Bonneville America Forums Forums Technical Forums Performance Mods Bike Hiccups when warmed up

Heres the bike...
04 SM with only 4900 miles on it. AI and snorkel removed. 132 main/45 pilot. Stock filter. Specialty spares shorts w/1/2 baffle installed.
The problem...
When bike is cold, it runs awesome! However, when bike warms up, it starts to hiccup or cough between 2400-3000 rpm's-any gear. Once I am through the cough, the bike runs great. It also backfires on decel like a cannon. I HATE IT!!! Any help would be appreciated. Also anyone know a link to download a maintenance book for the entire bike?
Jeff

Jeff,
After bike is warm and while running at the RPM's where it coughs, pull the choke out slightly to see if it helps or hurts.
I suspect you might have too big pilots but the choke trick should tell.

I run larger pilots than that but altitude has alot to do with those as with any carb set up. The backfire does sound like unburned fuel.

You are running rich. Cool air is more condensed and thus packs more 'bang' (hp) when ignighted. Go back to 42's and check the idle mixture screws. you should be about 2-3 turns out from full stop. As for the popping, look for exhaust leaks. Torque the header falnge bolts and look where the silencers hook up to the header pipe. I'd bet you have a leak...

you could also check the four rubber caps (squirrel condoms), on the carb jugs to see if they are cracked and leaking.

thanks all...The bike did the same thing when I had the 42's in it. I JUST changed them 250 miles ago. Heres a little backbrief on when it happened.
I was on a 1000 mile round trip with a buddy, at sea level to 4000 ft. Rode the first day of 500 miles in the desert and bike was awesome. Next morning we stopped after tooling around in the mountains of 4000 ft, we stopped and got gas at SEA LEVEL. 1 mile past the station, the bike died, then restarted with a MONSTER backfire, and now wouldnt run over 2500 rpms without constantly coughing and eventually dieing. When all this happened I was only running the stock jets, so I changed them out hoping for the best. (they came with my pipes from SS)
As for the squirrel condems, can you show a picture or explain where they are (or supposed to be)...I dont see any caps on my carbs.
ONE FINAL THING-does anyone have a schematic for the air lines that are going to and from the "can" located back under the frame by the back tire-It looks like I have some open ports on it.
THANK YOU ALL FOR YOUR HELP!!! SORRY ABOUT THIS LONG THREAD-I JUST NEED SOME HELP, CLOSEST TRIUMPH DEALER IS HOURS FROM MY HOME!

The caps are on the top of the intake manifold. Thay stop vaccume leakage. The AI used to be hooked to one of them if memory serves. Also same place you would hook a vaccume gague to while you are at it check the intake rubbers that the carbs mount to. leakage at those would cause a lean condition though and not rich.

This is the speed where the slides first begin to open. Good chance that a shim or two on the needles will fix it.

Forgive my lack of carb knowledge...Shim under main or pilot? Should I try to adjust the air intake on the carbs before doing this?
Brand new plugs put in 100 miles ago and they look like they are burning fine.

OK lets see if this makes sense-
I just came in from inspecting the squirrel condems...all seems to be well except for the cap I put on the port from the AI removal kit. It is cracked, but when blown in, I cant get it to leak. Would a pinhole in this create the problems I am having? ALSO, there is an airline attached to the center on the left side of the "can" (where the vaccuum lines go) that is not hooked up to anything. I cannot find ANYWHERE this would go...HELP!!!
From idle, when I crack the trottle, the bike hesitates then raps out.

Any size hole even a pinhole could cause problems. Replace it. Do whats simple first.

When I rebalance my carbs, during the time I pull off the rubber vacumn plug on the carb and replace it with the carb tuner hose, the bike will run very poorly. Any leak in those plugs will be very noticeable.

This sounds very much like a vacuum leak. Replace the 4 caps on the vacuum ports that are on top of the manifolds in between the carbs and cylinders. Also check to see if the rubber manifolds have cracks, are seated properly, and the clamps are tight.

Had the exact same symptoms on my wife's T100. It was hard to see the crack in the cap but it was there.

Those lines that go nowhere are drain lines for the airbox, in case any moisture gets in there, it can drain out and not get sucked into the carbs. Also check to see if you cracked anything on the airbox after the backfire. I blew the top of mine to pieces after a bad backfire. You'll have to remove the front seat to see the whole thing.