Bucking problems

Ok I have an XJ 750. Its the same one rubikscube2007 has mentioned before if you've read any of his posts. We just cleaned out the jets and emulsion tubes and basically gave the carbs a good cleaning.

Now it is for lack of a better word bucking in the lower gears. Some where round 30 mph it tapers off. Idle screws are set at 2 all across. Any idea what else could be causing this??

 

Ok just tuned it to 4 out and it has lessened it, but still doing it.

 

Possibly a stupid question. Read that the bucking could be from being too lean, but am worried about fouling the plugs. They are pretty dark as it is. What should they look like. Little brown? Black? Orange?

 

float levels ?
vacuum petcock ?

 

Fuel issue , Look for flow to carbs, Yep Petcock, fuel lines, Maybe rust in tubes on carbs blocking fuel flow, or plugged screen on petcock in tank.

 

It didn't start doing this till we cleaned the jets. Before it ran ok. Didn't idle very well, but didn't buck. Will go out and check everything though. Petcock was recently cleaned and 90% sure isn't rust in tubes on carbs. Rubik is out takin it for a spin to see if it's running any better.

 

Wouldn't fuel affect high end as well as low? And everything is clean. Only thing not sure on are the floats. Rubik cleaned everything else recently though.

 

Did you synchronize?

Bench sync is only an opener. You have to exactly match pairs of carbs.

 

Local mech hasn't been able to because they said was an air leak. But we've fixed that(or at least think we have. if not its a sneaky bastard that doesn't want to be found). And don't have the tools obviously to do it ourselves.

 

My bike would die when applying throttle after a carb cleaning.
I did a very accurate bench synch after the carb cleaning.
Carbs 3/4 were horribly out of synch when I hooked up the differential bottles. It took me several minutes of twizzling the 3/4 sync screw to get them in balance. Once they were in balance the engine took throttle like an Indy race car.

Do not do anything else until you can properly sync your carbs.
My gallery has a picture of the home made sych bottles I made and used to tune my engine.

 

Went to start it this morning on way to class and wouldn't. Had to run so couldn't give it time to see if it was the cold. Got back and it still wasn't. Pulled the plugs on off. Black as night. Even had some crusties in there. Cleaned them of really well and it fired right up. So going to get it synced and hopefully that will stop the bucking. Could that be what was causing the plugs to get nasty.

 

super-rich condition causes "sooty" plugs. those carbs need tuned.

 

Either your mix is too rich or you idled a long time with the enrichment circuit on.

 

is it a seca or a maxim. If its a seca did you put the fuel jets and air jets in right?

 

Can't remember off the top of my head who but someone here has a great home made "bottle tool" for syncing, gonna make one soon myself just a thought tho
Shaun

 

Yeah found it. Theres the paper clip one also. Did that. Evidently I was misinformed about last time it was synced. Going to do a vacuum one, but wasn't able to go get necessary tools. Waiting now to get the carbs put back on actually because I got pulled away in the middle of it. By the way Underworld is not worth giving up two hours of bike time. Damn in-laws making me go out.

 

Finished the bench sync then it got too cold to do anything else for about a week. Kept not starting and was attributing it to the cold. Turns out was the spark plugs. Swiped the ones off Rubiks bike threw them on and it fired right up. Took her out for a ride and the bucking problem is gone. Hopefully just getting a good vacuum sync on it now and tuned properly.

Though it did make an odd noise after I got back. Best I can describe it is a clack. Had it back in the garage after the ride and went to turn it on one more time to see how it was idling. Hit the start and turned over for a sec made the odd noise. Waited a bit then tried it and it started fine, but made that noise again. Wondering why it didn't when I first took it out. Mean stopped by a gas station and didn't do it there either. Think I should just wait till I get the vacuum synced and tuned well and see if that fixes it or are there any ideas?

Ohh and on a side not Scotch Brite is AMAZING!!! It makes stuff so shiny!

 

Rebelelf, be glad your inlaws are treating. I'm supporting both of mine.
The odd noise might be your starter/starter clutch which gives a weird but short low pitched whine when they get sticky. Since it sounds like it settles down after you warm it up, I'd say an oil change might be just the ticket. Try running some Seafoam in it at change-out time (never run it under load or for very long with Seafoam in the oil) just before you drain the oil. It will be good and hot and will clean out nastiness. That and pulling, cleaning and regreasing your starter. You might also try to shoot some carb cleaner in the starter clutch (accessible throught the alternator shaft port) rollers to free them up (do this just before the oil change so as to remove the contaminates and not ruin your bearings).
Did you know that Scotch Brite is available in different "grits" or grades?
You can get coarse (usually black), medium (red and green), and fine (white or tan). Check out your local supply store (Grainger, McMaster-Carr, etc...).

 

Scotchbrite is a good start, followed by 1200 or 1500 grit wet sandpaper and then a good metal polish:



This cover was corroded and SERIOUSLY torn up, you can still see the three scratches that wouldn't come out without sanding through it...

 

Ok so evidently I am not to be trusted to do anything on my own. Rubiks redid my bench sync. We adjusted the float levels. Bucking problem is still gone. However it still doesn't idle and is still running really rich and fouling the plugs. Took it out for maybe 20 minutes and checked them and yeah they are black and sooty already. Ideas? Aside from good vacuum sync?

 

WHY!!! It is still running rich. Tuned to 2 across. Colortuned it and still running really rich. What can be causing this? Can't get it vacuume synced till we get it to idle. Ahh.

 

I did something really dumb once. I had the floats in upside down and I bent the tabs to get the right float height and it was really running bad. I took off the carbs again for about the 10th time and figured out by looking at the pictures in the book I had screwed up. I settled down and got them to work pretty good. Don't know if thats your problem but your getting too much fuel and that would have to be float, needle / seat, height adjustment.
Did you try to bench test the fuel levels with the clear plastic tube up the side of the carbs to see if you were below the float bowl screw washer? Or are your drain screws stuck.

 

One more question to ask may be does anyone know the correct float height for a 1982 Maxim XJ750J? We set the float height off the user's manual for my 1985 Maxim XJ700N, which was 16mm.

Too high a float would run too rich, correct?

 

Yes & 17 mm