Bonneville America Forums Forums Technical Forums Exhaust D & D pipes...I did not know???

Well, tonight, my neighbor and I decided to make a run for Blizards at Dairy Queen. I elected to ride while he took his truck with his kids. While following me, he observed little blue flashes out of the pipes while hard accelerating, big 2 ft flames during the shifts and a total light show upon deceleration. I never knew this. Kind of cool....but so far lucky too. I haven't ever been hasseled by the fuzz.

Don't ride in a National Park in the dry season .

You might also be running a bit rich since you have a lot of unburnt fuel in the exhaust.

When I frist put D&D's on my bike and was experimenting with different sized pilot jets, when I used too large of a pilot I had flames coming out of the pipes. Don't know if thats your problem, but it's not normal for flames to be coming out of the pipes....

Ok, I just posted to share my experience, and it got transferred to the Exhaust tech section. Now, since it has gotten to be a tech post...here's my story. I bought the bike 2 years ago second hand. THe prior owner bought and installed the D & D's. He also installed D & D's supplied matched jets. I have not taken the time to see what jets are installed. It does seem to run a bit rich, but it runs good. The only thing I did when I got it was open the mixture screws out from 3 to 3.5 turns so it wouldn't backfire...and it doesn't anymore. Is the "lightshow a bad thing? I get about 40-50 mpg

correction...I turned the mixture out from 2.5 to 3 turns...oops/

Put it this way, your engine may be running good but it's not running optimally. Ideally, each engine cycle is going to burn X amount of the fuel/air mixture pulled through the carbs. Your engine is pulling X+Y probably because the main jets are too big. X will always get burned up in the engine no matter what because that how much it is designed to burn in a given engine cycle. Y is getting burned up in the exhaust or just getting spewed out on the road, person behind you, whatever. This extra fuel burning up in the exhaust can contribute to pipes blueing faster and while it looks cool, it's also lost fuel. You wouldn't ride around with a hole in your fuel line, why spit unburnt fuel out of the exhaust? As an engineer I want my engine running as efficiently as possible and as a tightwad I want to use every bit of fuel I buy to go towards running the engine and not entertaining the folks behind me. OK, I'll get off my for now.

First thing I would do is check out what size the main jets are and maybe drop them down a few sizes (i.e. take 135 jets down to 130 and check the plugs). You might even get better fuel mileage with the correct jets.

yeah, I agree with you...the weird thing is that I never knew this for 2 years!!

Get someone to follow you and record it!!!