Need help with my xj650

I have a 1981 xj650 Maxim that has the number 1 cylinder nit firing.
I ran a compression test and it tested good. I have confirmed that the spark is good. i have cleaned the carbs and the number 1 carb has been cleaned 3 times and still dead cylinder. I changed the carb for another carb known to be good. I have changed the coil for that cylinder to one known to be good. In the end I have determined that fuel is present in the carb bowl but for some reason is not uptaking from the bowl. Again I have cleaned carb repeatedly and still a dry plug and a dead miss. I sprayed a little starting fluid into the vacuum tube on the manifold boot and it makes the cylinder fire. Can anyone please help me with a suggestion about what this might be it has about driven me crazy.

Thanks, PAPPY

 

Pappy, something doesn't quite sound right to me about switching the carb since that's a huge job and doesn't sound right with cleaning the original 3 time....but it really doesn't matter...you know where the problem is if it fired with starting fluid....btw, next time use wd40 or the type of fliud with oil in it so you dont score your cylinder walls.


you didn't tell us if this bike was running great then died or if you bought it this way so it's hard to pick the correct path to go...but

I think that you need to suck it up and remove the bank of carbs and give them a proper cleaning. Spraying some cleaner in usually doesn't really clean them since it can't clean out all the small passages and pieces. Sometimes you can get lucky if you can carefully remove the float bowl and spray your cleaner into the jets and clean any passages in the bowl itself if your carb has them.

I know that you prob don't want to get into all that but think of it this way, you KNOW that your present problem is in the carb and if you clean/rebuild them now, you'll be able to ride trouble free all summer!!

jeff

 

Hey JeffK, thanks for your response to my quandry. I really did switch the number 1 carb for another identical carb from another identical bike I own. I just bought the other bike and had just cleaned the carbs on it and hadn't installed them yet. The swap took about an hour plus about 25 minutes to synch. I didn't dip the carb bodies. I did remove everything except the butterflies and cleaned thorouglly with carb cleaner and blew out every jet and opening I could find with air. Would you recommend that I dip the carb body and clean everything again to see if that corrects the problem. What bothers me is that I have done this a number of times successfully and have now hit a tough one. The thing that bothers me about this the most is that there is fuel in the bowl and jets are clean and clear, carb slides sliding smoothly and pleaty of vacuum present at the manifold. It just seems that the vacuum is not getting to the upper carb chamber to push the slide to open the main jet. but if this is true the idle jet should still provide fuel for the cylinder to fire at an idle. There must be something I just don't know. Thanks again for your help let me know if anyone has any ideas..

 

What pressure readings did you get off of the compression gauge? Are the valve clearances correct? Have you ensured that the little jet in the float bowl is clear? You will have hard starting issues if it is blocked. You say you have spark, what color is it and how did you determine the spark on that cylinder?
Sorry if this sounds like the third degreee but I want to make sure that all the bases are covered and there isn't an misunderstanding. I agree with Jeff, how was the bike running before all this happened?

 

make sure that all carbs pass the "clunk test".

 

While you had it apart did you put the one that is not working on the rack from the good bike to see if it would fire on the other bike? Just another double blind test for the faulty carb is all.
If it acts the same then it's def tha carb, if it runs then it's something else. Just sayin....

 

Could be massively leaking Throttle Shaft seals, or bad/cracked/broken intake manifolds.

Some massive air leak, so you're pullin air, not air/fuel.

 

Gotta back up further:

How are you setting your float levels? (My vote.)

What are you using to bench sync? (Paper clip, feeler gauge, strip of business card?)

Did you check the intake manifolds from the inside to be sure that any cracks don't go all the way through?

Did you remove the carb hats and inspect the diaphragms?

Since it's the #1 carb, have you pulled the throttle shaft clip and fiber washer off the outside and had a peek at the throttle shaft seal you can get at? Quite often it will provide a clue as to the condition of the others.

 

Thanks to everyone for your insight to my carburetor issue. I finally found the problem. The float was out of adjustment and was not letting the fuel level get high enough in the bowl for the jets to pick up. I have egg on my face but i guess I just happened to have two identical number 1 carbs with floats out of adjustment, go figure that. After about 15 hours she pulls like a freight train WOW! Thanks again you people are the best!

 

Just glad that you found the problem and are out riding instead of troubleshooting!!

jeff