So I just got my 91 f2 on the road and it has been running better than i had expected. The only problem I have been having now is the bike will not return to idle when warm. The bike will start fine with choke. After it warms up a little I will take choke off and it will idle fine. Then after like 5-10 miles of riding (when the bike is properly warm) the bike will not go back to idle with the clutch pulled in / sometimes in nuetral. If i engine break then the bike will go all the way back down, but if i pull the clutch in anywhere near 4k or more then the bike just hovers around 3k rpm. Once I let out on the clutch the bike again behaves normally and rides fine but if I put it in nuetral while it is stuck on the high idle then it usually stays around 3k still or might drop down to 2k but not to normal idle. If i turn the idle screw down then it seems to go back to normal but then the next time I start the bike cold i need to turn the idle screw back to where it was or the bike will not have enough to start. I should mention that I do not know if this was normal for the bike because this weekend was the first time I got it out to ride since I bought it. I also just stripped the carbs and only cleaned the float bowls, and jets. The carbs were not taken apart from each other. before i went through the bike it would not idle at all, then once i got it idling there was an air leak because of missing air box gaskets which led to a really shaky idle, and now it idles but has this problem.
Could my idle screw be vibrating into a higher idle while I am riding? (it is just zip tied to the frame)
Could my choke be getting stuck? (operated fine before I put the bike back together.
Is there an internal problem with the carbs or something I forgot to clean that could effect this aspect of the idle?

 

Did you remove or change the pilot jet screws while cleaning? Sounds like the pilot is a little bit lean. I've had to adjust my idle when the mornings get cooler and then adjust later when the temps went up. That's why it is on our bikes and so close at hand to adjust. If your choke cable was on too much, it would bog the idle down and die. It may need a slight adjustment on the cable clamp under the airbox. There is a groove in the ferrule, I've moved mine over to pull out slack that came as the cable stretched with age. It helps the cold start and idle.

 

I'm with gpfan1 on this, with regards to your pilot circuit being lean... what you're describing - a hanging in idle, and the fact that this problem begins when the bike is fully warmed up - is indicative of a lean condition.

Like him, I am also curious as to how thorough your cleaning was, i.e., did you remove the pilot jets for soaking, AND, remove the fuel screws as well, to get things nice and clean?
If you did remove the fuel screws, did you first turn them in, to count the number of "turns out" they were set at? Lastly what were those settings?

 

from what I know I did remove the pilot jets. I removed the big one, the one it is inserted into, and the smaller one. I shot carb cleaner and compressed air through all of the jets to make sure they were clear. I did not change the screws... are those screws the gold ones that are under each carb? (they need a little d-shaped tool) if so then mine are all jacked up and I did not adjust them. THose screws are all broken off and jammed up...

I guess I should get a screw extractor and put some new ones in?
And they control the fuel air mixture per cylinder? similar to the little idle screw i can adjust by hand but just more specific?

Thanks for the answer guys

 

Yes, those are the ones.

Oh my... that sucks, that means someone before you was an IDIOT! Get some good pics of each of those four screws, and post them up.

Yes, you could say it that way. Those screws, in a nutsheel, are your "fine tuning *****" for the pilot jet... the idle adjustment screw manages the overall idle speed on all four carbs, by changing the butterfly postion - the fuel screws "meter" the individual pilot jets operation, which of course, does affect your idle, as the pilot circuit governs idle, low RPM cruise, and small throttle openings at high RPMs.

It sucks that these screws are boogered up, but the good news is, at least you know where the problem most assuredly lies!

By the way, one way to know absolutely for sure that your pilot circuit is clear, after you've got the fuel screw dilemma dealt with, is to safely prop the butterflies open, remove the pilot jets, insert the straw on the carb cleaner can well into the pilot jet hole, kind of sealing around the opening with a couple of fingers, and verify that when you spray, you can see carb cleaner flowing nicely from the three small holes that are grouped together in the carb throat.

 

That is cool how you answered specific quotes... i got to learn how to do that.

When I cleaned the jets I put them back in, squirted some carb cleaner into them and then squirted some compressed air through them to make sure everything came out of that small cluster. It in fact worked.

It didn't take long for me to realize the previous owner / owners were idiots.... not too happpy about that. Everything on the bike is butchered, but from 10 ft. away while some one else is riding it it looks freaking sweet ahaha

Anyway I don't have a picture right now because I put the bike back together and have been riding. Pretty much 3 screws look to be broken in half but screwed in. The other screw is similar put part of the actual metal is chipped away. Today I went out for a ride and after warming the bike up and having the idle go up I re-adjusted it to be around 1.2-1.5k and it pretty much ran spot on all day after that, even after starting and stopping the bike several times. The exhaust pops occasionally under deceleration from over 6k rpm, which I have read is also from runnning lean. Is there any risk in riding like this?

 

That really depends on how lean it is. Running extremely lean for extended periods of time can cause all kinds of havoc on the internals. That's why most tuners for engines, be it car or bike, set initial settings rich. As long as it isn't way lean, you should be OK during your tuning. I won't recommend staying there permanently, but as my bikes po was a pos too, I understand prioritizing repairs. Good luck.

 

hi guys I hope you havent given up on the thread yet! I took pictures of the screws and a spark plug today. The screws are worse then i thought and do not appear salvagable.... any ideas? I think i need to buy new carbs. Anyone have any for sale?

The spark plug did look lean even though I am not 100% how that looks. It was light tan and had a smidge of white in there. look for yourselves. Sorry i took it on concrete and everything kind of blends. Any new thoughts on the condition of the bike and if i should riding it until i make repairs?

 

I should also mention these plugs only have about 200 miles on them so I am assuming that makes it harder to tell if there is a problem or not. From what I am finding online it looks to be an ok color.

 

sorry, also what i am finding is that the tip will be a certain color in correspondence with the idle and as the rpm rises it corresponds lower on the plug. is that true? Like i said before the exhaust pops under deceleration over 6k rpm which would make sense because it appears lean in the higher rpm range (i know 6k isnt even high for these bikes). And i also rarely go over 6-7k on a regular basis so i am assuming that is still really clean as well as lean. just some extra thoughts for anyone that will chime in to give me a suggestion on what to do.