KT100 not starting/no throttle response when push starting it

Hi, all,

I have been browsing the forums for a while and registered today because I need your help.

I have a direct drive KT100 which is able to start on the stand but it does not start when putting it on the ground and push starting it.
Carb settings are 1.25 turns for Low Speed and 0.5 turn for High Speed, oil/fuel ratio is 16:1 of AMSOIL DOMINATOR 2-Stroke Racing Oil.
The engine has a new spark plug (Autolite AR51), air filter, new fuel filter and hose and carb has been just rebuilt meaning changing the gaskets and all that.
When push starting the kart there are times on which it will try to start but there is no throttle response so, at the most the kart will move 10-20 metes and stall.
I’d greatly appreciate any insight that you may provide to troubleshoot this issue, thanks.

Hi Rick, welcome to the forum. A couple of questions to start off with. Has this engine run properly before and has anything happened since then? Have you tested the pop-off and does it hold pressure after it has popped off? Have you looked into the exhaust port to see if the piston is damaged or had the head off?

1 Like

Are you picking up the rear of the kart when you are pushing it?
Easiest way is with 3 people, sit in the kart and lean as far forward as possible ,have 2 others pick up the rear and push it, once they have done a few steps drop the kart but keep pushing until it takes off normally only need light throttle

How much time is on the motor since its last rebuild? Has the compression been checked? I have seen this symptom on motors with low compression. They run on the stand because there is little resistance but when you need power there isn’t any. The other thing I would look at is the carb, if it ran fine before the rebuild but since the rebuild you had your issue then you may have something amiss.


Tony, since the carb rebuild it was working fine. All of a sudden it started to have issues starting but it would eventually start until yesterday that I was unable race with it.

Aj, that is how we are push starting. We even tried starting it with 3 people (me included) and I jumped into the seat once it tried to start but there wad no throttle response so it stalled.

Robert, I have not checked the compression, there is no way to check it without a starter, right?

I bought this kart without any history about it, so I am not sure when was it last rebuilt. What would be the required parts for a rebuild?

I am just starting in the karting world, so I have a lot of questions.

1 Like

You’re in the right place :slight_smile:

Riddle me this, have you gotten it to run on the stand? You can check compression by push starting it or trying to turn it over on the stand.

Push starting is a bit of an art, if you have a video of what you’re doing that might help too

1 Like

Yes, on the stand runs ok

If you can, borrow a carb from a fellow racer and use his carb settings to remove the carb as the problem. Double check the wire mesh screen within the carb for debris. You might want to try push starting with different low speed settings. You could try a 1/4 in then a 1/4 out.
Also, after the engine doesn’t start or dies shortly after starting on the ground, does it start right up on the stand?

Pulse line on the carb hooked up?

1 Like

Yes, that is the weird thing. It does start immediately on the stand after stalling on the ground. As a matter of fact, on the stand does not take that much to start it, I checked the mesh filter yesterday and it was clean. It is a really weird issue.

Yes, I changed it yesterday to see if that was the issue but it still stalled on the ground.

Can you talk through your process when starting on the stand? If it’s starting there no problem, then there must be a way to emulate that when push-starting.

This is the process:

  • Set High and Low speed needle as described in my original post.
  • Remove air filter and cover the carb intake with a rag
  • “Prime” the carb by moving back and forth a rear tire until I see gas in the carb
  • Wrap a tire with strap and pull it.
  • Kart starts without issues

Hopefully you understand what I explained

Is the rag restricting airflow enough the choke the carb? If so, have you tried choking (while off throttle) when pushing?

Yes, it does restrict the airflow but the rag is covering the carb when priming it, once I see gas in the carb I remove the rag and start it with the rope wrapped in the tire, this is when the kart is in the stand.

Once I put it on the ground, I re install the air filter, move the kart back and forth multiple times and then push it but it does not start or if it starts it stalls since there is no throttle response.

Try richening the low speed jet to get it started. Whenever I had an issue with my sons KT where it’d start and then die coming out of the pits it was due to being too lean.


I was thinking the same. All of the KT’s I’ve ever ran have had the low needle at 2 turns or more.

1 Like

Just to be sure I understood correctly. Would it be something like this:

High speed needle: closed
Low speed needle: 2 turns

Push start it and once it starts open High speed and adjust Low speed

Something like that should work, though you may not even need to mess with the high with regards to starting procedure. What I was getting at is your baseline settings may be out of whack to begin with. If you’re unsure of the engine history then it may be prudent to send in for a rebuild and also send the carb to the builder. You could certainly do just a top end rebuild (piston, ring, circlips, pin), but it would be recommended to have the entire engine gone through.

1 Like

Got it, thank you.
I appreciate everyone’s help