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Old 07-23-2007, 08:13 PM   #1
L Bo
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Default 2 stroke tuner question: carb adjustments

I am to get my brothers 49.5cc scooter engine tuned and running right. I already replaced air filter, plug, for big improvements and just today I replaced the fuel filter. It has 3,000 miles on it.

Symptoms: After a 2-10 minute WOT run it will either bog down to idle for a little while (Will not rev or respond to throttle input, only happens after a long WOT run) or, like tonight just completely stall. I did just replace the filter hoping that was the problem. It started back up after a minute or so. The new fuel filter did give it a smoother acceleration curve, before it would skip and miss at high RPM's. I hope it's not over reit would take several hours after it would skip or misfire (like the next day) before it would start again.

FYI- The problem of it stalling and bogging out was present before plug and air filter replacement.

Carb Settings:

There are two needles to adjust. I have already tuned them to the best I think they can be via trial and error. One seems to set the low speed and idle, the other I am guessing air/fuel mixture at high speed.

Someone said it was water in the line causing it too stall, the carb needs to be disassembled and cleaned........something something water in the float. I don't know how that could be since the float has a drain tube attached to it.


Is it running too rich, too lean, or does the carb need to be cleaned?
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Old 07-23-2007, 08:32 PM   #2
jtdbsr
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Hmm, haven't touched a 2 stroke in about 20 years, but I'll give it a shot. If it stalls out after a WOT run, maybe the fuel level in the bowl is too low? Try to adjust it by bending the float carefully. Also, what color does the plug has?
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Old 07-23-2007, 08:54 PM   #3
L Bo
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Quote:
Originally Posted by jtdbsr View Post
Hmm, haven't touched a 2 stroke in about 20 years, but I'll give it a shot. If it stalls out after a WOT run, maybe the fuel level in the bowl is too low? Try to adjust it by bending the float carefully. Also, what color does the plug has?
Could be the bowl, something needs to be cleaned adjusted and not sure what you mean about bending the float though. Maybe it's not level?

FWIW---> The fuel guage is also off. It reads full when it is and then at about maybe 4/5 of a tank it reads 1/2 and by 3/4 tank it's reading empty. Thinking those are 2 different problems, maybe not though?

The plug is new, not sure what color it is but it's new (200 miles) and gaped/fitted for the engine.
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Old 07-23-2007, 09:01 PM   #4
jtdbsr
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The float should have a tongue that pushes against a needle that lets fuel into the bowl. You can bend the float up or down to set the fuel level in the bowl. What make/model scooter is it?

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Old 07-23-2007, 09:07 PM   #5
Bonzo
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I'm very familiar with higher perf 2's and no so much on scooters etc so here goes.


Possibles are:

float bowl running empty (as was said) adjusting float hieghts s ok for the confident and somewhat knowledgable diy-ers.

Cylinder running lean after long period of WOT. It simply looses power until temps come back to normal and piston to cylinder wall tolerances return. It is possible to burn a piston or stick a piston ring however some mopeds use oil injection as means of governing speed. In other words it simply loads it up with oil to take away top end. Oil also helps with engine longevity and typical 2s warranty and service claims.

Adjusting the low speed is relatively easy. The high speed udjustment sould really be done when the engine is under load or at speed. They are both easy to screw up as one eventually just "chases demons" and never gets it correct.


I'd say try a dealer but that costs at least $70/hr which is teh sux0rz.
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Old 07-23-2007, 09:42 PM   #6
L Bo
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Quote:
Originally Posted by jtdbsr View Post
What make/model scooter is it?
Thanks for the info. It's a 06 Eurostrada and Yamati? It does have a Yamaha engine though, at least the transmission cover says Yamaha "LINHAI" on it.



Quote:
Originally Posted by Bonzo View Post
I'm very familiar with higher perf 2's and no so much on scooters etc so here goes.


Possibles are:

float bowl running empty (as was said) adjusting float hieghts s ok for the confident and somewhat knowledgable diy-ers.

Cylinder running lean after long period of WOT. It simply looses power until temps come back to normal and piston to cylinder wall tolerances return. It is possible to burn a piston or stick a piston ring however some mopeds use oil injection as means of governing speed. In other words it simply loads it up with oil to take away top end. Oil also helps with engine longevity and typical 2s warranty and service claims.

Adjusting the low speed is relatively easy. The high speed udjustment sould really be done when the engine is under load or at speed. They are both easy to screw up as one eventually just "chases demons" and never gets it correct.


I'd say try a dealer but that costs at least $70/hr which is teh sux0rz.

So you're thinking I might be running it too lean huh? That would make sense, and maybe I will richen it up a little. My only 2 stroke experience is with small RC engines, they have a simple fuel/air mix with no floats or bowls. This is my inexperience.

No one thinks it's moisture in the fuel line or carb?

It runs 40+ MPH easy on flat terrain and no wind right now, previous fast speed was 35 or so before I changed plug, filters and messed with the carb. I guess richening it up some first, then look at then look at the carb. It is easy to remove.

Yeah the oil line is attached directly to the block, no worries there.
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Old 07-23-2007, 10:29 PM   #7
Bonzo
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running leaner will give a it a bit more high rpm power which would make sense with it having a bit more speed.

moisture or water would cause it to run just plain bad and foul plugs.

You could do a high speed "plug chop" to check to see how lean it really is. Run it wide open for as long as it seems (engine) safe then kill the engine and stop as quick as possible and pull the plug to view color etc. If it's white, light tan or gray it's on the lean side. fwiw reading plugs is also quite specific to plug type so this is a very general way of learning what your carb calibration is doing. Take a sniff too. An acrid smell means the piston is beginning to break down.

Other than that viewing the fuel wash on the piston dome is the best way to see how it's doing in there. A bit involved for sure.

In 2strokes, fuel is part of the engine cooling system as that poor piston never gets much of a rest or cool down time.
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Old 07-23-2007, 10:51 PM   #8
cucamelsmd15
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If it stalls when you let off the throttle, it could be rich at idle possibly? I had a problem similar to this back when I had a Banshee, but Im not sure it would carry over.

EDIT: Dammit, reading>me, I just skimmed the first post. After reading it again, Bonzo has given some sound advice, and that would probably be where I started.
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