Avenger 85- Low Power

Donnyten

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Jan 21, 2023
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Engine: Avenger 85 Stock Kit

Problem: Very Low power @ WOT & through-out any power band. It will not accelerate up hill without dying, and barely takes me on a flat road- even when pedaling. The engine kit was purchased last year, and ridden for a total of 25 miles before the bike was stored in the shed for the winter. Now that the season is here, I'm ready to finish breaking it in. Upon attempting to start, I noticed it would not idle, even with adjustment of the screw all the way in. Other times it would erratically idle as if it had an air leak. Fast forward, part of the issue was throttle cable binding (it wouldn't release properly). That fixed some of it but it still wouldn't Idle properly and the bike lacks all the power it had when I first ran it. There was also lots of smoke coming from the exhaust. I checked the spark plug and it was kind of fouled, I guess- so I replaced it. NGK bh6

Next, I checked for exhaust restrictions ( none ) and re adjusted the clutch for the better, and that's fine. I also removed some black sludge from the jet in the carb, and flow is normalized. Though idle improved slightly, the bike would shut off still if I didn't give it any throttle. Following that, I took cdi and magneto measurements to find that for whatever reason- I got no reading at all on the multimeter for the cdi, and about 440 ohms on the magneto coil. I ended up replacing them both, with both magneto and cdi measuring to spec. For whatever reason, it's hard to get a cdi measurement with both multimeter probes on both wires, most of the time I get no reading. I even cut the ends off the old one, stripped the wire back and wrapped them around the actual multimeter probes. No reading. On any of the settings.

From a few brief tests, the bike idle has normalized, however the power is still incredibly weak. So I check cranking compression which quickly gets to 145 without a problem. There are no oil leaks around anywhere on the engine, no indication there might be a crank seal or head gasket leak. I took the head off and the gasket looks fine. The cylinder is relatively smooth and piston appears to be fine.

I try to avoid posting issues here as much as I can but this one has me a bit stumped. I'm inclined to try another carb but I see nothing wrong with the one I have and Amazon sent me the wrong replacement anyway. Any thoughts?
 
Oil mix?

Age of fuel?

Was it stored full of fuel?

Do you have an inline filter?

To start, I'd pull the carb and let it soak in carb cleaner, remove and inspect jet, Replace the inline filter.

Any old fuel remove and get a brand new batch of fresh fuel 20:1-25:1 as it's still new.
 
Oil mix?

Age of fuel?

Was it stored full of fuel?

Do you have an inline filter?

To start, I'd pull the carb and let it soak in carb cleaner, remove and inspect jet, Replace the inline filter.

Any old fuel remove and get a brand new batch of fresh fuel 20:1-25:1 as it's still new.
The oil mix was whatever was recommended from the factory, I don't quite remember off the top of my head. Your ratio sounds about right.

Age of Fuel- New

Stored full of fuel- I ended up transplanting the kit to a different bike and disassembled everything after storage,. I dumped all the fuel out of the engine as well. Also, to see if that was the case, I also disconnected the spark plug, carb, and cdi and cranked it up a few times just in case it was flooded. But that was fine.

Inline filter- Yes, Oriented the correct way

Jet inspection- Already done
 
The oil mix was whatever was recommended from the factory, I don't quite remember off the top of my head. Your ratio sounds about right.

Age of Fuel- New

Stored full of fuel- I ended up transplanting the kit to a different bike and disassembled everything after storage,. I dumped all the fuel out of the engine as well. Also, to see if that was the case, I also disconnected the spark plug, carb, and cdi and cranked it up a few times just in case it was flooded. But that was fine.

Inline filter- Yes, Oriented the correct way

Jet inspection- Already done
New as in within a couple weeks from the gas pump? Once you mix oil to fuel that has ethanol in it, it goes stale within a month.

Storing it with fuel probably caused all your problems, bits of rust and paint from the tank and the gel that stale 2 stroke oil makes is probably everywhere now.

I'd check to see if you have a little screen on the tank end, if you do remove it, it clogs too quickly and your inline is doing it's job anyway.

I'd soak your carb, and if that doesn't work, replace it.
 
New as in within a couple weeks from the gas pump? Once you mix oil to fuel that has ethanol in it, it goes stale within a month.

Storing it with fuel probably caused all your problems, bits of rust and paint from the tank and the gel that stale 2 stroke oil makes is probably everywhere now.

I'd check to see if you have a little screen on the tank end, if you do remove it, it clogs too quickly and your inline is doing it's job anyway.

I'd soak your carb, and if that doesn't work, replace it.
Yes, new as in, Last week from todays date.

The engine was not stored with fuel. To test, I pedaled and cranked a few times without the spark plug, cdi and carb attached and nothing came out. I also removed and dumped all the fuel from engine prior to storage.

I'll try soaking. I have a replacement here due tomorrow, anyway
 
It's worth checking for air leaks too and checking head torque.

Many remove the acorns on head studs to keep them from bottoming out and messing up the threads.
 
It's worth checking for air leaks too and checking head torque.

Many remove the acorns on head studs to keep them from bottoming out and messing up the threads.
The head torque on mine is set to 144 inch pounds.

I also have had bad experiences with acorn nuts, those were replaced with hex nuts a while back.

Do you have methods for testing for air leaks?
 
The head torque on mine is set to 144 inch pounds.

I also have had bad experiences with acorn nuts, those were replaced with hex nuts a while back.

Do you have methods for testing for air leaks?
either water mist or carb cleaner by your usual spots like main crank seal, carb and jug base.

Water causes a stumble, anything flammable causes a stumble and sometimes a flare.

Could be tricky if it doesn't want to idle on it's own.
 
either water mist or carb cleaner by your usual spots like main crank seal, carb and jug base.

Water causes a stumble, anything flammable causes a stumble and sometimes a flare.

Could be tricky if it doesn't want to idle on it's own.
It idles now, so that problem is fixed.

I'll see if I can find an air leak with the water mist method.
 
I say don't worry too much. Run it for a while, take it easy. Don't try and re invent the wheel. Check for air leaks.
Well, this is what I say about most things in life.
 
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