Bike dies at idle

Hi everyone. I'm a complete beginner with motorcycles and I found this forum.

A friend gave me his '81 XJ 650. We've been trying to get it back into running form. I learned how to remove the carburetors and we cleaned them thoroughly and put them back on the bike last night. The bike now runs fine. The problem is that to start it you have to have the choke on every time (and leave it on), even when the bike is warm. Also, if you don't keep rolling the throttle the bike will die almost instantly. it doesn't even try to idle really.

Clean carburetors, new spark plugs...any idea what it could be or what I should check next?

 

You could try turning the idle up, its the knob between the 2 middle float bowls.

 

I am having the same problem--cleaned the carbs, still need the choke set high. I did notice some cracks in the intake boots that I need to repair w/RTV. Haven't done it tho. How do your boots look?

 

Can you explain to me where the intake boots or or what they look like? Like I said, I'm a total novice.

I will check later this afternoon. The bike is in my buddies garage still until we can get it drivable to bring to my garage.

I'll look for that idle screw in the middle of the carbs too. I know there is one on the left side of the bike where the throttle cable attaches. I thought that was the idle screw. but perhaps it is something else?

 

Don't worry, everyone is new at least once :wink:

They are those rubber hose thingies that are in front of the carbs. They might also be called joints or something. Someone told me that they are really important and can mess with the idle.

Go to this forum for ideas on how to fix cracks: http://www.xjbikes.com/Forums/viewtopic/t=11593/highlight=rtv.html

 

The carb boots are the short, fat, round black rubber hoses that connect the back of the carbs with the airbox which is under the seat and is where the air filter lives under a lid that's held down with two bolts and a screw.
If air gets into the air-fuel mixture, it can mess things up.
Start the bike, with the choke if you have to, and spray WD40 around the boots and carbs. If the revs climb suddenly, you've found your air leak. It's sucking in the WD40 and using it as additional fuel to push up the revs.
Next thing you do is this:
Go buy a Haynes Manual for Yamaha XJ Fours. Study this book carefully and follow the instructions to the letter. Using this website as solid back up and you'll have your bike running in no time. You might also buy the XJ CD set that's sold for $15 on the front page of the Forums section. There's tons of stuff in there you'll never find in manuals.
Good luck and let us know how things work out.
baz

 

hi, # 7 in the diagram is the idle screw.
#6 is one of the screws used to sync' the carbs, if the carbs have been synchronized & you turn these screws you will mess up the sync.

 

Worked on the bike a bit today. The hoses seem to be fine. I didn't noice any vacuum leaks when doing the wd-40 trick.

I attached a picture because I am stuck (sorry it's a crappy pic I took with my phone). The above diagram and the manual I have for the bike didn't point me to where my air mixture screw is.

I found the :edit: idle speed screw (A), but can't find the :edit: idle mixture screw. My manual says it should be above the throttle cable, kind of where the choke is. My bike was pieced together from an 80 and 81 XJ so perhaps that is why it isn't where I think it should be? Who knows.

I put in new plugs and ran the bike a little bit today. As long as the choke was on full, the bike would start just fine and "idle" between 3k-4k. As soon as I took the choke off the bike would die right away. I took out the plugs and checked them. Both were quite black. I'm assuming I just need more air mixed in with the fuel?

Anyways, just thought I'd update everyone and see if any more advice could be offered. Thanks!

 

The choke is an enrichment, so that would explain why the plugs are black - because with the choke you are running a little rich.

The idle mixture screw should be a big knob in between all the the carbs... Turn the screw in - clockwise to raise the idle.

Don't worry about the fuel/air ratios yet, lets get it idling first and seeing that your new, lets not touch those

 

Ok, I won't touch them then. But what should I do next to get it idling? Take off the carbs and clean them again? I just did that a few days ago.

I think I've probably confused my terms. There is the idle speed screw, idle mixture screw, and then the air/fuel mixture knob.

I'm trying to locate the idle mixture screw. Can I mess with that one a little or should I leave it alone (like the air/fule mixture knob)?

 

I am at my wits end. I don't know what else to do. Being a novice I think I have tried everything possible, within my abilities.

