I know this subject is tiresome, but I am getting frustrated not being able to solve the intermitent backfiring problem I am having. I have an 06 Road Star Silverado,(I will post pictures soon I just keep riding instead of shooting photos) with Cobra Speedster Slashdowns with baffles, BAK, 170 main, 4th groove on the needle, PMS 3 turns out, AIS removed, operating at sea level.

Initially I installed the pipes resuing the gaskets, and had terrible backfiring. I reinstalled them with new gaskets ($22 for a set so I hope that I can avoid doing that too often) and the problem was nearly solved. Still occasionally had a backfire, but thought that AIS was the culprit. I removed the AIS, checked the tightness of the pipes and found they were tight, but tightened them a little anyway. I have snugged them several times to the point the flanges are starting to curl.

When I finished removing the AIS I rode the scooter until it was warm and went out on the highway and ran it up and let off, no backfire. I thought it was all good. On most days when I ride to work I have only a very occassional pop ususally upon let off, but not until the engine has slowed to maybe 2,500 or less RPM. Then I get a pop not too loud, but annoying. This last Sunday I was riding with a Star Riders group and on the highway at 70 mph, everytime I fully let off I got a loud pop. It is getting annoying and I am at my whits end.

Are there any obvious places I have not looked where air is getting into the exhaust? I see no obvious leaks in the pipes at the heads or at the joint where the mufflers are attached. The AIS opening in the manifold is capped, the AIS port covers are snug, the carb is properly installed and snug, the manifold has never been touched, but if I go in there it is getting changed.

My next step is to remove and reinstall everything. This loud bang is annoying and unlike when I ride to work at highway speeds it happens almost immediately upon let off.

Sorry for the long message, but I need to get this fixed.

Recheck the gaskets at the head ... if they are distorted then you may be getting a slight leak. Try the cheaper aftermarket ones rather than the expensive Yamahas and double them up. The flange at one (or both) of the pipe may not be flush enough with the head (slightly cocked).

Trying turning you PMS out 1/4 turn.

You will not be able to completely elimiate the popping but you should not be getting loud backfiring.

Doc

Thanks Doc, this is frustrating and I feel like I have tried everything. I will try some new gaskets. Where can I get the "cheaper" gaskets you mention?

There's some discussions here ... http://roadstarclinic.com/component/option,com_simpleboard/Itemid,/func,view/catid,13/id,11383/#11383

Doc

Crusierbob wrote:
I removed the AIS, checked the tightness of the pipes and found they were tight, but tightened them a little anyway. I have snugged them several times to the point the flanges are starting to curl.

Thats TOO tight. Only curls you should be doing is in the gym. Docs right, maybe one of the head pipes are not properly seated. If not , fiddle with the pms alittle at a time. Do your baffles require a repack? Are you running baffles? Trying to throw some ideas at you.

Thanks guys for the suggestions. I know that the flanges should not curl and that is why I am wondering where else the leak could be??? I will try a fresh set of gaskets and reset the pipes. I will recheck everything again. Then I will open the PMS some more. It seems from all of the set ups I have seen on this board that 3 full turns is more than most run. I will try another half and see if the situation changes, then back off until it starts again. Hope to stop taking shots, while most people do not seem to notice it bothers me