Trying to Start it Up

[thatdood]

1981 GS750

I got spark.

When it fires over, it revs really high then shuts off. Any thoughts? It's leaning out, right?

My carbs were off about 3 weeks ago, and I'm not quite sure they are adjusted correctly, so that may be it. How should carbs be adjusted after cleaning a reinstallation?

And should the petcock be set to On or Prime?

[thatdood]

I just checked the carb bowls for fuel, and the number 4 carb didn't have any fuel in it. I've also had a problem with the air/fuel mixture valve on that carb. It only turns about a half turn in each direction. Could these problems be related?

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[Nessism]

I just checked the carb bowls for fuel, and the number 4 carb didn't have any fuel in it. I've also had a problem with the air/fuel mixture valve on that carb. It only turns about a half turn in each direction. Could these problems be related?

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Problems are not related. You have a float/needle problem AND a mixture screw problem.

[thatdood]

And I'm correct in assuming that if one of the cylinders is not receiving any fuel, then the bike will lean itself out and shut off?

I swear I'm not stupid, it's just that a lot of this stuff has been only theory to me, and this bike is the first time that I'm putting things into practice. Go easy on me.

[argonsagas]

Nobody will go easy on you.

We will just treat you like you are one of us.

Now, take your punishment!


You should expect to spend mor time that you may have thought of.

I would suggest removing the carb bank from the bike entirely.

Open each one and clean it carefully. The mixture screw can be removed. Blow the passage clean with a spray carb cleaner.

Blow the pilot and any other passage clear...do it from the engine side wherever possible.

A bristle clipped from a brass or steel brush will help to push out any stubborn debris, the blow it again.

Check the floats, set the floats, and be sure they are seating as they should. You can bend the arm a bit if the level is off. Remove the pin carefully....it pushes out, and you can clean the passage.

Check the diaphragms to be certain there are no splits and/or leaks.

Lay the carbs flat and check the butterflies to be sure that all open and close at the same time. To do this you have to release the tension on the idle screw....the knob/bolt in the middle.

Turn the mixture screws down to contact the base, but just barely touching....do NOT use pressure on them, then back them off one full turn, or go to one and one half turns, but not more.

You may need more, or less, but you can adjust this after it is running.


Check your tank for dirt....you already have it off anyway to get the carbs off. Shake it and see if anything rattles.

Buy an in-line fuel filter and install it between the petcock and the carb bank. It may not be necessary, but do it anyway. It is cheap insurance.

Install everything.

Set the petcock to ON.

Did you install an in-line fuel filter?

Start it up and ride.

[thatdood]

Thanks, my friend. I am gratefully punished. And I surprisingly feel like such a part of the family!

I will copy and paste this post to a Word document and have it beside me when I go through these carbs again.

I was just in Vancouver this summer. You have a beautiful country in which I hope to live really soon.

[thatdood]

Okay,
So I woke up this morning determined to get this thing running. I took off the carbs and went through the one that wasn't getting any fuel and found a rubber plug in the carb bowl.

I'm thinking, "Oh, okay. I'll just put this back where it goes and she should start just fine."

Nope.

I put it back in it's place and was even getting fuel to that carb. But still no start.

I have some starting fluid that I've been spraying into the carbs to assist in creating that vacuum, but when I start the bike, it will just run on the starting fluid and then lean out again. I will not start with its own supply of gas.

I cleaned the carbs when I first got it a month ago, so I'm fairly sure they are okay. I sprayed carb cleaner and compressed air through EVERYTHING in those carbs. They are as clean as I know how to make them.

The bike it firing and leaning itself out on the starting fluid, and it's not firing at all on its own.

I even played with the idle screw trying to set the idle a little higher just to get some extra gas in there. Nothing.

I'm beginning to get frustrated, and I don't know what I'm over looking. I don't want to take it to any mechanics, because I just don't trust them. But it looks like I'm going to have to do that.

Does anyone have any idea what is going on? I getting ready to punch this friggin' thing.

[Dave8338]

Have you determined that all carbs are getting fuel? How much flow do you have from the petcock fuel line? Is your choke circuit working correctly (everything move freely and all linkage pieces are working...not slipping)?

If all this checks out you may be in line for a soak and rebuild #-oNot a difficult job but one that has to be done methodically.