Today I took the carburetors back off and cleaned them thoroughly. I checked again for any vacuum leaks from the hoses.

Once back together the bike fired right up but only with the choke on full. It would idle itself around 4k. If I take the choke off 1/2 or all the way the bike immediately dies.

The Clymer manual that I got with the bike shows an idle mixture screw where it clearly isn't. (see pic above) I haven't messed with the sync knob, or whatever it is down between the 2 carbs.

I don't know what else to do...and I want to ride it so bad!

Help

 

I might be wrong, Sarthek, but I don't think they are the right carbs for that bike. (edit) I will go further to say I don't think it's a 1981 XJ650.

 

The guy pieced together this bike from an '80 and an '81 XJ 650 (according to him). He rode it for years until he got an '06 Harley about 2 years ago. He is now giving me the old bike and helping me get it running.

When he rode it, it ran fine and he had no trouble using it as a daily driver to work in the good weather months.

He's a very good friend of mine, and the bike is free, so I know he isn't being deceitful.

*edit* Here is a picture of the bike as of last week. Maybe you can tell what it is, if it's not an XJ 650? The tank said Yamaha on it earlier, but we used bondo on some dents and took off the emblems. Oh and the user manual he gave me that he used with the bike says "Clymer Yamaha 650cc twins 1970-1982".

 

Reading through the manual there is a supplement in the back and in the section titled Idle Mixture Adjustment it says, "All 1980 and later models have no idle mixture adjustment method."

I guess that is why I couldn't find it on the bike! But still, that doesn't help solve the problem...

 

1) That's a 2 cylinder bike. The 650 has four. If that is an XJ, the only one that people say has two cylinders is the 400... except that the parts fiche I'm looking at also says that, too, is a 4 cylinder.

2) Chacal would know better, but AFAIK, the 650 uses the same carbs as the 750... and those carbs ain't it.

Is that an XS model, perchance? Does that puppy have a kickstart on it?

 

Yes it does have a kickstart, in addition to the push button electric start.

 

I would say 80/81 XS 650 with a stack of mods / changes.
There are sites that deal more specifically with the XS, thats not to say you can't get help here. Wiz.

 

looks like an 80's xs650 to me



btw i have a seca 550 and mine is doing the same thing with brand new boots on the carbs. dies at anything less than 1/2 choke.

i have a feeling i'll have to take it to the shop to sort it out

 

DING DING DING!

I think we hae a winner here, folks.

 

I agree, it does look like an XS. Thanks guys!

Now, what do you think needs to be looked at next if an XS dies when the choke is taken off?

 

the carburetors...Synch and adjustment on a twin is a whole different procedure than on a 4cyl (XJ) suggest you start with the book he gave you, if idle settings (air/fuel either) or synch are wrong on a twin getting an idle is even more difficult than a 4-banger. Before you go too crazy messing with the carbs, though---check the timing. I'm not so sure those XS's didn't still have POINTS rather than electronically-triggered ignition. If the timing is way off, a twin won't idle right either...

 

Update again:

Ran the bike tonight with a friend. After a few minutes we were actually able to turn the choke off as long as we rolled the throttle! Barely holding the throttle open we were able to get it to run around 1500 RPM. Progress! If we released the throttle with the choke off it died instantly. If we released the throttle with the choke on full it jumped to 4k RPM.

But, as we were working on it a neighbor drove by and popped his head out of the window and said, "sounds like you are running on one cylinder." Sure enough, we checked it out, and the right side of the bike was running cold. The spark plug is fine, but there is no spark. I don't know what to do to troubleshoot it, but it appears to be a problem with the wire going to the plug or something with the coil perhaps?

 

Worked on the bike again last night. Helpful neighbor came over again to look at it with us. Doing some testing we found that the plug DID spark, so we traced the issue back to the carbs. We took them out and dissassembled them again. We found what we think is the idle jet and cleaned it really good. Couldn't get any carb cleaner or a wire through it though so both are either completely jammed, or something?

Let them soak for a bit and am going to try and put the carbs back on the bike today and see what happens.

 

Put everything back on tonight and started her up...she idled!!! We still have it running on just one cylinder for some reason. Going to see if we can figure it out tomorrow but things are going well.