Slight power surge at 3/4 throttle

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ninjaplatypus42

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Mar 16, 2016
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Let me preface this by saying that this issue is minimal and as far as i can tell doesn't affect the performance at all. I am as much curious as to what is actually going on as i am intent on fixing the issue, if there is one. Since I've had the bike (a little over six months) when I'm riding at about 3/4 throttle (or really at all) at a steady speed, the power will surge. It's barely noticeable. It feels like I'm just letting off the gas a bit but of course I'm not. Is this something that is inherent to these 2 stroke engines or is it an indication of an issue?

Thanks
 
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ninjaplatypus42

Member
Mar 16, 2016
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UPDATE:
I am also having trouble getting to top speed now. it takes a very long time to warm up enough and until it does full throttle seems boggy. I recently adjusted the needle to make the fuel mixture a little richer because it was at the leanest setting and I was afraid it wouldn't get enough oil ans seize up. It was running fine before the change though so maybe i just got an air hungry engine? Any insight would be appreciated, thanks.
 
2door

2door

Moderator
Staff member
Sep 15, 2008
16,302
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Littleton, Colorado
We need to know a lot more information before offering advice.

What engine? What carburetor? Any modifications?

How many miles on the engine? What oil/fuel ratio are you using? What spark plug gap? What gear ratio (rear sprocket size)?

What is the terrain? Hilly? Flat?

There are so many variables that play into how an engine performs that we need to know some specifics before we can offer advice on your particular issue.

Help us out here and hopefully we can help you.

Tom
 
Last edited:
crassius

crassius

Well-Known Member
Sep 30, 2012
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surging is almost always due to shaking the carb so the fuel foams

check motor mounts first, then look for frame cracks or an intake too long
 
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ninjaplatypus42

Member
Mar 16, 2016
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66/80cc 2 stroke. The carb that comes with it, no modifications. Around 200 miles on it. I'm using a 35:1 fuel ratio. Stock spark plug and gap. Standard rear sprocket. Flat terrain. I rode it for awhile today and it just seemed like the fuel ratio was too high and it was getting bogged down. That would be my guess anyways.
 
Agreen

Agreen

Member
Feb 10, 2013
792
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Southeastern GA
Bogging down means it's lean and you need to drill the main jet out more.

Sputtering (or 4 stroking) is toonrich and the main jet needss to be soldered shut and drilled to a smaller size.

Both of those conditions are when at WOT.

The needle adjusts fuel/air ratios at partial throttle. Above 3/4 throttle, the needle has nothing to do with the mixture. Idle mixture can not be adjusted. At 3/4 to WOT, the main jet is solely responsible for fuel delivery. A set of micro drill bits will get your mixture just right.

Also note that the float height should be set properly as well. When the carb is upside down with the bowl off, the float should be level (parallel) with the carb base.

And change the crappy stock spark plug for an NGK B6HS. You can find them at most auto parts stores, under $3.
 
Venice Motor Bikes

Venice Motor Bikes

Custom Builder / Dealer/Los Angeles
Mar 20, 2008
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Los Angeles, CA.
I would put the needle clip back where it was originally & call it a day... Most carbs are jetted a little rich which means you're getting plenty of gas.
 
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ninjaplatypus42

Member
Mar 16, 2016
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I put the needle clip back where it was and that helped alot. I also got a new spark plug and that completely eliminated the problem. It seems to have better acceleration too. Thanks guys.
 
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