General Category >> Rubber Side Down! >> Pilot jets with holes in the sides vs no holes
/cgi-bin/YaBB.pl?num=1354556010

Message started by DavidOfMA on 12/03/12 at 09:33:30

Title: Pilot jets with holes in the sides vs no holes
Post by DavidOfMA on 12/03/12 at 09:33:30

I'm trying to find the best balance between preventing backfiring and not stalling when choked. Going to a 55 pilot jet helped with backfiring but the bike won't idle when choked even with the idle mix screw turned almost all the way in.

I have two 52.5 pilot jets, one with holes in the side and the other with no holes. Which is the richer jet? I am hoping if I put in the richer "standard" pilot jet, I will be able to find a better idle mix screw setting rich enough to reduce backfiring but not so rich the bike won't run when choked.

Thanks!

Title: Re: Pilot jets with holes in the sides vs no holes
Post by Serowbot on 12/03/12 at 10:02:27

If there's a difference (and I don't think there is),.. I'd go with the extra holes...

... but,.. keep in mind... a 20% change in humidity will make more than one jet size difference anyway... 2k of elevation,... 20f temp...

Jetting, is not that precise... it's just finding a good average...
#55 sounds like it's too much... when in doubt go for the smaller pilot... (it'll help mpg's)...

Title: Re: Pilot jets with holes in the sides vs no holes
Post by Dave on 12/03/12 at 15:50:50

I did a little research on it, and I believe the holes in the sides of the Pilot Jets are used in carbs that use and "air" screw for adjusting the idle mixture. Our bikes adjust the flow of gasoline - while some adjust the flow rate of air. In those carbs that use air it is bled into the side of the Pilot Jet through those side holes.

So......using a Pilot Jet with or without holes doesn't make any difference in our bikes.

I agree that you need to use the smallest Pilot Jet that allows you to adjust your idle fuel mixture properly. If you have to open the idle mixture screw 3 turns or more to get the engine to run smoothly - then it is too lean. I believe a 52.5 is the biggest you might need, but mine runs best with a 50.0......and a 150 main.....and I have adjusted the slide needle until it runs best. (Someday I need to measure the thickness of the washers).

Title: Re: Pilot jets with holes in the sides vs no holes
Post by DavidOfMA on 12/03/12 at 15:53:30

I was hoping there was some kind of intermediate jet between 52.5 and 55. At least in my area, with current weather, the bike seems too lean with a 52.5 and the idle mix screw turned out 3 turns. It backfires. With the 55 jet and the idle mix screw turned out 1/2 turn, it doesn't backfire much but stalls out at idle when cold. Something like a 53.75 jet seems like it would be the best compromise. I'd hoped the ones with air holes on the side were a little richer. What else would have the same effect?

Thanks.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by Serowbot on 12/03/12 at 16:09:03

How's your idle speed?...
It's not real lopey slow, is it?...
You'll cook yer' cam with a slow idle speed...

Title: Re: Pilot jets with holes in the sides vs no holes
Post by ralfyguy on 12/03/12 at 16:19:30

37313C3C38313A3D373621530 wrote:

I was in the same boat. 52.5 too lean, 55 too rich. What I did was make my own in between. Since I didn't have any small enough drill bits, I found me a safety pin that was too big to fit the 52.5, and would fall loosely into the 55. Then I took a grinder to the tip of the needle and shaped it like a screwdriver tip. Then I put the needle in the vise and force twisted the 52.5 all the way through. If you keep twisting and backing out frequently, the needle will go through eventually. There is only about a 1/4" of brass to go through.
Now I have a jet that is in between the two and it runs just great.
Although i wish it would've been a tad smaller as the the mixture screw is only about a 1/4 turn out versus 2 1/2 turns before. I wish it would have been around 1 turn out to have a little more adjustment if necessary.
But it's fine the way it is now.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by Cavi Mike on 12/03/12 at 16:20:40

I'm not sure I understand the question. What does your choke have to do with this? Have you been needing to ride around with your choke on just to keep the bike running or are you talking about when you first start it cold? Either way - you don't tune the carb to how the bike runs with the choke pulled. How the choke makes the bike run has to do with the choke, not the jets.

Another thing - there are 2 or 3 notches in the choke, not one. You may just not be putting the choke where it needs to be to keep the bike running.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by LANCER on 12/03/12 at 16:49:33

There is no difference between the 2types of jets for the AMOUNT of fuel they will flow. The theoretical difference between them is that the one with holes will transition between throttle settings more smoothly.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by DavidOfMA on 12/03/12 at 17:13:56

5577607F5B7F7D73160 wrote:

Since I went to the 55 pilot jet, the bike stalls when cold when I give it any amount of choke (but won't idle with no choke, either). It didn't do that with the 52.5 jet, but with the 52.5 jet it backfired. Going to the 55 jet mostly fixed the backfiring but seems to have caused the cold idle stalling problem. I have to palm the throttle to keep it from stalling at stop signs until it's warmed up.

