missing cyl. at idle

[Dad2g5]

I Have the same problem. I'm going nuts! Only diffeference is now it stoped firing all together. idle or after 4000RPM. And on the highway it feels like im dropping two cylinders. I took the carbs back apart for the fifth time and they were clean as a wistle.
I know its a little dangerous but while riding on two cylinders I have pulled the wires and found spark. Exhaust temps Cyl 1-303F
Cyl 2-152F Cyl 3-312F Cyl 4-323F. Please Help!!!!
^^^^
Bad One!

[prometheus578]

Remove the caps, as John said. That plug is just cheap aluminum. Get a drill and gently drill a hole in it. Gently, not too much pressure as when it gets through the plug, the pilot screw is almost right underneath. Pull out the screw, spring, washer and o ring and make sure everything is clean and open.
Yes, a cylinder with low compression can miss at idle, but also fire at higher RPM.
A long shot, but if the compression is low on your bad cylinder, check the valve clearances. May be tight, and holding a valve open. I would bet on it being an exhaust valve if that was the case.
Even if the compression is good, check the valve clearances anyway.

Dad2g5, I think you're in the same boat, so paddle over to the bike and check it again. You state spark on all four... carbs or valves.
All problems are simple ones, and if a simpleton like me can fix them, there's no reason that someone else can't. Takes a little time and a little thoroughness.
First step is always new spark plugs. Being cheap here will always bite you in the a$$ later. (One man's "GOOD" looking plugs often means "CRAPPY" running to me)

[tomeriker]

carb swap

I have an 1980 xs11 that runs like a dream. I am going to pull the carbs off it and put on the 1979 and see what happens. If the miss is still there, then at least I know its not the carbs. The plugs are brand new and spark at the gap. switching plugs from cyl. to cyl. had no effect. Still need to switch wires from one to another to check.

I had a friend come over and do a compression test on it while I was gone today... not looking good. hope he is wrong.

#1=approx. 130-140lbs
#2=approx. 70-80lbs
#3=approx. 50-60lbs
#4=approx. 160-170lbs

I wasn't there to see it, but if that is correct I prolly have some valve trouble.. the engine only has 19,000miles on it. Hopefully it can be adjusted at the top of the valve and I won't have to go into the motor.

Thanks for the replies

[tomeriker]

tech question

I was wondering, are the valve seats hardend on a 1979. I have seen a set of Ford heads where the valves had recessed pretty deep into the seat because there was no lead in the gas and the seats weren't hardend.. I know I'm grasping, but.......

[prometheus578]

"Assuming the compression test is correct...."

I would remove the valve cover and check the clearances. Easily done: remove the tank, remove the ballast resistor on the left side(phillips screw), and then the valve cover itself.
Follow the proceedure to check the clearances.
You made no mention of smoking exhaust, so any compression loss would be due to the valves, not bad rings.
Valve clearances for the offending cylinders could be too tight, meaning the valves are not being allowed to close completely.
Valve clearances could be extremely loose, meaning valves are bent and not fully seating.
Valve clearance could be within spec., and you have one of two burnt valves or valves that are otherwise just not sealing.
Not hard work to check... just time consuming; and as it's part of regular maintenence, should be done regularly anyways.
It's always good to recheck a compression test that shows differences like this. Forgetting to hold the throttle wide open while cranking will give similar readings.
In extreme cases, a fried head gasket or warped head will give low readings in adjacent cylinders.(not too common an occurrance)
Recheck the compression test, check the valve clearances, and post the results.

[tomeriker]

thanks for the advice

I am going to recheck the compression. I have a manual on the bike so I should be ok. The engine doesn't smoke so I agree it most likely isn't rings. hopefully its the clearance is too tight.. I really don't want to have to remove the heads...

Thanks for the info about keeping the butterflies open.. I didn't know that.. always figured as long as all were tested the same way, I would get an accurate reading. Makes sence though. I will do the test with the carbs off anyway. I want to apply some air pressure to each cyl. to listen for leakage past the valves.

The only reason I'm spending time on this bike is a friend is wanting a bike and I would like to get it running for him. Then maybe we could make one of the rallies..

Thanks for all the info

[prometheus578]

I want to apply some air pressure to each cyl. to listen for leakage past the valves.

I was gonna suggest that you do a leakdown test or put air to the cylinders, but only after the valve clearance check. If you put air to it prior and it leaks, you still don't know if you have an open valve due to bad clearances, or a burnt or stuck valve.
(But you knew this already)

[underdog57]

Also after you take compression , if it low . Put a teaspoon of oil in the plug hole . Then retest . If the compression goes up , it rings ...

Bob

[planedick]

Probably...

just needs synchronizing...

[tomeriker]

I didn't do anything to the bike today but I don't have to worry about how quickly I fix it now. My friend just went and bought a 2007 V-Star 1300.

If I can get it running I think I will put the fairing and backrest on it. When I bought the bike all that was in a corner.

I feel like I have a motorcycle graveyard.
1980 Kawasaki 750 ltd 4cyl
1982 Kawasaki 750 2cyl
1979 Suzuki GS1000
1979 Yamaha virago 920
all parts bikes. the ltd runs

1979 Yamaha XS11 special
1980 Yamaha XS11 special

If I get the 1979 XS running my next project will be the GS1000..

[goldcoastguy001]

I have to say that i agree with the Carb solution.......having gone thru this same prob and exhausted all the tech tips on the electrical side of things i found the prob to be dirty pilot jets....i would definetly start there....in fact i would put $$$ on it....give the carbs (all of them!) a good clean then do it all over again another couple times...(yep broken record syndrome.....TRIPLE CLEAN)....lol.....also make sure they are sync'd....cheers

[tomeriker]

easiest first

I will start off with the easiest test first. I will take the carbs off my other bike and put them on the 79. If it still does the same thing then its has to be a valve or rings.

good spark on all 4 cyl.. only thing left would be compression, while I am going to test today.. I will let you know how that turns out.\

[tomeriker]

update

Well, I pulled the carbs off and did a compression test. When my friend did his test, #3 cyl. was really low. My test showed approx 140psi on 1-2-3, and approx 20psi on #4.

Very strange. I decided to take the valve cover off and check my clearances and found that all the intake and 2 exhaust had zero clearance. In fact I believe the valves might be held open a little.

I loosened the intake cam to get an idea of just how far off they are. wow. It looks like the #270 shims could be changed to #170's.. I don't have the exact measurements but they are way off.

Went to the local shop to see about a shim kit. they said they would have to order it and for 8 shims it would be over $200.00.

WOW

[Pat Kelly]

Some shops will trade you shims, sometimes free, sometimes they may want a dollar ot two. Go around to the shop and ask the mechanics if they swap shims.
Our shims ar 29mm diameter. Other bikes use the same diameter shim. I have traded at the local Yamaha dealer before and I recently bought some for about $3 each from a Kawasaki outlet. I'll post which place is was when I get home.

[Pat Kelly]

Here's where I just bought some 29mm shims. Super fast shipping.
KLR 650 dual sport

Thinnest is 200 and thickest is 310. Bike Bandit shows a 320 but they are $11+ each. This place is $3.95 each.