So I'm getting my wife's '99 F4 out and around. The bike hasn't been ridden much over the past few years but I always keep up on it. I run it to operating temp regularly if not take it for a quick ride to keep the carbs clean and always have the tank topped off with stable in it. Now that I'm getting ready to sell it it has a miss. I ran a can of Seafoam through it hoping it was just a clogged jet but that hasn't helped yet. I installed a new set of plugs, didn't help either. I hooked up the carb sync gauges and what I found is weird. #4 cylinder isn't reading much if any vacuum. I thought it may be my old gauges at first since I haven't used them in years so I switched the lines between #3 and #4 and then the gauge didn't read anything on #3 (now hooked to #4 cylinder) so I at least know my gauges are good and there's a problem with cylinder #4. What the hell should I be looking for? A serious vacuum leak, a stuck valve, what? The bike starts ok and idles pretty well until it gets down to the last 1/3 of the choke then idles rough and dies. Help me please this thing is on my nerves

 

if you give it some gas do you see some life in #4 ?
if not, there is some problem with the butterfly valve (I hope the translation is correct), or connection to the throttle .linkage
if it's just the idle part, start with the sync screw .

next on my would be the carb itself, possibly a a dirty idle (pilot) jet. note seafoam is hardly a proper replacement for a good carb cleaning. it's only good to make the job easier

if the carb is fine, and I doubt it, then you have a problem with the suction from the engine. one option is that the manifold is torn. the second is the engine itself doesn't create the suction. that is rather unlikely, but if there is some problem the rings are toast, or the valves won't open, then there want be the same intake suction. if that is the case you are looking at major engine damage.

none the less, I think the worst it can be is the manifold.

 

Sounds like a vacuum leak on that cylinder. Maybe boot is cracked. If no vacuum leak and boot is ok then I'd say sticking intake valve.

Good luck getting it running on all 4. But remember, to sell items on CBRF you have to be a senior member (100 + posts).

 

Yes I do see some life in #4 when I bring the revs up. #4 is the base carb though and I don't believe its adjustable. I know that Seafoam isn't a proper cleaning method. I was just hoping it would work because I'm trying to avoid removing the carbs on this bike I've got enough other projects going on right now. Wishful thinking I guess.

 

Sorry about the "sell" word. I know the rule but I wasn't thinking since I wasn't posting in the classifieds section. Sorry about that. Actually I have several people in my area already interested just by word of mouth.

Thanks for the advice. Any other ideas, please let me have them.