I'm hoping someone is able to shed some insight on why my kart is idling so high. I've got the carbureted Trailmaster 300 XRX. I purchased it new, and I've put about 400+ miles on it. The high idle issue started after I replaced the carburetor. My old caburetor had been giving me trouble, and I took it to a small engine repair shop. They were able to milk some additional life out of it by swapping the auto fuel petcock with a manual (on/off). However, I continued to have trouble with the engine dying when stopped and figured I'd replace the carb. The new carb fired right up but idled at near WOT and was unaffected by any idle or air screw adjustments. There is no hanging or stuck throttle cable either. Thinking the carb was faulty, I tried another and the same crazy high idle is occurring. Any suggestions are greatly appreciated, thank you!
Trailmaster 300xrx High Idle
- Thread starter Ryantect
- Start date
Hellion
Moderator
- Messages
- 8,910
- Reaction score
- 3,921
Well in the most simple of terms, carburetors have a screw that determines the idle speed which works independent of air/fuel mixture screws. The idle speed screw is usually located right on or at the carb's throttle and it determines how open or closed the throttle plate is when there is no tension on the throttle cable, in other words when the gas pedal/cable is at rest.
It is unlikely that the carburetor is factory set at the lowest idle setting, so you will have to adjust it til the throttle "butterfly" or "slide" is just barely cracked open, letting in a minimum of fuel and air.
Welcome to the forum, n00b!
It is unlikely that the carburetor is factory set at the lowest idle setting, so you will have to adjust it til the throttle "butterfly" or "slide" is just barely cracked open, letting in a minimum of fuel and air.
Welcome to the forum, n00b!
Last edited:
Thank you for the welcome! I'm attaching an image of my carb. The air screw is set to factory at 2 3/8 turns and the idle is screw is backed off to it's lowest setting. I've been wondering if a possible culprit is a faulty choke signal. It's equipped with an automatic choke, but I'm not sure if a bad electrical signal would cause it to malfunction.
Denny
Canned Monster
Poorly adjusted throttle cable?
Hellion
Moderator
- Messages
- 8,910
- Reaction score
- 3,921
Could be that 
There are instances where a choke will run the engine faster instead of choke-ing it out. If the choke is fully applied and the engine starts racing it means the Air/Fuel mixture is too lean. When you choke it at those conditions, there is less air and more fuel because you are restricting the air. My mower will do that after I shut off the fuel supply but let it continue to run. It starts sputtering and coughing as the fuel supply thins out and when I apply the choke to help it along, the revs will go up until all the fuel is finally expended.
Could be a bad choke/faulty choke signal and a too-lean condition. Make sure also, that the carb is firmly installed, the gaskets are good and seal properly and that you have not induced a vacuum leak through a bad carb seal/gasket. A vacuum leak means more air than you need is getting into the engine and leaning out your A/F mixture. Make sure also that you have your air cleaner installed. The filter provides a slight air restriction but you adjust your carburetor to compensate.
Egad, automatic electrical chokes. The machines are running US! Lol
There are instances where a choke will run the engine faster instead of choke-ing it out. If the choke is fully applied and the engine starts racing it means the Air/Fuel mixture is too lean. When you choke it at those conditions, there is less air and more fuel because you are restricting the air. My mower will do that after I shut off the fuel supply but let it continue to run. It starts sputtering and coughing as the fuel supply thins out and when I apply the choke to help it along, the revs will go up until all the fuel is finally expended.
Could be a bad choke/faulty choke signal and a too-lean condition. Make sure also, that the carb is firmly installed, the gaskets are good and seal properly and that you have not induced a vacuum leak through a bad carb seal/gasket. A vacuum leak means more air than you need is getting into the engine and leaning out your A/F mixture. Make sure also that you have your air cleaner installed. The filter provides a slight air restriction but you adjust your carburetor to compensate.
Egad, automatic electrical chokes. The machines are running US! Lol
Thank you for the responses! They are very much appreciated! Carb seems to be installed nice and tight and the throttle cable doesn't appear to be maladjusted. I still can't rule out the choke, but I'm not sure how to test it. I'm also going to examine everything on the intake side including the air filter box and make sure everything is properly installed. I've found a local shop that does gokart repair and if i dont have any luck, I'll be dropping it off and let them perform diagnostic. They specialize in Hammerheads but can also work on the Trailmaster brand. Hopefully, I can get to the bottom of the issue, and I'll post the result.
Karttekk
Well-known member
What happens with the throttle cable disconnected?
Karttekk
Well-known member
These have electric chokes. There is a pintle in the choke that is wide open to let excess fuel into the intake cold starts. As the engine warms up the pintle closes into a bore and reduces fuel flow. If it was working before the carb swap you have something else "effed up." Check what Denny says, see if the throttle cable is set too tight.
Denny
Canned Monster
He he, you said pintle.
Karttekk
Well-known member
Take the electric choke off of the original carb and put it on the new carb. See what that does. Are your vacuum hoses hooked up correctly?
Karttekk
Well-known member
Check for a cracked carb base gasket, could have a vacuum leak causing a lean condition. You may have cracked the intake manifold, the part the carb bolts to. Take it off and check for cracks.
www.rollingwrenchdenver.com
GY6 Intake Manifold
Intake manifold with two vacuum points for 150cc and 125cc GY6 4-stroke QMI152/157 and QMJ152/157 engines.Connects the carburetor to the cylinder head.Tip: This is a common failure part for two reasons; one, because it is the only mounting point for the carburetor, and two, because of the...
www.rollingwrenchdenver.com
Denny and Karttek, I took your advice and disconnected the throttle cable. Started it up, and it idled just fine! It appears that the cable is about an 1/8" too short. Maybe the new carb had a slightly different position on the throttle plate? Now i just need to get this cable adjusted. Either way, thank you!!!
Karttekk
Well-known member
Glad to hear it!
Denny
Canned Monster
Glad we could help! Now get to riding have fun and be safe!