Bonneville America Forums Forums Technical Forums Performance Mods About that f.... popping and sh....

I have SS-pipes, air..whatever..set removed, main jet 135, about 3 turns out (and every other settings between) but i can`t get handled the popping. I have not put shim or changes pilot. The question is: if I "reset" everything to stock-setting, and only have shiftet the pipes, will the popping dissapear. The bike did not pop when it was new...of course...

From a review of a Ferrari Dino 246GT

Quote:

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As the accelerator is released, there’s a crackle and pop from the exhaust on the overrun. It's a real race-car noise that’s wonderfully addictive.

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My 60's BSA crackled popped and burbled on decel, my America does it now, I love it. It's a feature, not a problem.

Norseman... I have the same pipes & setup as yours, but for a couple of things. At the time that I installed the 135 mains, I also changed the pilots to 45's. Also, I never shimmed the needle.

My air mixture screws are turned out 3 1/2 turns, & I have NO popping on decel. Try this combination... good luck !!

My untechnical understanding of it is the pilots work all the time not just at low end. Your mains are big enough. 45s would be the next logical step. Your mains are not working on decel as the throttle is not open, your pilots are doing all the work at that point. As your pilots work all the time you will dump more fuel at wide open throttle too, that should not be a problem.

Popping is generally a lean condition, reduce the air flow, add back pressure or feed it more fuel. I think you have one option, that being fuel.

For all that have switched out your pilots, were you able to change them out while still on the bike. I have switched out mains but it doesn't look like the pilots are quite as accessable. Any thoughts or suggestions?

I found this via Google.... it's from a site about airplanes but engines are engines....

Here's something a little more scientific and possible things to look at. Engine backfires: It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm. The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers for this to occur. (No mufflers/headers etc.) Why This (normally) Happens: 1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system. 2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat. 3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there. 4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires Other possible causes: Air Leaks: Any source of fresh air into the exhaust system can create or worsen the conditions that bring about exhaust popping. The most common entry point is the junction of the header pipes and mufflers. Even a small air leak can dramatically increase the intensity or likelihood of exhaust system popping. A high temperature silicone sealant, as can be found in many auto parts stores, may be used to seal the pipe/muffler junction. Lean Carburetion: While exhaust system popping may be considered normal, it is certainly made worse by an overly lean idle circuit. Be sure that your carburetor's pilot jet is the correct size and that the idle air mixture screw is correctly adjusted before looking for other causes of popping.

Geir,
I have stock pipes that are almost "gutted". 130 mains and stock pilots. I could not get the popping to stop. I checked my float bowl level and found my left carb level was 7mm low and the right one was 6mm high (rich and occasionally flooded). I got my float bowl levels set right, then adjusted the idle mix screws the old fashion way. (by removing one spark plug and starting the bike on one cylinder - adusting the screw out until it it sputtered and screwed it in until maximum idle was acheived. Then I split the difference on the screw setting. Then the same with the other cylinder.) After I did that, I balanced the carbs with a mercury manometer. My acceleration and deceleration are as smooth as silk with no pop or backfire.
OK, my left screw is turned out 4 turns. My right screw is turned out almost 3 turns. Why so much difference?
That darned right carb fuel level is high again!
I may get someone to help me in Georgia this week.

Yes you can change the pilots with the carbs on the bike.
I use a small screw driver that I cut most of the handle off.
If the pilots have never been touched you may have to grab
the screw driver with pliers to get the pilot to break free.

Excellent advice Skillet. Especially the pilot screw adjustment. We did that same method to Mike's bike the other day and in runs better than ever now and minimal popping. He'll be the one in Georgia with the frozen grin and his teeth full of bugs.

Thanks Pete, I will be tinkering with her this week, I am going to try 45 pilots and 145 mains. I will post results.

Hey Pat,
Please don't make my head bigger than it already is (you'll see soon). I do have a big head. I had to crawl backwards until I was 3 - I couldn't get that big head off the floor.
I can't wait to see Mike's GRIN!!! and hear your loud pipes.
See YA'LL Wednesday Evening!

BonnyBeamer says he got his air mix. screws out 3,5 - you are talking about the pilot screws adjustment. I have been adjusting the pilot screws back and forward (thoose "under" the carb when its on the bike). Where are these air mixture screws? Maybe my popping etc. dissapears whith only adjusting on these???

That's the correct screw(s), Norseman. Go ahead and try adjusting, but you will probably go with the pilot-jet "change-out" eventually.

ALSO: As did snekeptp, I used a very small screwdriver, but also clamped the handle with needle-nose channel locks for grip.

Dennis...
Have used this method on my old Beemers for years... works great. One thing: I always slip a sparkplug into the connector that I've removed (& make sure it's not touching anything). This, I've always been told, will ensure that your electronic ignition doesn't get hosed (???, it doesn't hurt).

Thank you folks!!! I have ordered pilot jets size 45 at Brents, and I`ll be back with how it goes. In the mean time I will try to put on som pictures of Thye Great Iron From Tha North.