Bad throttle response.

Tony Thomas

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Sep 3, 2021
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Ok the full story here. I got a new 2cycle engine I put on a frame. I got it running only to find a vacuum leak around the intake at the cylinder head so I try to tighten a little more and end up stopping the threads in the head. 🤦‍♂️ So I drill it out and tap to std thread. I install the intake using a new gasket and used 3M gasket maker just for insurance sake. I used the short intake after making sure it was flat by using Emory cloth on a flat surface on the intake. I get it running and it idles great and has good throttle response up until half throttle and above. It just noses over and every now and then it would backfire out the carb. So someone please tell me what I am missing here.
 
Still in the break in period? It'll run like crap until at least 1.5 tanks of gas (assuming 2L fuel tank).

Mine would barely run above 1/2 throttle until it was broken in.
 
I get it running and it idles great and has good throttle response up until half throttle and above. It just noses over and every now and then it would backfire out the carb. So someone please tell me what I am missing here.

Sounds like 4 stroking
Idles fine but 4 strokes at higher RPMs
This happens when your running too rich

Try moving the needle clip up one notch
 
Weedek, I was hoping that is what it was. I’ve tried everything I know so far. Just had it on the road for a few minutes so far.
 
Wrench, there was no evidence of 4 stroking. It would run smooth like you would expect it too. I can feather it and eventually make it to full throttle. Clutch not engaged and would only run it till it appears to be running hot. Don’t want to damage the cylinder.
 
It's because the rings haven't seated yet. Most places on the forum you'll see recommendations to not even bother trying to tune the engine before it's broken in.

I wouldn't idle it too much until it's broken in properly. Speed up, slow down, varying speeds / rpms for awhile.

I went for many a joy ride in the country side during the break in just because I was impatient.
 
Weefek thanks for the info. I’m taking it with us when we go camping so that will give me ample opportunity for myself and the grandkids to break it in.
 
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