Once it's warm enough to run with no choke, it runs pretty well with the 55 pilot jet. Finding a jetting balance between not backfiring and not stalling at cold idle is what I'm looking for.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by DavidOfMA on 12/03/12 at 18:52:19

Quote:

Thanks, that's an interesting idea! I had considered the possibility but didn't really know how to proceed.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by singlesgoinsteady on 12/03/12 at 20:07:54

You can always drill it out bigger, solder it, then drill it out to the exact diameter you want it if you have the bits.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by LANCER on 12/04/12 at 03:55:36

If the stock carb is functioning as designed, the pilot jets should have about a 1/3 overlap from one size to the next size. Ex: say you have. 52.5 @ 2.5 turns out, replace it with a 55, then you should find the same state of tune at about 1 turn out. +/- a little.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by strang on 12/04/12 at 04:50:09

A couple of weeks ago I did a back and forth with the stock jet (no holes) and aftermarket (with holes) of same sizes - didn't notice one bit of difference.
oh and that troll thread disappearing has just made me more paranoid :o

Title: Re: Pilot jets with holes in the sides vs no holes
Post by DavidOfMA on 12/04/12 at 05:11:30

525F505D5B4C0C093E0 wrote:

Thanks. This is really helpful info for troubleshooting, as that's not what I'm experiencing.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by DavidOfMA on 12/04/12 at 05:13:14

707771626D64030 wrote:

Thanks. Then that eliminates trying the jet with holes.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by justin_o_guy2 on 12/04/12 at 09:30:12

Maybew I missed it, BUt Rowboat asked What is your Idle Like,,
& Stated, If its slow & lopey like, it'll cook yer cam,, & It will,, Gotta keep that idle up around 1,000..

Title: Re: Pilot jets with holes in the sides vs no holes
Post by DavidOfMA on 12/04/12 at 10:09:00

Idle's fine (at least 1000 rpm) when hot, but now it dies when cold. I'll try going back to a 52.5 jet. Running rich with the 55 got rid of the backfiring, but now any amount of choke stalls it. Must be another way to get rid of the backfiring.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by Dave on 12/04/12 at 11:38:38

You will not be able to eliminate backfiring until you get a bike with fuel injection......your Savage is going to backfire sometimes when you shift or go down a hill, or slow down. The backfiring is a result of having a primitive carb on the big single.

I have a Fuel Ratio monitor temporarily on my motorcycle, and I can see when the engine is running rich, or correct, or lean. When I am cruising along at a steady speed and roll off the throttle - the fuel flow to the engine is cut drastically and the engine goes waaaaay lean - so lean that the spark plug will not ignite the mixture that goes into the cylinder and unburned fuel goes into the exhaust pipe. Then when I open the throttle and the mixture again burns, the flame going out the header pipe ignites the unburned fuel in the exhaust system and "BANG". Our carb has a TEV valve that is supposed to sense the large engine vacuum and allow additional fuel to flow through the carb - but it does not stop all the backfiring.

If you start to richen the carb mixture up to eliminate or reduce the backfire you might help things a bit - but if you richen too much the engine will not run well as it will be too rich when cruising or accelerating.

You can adjust your riding style to reduce the backfire by shifting between gears quickly - and do not completely close the throttle while shifting. You don't have to shift as if you were in a drag race - just don't be lazy about it and hustle through the clutching and shifting so you can get the throttle open again before too much unburned fuel gets into the exhaust system.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by Dave on 12/04/12 at 13:23:29

This question is mostly directed at Lancer or anyone that has replaced the stock Constant Velocity Carb with a Mikuni Round Slide.

Does the Savage continue to backfire as often (or more) when a properly letted constant velocity carb is replaced with a properly jetted Mikuni VM carb?

Title: Re: Pilot jets with holes in the sides vs no holes
Post by DavidOfMA on 12/04/12 at 13:28:05

Thanks for the analysis. I ride as you describe and don't get backfiring when I shift. With the 55 pilot jet, I get almost no backfiring when I roll off the throttle at a turn or when stopping, but now it stalls at idle when the engine is cold and even slightly choked. I can start and run without the choke with the idle mix screw almost all the way in, but I assume I'll have problems running too rich when it warms up here in the spring, and I'll have no room to lean it out. Maybe this is a problem that can't be solved, just worked around, as you suggest. It does seem like a 53.75 jet would put the idle mix screw right where I want it, though, and let me find a better compromise between cold engine idling and backfiring.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by Dave on 12/04/12 at 13:39:43

You might try another option....which is the slide needle. Drop the Pilot Jet back to the 52.5 or even a 50, and raise the slide needle by taking out one more washer.

My bike is running really nicely with a 50 Pilot, 150 Main and only 2 washers on top of the needle.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by DavidOfMA on 12/04/12 at 17:49:10

447F7265747863657E767B64170 wrote:

Does raising the needle make the mixture richer throughout the entire throttle range? I vaguely remember doing something like that 35 years ago, on a Yamaha 2-stroke that was running hot but can't recall what throttle range it affected.

Title: Re: Pilot jets with holes in the sides vs no holes
Post by Dave on 12/05/12 at 05:33:29

Raising the needle richens the mixture from somewhere around 1/4 throttle to 3/4 throttle - then above 3/4 the main jet takes priority. There is some overlap below 1/4 and above 3/4......

Title: Re: Pilot jets with holes in the sides vs no holes
Post by DavidOfMA on 12/05/12 at 06:57:29

So, that could improve mid-range performance (say, accelerating to pass)?