Engine Trouble Another power loss story

[Hawaii_Ed]

After over 1200 miles of happy commuting, my happy time started not being so happy My friend 5-7 Heaven and I are planning on some fun Island rides, and I am trying to get the old girl together. I was sorta thread jacking the carb thread, so started here.

Details are:
- 66cc Gasbike kit, just a basic motor on a cheap beach cruser
- 36T sprocket, 12 gauge spokes and upgraded rims
- NGK plug, upgraded wire, and sickbike parts bolt kit
- Rubber fuel line with inline filter

The bike was running great, rolling at 25-28 easy, had hit 35 on flats with no wind. I rode it over 100 miles a week, and was a daily rider for months. I was just bragging to a friend how great the bike was running. Then I rode it home, and noticed no power, serious bog when I hit the throttle, and it was surging RPM at idle.

- Started to investigate, my main guess was a carb problem.
- I redid the gasket on the intake port, and 5-7 had a sparke pocketbike carb setup. After that the bike ran better, no surging, but would not rev up on the RPM's.
- Checked the fuel flow, and it was a trickle. Pulled out the in tank filter of the petcock, it is better, but still not a gush.
- Really no change in performance.
- Thinking the exhaust might be clogged, I put a spare I have on the bike, also no change.
- Swapped the plug with the unused stocker, and it is about the same still.
- Pulled the head, and I was suprised to find no gasket. No signs of blow out though. It was greasy and wet, I cleaned it up. Cmpression seems strong with the thumb test, I can get a gauge to check if needed.
- There is some leakage at the base gasket. I will prob try taking it off and just doing the high-temp RTV.
- I ordered a new head gasket and slant head, will see if that helps.

I will keep everyone posted. Not sure what else to try yet. If I have to buy a new engine I will. I my gasbike

Ed

 

[give me vtec]

from what I have read here I just plan on having to replace the engine every year or so... if I am lucky. Makes sense that is a lot of work for one, tiny piston. Still a very cheap form of transportation IMO.

Must be nice to sport a MB in the Islands... Hope my summer at shell beach will be as nice

 

[2stroketech]

I would pull the cylinder and check the piston and rings. Most likely they are worn and you are loosing compression. An easy way to tell is to put a drop of heavy gear oil in the spark plug hole and then run the engine. If you pick up on power significantly then you have a worn piston or rings.

 

[Hawaii_Ed]

I tore it down today, things looked pretty good, some light scoring on the piston, but nothing terrible. I ported the intake and exhaust ports, matched the exhaust gasket and opened op the muffler pipe some, as well as the intake tube. I found it did have a gasket, jsut was stuck on the head lol. Put together with no base gasket, used RTV copper, and reused the stock head gasket. It seems to run quite a bit better, still not revving quite like it did, but was hitting 25-27 MPH. I have a slant head and gasket coming, with the petcock too. Will see how that does.

 

[Mountainman]

thought we would see if we could get some ideas here
my cousins HT with less than 200 miles -- has lost a lot of power ??
top speed way down
he thinks that he needs new rings ??

MM

 

[BoltsMissing]

H-Ed, in picture 5 where it shows the cylinder, does that look like a crack in the chamber. It's only a picture from here, but it also
does seem like the bore is excesivly scoured as well.

 

[2stroketech]

What was your ring gap like? You seem to have a very serious blowby problem on the exhaust side.

If the ring gap is good (no more than half the width of the retaining pin) then you need to check your piston and cylinder for concentricity.

For those that might not know how to measure the ring gap: Remove ring from piston and put it in the cylinder making sure that it is level. Then use a fealer guage to check the gap in the ring. You do not want the gap to be any wider than half the thickness of the retaining pin in the piston for a proper seal.

 

[Hawaii_Ed]

Thanks for the tips guys, I wanted to see what people who have torn these engines down thought of the pics. That scratch/pit was the worst one. Checking the ring gap is a good idea. I might just go with a new motor, and keep this one for parts. I have a good friend that owns a machine shop, I can let him check the cylinder out. I do love how easy these things are to work on lol!

 

[Hawaii_Ed]

thought we would see if we could get some ideas here
my cousins HT with less than 200 miles -- has lost a lot of power ??
top speed way down
he thinks that he needs new rings ??

MM

200 miles is pretty low miles, mine was still breaking in at that point. I would check out everything else first, see how the plug looks, make sure there are no air leaks, etc.

 

[davidsis]

Wow, hawai that is one fine lady. Ya, your engine looks pretty good. I think you might have some kind of carb problem, or maybe your magnito is getting crusty or something.