Honda GX 270 rough idle!

[DieFeuer]

Hey guys!

I am doing this gokart project at my school, and i've used a Honda GX 270 engine, with big satisfaction... UNTIL NOW!

From one day to another, the idle went from perfect to non acceptable. I've tried cleaning the carburetor, i've tried changing the intake gasket (i made one myself from proper gasket material), and i've tried adjusting the mixture screw.. No results whatsoever. When i spray ether on the carburetor, the rpms will increase for a brief period. But as i mentioned earlier, i've tried changing the gasket.

If i have a bit of choke on, it will also increase the rpms

By the way.. When i drive the gokart, it goes perfect. But if I let of the gaspedal from 100% to idle, the engine will stall.

What is happening? This is quite critical, as i have to present the gokart in two weeks. And i simply HAVE to pass.

UPDATE: The problem is fixed. I've changed the two gaskets and the insulator on the intake side, and i also changed a messed up up o-ring on the idle jet! (The o-ring was most likely the cause of the problem)

Here is a video of it when it ran rough https://www.youtube.com/watch?v=L6bCqreuj0s

 

[KartFab]

Order new oem gaskets from the part manual based on your engines serial number. You have an air leak. Iirc there are three gaskets, two paper type and 1 metal/rubber type.

Also, did you clean out tank? No rust? Fuel line?

While you are waiting for new gaskets, disassemble carb, then clean it. Focus extra on removing jet and cleaning e-tube/jet. Spray carb cleaner through idle pilot etc. all the tiny holes. Did you get them all?

You didn't jack with governor or linkages did you?

Have you tried adjusting idle speed with black plastic screw on top of carb? If you have a functioning idle mixture screw(different from black plastic idle speed screw) I think you bottom it out then unscrew about 1.5-2 turns as default mixture.

Also, after watching your video, I think you should look into adding a secondary throttle return spring. If your throttle doesn't return far enough, the idle could be erratic/high. Does the kart have a good return for throttle pedal that allows throttle lever to return all the way?

 

[Joe-405]

Sounds like you missed something in the low idle circuit or the o ring is messed up on the idle jet.

 

[DieFeuer]

KartFab

I have cleaned the tank, but not the fuel line, as thought it would have been flushed sufficient with clean gas.

As far as i am concerned, i dont have enough time for new gaskets to arrive... I only have 10 days left, and my order from the states will take 8 days at very LEAST.

To be fair, i could not lift the pilot jet from the carb body (it seems to be quite stuck!) i just tried to blow air through all holes. And concerning the Jet/tube, i only cleaned the main jet, and not the tube. I will do this, when i am by the cart again.

I will try to cut new two paper gaskets as well. But i am in doubt about the insulator, which is situated on the intake manifold, should i suspect that for drawing false air?

I have to strong springs to return the gas, and you need to apply a lot of force to move it. So i think that is okay!

And thanks for you reply!

---------- Post added at 06:10 PM ---------- Previous post was at 05:32 PM ----------

Well, i should give it another try.. I couldn't free the jet in the plastic seat, as i thoughtit was stuck. So maybe that could cause it.

But regarding the rise of revolutions pr. minute, as i spray ether on the area

 

[Bbqjoe]

Can you take a cart that has already passed, give it a quick Earl Sheib paint job, and present it as your own?
JK

Is it possible that there might be cracks in the carb body?
Maybe find a high E guitar string and run it through all the carb holes.

 

[DieFeuer]

Bbqjoe

Oh i wish i could!

Well it doesn't seem to be broken. But i will take a look when i can! Oh it's time for the Gibson to serve a real cause!

 

[megacat]

There should be a black separator between the carb and the head, if you tighten the nuts that hold the carb too tight, it can crack and draw air, you need to take of the carb and inspect that part, the crack will be very thin, so you need to look closely. also, double check all the 3 gaskets for tears and the rubber on the big metal one

 

[anderkart]

When i spray ether on the carburetor, the rpms will increase for a brief period. But as i mentioned earlier, i've tried changing the gasket.

Sounds like your carb insulator might have been installed upside down. They'll fit on either way, but if you look closely you'll discover they're made slightly off center and can only make a perfect seal in the correct orientation...

 

[Joe-405]

That's possible but every engine will change rpm's cause the throttle shaft will let a small amount of fluid get sucked in. So the fluid spraying doesn't work everytime.

 

[DieFeuer]

Hey guys, i just wanted to update you.

I've inspected the carburetor once again, and this time i pulled out the plastic idle jet. The o-ring was totally messed up. So that's a start. I do have trouble getting a replacement. But I will try tomorrow.


I will update you!

 

[DieFeuer]

I bought a new 3x1,5mm o-ring. The fit in the carburetor was a bit snug. I assembled it with new insulator, and gaskets as well. It runs perfect now!

The cause was most likely the o-ring in the idle jet.

Thanks everybody for the help!

---------- Post added at 06:25 PM ---------- Previous post was at 06:24 PM ----------

Sounds like you missed something in the low idle circuit or the o ring is messed up on the idle jet.

You were right!