Lack of power and speed can anyone help?

[KoolBreeze420]

I have a 66cc motor kit with the nt speed carb, A few days ago my spark plug blew out of the head and I had to buy a replacement becasue of inventory issues I bought the rebuild kit, it consisted of the cylinder head, cylinder body, a new piston with rings.
I used all but the piston and rings the bike runs but I can't get above 30 KM per hour. I took the carb off and cleaned it and it had no effect I was thinking that today I would inspect the clutch and other areas but to be honest I am a PC technician and I have tinkered with cars and have been able to fix many issues with the manual but this problem has me stumped and I don't know what to look at or for.
Should I change the Piston and the rings and should I go back to break in procedures?
Could the cylinder head nuts being a few pounds above or under cause any issues?
I think I have them torqued to around 15 to 18lbs I redid the wiring on the CDI and changed the spark plug but it still is lacking speed and also low speed it's doesn't like at all anymore it used to have more power and it used to go about 15 KM per hour faster when it's not under load the engine sounds great but under load it lacks power and speed please if anyone can point me in the correct direction to figure out what the cause is that would be awesome.
Could it have to do with it needing to be re-broke in or something?
I was going to put the old cylinder body back on just to see what would happen then I decided to write this post to get advice on my next move.
Thanks in advance for taking the time to read,answer and help me..

 

[2door]

Mixing a new cylinder with old piston rings is more than likely your problem. I have to ask why you replaced the top end just because the plug came loose? If the spark plug threads in the cylinder head were damaged you could have simply replaced the head, not the whole cylinder. It's hard to say if you'll regain the lost compression from mis-matched cylinder and rings.
I'd suggest putting the old cylinder back on and testing it.
Yes, the cylinder head fasteners can be too tight or too loose. Your torque values are at the top end of recommended so be careful and do not exceed what you have.

If the head gasket looks good, no evidence of blow by, it will probably suffice. Lapping the head is always a good idea to assure a good gasket seal.
Good luck. Let us know what happens.

Tom

 

[Greg58]

It sounds like the replacement head is a low compression design, did you compare the two heads for chamber size? If you compare the two and find no difference it could be that the rings are not seated to the new cylinder.

 

[maniac57]

I always try to use a new piston and rings with a new cylinder.
Worn rings won't seat as well since they need a new surface to break in properly.
It's okay if that's all you have, but you should go ahead and use the new piston and rings since you have them.
These cheaply coated cylinders are marginal at best anyway.
Just my opinion.

 

[crassius]

First, I would measure the distance between all the ports on both the barrels to be sure they are exactly the same. Then I'd measure the heights of both barrels from base gasket to head gasket to be sure they are exactly the same. If all is the same so far, I'd check the pistons and the thickness of the gaskets.

As mentioned above, if heads have different combustion areas, that also may be it.

I'm seeing a bit of difference in port heights on barrels that are otherwise exactly the same & not sure why except that some may be intentionally detuned for longevity or to meet some local top-speed req.

 

[SuperDave]

First off, the new jug isn't broken in yet, its tight, extra friction is a parasitic powerdrag.
Second, compression blowby from unseated rings could also explain powerloss.

I hope that your using the new rings on the old piston, or it may never seal right. You might be able to get away with an old piston if the skirts aren't too worn, depends on how many miles it already saw & riding habits.

 

[KoolBreeze420]

This is pretty much all new I built it between Dec 25 and Jan 1st and the old rings really aren't that old they have maybe 100 km on them.This is why I didn't see the need to change them the only reason I changed the cylinder body was becasue the head didn't seem to seal properly on the other body. I went and brought the torque down to 10lbs and it had no effect it still is lacking power and speed tomorrow I will change the cylinder body to see what happens and I will report back I would do it now but it just started getting dark and is raining water would just compound on top of my current issues.

 

[crassius]

again, if the head didn't fit, then something is diff between the two barrels

 

[KoolBreeze420]

I always try to use a new piston and rings with a new cylinder.
Worn rings won't seat as well since they need a new surface to break in properly.
It's okay if that's all you have, but you should go ahead and use the new piston and rings since you have them.
These cheaply coated cylinders are marginal at best anyway.
Just my opinion.

The "old" rings only have like 100 km on them I figured why change them since they are not even broke in yet I am just getting through my second tank of gas and it says 3 to break in.

 

[KoolBreeze420]

again, if the head didn't fit, then something is diff between the two barrels

I am pretty sure I said that it appeared to not fit,if not my bad in any case I was wrong about that and since I had already put the new body on I left it on.
I am going to go and try the old body to see what happens.

 

[Greg58]

Compare the cylinder and head to the old ones, something has to be different.

 

[KoolBreeze420]

I changed to the old cylinder body and it had no effect..

