81GS650L: First Start, Running on 2 Cylinders

[DaveP]

Got the bike started for the first time last night, but it is only running on two cylinders...

Current status:

• Valves adjusted
• Carbs dipped, o-rings replaced
• Intake o-rings replaced
• Auxiliary fuel tank
• Cylinders 2 and 4 dead

Checking spark before trying to start, no. 4 spark plug boot is bad, but cylinders 1-3 had spark. Hopefully getting cylinder 4 running will be just the boot replacement. I will be ordering the NGK spark plug boots since I can't find anything at the local auto parts stores.


Cylinder 2 has spark outside the engine and the float bowl has fuel. Any suggestions on what to look for here?


Thanks,
Dave

 

[DaveP]

Forgot to mention that I had checked compression previously, but just double checked again now.

Cold Compression:

1. 120 psi
2. 120 psi
3. 120 psi
4. 115 psi

Photo of the spark plugs as received from the PO and after trying to start:

No. 2 does appear to be wet.

 

[tom203]

Auxiliary tank- got vacuum port blocked off on #2 ? Try different spark plug on#2 or dry that one off with air or lighter,cuz it looks too wet.

 

[DaveP]

All new OEM fuel, vacuum, and vent hoses installed and I do have a golf tee in the vacuum hose. Had tried both ways on the vacuum line and golf tee was in when it was running last night, but exhaust still cold to the touch.

 

[Steve]

Did you sync the carbs?

.

 

[DaveP]

Bench sync was done before reinstalling the carburetors. I used a fairly thin wire and they are about as close as I think I could get them. Backed off the idle control knob after the bench sync.

 

[tom203]

Strange. Did you let it run for a while on two cylinders (10 minutes) ? Raise idle if needed and see if getting warm changes things. Use fan blowing on engine in case it's hot there!

Your idle/ air mixture screws all looked good and about 3 turns out?

 

[Steve]

I gave up on trying to use wires, sticks, etc. to do a bench sync a long time ago.

I get better, more-consistent results just eyeballing the sliver of light under the throttle butterfly.

Turn the idle speed screw until #3 is just barely open, adjust the others to match. Snap the throttle open and closed a couple of times, check the light sliver again. Move the idle speed knob both directions to verify all the slivers are co-operating, put the carbs back on the bike.

.

 

[DaveP]

Only ran it for a few minutes on two cylinders anticipating it to be running on 3 cylinders with the spark boot issue.

Air screws were set at 2.5 turns out.

Fan ready to go once it is running longer.

 

[Steve]

Air screws were set at 2.5 turns out.

Just for "fun and games", try another half-turn.

Some bikes need just a bit over 2.5 turns, won't run worth crap with less.

Starting at three turns is like adding a little bit of "choke" and lets it start easy, then warm up and be ready to tune properly.

Also be aware that not all the carbs will necessarily end up with the same setting. The other carbs might be OK at 2.5 or even 2.25, but that one carb might need 3 or more. Don't be afraid to adjust them out until it runs properly, then turn them in slowly to fine-tune.

.

 

[DaveP]

Thanks for the tips. Went away for the July 4th weekend, so will try again later next week and post back with the results. Wish I was home right now since I am sitting in the rain in NH...

 

[DaveP]

Received the NGK spark plug boots and tachometer cable tonight.

Bike now appears to be running on all four cylinders, although the number 4 exhaust does not seem as hot as the others.

It is idling fairly steady at 1,100 rpm, but has some misfiring at idle. At first I thought it was primarily on the no. 3 and 4 side, but now at idle you can see it happening at the same time on both sides when watching the exhaust.

Runs smoothly above 2,000 rpm and accelerates and decelerates smoothly while still no load on the engine.

Any thoughts on the misfire? Pilot screws currently out three turns.

Will be attempting the Morgan Carbtune and Colortune this weekend hopefully.

Thanks,
Dave

 

[tom203]

Before putting on new boots,did you cut back each plug wire about 1/4 inch to get good contact?

 

[DaveP]

Spark plug wires were trimmed before replacing the boots.

No. 4 carburetor was also the worst of the four when cleaning. Slide and needle were both stuck in place. Everything seemed ok after cleaning and putting it back together and the float test/adjustment was good.

Compression test numbers above show no. 4 as the lowest of the four and compression was checked with the throttle closed. I am wondering if my bench sync was a little off and it is just not getting the same fuel as the other 3. Vacuum sync might change that balance.