Cylinders 1 & 2 not firing

[Guest]

(Moved from Discussion... not sure if this is a carb/fuel question, or electrical/ignition, so flipping a coin...)

After letting my 1980 GS1000G sit, partially disassembled, in my garage for the past year (I know... bad owner), I've been putting her back together, but am running into a problem with the left pair of cylinders not firing.

Last year, I did a valve adjustment and carb teardown, with carbs fully disassembled, dipped, and cleaned (#1 had been clogged up due to tank rust), new (oiled) filter, new set of o-rings, new fuel/air lines, and resealed the airbox. The airbox boots were pretty new (still soft and flexible), but I added new boots/pipes between the carbs and engine. When I reassembled it all last year, I couldn't get her running, which I assumed at the time was because, like an idiot, I hadn't dealt with the tank rust.

This month, I pulled the carbs again, stripped and re-cleaned them following the guides (though they were still clean), did a bench sync and reassembled it, and set all 4 adjustment screws to 2.5 turns from the bottom. My next step was going to be to try out my new carbtune, using a clean coolant reservoir for fuel. After plugging the vacuum line to #2 (per the carb balancing instructions), it started up with minimal choke. It ran at a pretty high idle (1500-2000 or so) with the throttle released, but the RPM fluctuated (loping and racing) so much that I couldn't dial the idle back to normal or else it would stall.

After I let it warm up (with a fan on), the headers for #3 and 4 were hot (they tested around 190F), while those for 1&2 are cool to the touch (around 85). I checked the #1 float drain, there was fuel. I checked spark plugs and gaps (1 & 2 were wet), and pulled the plugs to visually confirm spark off of all 4 leads (which are pretty new NGK). I confirmed that the leads to 1 & 2 do not share the same coil. Battery is brand new, and had a full charge when I started testing. Tried again, but headers for 1&2 still were cool. I tried fiddling with the air adjustment screws - tweaking 1 and 2 had no affect on the RPM (not surprising, if they're not firing). I also checked compression (cold though), which seems to be within spec (120-140).

One thing I neglected to do this time was measure the float heights, but when I did it last year they were all spot on, no adjustment was needed. I suppose they could both be off now for some reason, but but before I pull it all apart again to check, I'm hoping y'all might be able to point me to something else that I might have overlooked and/or screwed up.

Thanks!
Chris

 

[tom203]

"confirmed that the leads to 1 & 2 do not share the same coil."

Ok, but best make sure that left ignition coil plug wires connect to 1 and 4

 

[Guest]

Confirmed, left coil to 1 and 4

Thanks,
Chris

 

[80s cars or gtfo]

Have you smelled the oil? Maybe the left hand carb are getting flooded as you bike tilts left on its kickstand. Test the petcock and make sure it's not set to prime

 

[Guest]

It's up on the center stand, but your point is still valid. I'd checked the oil when I was testing, and it looked fine. But, re-checking now, I see that I've "gained oil". I was running it off of an aux tank (coolant reservoir) with no petcock, with the vacuum hose plugged (following the directions for the carb sync). Clearly, it flooded, either during or after the test.

I'll be finishing the tank clean this week, I think my next step will be to put it back on and try it with the petcock in place. After replacing the oil, of course...

Thanks,
Chris

 

[Big T]

Well, it takes spark, fuel and air

So, you're getting fuel. air is a given, so take a look at spark

Swap the 1-4 leads and the 2-3 leads and see of the problem moves

 

[2BRacing]

The 650 I recently worked on, started OK and idled OK but seemed to lack power when trying to pull away in 1st gear.

I discovered that exhausts 3 and 4 were cold. The plug wires and caps checked out OK.

All 4 spark plugs were brand new, but plugs 3 and 4 did not fire anymore - they had been "killed" by over-rich mixture from just starting up a few times and running at fast idle to set and synch carbs.

I replaced those 2 spark plugs with the "old" ones, and those two exhausts also heated up quickly. So I suggest that you switch out plugs 1 and 2 with others.

 

[Guest]

Thanks for the suggestions, guys - it helped clarify my troubleshooting steps. Though it looks like I'm going to be pulling those carbs again this weekend. Here's what I did:

- swapped plug leads (1 with 4, 2 with 3), which I think rules out the coils, caps, wires, and connections
- swapped plugs between left and right sides
- put my cleaned tank back on, hooked up fuel and vacuum lines, checked for kinks
- drained and replaced the oil as a precaution (level was high and smelled like gas, so I guess I did flood it last time)

After a few minutes on prime, the bike started right up with choke, ran at a fairly high rpm, but only the headers for 3 & 4 got hot - same as before. There was fuel in the bowl of #1 again (didn't check #2 yet). But this time, the plugs were mostly dry in both (#2 was just slightly damp). So, while I have spark, and at least fuel is reaching the bowl, at this point I guess everything points back to those carbs, unless I'm missing something. I'll re-check all the passages, etc, and this time will check the float height. If there's anything else in particular that I should look at while I'm in there, I'm all ears.

At least now I know what I'll be doing on Saturday while the ribs are in the smoker

Thanks,
Chris

 

[Big T]

Your diagnosis of plugged carbs seems spot on

 

[Guest]

Quick update: It's Alive!!! (mostly).

After tearing down the carbs again, and made sure that the small passages, jets, etc., were all cleared. I measured the floats, which still appeared to be spot on. However, I re-read the float adjustment writeups (as the factory manual wasn't entirely clear on this point), and determined that I'd measured at the wrong spot, at the flat along the "top" (really, bottom) of the floats, which made them a few mm too high when assembled. I adjusted them all to spec, put everything together, and it fired right up. Now, I'm not sure that the floats were the problem, as it was like that when I bought it and ran pretty well then. I assume I must have just unclogged something.

Next problem: when I was hooking up the Carbtune to the test ports, I found a piece of damaged o-ring sticking out from the #2 intake. Sure enough, the carbtune showed that vacuum on #2 was very low, near zero. I'm not sure how I managed to do that, but at least it's an easy fix (assuming that's the only problem). And Mr. Barr gets another order

If anyone's curious, here's how it's currently idling https://www.youtube.com/watch?v=dDGUV00lHSU

Thanks, all, for your input, I think you've saved me some hair-pulling,
Chris