Gutted Exhaust, low end increased WOT splattering?

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Pcain

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Apr 30, 2012
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Hey guys,

Been a really long day of mounting two engine kits to some very tight low rider frames. Had to do some real work on them and one is still only 80% complete.

After a trial run of the first bike, we broke her in for about a tank. A bit under load and a little with no load.

Scenario:

- 66cc china A80 engine kit, 39T, 20" low rider rims
- Running rich as we are still breaking her in ~20:1
- Gutted exhaust
- Low end increased 2X (Most increadible performance enhancement i've ever experienced with a two stroke)
- Bike sounds deep, but incredibly loud (don't mind, I live out in the bush)
- Top end when riding WOT, splatters. Like it's struggling. It will hit the "in tune" frequency for about a second, then splatter for about 5 secs.

Could this be a lack of back pressure as the exhaust is gutted? (seems unlikely to me tho)

Or is this possibly a tuning issue?

Any help would be greatly appreciated!

Cheers
Chris

Tomorrow, i'll upload videos and pictures for all to see. They are looking and sounding awesome.
 
Bikeguy Joe

Bikeguy Joe

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Sounds like it's four stroking at WOT. If it's doing that with a load, it's too rich and needs a smaller jet.
 
P

Pcain

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Apr 30, 2012
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Thanks Greg, I might end up doing the same thing.


Bikeguy Joe said:
Sounds like it's four stroking at WOT. If it's doing that with a load, it's too rich and needs a smaller jet.
Click to expand...
Would adjusting the clip in the carb "tuning" solve this issue? Maybe leaning it out a bit. Or possibly running a leaner mixture of 30:1...?
 
2door

2door

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Sep 15, 2008
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At WOT the needle and/or clip position doesn't have anything to do with fuel flow. At WOT the needle is all the way out of the jet and jet orifice size then determines how much fuel flows. The needle and clip only control fuel at about 3/4 throttle and below.

Tom
 
Greg58

Greg58

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May 1, 2011
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Like Joe said it may be that the jet is to large, but don't worry because after you get it broke in the power should increase and rejeting may not have to be done. Most here run fuel mixture at 24/1 for breakin then maybe 32/1 after. I. Run Lucas semi synthetic at 40/1 in both of my bikes. You need to look at the spark plug chart in the classic thread area and compare your plug.
 
Greg58

Greg58

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Most here would not recommend you keep running without the end cap on your exhaust, but if you like it that way have fun.
 
Bikeguy Joe

Bikeguy Joe

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Or in your case, I see you are already at 20:1. I would break it in and then see where you are at.

Also, with very little or no load, these engines will break into a four cycle. Normal.
 
P

Pcain

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Apr 30, 2012
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I would have said leaner fuel means less oil... But yeah I know the difference in ratios. Currently at 25:1 I'll be going for 32 or 40:1 after break in
 
Bikeguy Joe

Bikeguy Joe

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A higher ratio of fuel to oil (40:1) will make a richer ratio of fuel to oil. The bike will run richer @ 40:1 than at 16:1.
 
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Pcain

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Apr 30, 2012
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I'm quite confused now. Running richland too much oil... Rich in oil doesn't it?

Therefore 25:1 being a higher ratio of oil to petrol woul therefore have a rich fuel mix...

This is how I've been going for years. Built a heap of two strokes and working on gopeds. Maybe I just got the wording wrong but it makes more logical sense to me this way...

Not arguing, I'm but confused mate :S
 
Bikeguy Joe

Bikeguy Joe

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The more oil you put into the petrol/oil mix, the less petrol in the petrol to air mix.

More oil = less petrol, and a "leaner" condition fuel to air wise.
Less oil= more petrol, and a "richer condition fuel to air wise.

On the other hand more oil in the mix makes for a "richer" oil to fuel mix
Less oil makes for a leaner oil to fuel mix.
 
Bikeguy Joe

Bikeguy Joe

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If you add say, 10:1 fuel to oil, your fuel to air mix will be dangerously lean.
That makes it as bad a too little oil, but for different reasons.

Sooooo. run it at 24:1 for break in, then go to 32 or 40:1 for regular running. Change the main jet to get the proper running you seek once you get the engine broken in.
 
P

Pcain

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Apr 30, 2012
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Ah I see, two different environments. Within the tank and within the engine.

Thanks for clearing that up mate.

Hopefully WOT hits that harmonious peak after break in. These carbs don't seem to be as easy to work with as a walbro, where I could adjust the high and low for ideal tuning on the day.
 
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