1 cylinder idle!

[Anonymous]

Hello,

I have a problem with my 1979 GS750e. One of the cylinders does not work!

I have checked the ignition key and there is nothing wrong with it so I guess there is a carbonator problem?

Anyone know what it might be? And do you think I am capable of fixing it myself or do I have to leave it to a profesional?

[Anonymous]

Before checkings the carbs, check to make sure you're getting spark on that cylinder. Remove the plug, put the boot back on and lay it against the head. Look for spark as you try to start the bike. If no spark, check the other lead for that coil. If one lead sparks, and the other doesn't, swap the plugs. If no change, the lead is most likely bad.

[Anonymous]

Thank you Jeckler but there was a spark when I laid it against the head.

[lhanscom]

Take the carbs off and give them a good cleaning. You can do it, just take your time. You will learn a lot about how they work.

[mdole]

Another thing you might want to check before going too far along the path on the fuel system.

Even though you have spark it still may be worth trying a new plug. When I got the 750 I had a bad miss in one cylinder that turned into a dead cylinder. I was getting spark when I checked for it, I pulled and cleaned the carb checked for air leakage, and cleaned the air filter and air box on the chance it was constricted. Still had a dead cylinder, then just on a whim I swapped spark plugs with an adjacent cylinder and I had a different dead cylinder. I don't know what the problem was with the plug the insulator looked good and it wasn't fouled. But I have had other plugs, some of which were brand new out of the box, that wouldn?t fire under compression.
So try the simplest things first, rather than the way I do things.

Mike

[AOD]

have the bike running and hit the air filter/intake with some carb cleaner. watch so the speed doesn't pick up too much, but this might help clean out something without having to take apart everything right now.

[lhanscom]

Try starting it, then shut it off and take out the plug, if it's wet, it's getting fuel, if not, then it isn't.

[Anonymous]

Regarding Mdole's post:
I tried emptying the carborator on gas (I was told to do so before changing spark plugs) and then replaced the plug on the dead cylinder.

However, when I tried to start it up again (I guess it takes some time to refill the carbs with gas) I ran out of battery.
Will charge my battery today and try again tomorrow.

Thank you all your for help!

[Anonymous]

I had a cylinder getting too much fuel and flooding out. I replaced some o-rings and the problem was solved.

The o-ring on the fuel needle seat was in such bad shape that the it had given up doing its job.

[Anonymous]

Has this cylinder run recently? Was it running and one day stopped, or did you get the bike without it running?

You do not need to drain the carbs to change plugs. Is the spark bright and blue/white, or is it weak and red? To eliminate the electrics, an easy way is to swap the leads. The leads for cylinders 1 and 4 are interchangable, so are 2 and 3. So if #1 isn't running, take the spark plug and boot off #4 and run the lead to the other side of the engine and put it on #1, along with #4's plug. These two cylinders run off the same coil and have spark at the same time. I once had the spark plug boots be real weathered and they wouldn't work until the bike was really warm for a while. So if the cylinder now runs, you may need new boots, new plugs, or a new coil. Swap as appropriate to figure out what you need.

If that fails, it could be lack of fuel or compression. If the spark is wet, you're getting fuel, and the cylinder should at least sputter. If the spark plug is dry or if it runs but not well, clean the carbs. Does it run on choke? Does it run on open throttle but just doesn't idle? If yes, time to clean the carb and replace the o-rings. You can get rebuild kits on ebay for fairly cheap, and they include everything you'd want to replace.

A compression check is easier to do than to take the carbs off and clean them. If you don't have a gauge, you'll have to buy one or take it to the shop. If the cylinder used to run and stopped, this probably isn't the problem, but it could be. Do a dry test and a wet test. A dry test is by just cranking it and seeing what the pressure is. If it is too low, you do a wet test. This is when you pour a tea spoon of oil into the cylinder. If the pressure now increases, chances are that your piston rings are shot. If not, maybe the valves.

Good luck, and I hope that all you need are some new boots like I did

[Anonymous]

Damn I never should have started fiddling with it myself!

Only things I made were:
1. Empty the carbonators on gas.
2. Change one spark plug.
3. Charge the battery.

And now the bike dies when I give it throttle :x

[Anonymous]

Never mind my last post. I got it working again.

Still only on 3 cylinders though.