 

[KoolBreeze420]

Compare the cylinder and head to the old ones, something has to be different.

Here's the problem it still does it even with the old cylinder body, however there was one difference and it was the neck where the carburetor attaches but I changed that to the old one because I can't use it until I get more gas hose but the neck that came with it is one that can be drilled out for a boost bottle. If there was a difference between the cylinder body's then changing to the old one should've corrected the issue shouldn't it?
I don't think the loss of speed and power has anything to do with changing the cylinder head or the cylinder body.
I just don't know where to look.
If the clutch was too tight would that cause this issue?

 

[Master-shake]

One time I tightened the clutch on my onex really tight and the engine would not reach the same top speed. I don't know what the deal was. I guess the engine was used to running against a looser clutch so it could easily rev higher and acheive more HP or something enabling a higher top speed. Because when I tightened the clutch it stopped squeeling but got "stuck" at a certain speed where the added resistance of a properly tightened clutch actually stopped the engine from going full throttle.

 

[Theon]

Is the new head the same chamber volume as the old one?
If you have a low compression head on a motor that had a high comp head, that would seem the most likely to me.

 

[Greg58]

Since the head is the only new part being used I'd do a volume comparison. Take the old head and screw a plug in it if you can, Teflon tape will help hold of in for a comparison. Start with the new head and fill it with something like play sand or maybe salt and take a ruler and scrape it off level, then pour the sand into the new head and see if it fills the head chamber completely. I do this with water and a 10cc syringe but since the threads are bad in the old head it might leak causing inaccuratesys. Be sure and blow out the plug good in the new head to keep from damaging the engine. If the heads are the same try lapping the new head to check for flatness, fine sandpaper and a sheet of glass will do it . just sand the head gasket surface in a circular motion keeping the head flat on the sandpaper, after a few seconds of sanding look at the sealing surface for low places. Keep sanding till the surface is level.

 

[SuperDave]

I'm with Greg & Theon, new head's lower compression is to blame. If sand or liquid sound too complicated to measure, try clay or playdoh: stuff the chamber, scrape flat & flush then weigh the clay. Repeat with 2nd head then compare the weights. Higher volume is less compression is less power.

You can increase your compression of the new head if you hand lap it by taping sandpaper to a glass sheet & rubbing the mating surface on it in a circular motion, rotating the head 90° under your palm once a minute so it works material off evenly. Takes time to do it right, anything less than 15 minutes using this method probibly won't make any noticable difference.

 

[KoolBreeze420]

Since the head is the only new part being used I'd do a volume comparison. Take the old head and screw a plug in it if you can, Teflon tape will help hold of in for a comparison. Start with the new head and fill it with something like play sand or maybe salt and take a ruler and scrape it off level, then pour the sand into the new head and see if it fills the head chamber completely. I do this with water and a 10cc syringe but since the threads are bad in the old head it might leak causing inaccurate. Be sure and blow out the plug good in the new head to keep from damaging the engine. If the heads are the same try lapping the new head to check for flatness, fine sandpaper and a sheet of glass will do it . just sand the head gasket surface in a circular motion keeping the head flat on the sandpaper, after a few seconds of sanding look at the sealing surface for low places. Keep sanding till the surface is level.

Thanks for answering this is not the issue followed your instructions using salt and I even used one of my drawing tools to take precise measurements and they are the same except for the spark plug hole the hole on the old one is a little larger then the new one and since the plug doesn't screw all the way in that must have been original I have had to tighten the clutch in the past I was having trouble with water and fuel getting in. The fuel was due to a defective float and the brass thingy that pulls fuel would vibrate out I have now corrected that with locetite and a bike cover and that no longer happens this is why I asked about the clutch maybe being to tight as it no longer has any lubricant from gas over flow and water

 

[KoolBreeze420]

I'm with Greg & Theon, new head's lower compression is to blame. If sand or liquid sound too complicated to measure, try clay or playdoh: stuff the chamber, scrape flat & flush then weigh the clay. Repeat with 2nd head then compare the weights. Higher volume is less compression is less power.

You can increase your compression of the new head if you hand lap it by taping sandpaper to a glass sheet & rubbing the mating surface on it in a circular motion, rotating the head 90° under your palm once a minute so it works material off evenly. Takes time to do it right, anything less than 15 minutes using this method probibly won't make any noticable difference.

What if there is no difference that can be seen would this still work?
Could the head gasket be a little to thick or something?
I should also tell you that the bike runs great until it is given load in the past this was a problem with the carburetor getting too much fuel or the big screw on the small gear that is under teh clutch cover but both appear to be working correctly right now.
I will email the place I bought it from and ask them if they could have sent me a low compression head.

 

[crassius]

when you worked on the carb, did you change the float level?