2011 VIP losing power at 5000 RPM

[merrikii]

Hi, I have a 50cc VIP with a 150cc carb, it also has one of those metal pod air filters. It has been unrestricted in the variator and I freed up the air flow through the exhaust. The carb has 105 and 35 jets. 

The bike was this way when I bought it. It did not run very well as it was. 30-35 mph. I adjusted the valves to .002 both sides and the bike ran 50-55. (The speedo stops at 50--I really have no idea how fast it really went.) It got terrible gas mileage but had three times the power than when I bought it.

Well, the other day I got into the rum. I was riding it like a dirt-bike. I live in the country and there are dirt roads everywhere. I covered the engine with a sand so fine it turns into cement-like when wet. It did get wet and the entire engine was coated.

From that point on, the engine does idle and start seemingly normally, but if I try to ride it, it will just shut off. It loses power when the belt starts grabbing. I can sometimes get to about ten MPH if I barely hit the gas. The engine just bogs down like it's getting no gas. But, sometimes, when the auto choke is on, I can get the engine to rev up to 8-9000 rpm. It has one of those CDI's with the higher rev-limiter. It has pegged the 10000 tach before when I rode WOT for about a mile.

I've taken apart the carb twice and thoroughly cleaned it. There was some fine sand in there and in the garbage metal air filter.

I really do not know what else to do. I checked the valve clearance again and the top was super tight again but I readjusted it again.

Does anyone have any suggestion short of tearing down the entire engine?

[Rebel]

See if the sand messed up the variator, but with cement caked cooling fins you will need to change the cylinder out just ti keep it from over heating. Still sounds like a air/fuel thing or perhaps the valves got burnt.

[merrikii]

Thanks for the quick reply.

I have already checked the variator yesterday. It was clean inside the cover. I am almost positive the problem is fuel/gas ratio. If I spray wd-40 into the manifold the engine will rev up.

Sometimes when the engine is trying to gain rpm's it sounds really choppy. Like a dirt-bike. Is there anything special to be done when breaking down a carb and putting it back together? I just took it apart and cleaned it and put it back together.

Oh, I never rode the bike with the sand on it for long. I cleaned it immediately the next day.

Is there a sure-fire way to know if the problem is fuel ratio?

[merrikii]

Also, do I need a ring compressor to change out the cylinder? Would it be better just to change the entire head?

If I do end up taking the entire top end off, do I need to purchase anything to put it back together? Could I peek inside without buying new gaskets and such?

[Rebel]

Check for a vacuum leak before you start taking things apart a loose hose or cracked intake will leak enough air in to make it run vey poorly.

No you don't need a ring compressor for these, if you have a hard time ust use a big hose clamp to compress the rings. No special tools are needed for a top end job.

I have a gizmo I got at harboe freight that lets you look inside a motor. Never used it yet but you would not get a good view of it all.

Doing a compression check will give you an idea about if you have ring or valve problems.

[merrikii]

I've checked all lines and hoses. There was a leak on the fat bottom hose coming out the front. It had a bolt in it stopping the air flow. I cut the hose and screwed the bolt back in. The engine has quieted but no other change.

Is there a way to check the compression without a gauge? I've read that I can turn the engine over with my finger over the spark plug hole. Is this method viable?

[Rebel]

I use the finger on the hole method a lot, it gives a gross idea if you have compression. It is best to use a gauge and it should be over 110 psi, 120 is really what you should have.

Any chance the air filter is plugged?

[merrikii]

No, I've made quite sure there is no occlusion from the air filter. I tried to run the engine with and without the filter. Yesterday, before I broke the carb down a second time, I did take the filter off and ran the engine.

The engine actually would run better if the filter was off and I retarded the airflow some with my hand hovering over the intake. When I look through the filter up-towards a light, I can see light. When I try to breathe hard through the filter, there is no resistance.

I am going into my kitchen to try the finger method. I'll post the result in a moment.

[merrikii]

I've checked the compression. There is plenty. My wife turned the motor over. I'm not a small guy--no matter how hard I tried to stop the engine from pushing my finger off, the engine would blast my finger from the hole. I had her turn the motor over probably for fifteen rotations twice. I honestly do not know if that is enough?

Is there any way to tell if my issue is based on a carb-fuel/air ratio-problem? Is there any way to run the fuel straight to the intake and see if the engine still will pick up rotation?

This bike is obviously not stock--what would you do to diagnose the problem if you really had no money to spend and limited tools?

[Rebel]

If the plug electrodes are black tou are running too rich. Sounds like the compression is ok.

[merrikii]

It is super black. It's not like burnt. It's wet. It smells strongly of gas. When I lifted my finger off, there was overlapped black rings smelling of gasoline.

There is nothing wrong with my carb. It's only three weeks old. I did take it fully apart. I might have even taken out the brass jet-holder-thingy in the middle of the carb. It's a K H Japanese 150cc carb. I can not seem to tune it, but, it does run nearly as bad--probably worse-since I first took it apart.

I always did think it was the fuel/air ratio. Do you have any suggestions on how to start from scratch?

[Rebel]

Well you said it was a carb off a 150 and you have a 50. I would order a carb for a 50 and maybe upjet it a little something like a 88 main jet and see how that works. When tuning a carb you have to do plug reads to see how it is running.

[craisin]

I agree with Rebel about the size of the carb.

but if your broke try lowering the needle by shifting the circlip

[Rebel]

Sure, you can lower the needle and that will help, you can also put smaller jets in the carb.

[merrikii]

I have a 31 and 88 jet I have not tried yet. When you guys speak of lowering the circlip, is the the brass holder in the middle of the carb holding the higher number jet. I've heard of the circlip but I don't know what it is.