Bad Idle Help

Hey guys,
I've got a problem with my 1980 xj650 idling. When I adjust the idle screw I have two options is seems like.. Either it idles down like a normal bike but then at a red light I have to keep some on the throttle so it doesn't die. Or it idles super high to the point where I feel like I'm hurting the bike, and never comes down. I usually have to hop off as it warms up too so I can adjust it so it doesn't idle too high.

When I let the bike warm up and rev it a little bit, it will stay at a high rpm. Eventually, after adjusting the idle screw, there is a loud squeak and then it idles back down.

I hope I'm being clear in what I'm saying here. Thanks.

 

slides may be sticking, do they pass the clunk test? you may have vacuum leaks, test with carb cleaner at boots , nipple caps throttle shaft seals. in the mixture holes. see if rpms change when you do this. you can use a propane torch un lit if you want.

1050 rpm is spec 1100 to 1200 is ok . check the temps of header pipes you may be able to isolate problem to cylinder and carb.

idle to 2 or 3 k rpm is run off of the pilot jets, mixture screws and adjusted with the knob .

carbs been synced?
are you running pods or stock air filter.

valves in spec?

clamps on intake and airbox boots tight ?

enrichment plungers closing fully ? push down on them.

 

The slides are all very smooth. I replaced the springs the push them closed and they all slide well.

I'll try the vacuum leaks test and see what I find.

I'm running off of the stock airbox and all of the boots seem to be tight. But I'll see what happens when I test them.

When you say are the carbs synced, do you mean the butterfly flaps? I made sure they were all the same and all closed before I put them back on the last time.

The enrichment plungers are all closed and move freely.

My #1 cylinder header doesn't get hot at all. That's probably why it doesn't run smoothly but I don't know what to do to fix it. I've tried adjusting it and I've checked for spark and it has both.

 

Oh and I got to ride it around last night and I noticed that there was next to zero engine breaking. I had to use my breaks for everything. I don't know if that's just how these bikes are, this is my first one and first project in general.

One more thing: my exhaust is basically a straight pipe. All of the insides are rusted out and there is a huge whole in the bottom of one of them. The guy who had it before me let in sit in the rain or something

 

Is the #1 cylinder getting fuel? Check the bowl drain and fuel level.

 

I haven't checked the level, but it's definitely got a good amount in there

 

Setting the fuel levels


maybe open up mix screw 1/4 turn see if pipe fires

 

Does it heat up if you run it with enrichment open?

 

So now I've tested leaks with a propane torch and found that there was gasket between the boot going from the carbs to the engine on cylinder 1 and 4. Do you think I could do a good enough job with a gasket maker instead of having to buy new ones? The rest of the boots look good otherwise.

Adjusting the mixture screw didn't make the #1 cylinder fire but the propane made it fire. So I think that means I can reduce the trouble shooting to a fuel issue. Especially if it doesn't fire after getting a new seal.

When the enrichment is open, the #1 header gets warm but not hot.

 

Gasket maker would work or get some gasket paper from a parts store and cut your own. Less mess, cleaner look and no dry-time

 

sounds like you found the issue with a vacuum leak at gasket

 

Yep. I sealed it up yesterday and fired it up this morning. The #1 cylinder finally got hot!! Now the 3rd and 4th are not very hot but that's probably just a mixture thing.

Thanks so much!

 

mixture and/or need to be synced. unless the jets are reversed.

 

Here we are again...
My bike now isn't getting warm for the 3 and 4 headers. I've replaced the throttle shaft seals, the gasket between the intake manifolds and the engine and I've done the propane idle test and nothing seems to be leaking. The mixture screws are all at 2.5 turns out and I've bench synced the carbs.

I get backfire consistently when I let of the throttle if I ride it. Adjusting the mixture screws I the two cold cylinders don't seem to change anything. If I pull up the choke plungers on only one of the cold cylinders they rev to life it seems...

Why could be the problem? I feel like I've done everything right.

 

Sounds like you've got a blockage in the pilot circuits of 3 & 4.

 

On my 1980 (UK) XJ650, it was only idling on three cylinders, it wasn't firing on #3 cylinder, the header pipe was cold. Adjusted the pilot air screw until it fired up. Took the bike to a dyno centre which was able to do exhaust gas analysis on each cylinder from the tappings on the header pipes before the 4-2 collector box. The pilot air screws were set on each cylinder to get the correct air/fuel ratio. After that, the carbs. were balanced using vacuum gauges. If the engine revs hangup too high or drop down too low, the carbs. are likely not to be balanced correctly. Since this was done, I've had no further problems at idle.

 

I just went through this with my Johnny Cash bike, had two sets of carbs went through them , felt like it was running on three cylinders. Think I have it straightened out , the carb boots were bad , I coated with RTV but no luck . Put a set of Chinese new boots on , this looks like it cured problem . I will see in morning if bike starts and idles correctly . You might look very closely at your boots .

 

I have my suspicions that is what my problem is. There aren't and cracks on the inside that I can see, but the outside is pretty dry and there are a few cracks on around them. The only thing is that I did the propane test to no which I had no change. I thought that would have an affect but it didn't... Left me a bit confused.

I'm going to take the carbs off and look at the pilot. But I made sure they were clean before I put the bike away for the winter and I let the carbs sit dry, outside of the bike. So I didn't think that could be the problem, but I could be wrong. Maybe there was stuff that sat at the bottom of the tank and went straight into the carbs when I opened the petcock... Even though I have an in-line fuel filter.

 

The bike really hesitates at the lower RPM's when I first start riding it. Maybe that has something to do with it.

 

air filter clean ? maybe a mouse lives in it