‘87 YX600 idles fine, but drops after short ride

Happy Thanksgiving.

It’s not an XJ but I think it has the same engine and Mikuni carbs. Having issues with it staying at idle after very short rides. It will idle fine sitting still but after a short drive it will cut out. I can work through the gears and it rides smooth. As soon as I come to a stop with the clutch in it cuts out. In order to start it I have to adjust the idle screw as if it back out. Here’s what I’ve done so far
1. Fully rebuilt and cleaned the carbs, 3 times.
2. Synched carbs
3. Colortuned fuel/air mixture. One consistent issue is that 2 and 3 have to be all the way in for proper ratio. I know that’s not right so any help worth this as well. I tested spark and the spark jump and it goes an inch or more. So I feel the coil is fine.
4. Cut back the spark plug wires 1/4 of an inch.
5. New carb boots
6. Checked float bowl measurement and it’s not perfect but fuel volume doesn’t seem to be an issue.
6. Valves shims to within spec
7. It does have pods(not my choice, prior owner had them on and no air box). I Gerry-rigged a cone like sheeting for the inside of the pods to limit air intake. It’s seemed to have worked and runs smooth from idle to fully open and everything in between.
8. new E3 spark plugs
9. Changed oil three times.

I just recently realized I’m missing the spring on the idle screw. So I thought it was backing itself out after riding. But, I put loc-tite on the threads and set the idle after it warmed up. I feel confident it’s not backing out. Does the spring play that much of a role in maintaining the idle?

Any help?

Sean

 

well yes, it puts pressure on the idle screw to stop it moving , did you break the "bond " on the loc-tite after it set ,to set the idle.
what are E3 spark plugs, i think your engine uses the same as my xj600 engine,
NGK DR8 ES-L

 

I did break the bond on the loc tite but doesn’t loosen or tighten freely. It takes some torque either way. Not sure if it’s loosening or if it’s something else.

I read in one of the posts that describes a ‘schitzoid’ engine with this type of symptom. Said it was likely the throttle shaft plate could be a culprit.

E3 is a brand and the E.36 version is compatible with NGKs.

 

so ,is it still cutting out after you did this mod?
do you have the carb to airbox boots, apparently if you fit the boots to the carbs ,and put the pods on the end of the boots, it acts as the same as with air box , causing a venturi, to operate the slides

 

Idle issues will not be because of the pods - look for leaking throttle shafts, float valves and or levels not constant, air leaks in the manifolds, or jets semi blocked. All carbs should be correct at something like the same turns out on mixture screws. Is the running synch correct?
Just my opinion of course.

 

How do I check for leaking throttle shafts? Wouldn’t the float bowl levels impact my ability to run wide open through 4th gear? I can drive it a 1/2 mile (possibly more, but not risking taking it out of the neighborhood) wide open and it cuts out only when I pull the clutch in to slow down.
The running synch is perfect. It idles nice at start up and seems steady if I just let it sit. It’s only when I take it out.
Oh, it cuts out if I try to use the choke. The cable isn’t connect. I just pull up the choke when it’s idling and then it cuts out. Does that indicate anything?

 

1 and 4 are 2.5ish turns out and seem perfect. Whereas 2 and 3 are almost all the way in before I see blue on the color tune.

 

are you certain you removed all the o rings and washers on the 2&3 idle screws?

Some things you can try:
Check sync when starting up and a short warm up
After its warm and you need to turn idle screw in, check sync again. It may tell you which cylinder(s) is the issue.
Are you sure when its warmed up, that all cylinders are firing?

Check timing before and after the ride. (got a timing light?)

 

Yes, it does, quite what I don't know. You need to explore this further. Part of the ownership of these old bikes is developing a knack for fault finding and diagnosis. I'm thinking an electrical issue,perhaps losing you the coil supply, linked to the kill switch or the stop switch circuit?

 

.

After reading through the thread so far I'd venture to say that you still haven't gotten the pilot circuits on the carbs properly cleaned out.

There's two different methods to do this, one is dipping the carb bodies in an ultrasonic bath with a cleaning solvent and the other using a specialty carb cleaning product like Berrymans carb dip. I've personally tried boiling the carb bodies with a 50/50 mix of Pine Sol and water but in the end the results where not as good as the first two options.

In order for either of those to work properly you'll need to stop EVERY part off the carb bodies and yes, you will need to replace every piece of rubber in them including the shaft seals. With it being the end of the riding season for the majority of the country now is the time to get it done right so you can enjoy trouble free riding next spring.

 

I also have a yx600 and replacing the pilot jets cured the idle issue I was having.
Derek from motolab recommends replacing the pilot jets every time you rebuild these bs30’s. Mikuni brand jets are readily available.

The other issue I fixed yesterday was my throttle cable, which was a bit too tight..

 

I am losing it now. Every time I think I’m fixing something I feel it’s getting worse. Took them off and felt like I cleaned everything well. Put them back on and when I turn the fuel spigot on fuel is coming out of the air intake side, the small hole that I think goes to the main jet circuit. When I start the bike the fuel stops coming out. Does that mean the floats aren’t set properly? I reset those to spec. They were all off but it seems like a huge difference between the old setting and the new. If they are too high will it cause too much fuel and therefore overflow into that air intake hole?

I do have the Berryman chemdip so will try that. Round 5 of cleaning.

 

This is where the fuel is coming from.

 

Either/ and / or:
1) Your float(s) are set too high - (20mm works well for me) on my bs30’s
2) one or more of your needle valves are getting hung up (stuck), causing the carb to constantly call for fuel.


I had this same issue. I fixed by replacing all four needle valves and seats. Yamaha Needle Valve Set part number: 25g-14107-23

 

you need to wet set the floats.
3mm from top of bowl with carbs level.
Another thing you can do now:
You can hook up fuel line to the drain and inspect them while they are still on the bike to see which carb is out of wack.
This is NOT the method to set the carbs but its a good indication if something is wrong or not.