Yellow '76 Carbs, Back On The Bench

[Lucien Harpress]

(I'm slapping this here rather than in the project section because if it graduates to a full-blown project, something's gone horribly wrong.)

After about a year and a half, maybe two years, my GL1000 started playing up. For whatever reason, I'm dropping cylinder 1 on idle, but ONLY on idle, and it just started happening a couple days ago. Messing with the mixture screw didn't change anything, changing the spark plug didn't change anything, and once I accelerate on to the main jets the bike smooths right out and goes back to the workhorse I remember. So I'm hoping whatever is up is a minor thing.

But that meant pulling the carbs.



First impressions didn't have anything jump out at me. Mains are clear, plus the idle jet as well. The tangs on the one emulsion tube that line up with the idle jet tower weren't lined up correctly, but there's a chance those rotated as I removed the main jet above it.

While I probably won't split the rack, carb 1 is getting as torn down as possible. I may find something deeper in, who knows.

[CYBORG]

Any chance it has a dyna ign.?

[Lucien Harpress]

Electronic? Yes. Dyna? Not sure. It certainly might be.

[CYBORG]

I had a number of problems on my78 that made no sense. At first thought carbs. But turned out to be a problem with the Dyna. One side of one coil would come and go. Dyna has a history of problems. Low voltage turned out to be the problem I had. Just takes a few minutes of low voltage to screw up the coil

[Track T 2411]

Randakk's big thought: "Nine out of ten carb issues are ignition..."

[Fred Camper]

I also had a similar issue with the dyna, but mine would drop 2 cylinders. And not just at idle. When I first installed using the ignition feed, it would drop a cylinder when the blinker blinked. Since I put the dyna on a relay, that issue is gone.

[Lucien Harpress]

That's interesting. I'll definitely check it once the carbs are back on. Easy enough to swap the wires for 1 and 2 to see if the problem moves.

It's odd that it'd only happen on one cylinder, though. Number 2 runs nice and strong, and I can swear I hear arcing if I just pull the wire on 1 slightly off the plug. That said, electrical is weird, and I haven't updated my battery in a while. So it can't hurt to look.

[redglbx]

I had a number of problems on my78 that made no sense. At first thought carbs. But turned out to be a problem with the Dyna. One side of one coil would come and go. Dyna has a history of problems. Low voltage turned out to be the problem I had. Just takes a few minutes of low voltage to screw up the coil

Cyborg, have you only seen this on Dyna Coils ? Also have you had any experience with the Chinese Dyna copies on eBay ? What do you normally use ?

[CYBORG]

I have only seen this problem with Dyna. I did not like the points on the 78. Came out of adjustment to often. So went to the Dyna. And then the problem was coils. Had at least 5 go bad. different ones, at different times. Usually on the road someplace. Switched to a C5 system. and never looked back. Easy install, has curve options on the fly, and in 30K miles has never let me down. And has never needed adjustment. No experience with the Chinese ones. 1200's use stock ign. and coils. Been working well for me. By the way, I was looking for something the other day and came across a box with some Dyna coils in it . 3 or 4 I think. any one wants them, they are yours for shipping. Not sure if they are all good,(probably). Or wht generation they are.

[Lucien Harpress]

I finished disassembly on the rest of the carb, and nothing jumped out at me as being super wrong. Air jets clear, float valve strainer clear, etc. I still have to hit the body itself with some brake cleaner and air, so we'll see how that goes.

Just for fun I popped a spark plug in the wire for cylinder 1 and grounded it on the case as I hit the starter. Got a nice blue spark, snapping loud enough I could heard it, BUT that might be because of the resistor bypass when you hit the starter. But at least I'm getting something.

For the record, my ignition pickups are definitely electronic, probably Dyna. My ignition coils are stock.

[Fred Camper]

Bad coils almost always put down two cylinders but...

[Sidecar Bob]

But spark plug caps are cylinder specific......

[Lucien Harpress]

Carb is cleaned, and the whole rack is back on the bike. I didn't see a whole lot wrong with the carb, so naturally I wasn't surprised when nothing really changed. I took it for a spin up and the down the road, long enough to kick the fan on, and confirmed a few things.

-She definitely only idles on three cylinders- 2, 3, and 4.
-1 definitely has spark. I ran it, at idle, with a spare spark plug laid on the valve cover, and spark was nice and blue.
-Once you're off idle even the smallest amount, she runs great.
-Turning the idle screw on 1, while at idle, makes not difference. Even screwing it all the way in.
-I have NOT swapped plug wires on 1 and 2 yet.

The only thing I haven't touched in a while is the carb sync. It's been at least 2-3 years since I set it last, and while I didn't think they went out of sync that often, it can't hurt to double-check.

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Just for fun I popped on a set of sync gauges. While I didn't get the bike to fill operating temp, I did get it to idle off choke for a little bit, and carb 1 is definitely off a little. It's not off by much, but it's also the closest thing to "wrong" I've seen so far.

[cfairweather]

From my experience, clogged idle discharge tubes are the second biggest reason for a dead cylinder at idle. The most common is a clogged #35 slow idle jet. In a different post, I recently had a genuine Honda Coil get weak on one side. It did exactly as you described. Ran great at high RPMs and was dead at idle.

[cfairweather]

While the bike is off, remove the pilot jet from the brass elbow and the idle fuel screw. Then squirt a bit of gasoline into each hole. Then use a rubber tip air compressor fitting and force air into each hole. Sometimes this will clear the blockage.

If you still have the carbs off the bike, recheck the slow idle jet and make sure you can get an "E" string through the hole. Hold it up to the light and verify it is clear, because sometimes after you pull the "E" string out, it will be clogged again.