how to eliminate popping on deceleration

[maskedman72]

the bike is a bone stock (except for the holesaw mod)2003 ss750.

do i need to re-jet to the next size up or simply adjust the mixture screws?

to anyone else that has had this problem-how did you get rid of it?

i thought i saw a thread with photos on how to drill out the plugs to gain access to the screws but i cant seem to locate it. can someone provide a link to it here?

[RustyJake]

Check out this page: http://www.sa750.com/mixscrews/mixscrews.htm
This is the information you are looking for and should eliminate your popping on decel.

[maskedman72]

cool, never came across that info before. that is exactly what i was looking for. thanks!

[maskedman72]

just finished doing the carb adjustments. the screws were only 1 1/4 turns out!

i set them to 3 1/4 turns out as the article says to and the popping is totally gone. runs great now!

the exaust gasses smell more potent now. richer. could 3 1/4 be to many turns out?

could it foul the plugs? could it alter the bikes mileage?

[RustyJake]

I'm sure Nav will chime in, but at 3-1/4 turns out you should be going up one size in main jets. I would also think that you are almost at the point of having the screws fall out. I don't think for your set up you would require that much. I know the article states what they feel you should be set at, but it's not for all bikes in every case.
When I originally set mine when I had the stage 1 kit in the bike and the stock main jets, I had them turned out and I adjusted them in by 1/4 turns until the popping returned, then I just turned them out to eliminate the popping on decel. The article is a guideline, your bike may be different, so try small adjustments in and take it for a test ride.

[navillustoo]

Now RJ, what makes you so sure I'd chime in? LOL! I guess I gotta keep up my reputation! Sorry, but I only agree with part of what you said.

MM,
3-1/4 turns out may be too much, you need to take it in 1/4 to 1/2 turn increments to get it just right. I'd bet though, that they're out farther than they need to be. The part I don't agree with is about the main jets. Your bike can benefit from a rejet, even if nothing has been modified, but it's not a necessity with just the holesaw mod. The only way to know for sure is to take a sparkplug reading and go from there. What you'll need to do to get an accurate reading is to ride the bike at your normal cruising speed for a few miles and without letting it idle, shut the engine off. The best way to do this is find a lightly traveled road with a safe place to pull off, ride to that spot and with the engine at a steady speed, hit the kill switch while pulling in on the clutch. Coast to the side of the road and pull off. Let the bike sit for a few minutes while it cools down a bit, before attempting to pull the plugs. Then, with the plugs in your hands, look at the porcelain insulator just below the threads. This area should be a light tan if the Air/Fuel ratio is correct. If they are white, you're lean and if they are dark brown to black, you're too rich. At cruising speed, you are checking the A/F ratio determined by the needles. To check the main jets, you will need to do a WOT shut off and read the plugs in the same manner.
The reason you got the popping after hole sawing the baffles is because these bike's idle circuits are set lean from the factory. This is to please the EPA. The other circuits in the carb are calibrated on the rich side, so we don't blow up the engine while under warranty. The holesaw mod normally does not cause a too lean condition in these other circuits, but since the idle circuit is already a little lean, it becomes too lean when you open up the exhaust with the holesaw.

One thing to remember is that the mixture screws have NO bearing on any other circuit but the idle circuit. So adjusting those screws will do nothing to correct an off-idle A/F ratio discrepency. Nothing short of a rejet will correct that problem. But I don't think you have a problem other than being a bit too rich with the idle screw adjustment. Try going back to 1-1/2 turns out and ride the bike. If it popsgo to 1-3/4 and repeat until there is no more popping. I'll bet it'll quit before you get to 3 turns out.
Take a plug reading and let us know what you find. Just pulling the plugs with the bike sitting in the garage will only show you how the idle circuit is doing, you must ride the bike to get an accurate reading. It must be under a load when you shut it down, so just reving the engine will not do either.

Sorry for the length of this, I tried to keep it short and sweet, but wanted to cover all the bases.

