Question

I have a 1986 XJ700 Maxim-X with 18,xxx miles. I bought it in February and have been working on it for a few months now. I have done a fair amount of work on it including syncing the carbs to perfection, adjusting air fuel mixture just as well. I also added a set of DC1-1 dyna coils a while ago.

However, it still doesn't idle quite right, it seems like once it drops down to about 1,500rpms it begins idling on 3 cylinders and then it drops down to just a few hundred rpms where it sits for 30 seconds to a minute before dying.

Considering the mixture has been adjusted properly, the carbs are clean and synced and it has dyna coils what could be causing this? I don't really know where to look next.

thanks in advance,
-Ryan

 

By the way the petcock seems to be in pretty good shape, it doesn't leak and fuel flows freely when set to "PRI." The problem also occurs when set to "PRI" which says to me that the petcock is also not the problem.

edit: I've tried new plugs too, iridium and otherwise

 

How long since the carbs were thoroughly cleaned? Seems to be a common issue with these bikes. Search the forum for carb cleaning advice, there's plenty of it.

I take it your adjustment of the mixtures refers to reading the plugs. This can have a big effect on idling performance.

Did you use a YICS tool to tune and balance? Some here say it's absolutely necessary, a few disagree. Search the forum for "YICS" and you'll find several threads discussing this issue.

Wait around a bit, the forum Wizards will be along with better advice. They've helped me a lot along the way, I'm sure they'll do the same for you.

 

The carbs were cleaned WELL in february when I bought it, idle performance has not changed since and I have sea foamed it a couple times now.

I did adjust mixture by reading the plugs.

Its not a YICS motorcycle.

 

I should clarify, I tore the carbs apart originally, clunk test, checked all the jets etc, they are really really good and clean.

 

Does it idle OK when you first start it up?

 

It idles a tad better when it first starts up from cold with the choke still full on

 

Sorry for the delay, had to go mow the lawn.

Any chance there's a linkage issue? Could be some play in it maybe letting the butterflies sneak shut?

Maybe I can help you keep your thread on the front page long enough for one of the Wizards to come a long and tell you how to fix it?

 

I know this one's a real bummer 'cause it's an "X" but when were the valves last adjusted, or were they ever? If not, it IS overdue. They were often overlooked on the X's moreso than the other XJs because the camshafts have to come out to make the adjustment.

You don't have to pull the cams to check them however.

A tight valve will prevent a smooth idle.

Just a thought.

 

Do the "unlit propane" test. You could also use starting fluid.
See if the idle picks up. While idling on 3, spray water on the exhaust- - that tells ya which carb is being lazy.
Check the "wet set" of the floats while on the bike??
I'm sure there's lots of other things. . .

 

I'd also suggest hooking up a battery charger just in case it's a low voltage problem... see if it runs better with the charger ensuring a good 12V supply.

 

I see you checked and cleaned the jets but did you also clean the emulsion tubes? I do believe this will also effect the idle. I know on mine, I cleaned the carbs including the jets, but missed the emulsion tubes and it ran like crap. I cleaned the tubes and boom ran like a champ. Just a thought

 

What is the wet set? Float height?

 

Really? I think the service manual says to check them at 24,000 or something, I'm just now coming up on 19k.

 

Find-out what Hole isn't hitting.
Determine if the miss is Fuel or Spark related.
Swap the Coil Plug-ins and see it the miss moves to another Hole.
Look at your Spark Plug wires in the dark and see if ones shorting-out to ground.
Measure the Voltage at the Batt. with the Bike at 2K rpm's and read the Voltage at the Battery. 14.2~14.5 Volts OK. Less indicates Elect problem.

 

Yes, bike assembled and running, idleing on mainstand, clear tube on the carb drain. Be careful. But due to the carb angle, the "bolus" is compared to the center of the carb, not a rear screw. 3 MM down from the gasket, a picture here would be nice. . .

Float Height Illustration:

 

thank you much