GX200 Clone running rough

[Ken]

The Greyhound clone has only run for a few hours. Changed the break-in oil, removed the governor, put an aftermarket throttle linkage, cone air filter and wienie pipe. Starts great but misses at WOT and will stall if you release the throttle suddenly. I checked the sparkplug for evidence of a fuel mixture problem but it's nice and tan. No soot or white coating so I think the OEM jet is fine. Plug gap is correct so there has to be something else in the ignition.

Can the flywheel or magneto degrade over time? The engine did sit unused for 4 years since new before I recently started it. Flywheel has some flash rust, but perhaps I'm missing something else obvious.

Open to any and all suggestions

 

[bob58o]

With the Filter and Exhaust you gave it more air.
What about more fuel?
Did you rejet the carb?

Most people run a 0.036" to a 0.039" main jet after the air filter/exhaust mod.

 

[Ken]

Did not rejet the carb. But will gladly do so. It's just that I was told to check the plug for lean running indications which I did not see. But jets are cheap, so I'll pick up a larger one. Would that explain the sputtering and missing I'm sensing?

 

[bob58o]

How exactly did you check the plug?
Did you kill the engine while holding WOT and immediately pull the plug? Or did you just look at it after regular use?

Sometimes lean/rich symptoms are confusing. Search the internet and there's a bunch of seemingly contradictory information. Generally a lean top end will run hot and lack power.

Not sure how this might apply to you but some info I learned when studying up on deceleration after-fires.

When you decelerate, the throttle closes faster than the RPMs drop. The engine is spinning fast and the the throttle is closed. This creates high "vacuum" in the carb and the idle circuit is providing all the fuel. This can create a lean condition. Sometimes a lean mix will not ignite in the chamber, get pushed into the exhaust, and then burn in the tail pipe. This is why engines with open exhausts will pop when you let the throttle close rapidly. Maybe a severe case will kill the engine????

I would try bigger jets and see if that helps, but I'm not positive here. I would recommend bigger jets to anybody who does the filter/exhaust. At least around sea level.

Many of us use micro drill bits with a pin vise to fatten up our jets.
Like I said, maybe 0.036 - 0.039" on the main and maybe 1 or 2 drill sizes bigger on the idle

---------- Post added at 05:55 PM ---------- Previous post was at 05:41 PM ----------

OR
Clean the carb.

 

[Ken]

Will do. I'll pick up some larger main jets but are larger idle jets available? Engine only has a few hours on her so I'd be surprised if the carb needs cleaning. But once I get into it, I'll Give it a once-over. Thanks for the input!

 

[bob58o]

Will do. I'll pick up some larger main jets but are larger idle jets available? Engine only has a few hours on her so I'd be surprised if the carb needs cleaning. But once I get into it, I'll Give it a once-over. Thanks for the input!

I don't think so. That is why I mentioned the drill bits. IIRC a lot of people keep the stock idle jet. i'm pretty sure I drilled mine. Or maybe I kept the stock idle jet and used the gx140 emulsion tube. I don't like anything not customized.

 

[OzFab]

Starts great but misses at WOT and will stall if you release the throttle suddenly.

This could simply be a result of valve bounce but, it wouldn't hurt to give the carb a once-over...

 

[Hellion]

Sounds like the classic symptoms of fuel starvation. Your idle jet/circuit should be fine...after all, you said it idles fine and starts fine.

What Bob said about reading spark plugs is on point. You’re likely reading the plug after a session of mostly low RPM and idle engine speeds. When you pull the plug, it looks “fine.”

Best to hop on that kart and do some good running; 10 minutes or so, run some laps, making sure to get the engine up to full operating temperature then kill the engine, pull the plug and read it.

As to the best carburetor tuning, it is better to be on the rich side of lean...and if you’re idling the engine most of the time, you’d be fouling your plugs...



As long as you have decent ignition, your flywheel and magneto are fine. They are not known for degrading while dormant unless you’re abusing the engine, storing it in a hostile environment, etc. Even then there’s not much to go wrong.

 

[KartFab]

The Greyhound clone has only run for a few hours. Changed the break-in oil, removed the governor, put an aftermarket throttle linkage, cone air filter and wienie pipe. Starts great but misses at WOT and will stall if you release the throttle suddenly. I checked the sparkplug for evidence of a fuel mixture problem but it's nice and tan. No soot or white coating so I think the OEM jet is fine. Plug gap is correct so there has to be something else in the ignition.

Can the flywheel or magneto degrade over time? The engine did sit unused for 4 years since new before I recently started it. Flywheel has some flash rust, but perhaps I'm missing something else obvious.

Open to any and all suggestions

So more air flow in, without increasing main jet means you will be even more lean at wide open throttle. As others have said, get a new main jet. I have seen the recommended range .033 -.039. Stock is .028" This is a greyhound engine so it is a true clone, so you might not need as much jet as a predator. .036-.037 at near sea level should be 'good enough' if you just drop it in.

Also, im worried that you are running at WOT with governor removed but you have not mentioned anything about a billet connecting rod or heavier valve springs. Once you get into the 4800-5500 RPM range, your valves will start to float and (besides having valves float- which is bad on the valve train) you could end up dropping a valve and the piston will send it through the head, or the float could be so bad that the piston hits the valve and bends it, or you bend a push rod, or you will destroy the connecting rod, typically from the poor oiling capability that it has at the crank journal at high rpm. If con rod fails, you are usually able to see into your engine block without even opening the side cover

If i were you, i would at a bare minimum get a billet connecting rod, and heavier springs, and jet it to avoid that lean condition you are experiencing.

 

[KingCobra]

4 years? Don't matter if it's new or not, it's been run to test it. Nobody can stress the importance enough of removing the float bowl and taking a look inside after an engine sits maybe even for one year. I did not see reference to taking a look in the float bowl to see if something is bouncing around in there, just "CLEAN CARB" came and went. Check that needle to see if the rubber tip ( some don't have one' is even there or rotted off. I generally loosen the bolt under the float bowl and look for fuel dripping out. Then I look for the color of it ( medium to dark orange is bad). Maybe it's jelly or smells like(turpentine) by now. Then I remove the float bowl and do a needle test by lifting up in the float to see if the fuel stops and then releasing it looking for adequate flow. I just did this on a buddy's 200cc clone and found old fuel and mild debris inside the bowl. It's a simple task and should be done when sitting over 6 months IMO. There is a reason that bowl is removable, so it can be cleaned out from time to time. It's more or less, a garbage catch but junk can bounce around depending the throttle rate and the terrain. I have not heard you mention that you did this and I don't think it was explained so I just wanted to get this out there. While you are under there, remove that main jet, blow it out with compressed air and inspect it and the needle. Thanks.