Brian

[maskedman72]

thanks for all of the info guys!

just for the record the popping was present before i did the holesaw mod.
once i did the holesaw mod,it did not get worse or better,it was always there to begin with.

i will fiddle with the screws some more and see what happens than try pulling the plugs to check it out.

i am going on vacation for 2 weeks so it might be a while before i get to report back,but if i get the time to do it before i will post the results.

i am guessing that i can get the popping to go away with less than 3 1/4 turns out.

in either case,will i have to re-jet the carbs anyhow?

thanks -jay

[RustyJake]

Now RJ, what makes you so sure I'd chime in? LOL! I guess I gotta keep up my reputation! Sorry, but I only agree with part of what you said.

MM,
3-1/4 turns out may be too much, you need to take it in 1/4 to 1/2 turn increments to get it just right. I'd bet though, that they're out farther than they need to be. The part I don't agree with is about the main jets. Your bike can benefit from a rejet........

Brian
Now my bad for not saying 'slow jets' (not mains, like I said in my post). My statement about needing new slow jets was in regards to having to run at 3-1/4 turns out. "IF" that were the case, then he should benefit by going up one size in slows. Having the mods done that he does at this point, he shouldn't need to change them.
If you could see inside my head, you'd have seen what I was thinking :_blank:

[navillustoo]

i am guessing that i can get the popping to go away with less than 3 1/4 turns out.

in either case,will i have to re-jet the carbs anyhow?

thanks -jay

jay,

That is what I was saying, you may be able to eliminate the popping with a lesser adjustment than 3-1/4 turns out.

I don't believe that you will need to rejet with just a holesaw mod, but even a bone stock engine benefits from a rejet.

Brian

[navillustoo]

Now my bad for not saying 'slow jets' (not mains, like I said in my post). My statement about needing new slow jets was in regards to having to run at 3-1/4 turns out. "IF" that were the case, then he should benefit by going up one size in slows. Having the mods done that he does at this point, he shouldn't need to change them.
If you could see inside my head, you'd have seen what I was thinking :_blank:

OK, you're forgiven! LOL! Hell, sometimes I can't read my wife's mind and I've lived with her for over 31 years! But she is a female! LOL!

I think most folks on the site know how I feel about changing the slow jets, it IS a last resort as far as I'm concerned. Everyone that has changed their slow jets has complained about the excessive fuel consumption. This is the trade-off. You CAN avoid all of this by raising the float level slightly, which is another tuning trick to eliminate the popping if the screw adjustment doesn't take care of it. I know Machinehead vehemently disagrees with this, but the Dynojet engineers have never steered us wrong, have they? It works. And it doesn't cost you fuel economy!

Anyway, I think we agree in Jay's case, he doesn't need to do anything but re-adjust his idle mixture screws.

Brian

[maskedman72]

i turned the screws last night to 2 1/4 turns out and went for a spin.

the popping is there just a tiny tiny bit. not near what it was before. this is probly as good as it will get so i am guessing i should either stay with that setting or do the next size up in jets.

-jay

[RustyJake]

If you are 'just about there' at 2-1/4, open up the one that's still popping about 1/4 turn and it should go away completely. Sounds like you'll be good to go once you fine tune the settings.

[maskedman72]

yes that is what i will do. back them out a hair more and it should go away totally.

but now let me ask this; when it does go away totally ,that dosent mean that the bikes fuel/air mixture is perfect at that point right?



so i would like to try to obtain the perfect fuel/air mixture and get the popping to go away.

is it possable to have the best of both worlds in this case?


thanks for all of your great knowledge guys,you are helping me out a ton on this!!!


-jay

[RustyJake]

I don't think there is any "perfect" setting. Temperature changes as well as barometric pressures and if you have any altitude changes will effect settings. High performance motors require adjustments, I know some people with the DP mods on their bikes have a bike that behaves differently in all kinds of conditions.
I think what you'll find is you have the ideal setting for your bike in normal conditions and it works fine. I don't think you'll comprimise your fuel economy with with you've done. You may even improve it with better performance from the airflow.