Won't run w/out choke on..

[Anonymous]

Hi all, I just boutght some replacement parts for my 81 GS650GL, now, I know that the original stator, rectifier/regulator and ignitor unit were toast, so I got the parts from a part out bike on eBay. I put in the parts and lo and behold, the bike roared to life in under one second with the choke on from cold. I let it warm up for a bit, and tested voltages for charging, getting an average 13.5 - 14.2 VDC from battery leads. that's fixed.

My problem now, is the bike won't run once it's warmed up and I take it off the choke... put choke back on and it runs, off and it doesn't. It also lacks power (won't move in first gear more than an inch before dying even at 6000 RPM). #1 Cylinder is not firing also, I get lots of spark, but no bang. #2,3,4 all fire fine (burned myself a good one figuring it out too!). If the bike is left running on the choke for too long, it bogs and dies by itself (normal for bikes I have owned before to die when engine warn and choke is activated). If it's cold and on choke, I can rev it no problem, but 2 minutes on choke and I can only bring it up to 2500 RPM, any more and she'll bog down and die.

What am I looking at here? Coil, Carb, or other issue? (or combination?)

like I said, it won't fire on #1 at all, but starts from cold on choke in < 1 Sec.

Please help, I know a little about bikes, but it all comes from my being electronically and mechanically adept. A little common sense and intuition come into play here too, but I can only go so far before I have to bug you fine people for some assistance (which is greatly appreciated BTW)

Thanks in advance for all your help,

-Scott

[luc8421]

I personally would suggest that you have a carb problem.
Right about at 2500rpm your bike stops using the idle/choke circuit, and moves on to a more open running circuit in the carbs, which would explain your choke problem. I think dirty passages in the #1 carb would explain that cylinder not firing.
I came from the same background as you, mechanically and electrically proficent, however not specifically to bikes. I've taken my carbs off and completely apart, not a problem at all as long as you have seperate containers for everything, to keep it all orgainized.
I would suggest buying the cheap (money wise only) o-ring kit from Robert Barr on this site before you take the carbs apart, because it'll probably need it, along with new intake boot O-rings.
Follow the carb clean up series from the homepage, and you should be good to go.

[Anonymous]

I think I understand...

Thanks luc8421 for the reply,

I have come to another 'intuitive' conclusion... partially faulty petcock on the tank, as soon as I opened it up to prime and then back, the bike ran MUCH better, I was able to rev it up >5K RPM, but I still don't think #1 is firing, I didn't check though, I would imagine the engine as a bit smoother running if it was running on all fours. I have replacement coils from a parts bike, and will change them out as well as the plugs. I know from experience, that a spark is influenced by the pressures of it's environment. ie. in a vacuum, the spark will jump further with less effort than in higher pressures, so what appears to be a good spark in open air, may in fact not be a very good spark in the compression stage of the cylinder.

I will laugh if it is a stupid little thing like the plug wire 'boot' having too high a resistance. Either way, it's now an excuse to change out the coils.

Thanks again and I am bringing the bike to my favorite bike shop: Van Shaik & Sons in Nanaimo, British columbia. They are by far the best price for the job. ($45 CAD for a 2 hour valve adjustment on my Yamaha including labor and parts, and have quoted $65 for a complete tip-to-tail tune-up and inspection on my GS).

Ok, Ok, enough yammering right? lol

If anybody else has any input, please, by all means leave me a post.

-Scott

[snowbeard]

I was going to guess fuel starvation from your first part, sounds like it was of some sort. when I first got mine I had alot of rust in the tank, to the point it really didn't run.

check the float bowl drains on the outside carbs (easy enough without removing anything) see if there's gas in the non-firing one. if there is, is it clean? put towel or rag under it when you open it so you can see if there's crap in the gas from it. you might be able to get away with pulling the float bowl off and cleaning it up?

if you've fire(spark) to the non-firing one, it's most likely a lack of fuel. also check the spark plug for gap and such?

good luck!

[KEITH KRAUSE]

If only one plug isn't firing, the coil is fine. The fouled plug could be a bad lead connection at the coil or the cap, carburetion, or low compression.
Check the connections first because it's easiest. Then I suggest a good carb cleaning by someone you can trust. Besides the dead cylinder burdening the engine, the bike is definitely not getting enough fuel in the mixture without the choke assisting.
Clean the carbs, with special attention to the pilot circuit, replace any o-rings, adjust the floats, verify the correct jets are in it, and synch the carbs.
The petcock and tank should be cleaned too.

[Anonymous]

Re: I think I understand...

I will laugh if it is a stupid little thing like the plug wire 'boot' having too high a resistance. Either way, it's now an excuse to change out the coils.

-Scott

Hi Scott,

The plug boot should have a 5k ohm resistance to suppress radio interference. However, the boots do break down and need replacing. Try a new boot, it might just get you laughing. And if it works, replace the others, as they will go down sooner or later as well.

Kim