missing cyl. at idle

[tomeriker]

This is my first post here, so bear with me..

I have a 1979 special and a 1980 special. I bought both as non running bikes. I have the 80 running great but the 79 seems to have me scratching my head.

I have the bike running, but it just won't idle right. I have looked at the carbs several times, coils are good, spark to all cylinders, fuel etc...

once it gets to about 1500-2000 rpm's, all the cylinders kick in and the bike pulles really hard.. better than the 1980. The only problem is the missing at idle. If I remove the #3 plug wire while the engine is idleing it doesn't change anything.

What am I overlooking.. I have searched the Climber manual but am out of options.

Thanks for any help

[Czekus21]

Lets start from the simplest and work toward the hardest.
Spark plug.
Bad-------Change it,
Good-----Check the plug wire cap.

I'll leave out the change it part. I'm sure that you can figure it out.

Check the coil to plug wire.
If it's a spark issue and cyl#2 is fireing, Then the coil should be good. This is about all it can be based on the description you gave. Now if it did change the idle a little, I would be looking at the pickup coils under the left engine cover.
I just reread your post.
You said that you had spark to all cylinders but yet pulled the plug cap for number 3 and was no change in the idle. This points to spark in #3. Yet you have spark. Do a search on the pickup coil fix. If anything, You'll know that its not the culprit.
All a motor need to run is compression, air/fuel mixure, and spark. If you have all of these, and are throwing them together at the right time, That motor should be purrin like a kitten.

[tomeriker]

will do

Thanks,

will look at the pickup coil. It just doesn't make sence that it would run so good at the higher rpm's. ( above 2000) I havn't ran a compression test on the engine... maybe that would cause it..

I would think a cylinder with low compression would smoke?

I have the 80 that runs perfect, I guess I could pull parts off it, one by one to test..

If I were to think about pulling the heads off to inspect the valves and cylinders, would that be something I could do at home with out specialty equipment? I can rebuild car engines and trans but have never been inside a bike engine.. Clymber manual makes it look doable...

Thanks for any advice.

[Czekus21]

Why take the motor apart if not neccecary.
I would be checking the spark issue. If it's only #3 without spark, your problem is within 1 foot of the top of the engine.

[tomeriker]

spark

Oh, I have spark to all the plugs. all the plugs are good and firing. that is what is wierd. As you said, fuel/spark/compression... I have fuel and spark, so maybe its a compression issue. I will check everything else first before considering taking apart the engine.. quite frankly the bike isn't worth all this effort anyway..I just thought it would be nice to get it going too.

thanks

[Czekus21]

Well if you decide that you don't want it anymore, I'm in need of a good doner bike for MIYAMI.
May want to check the Intake manifold vaccume plugs also.

[Pat Kelly]

I would check the #3 carb pilot jet.
When I got my Colortune I saw I had spark on my #3 cylinder (a coincidence) but no combustion until about 4,000 RPM then things lit up. I knew #3pilot was bad so I moved it to cylinder #4 and the symptoms followed. I ordered a new jet and all is well ever since.
Just another place to look.

[audijunky]

Along with the pilot jet I would check to make sure that your idle mixture screw isnt turned all the way in. If it is it would restrict fuel from getting to the cylinder at low RPMs. Stock setting for the screw is 1 1/2 turns out from fully seated.
JM2C

[prometheus578]

I agree with Pat.
It's the pilot circuit on that cylinder. Pull the carbs, check them again. Make sure the tip of the pilot screw isn't broken off in the hole. Spray carb cleaner into the air jet for the pilot circuit. It should bubble up from the pilot jet's tower. Try to plug the pilot jet tower with your finger... the spray should then come out the pilot screw hole, etc.
You get the idea.

[fredintoon]

To be sure it's not an iggy problem, swap the #2 & #3 plugs and plugwires. If the problem moves from #3 to #2 it's spark.
If it don't, it's the #3 carb.
You are not alone here. Two years back Mr Stupid spent a week to no avail checking his iggy to get #4 running. An hour cleaning #4 carb and the iggy problem went away. This is balanced by this spring's adventure. Fired the pig up and it ran like crap. F***ing carbs! Cleaned & cleaned, no help. Four new plugs and Vroom! Trust nothing. Check everything.
Fred Hill, S'toon.

[audijunky]

Hey Fred,
I am guessing that 2+3 pistons are at TDC at the same time?
So you can swap the plug wires and all should be fine?

[fredintoon]

gotta swap both

Hi Audi,
Yes, the same coil works #2 & #3.
But, if it's an iggy problem it can't be the coil itself because #2 works fine while #3 acts up so it has to be the plug wire + cap or the plug. So you must swap the plug and the wire that works it to have a sure check for an iggy problem.
Fred Hill, S'toon.

[Ken Talbot]

Like Prom, I'm putting my bet on a dirty low-speed circuit on the offending carb.

[tomeriker]

will retry

Thanks for all the suggestions. I will take everything back apart and recheck. I can take the plug out and it gets spark btween the gap so I pretty sure the iggy is OK. ( But will recheck) I can't adjust idle mixture screws because the carbs are blocked off.. no screws. These carbs are not the originals. I bought these because I had the same problem with the original set. The idle mixture screws had been turned in and 3 were broken off and I couldn't get them out.

I took these carbs off and blew carb cleaner through all passages. OK. Checked the diaphragms. OK. Float levels, etc,etc...

I did not disassemble them completely. but I figure since I have the same missing cyl. it has to be iggy. But I have spark. (scratching my head)

I guess it could be compression, but if the compression was that low in that cyl. that it wouldn't fire, would it fire at higher RPM's?? I will borrow a compression tester this weekend and check that.

once again thanks for all the good info..will let you know what I find..

[John]

All symptoms point to the pilot circuit. Are the pilot screws capped off? If they are, you'll to remove the caps, and remove the screws, to make sure the passages are clear.