3 down one to go... carbs again?

[Anonymous]

Hello All,
On my 1982 GS650G, I have cylinders 1, 2, & 3 now working, pipe number 4 is not hot after warming up. I have checked the bowl on the carb and it has gas in it. I have checked the plug and it is getting spark.. could this be a sync problem? I have yet to get the carbs sync'ed, I took them out and gave them a good cleaning about 3 weeks ago, (bike would not run at all before that) I have ruled out the coil, but could it be the timing? Plugs look like they are running a bit lean, but the air filter is quite old and needs to be replaced. plug in # 4 looks brand new still..
any comments?
BTW, I admire the wealth of knowledge on this site, and have learned a great deal from those that post.
also, I have not messed with any settings on the air screws or carb adjustments.. the bike was running great 2 years ago, got it free from original owner.

Thank you all
Tom

[Anonymous]

The ignition is electronic, so there's no points, and the timing cannot be altered.
Even if #4 is getting spark in the open air doesn't mean it sparking under compression. Change it and see what happens. Since #1 is working, that rules out the coil, but swap HT leads between 1 & 4 to see if the problem is there.
Have you checked the valve clearances? How about a compression check? You might have a hung valve. Any raw fuel or fuel smell out the right tailpipe? Is the plug wet when you check it?

[Anonymous]

are you talking about switching out the plug wires between 1 and 4? HT leads is new lingo to me, The plug is not wet, and the wierd thing is, I go out and start it every night, and some nights, #4 works, and some nights it does not.. I stuffed a t-shirt in the air box, and started it up 2 days ago.. as I let off the choke, I pulled out the t-shirt (slowly) until I got the air restriction just right.. Cylinder # 4 was working when I did this, I put the air filter back in and waited till the next day, and #4 stopped working again.. Can the air filter in an air box cause only 1 cylinder to not work properly?
Tom

[Anonymous]

Yes, HT (Hight Tension) leads are the spark plug wires. I can't remember where I first heard the term, and I live in the US, but it seems to be a British term. *shrug*
If the plug isn't wet and it sometimes works, I'd say you've fullfilled ignition. Now you need to check compression, then fuel (I put it in that order since you said you've gone through them once already, but if compression checks out, you'll have to do it again).
Another thought, in your original post you said it doesn't work after warm-up. Is that just sitting idling? If you ride the bike, or at least get the carbs pulling fuel through the main jets instead of pilots, by raising RPM, does it seem to work better then?

[Anonymous]

I rode the bike for about 20 minutes last night, and #4 did not get hot.. averaging sppeds from 55 to 85 MPH.
But the other day when it was working, it was at Idle.. You just made me think of something.. When I cleaned out the carbs, I didnt take them completely apart.. however, I did take the cap off of one of them.. I think it was #4. to look at the diaphram. I had some difficulties getting the cap back onto the carb with the diaphram setting in it right. I bet the diaphram is not in correct, and the slide is not moving up and down like it is supposed to.. this would explain the hot pipe at idle, and not after riding. hmmm sound feasible to you?
Thanks
Tom

[Anonymous]

Sounds good to me. You might have holed it, or it's stuck (hope it's the latter, not the former).