Snapping or popping on rev?

[JLamb]

91 ST1100 w/ 80K miles. Overall the bike runs pretty good. Seems to have good power, pulls to RL without any noises, hesitation etc. Doesn't use oil. However - when I rev the motor with the clutch in or in neutral there is a loud sharp snapping noise that seems to be coming from the exhaust - or rather happening inside the exhaust. It sound like a really fast hard metal to metal snap. Several occur each time the throttle is twisted. It doesn't sound like knock - maybe detonation? But at the rate they occur I think detonation would have caused some damage by now? Any ideas?

 

[ST1100Y]

Downpipe heat-shields cracked/loose... m2c...

 

[John OoSTerhuis]

Downpipe heat-shields cracked/loose....

+1

John

 

[JLamb]

Good thought but not the case as far as I can tell. Lower fairings removed - all heat shields present and accounted for - no cracks or loose parts. The noise seems much sharper that a loose part might generate. Could it be unburnt gas combusting in the exhaust? Plugs don't look like I'm running rich. Bike starts well on full choke and requires some choke until fully warm. It has never sounded great at slow idle - a little lumpy but no issues, no smoke, no stalling, etc. I have synced the carbs, changed the main air filter and the little air filter but otherwise haven't touched the carbs.

 

[Kevin_56]

Not meaning to be a smart *****. If it only does it when you have the clutch in or in neutral. Yet runs strong and quiet when accelerating through the gears. Stop reving it when not moving. If it was a detonation issue, one would think it would do it under a load also. I am sure someone will come up with the correct answer to your noise.

 

[vinny]

I am guessing dirty pilot jets because ( It has never sounded great at slow idle - a little lumpy but no issues );( Bike starts well on full choke and requires some choke until fully warm ). Being a 91 with only 80K on the clock and with the mandated ethanol in the gas... that's where I placing my bet. You will never get a great carb sync until they are clean. I recommend you pull the carbs and 1) check the isolators for suppleness, 2) pull the bowls and clean them and the jets, both the pilot and high speed. Clean them with a good chemical dip or possibly boiling them in pine sol. Replace the isolators if they are hard or cracked. After reassembly, continue to run some "seafoam" for several tanks, then resync the carbs. As an added bonus, you might want to pull the pair valves and clean them inside as they can become clogged with oil residue and that can hurt the effectiveness of detonation in the exhaust.

 

[JLamb]

Sounds like now is the time to do this as it is exposed. Is there a link to a manual or procedure for carb removal?

 

[JLamb]

I Found many links in this forum. Thanks