Bonneville America Forums Forums Technical Forums General Tech misfiring any ideas????

at speed about 90mph loosing one cilinder slowing to about 70 is ok traveling a bit this month and this happend after about 2000 miles trip two weeks ago , was riding bike today again after 2 week brake and happend again .....have nology coils and iridium plugs no problems at constant speed 70-80 mph any ideas coils ? plugs?

In a very general sense (not specific to Triumph), your symptoms sound more like fuel starvation or exhaust restriction. You can probably rule out the latter if you have an exhaust crossover pipe and you're certain only one cylinder is affected.

Jack

Any chance you forgot to shift? Sounds like the rev limiter is kicking in and the speed is right for that.
I'd start by closing the petcock and shutting the engine down while it is acting up, then check the contents of the float bowls to see if there is a problem with fuel flow.
Next, since it's easiest to do, make sure the idle screws are both tuned for best idle speed. At around 85 - 90, the idle jets come back into action as a power enrichment circuit, so this could possibly be the problem.
If you can tell which cylinder is cutting out, try swapping the plug wires to see if it follows the wire. If so, the problem could be a weak coil or the timing sensor gap. If it doesn't, swap the sparkplugs from side to side to see if one plug is breaking down.
A long shot is a floating valve caused by a weak spring or sticky guide.

Try repositioning your vent line that drops from the float bowls. This solved similar problems I was having. You should probably check your float levels using the clear tubing on the drain method ( if it is back firing when the cyclinder cuts out then it is going lean if it is not then it is probably a spark issue.

for me seems like fuel starvation have to check carbs (CR Specials) will try new plugs and can put back OEM coils on bike.good idea to check bowls while its running badly, with those carbs only one bolt and will see how much fuel inside BTW epco exhaust and for sure is not restricted my next suspect is this small hidden fuel filter ..........and with speed about 70mph and 158 miles done bike took 12 liters of fuel only !!!!!!

it was fuel problem having CRII have fuel line to each carb and one was bent

Glad you got it sorted Greg

that was easy ..more fun was to change swingarm needle bearing