Carb#1 CV Boot question/running ice cold

[Guest]

During tonight's ride, I completely lost cylinder#1 on my '82 GS850L. Carbs have been completely rebuilt three times (please don't ask!). Question is...if cylinder #1 is dead cold after a long run, but heats right up when I put petcock in "prime" rather than "run", could a defective CV Carb boot do this? I pulled the top cover off, and the diaphram looks just like the rest; seated evenly in the groove, with the little tab lined up with the carb body, and kind of wrinkly like the others with no obvious tears or gaps. Doubt the petcock's at fault as all three other cylinders run great and hot. Could the starter plunger have anything to do with this problem? (God-I wish we had fuel injection in 1982; carbs blow!)
Thanks guys,
Larry
By the way-plenty of spark from plug #1-so not ignition.

[bwringer]

Since it's easy to reach, take the drain screw off #1 and see if there's fuel in the float bowl. Or if you've already done this, what were the results?

The vacuum line that operates the petcock is on #2, so this seems pretty odd...

[bwringer]

If you mean the boot between the carb and cylinder head, a broken or defective boot or o-ring (or missing o-ring) could cause the mixture to be so far off that it won't ignite.

More likely, that cylinder would first overheat quite badly as it sucked in air to make the mixture far too lean.

But my leading theory at the moment is some sort of fuel delivery problem in #1.

Is the petcock of reasonably recent vintage?

You could also have some sort of really wacky linkage or sync screw problem that's causing the #1 throttle plate to stay closed.

I'm sure other ideas will occur to me and others at random intervals...

[Rocketman]

I knew I could count on you to help. No, I have not yet dropped bowl #1 to check for fuel. as I'm just getting ready to sit down for dinner. The boot I'm referencing is the rubber diaphram around the slide and pin. Is this diaphram supposed to be glued into the recess in the top of the carb, or just rests in there and is compressed by the crab top when its screwed in? Petcock is bone stock original from 1982 never been touched or maybe never even been seen. However if it were defective, I'm thinking it would affect all 4 cylinders, not just #1. Fuel delivery is my guess too, but baffling right now. Maybe after a meal I can think with a mroe clear head. I'll let you know later if there was fuel in the bowl.

[RobGS850L]

1 thing came to mind. The carbs have screens at the needle and seat and #1 might be a little clogged. I know the petcock runs a bit more fuel on prime so maybe that's helping the situation but I really wouldn't bank on it.

[Rocketman]

I was also thinking that unscrewing the bowl screw to check for fuel won't help me a lot, as when I turned it from run to prime, cylinder #1 kicked in and got hot pretty quickly. Any way to clean these screeens out without disassembling the carbs for a 4th time that you know of?

[RobGS850L]

No my friend. Taking those badboys off the bike has to happen. But the cool part is is that you only have to remove the #1 fuel bowl. Take out the pin holding the float in place, unscrew the phillips screw holding the needle and seat assy and out it comes.

[Rocketman]

I can basically remove my air box and carbs with my eyes closed now. I just absolutley HATE doing it. Think I'll wait until tomorrow and see if any other ideas pop into my head. Supposed to bring that '98 BMW R1200 to the dealer tomorrow at 11:30 to have it checked out. Ahhhhh....fuel injection alone may make the purchase worthwhile. Can't really ride both bikes at once now, can I? Will fix the 'Zook fuel dilemma tomorrow or Saturday. Thanks guys. Feel free to add on if you come up with any other suggestions before disassembly.

[UncleMike]

If you really wanted to get wacky, you could always switch the diaphragms from one of the other carbs to #1 and see if the problem moves.

[Rocketman]

I was thinking of trying that earlier, but exactly how do you pull a diaphragm off? When I pulled the slide and needle out, it looks like the diaphragm is part of the slide...

[UncleMike]

I was thinking of trying that earlier, but exactly how do you pull a diaphragm off? When I pulled the slide and needle out, it looks like the diaphragm is part of the slide...

Yeah, I meant the whole assembly. Diaphragm/slide/needle. If it's shot, it's shot, I believe.

[chef1366]

If moving the petcock seems to cure the problem then get a new one.

[UncleMike]

If moving the petcock seems to cure the problem then get a new one.

Yeah, but why would that cause a problem in only one cylinder?

[Rocketman]

Cylinder # 1 has a bad attitude. But swapping slides might not be a bad idea. We'll see. Maybe just a trip to the mechanic and let him deal with my headaches.....

[hwb120240]

Yeah, I meant the whole assembly. Diaphragm/slide/needle. If it's shot, it's shot, I believe.

I may have posted this before, but the Madura site (http://forums.delphiforums.com/TAZZZ2U/start) has a diaphram repair procedure in the "Repairs Everyone Should Know" Section. Much thanks to Tom "Wheels" Reese.

http://forums.delphiforums.com/n/mb/message.asp?webtag=TAZZZ2U&msg=2583.1

Several people report success with this method.