Carb/revving issues

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My compression tester doesn't fit the plug holes. The tapered rubber end is worthless as I can't hold it in tight enough to get an accurate reading.

Heaven knows I sure don't want to pull those carbs again to check the diaphragms...

http://www.compperformancegroupstore...&Category_Code=

Here is the adapter you need in 12mm for your standard compression tester It will cost you as much to ship it as buy it but worth every penny and fedex quick. $5.95 + shipping

So I took Nessism's thoughts to heart about his 550 not running with any less than 3-3.5 turns out on the air screws. I turned mine 3 out from bottom and it made a world of difference. Idles, responds to throttle input, actually runs really well. I haven't had a chance to get it on the road and do a plug chop but am looking forward to the results! What I don't understand is why it ran well, then didn't. Only thing I can come up with - and this may sound absurd to those who know much more than me - is that when I added some Seafoam to the tank it might have loosened up some goo inside that allowed it to run on an extremely rich setting (air screws too far in). Once those passageways were "cleared out" everything started working as it should, i.e., like crap at those settings?
Total shot in the dark here.

At any rate, its much better!

[Nessism]

Thanks Ed, I may try that next (winding out 3-ish turns) but probably not until I replace plugs (cheap insurance) and get the air filter in place....

And I would have changed those o-rings were I able to get the airbox out of the frame, allowing access to the screws (not bolts, mind you) holding the intake boots on. Maybe I'll regret it but for now, seeing as how every other piece of rubber on the bike is soft and pliable, I'll take my chances.

Lord knows I don't want to pull those carbs again[-o<....

If you grab the outer screw sideways with vice grips you can usually crack it loose. After that, it's about a 50% chance that you can turn the entire boot to crack loose the inner screw. Worked great on my 550E but not on the 850. At any rate, good luck with those old o-rings. They leak on just about 90% of the old GS bikes that have the originals in place. Hope you are in the 10%.

Thanks for the input, I appreciate any help offered.

Basic, I don't think the fuel valve (petcock) is leaking as I've had the tank off for three days, valve in the "on" position, and no leakage on the garage floor. Haven't had a chance to fiddle with it and probably won't until next week. Time is at a premium with little kids...

Thanks again, I've got an air filter on order so we'll see if that makes any difference.

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Thanks Ed, I may try that next (winding out 3-ish turns) but probably not until I replace plugs (cheap insurance) and get the air filter in place....

And I would have changed those o-rings were I able to get the airbox out of the frame, allowing access to the screws (not bolts, mind you) holding the intake boots on. Maybe I'll regret it but for now, seeing as how every other piece of rubber on the bike is soft and pliable, I'll take my chances.

Lord knows I don't want to pull those carbs again[-o<....

[Nessism]

My old '81 550 wouldn't run for crap until the pilot screws were set at 3-3.5 turns - had a hanging idle before that. Also, you are on borrowed time with the intake boot o-rings - if they are not leaking now, they will be soon.

So here's where we are now:

I just did a compression check, thinking maybe blown head gasket. This is before valves have been touched, engine warmed up but not operating temperature.

#1:130 #2:140 #3:145 #4:145. All appears well and ok there.

Checked coil voltage: Left was 12.62v Right was 12.60v. All appears well and ok there.

Battery (ignition on) was 12.84v. All appears well and ok there.

Air screws were a uniform 1-3/4 turns out. Maybe thats a bit lean on air, but they were all the same so I don't think they are the culprit.

My fuel valve may be leaking a bit, I'll have to look at that when I get a chance. I haven't noticed anything on the garage floor after the tank has been sitting there, but the nipple is a bit wet after an hour of fiddling with other things. Doubt its leaking enough to cause real problems.

It will start immediately, rev to the moon on full choke, but once you back off the choke it will stumble and die. It takes quite a while to get up to temperature where it will idle, but then you whack the throttle and it stumbles, then will race to the moon, sometime hitting a wall at around 6k rpm, sometimes not.

Any thoughts?

yep, it's the side of the coils with a ' + ' on it, people will tell you 10 to 12v, but my kat fouled plugs with anything under 11.

check your valves too.

They are a PITA to get to stay seated.

Yes, SIR, they certainly are.

to measure voltage at the coils, stick the positive end of the multi meter and put it on the orange wire at the coils. the black end of the multi meter goes to engine ground or battery ground. should be 10-12. the more the better. look into the coil relay mod if its low.

Esco,

How do I check voltage at the coils? Are you referring to the wiring into the coils? Probably as the voltage out (to the plugs) is obscenely high.....

Is this measurement taken when the engine is running?

Thanks for the help, folks!!

well if there's no leaking from the tank i would say the petcock is out. The filter will help though. As an experiment i ran mine without the filter (or tried to) and it didn't run well at all. Didn't check the plugs after though. It would seem to me that without the air filter the mixture would go lean do to more air passing through more easily. The sooty plug could be due to burning oil. You mentioned there's a very slight amount of oil and smoke on the #2 exhaust, so I would check compression to make sure everything is ok there as well.

I learned a hard lesson with the same symptoms you have. Check your voltage at the coils, it has to be AT LEAST 12v.

I was at my wits end with my Kat's hunting idle and rough running under load. Pulled the carbs 4 or 5 times. #'s 2 and 3 kept fouling plugs.

All because of the *&^%$#@ coils.

The worst part is PEOPLE TOLD ME, but I thought "she's got good spark, gimmie a break".

It takes 1 minute, try it if you haven't already.

Thanks for the input, I appreciate any help offered.

Basic, I don't think the fuel valve (petcock) is leaking as I've had the tank off for three days, valve in the "on" position, and no leakage on the garage floor. Haven't had a chance to fiddle with it and probably won't until next week. Time is at a premium with little kids...

Thanks again, I've got an air filter on order so we'll see if that makes any difference.

i think steve was saying you may have a leaky petcock diaphragm, allowing fuel into the #2 piston.. As far as the hestitation off idle, does it change any with the choke slightly engaged? I had a leaky airbox to carb boot and my bike would do wierd stuff at low RPM. partially engaging the choke (maybe 1/8 to 1/4 the total travel) fixed it kinda...so i replaced the boots and things are hopefully better. They are a PITA to get to stay seated.