Hello,

I'll just type up my story, and if anyone has any suggestions as to what could be wrong or how to fix it, I'm all ears.

So yesterday I finally got everything sorted out for my '87 rebuild. I got it started (although it was running pretty rough) and put about 3 miles on it. I'd start it with it fully choked, and it would immediately rev itself up to about 4k. After that, it would either run at 1.5k, or rev itself up to about ~4k all on it's own. It seemed to go back and forth in no real pattern. Anytime I went to un-choke it, it would run, but if I let it try to idle it would die. With those symptoms I went out and rode it, all the time while choked a little, and never letting it idle completely.

So today I go out to do some more troubleshooting. It took a while to get it started, and when I did get it started, it would idle at about 1.5k, and randomly take itself up to ~3k and hold for a while, then back down, etc.. If I unchoked it at all, it would completely die (it would run if I was giving it a fair amount of throttle, but as soon as I let up any it would die). I figured I'd try some different things and see if anything I did changed the symptoms. I started by taking off the entire airbox (to see if restriction in airflow had anything to do with it). It did pretty much exactly the same things with the airbox off as it did with it on.

I know my fuel pump is working, my petcock isn't blocked, and my fuel is good. So that means that at the very least my carbs are getting gas. After my test today, I don't think air delivery has anything to do with it. Does this sound like a problem with carb adjustment? Maybe something to do with valve adjustment?

I REALLLLY don't want to tear the engine apart three days after I got everything together and satisfactory to ride it, but if it genuinely sounds like a valve problem I guess that's what I'll have to do.

Things I plan on picking up in the very near future (maybe they'll fix the problem?):
New plugs and wires.
Manual CCT.
Carb rebuild kit (where's a good and cheap place to get a rebuild kit?)

Thanks,
-Matt

 

sounds like possibly a idle circuit problem in the carbs. had you done a sync? is your valve timing correct, no retard or advance. what happens if you leave the choke on a little after the bike is warm?

 

I agree you should clean the idle portion of your carbs, or just do it all while you're at it. Take the bowls off and take the floats/needles out. Take out the idle jet and the main and clean the crap out of them. Make sure the 10 side holes in the main and the 8 in the idle one are clear. remove the idle adjust screw and don't lose the spring, washer, and seal. Shoot some carb cleaner in the mixture screw hole with your thumb over the hole the idle jet goes into. You should get a nice mist out of the tiny hole on the head side of the butterfly. then shoot some without your thumb there and it should come of that hole pretty easily as well.

There's no such thing as a cheap carb rebuild kit. But you could do new gaskets, seals, seats-needles, and an idle jet for maybe $50 a carb. If I only replaced one jet, I'd do the idle, because the openings are a lot smaller.

Edit: Also while you're in there, make sure your floats actually "float" in a bowl of gas. Sometimes they get little cracks in 'em that you can't even see, and that will mess up your mixture also.

 

Alright,

Went out today, drained the gas from teh carbs, pulled 'em off the bike, and took 'em apart. Everything's soaking in carb cleaner now, and tomorrow I'll probably have time to confirm that the jets are completely clean and gunk free. I did what you suggested about with the idle adjust screw, and there seems to be very good flow throughout that portion of the carb. So tomorrow the jets and everything will be completely clean, and reassembled and put back on.

How do I know to adjust the idle adjust screws initially (before first start up)? How about after it's running/warm?

Also, new plug are on the way, so that should help a bit.

 

hey just wondering but where is the idle screw for the 600 model cause i kinda have some similar problems, my tach doesn't work, but my bike will idle fine after i start it its just after i start riding it and come to a stop the idle starts to sound a little low and rough and eventually it dies.

 

The idle adjustment is on the left side underneath the carbs. It's a decent sized ribbed black ****.

For clarity: my post was referring to initial position of the idle adjust screws on each individual carb.

 

Woo hoo!

Got everything all fixed, cleneaned and put back together, and now she runs like a DREAM. The problem was definitely in the carbs, I found a tiny clog in an idle jet.

My next question: is there any way to test my brake/running light bulbs, to see if the running lights in them are good? They don't come on when the bike is on, but the filaments look perfect. The brake lights work fine. How do the running lights work? If I knew how they worked, I could probably just source the problem myself (I assume it's in the wiring since I did a lot of it myself, putting together multiple chopped up harnesses.) But if there is a test for the bulbs then I'll definitely try that. Don't want to buy new bulbs if I don't have to.

Are the brake bulbs even supposed to function as running lights? What exactly is the second filament for?

Thanks everyone,
-Matt

 

Good Job, Matt.

Maybe take off the plastic of your lenses and wiggle/turn the bulb with the key on. See if the running light comes on. If so, then it's just dirty. In an dual-element bulb one of them is for the running light and the other should come on when you hit the brake. It may just be in there backwards, too.

 

I can only get the bulbs to fit in one way, but it is possible that some dirt/gunk may be in or on the connections. I'll definitely clean them up.

Thanks,
-Matt