No power on new motor

[James Owens]

So I accidentally destroyed my last motor and ended up getting a new one a couple days ago. I ended up exchanging just the motor and used pretty much all of the old components. The old motor was working fantastic before I broke it (stripped head stud holes, then stripped the helicoils). After getting everything assembled, the new motor was running piss poor. It will idle, but once the clutch is engaged it has very little power (cant go up any inclines without having to pedal assist, top speed on flat ground at WOT only around 15-20mph.) It seems to be fourstroking, but I'm not entirely positive on that.

I first thought it was something electrical that was the problem as I got sloppy with the wiring. I then replaced the kill switch, magneto, and CDI. Problem persisted.

I then replaced the spark plug with a b6hs and the problem still persisted.

I then took the air filter off the carb to see if it was restricting the airflow. Still had the problem without the filter.

I then swapped the carb out for a different one. Still had the problem.

Adjusting c-clip also seemed to do nothing.


The exhaust is super smokey and the plug looked wet with oil after all this testing so I assume it must be running way too rich. I just don't understand why, as both of my carbs worked great on the old motor with the same jets.

I don't see any sort of gasket leaks, but my second guess is a loss of compression due to the problem being only while the motor is under load.


Next I guess I will swap out the muffler in case it's clogged, but the muffler I'm using had less than 100 miles on it running 1:32 full synthetic, so I doubt it's clogged.

The only other thing I can think to do is just port and polish it and trim the piston skirt to get better flow, but I doubt it will help.

Any ideas or suggestions? I'm more or less at a loss

 

[Wolfshoes]

Questions I have are: What brand or vendor was it purchased from. What size engine. If you know; is it a "long stroke" engine. How many teeth on the rear sprocket, assuming there is no shift kit. Do you need to be riding down hill to start the engine. Does the rear tire lay rubber on the pavement when you release the clutch to start the engine. Is there more power briefly for a minute or two after you start the engine. Will the engine idle at a normal rpm or will it stop running. About how many hours or minutes has the engine been running as a break in at this point.

 

[FurryOnTheInside]

How much compression has it got?

 

[James Owens]

Questions I have are: What brand or vendor was it purchased from. What size engine. If you know; is it a "long stroke" engine. How many teeth on the rear sprocket, assuming there is no shift kit. Do you need to be riding down hill to start the engine. Does the rear tire lay rubber on the pavement when you release the clutch to start the engine. Is there more power briefly for a minute or two after you start the engine. Will the engine idle at a normal rpm or will it stop running. About how many hours or minutes has the engine been running as a break in at this point.

It's an off brand 80cc china girl from ebay. In all aspects it looks identical to my last one.

I'm also using the same sprocket as my last one, so a 44 tooth

It starts just fine, very little effort is needed, I just have to get it started rolling and release the clutch and it comes right to life.

It also is idling perfectly, it only seems to be losing power when the clutch is engaged/ when it's under load.

When under load it seems to four stroke badly. As of my last try for the night a few minutes ago, I also noticed some sort of metallic clicking sound that seemed to be in time with the motor.

I took the head off and didn't see any signs of a blown gasket or anything.

I have only actually ridden the bike for about 5-10 minutes total between all of the trials. I don't feel comfortable riding it as is because I don't want to have to sit at WOT on an engine that hasn't been broken in.

As far as idling goes, it has probably idled for a total of about 20-30 minutes.





Unfortunately I don't have a compression gauge or know anyone who does so I can't test foe that.

 

[crassius]

you may have gotten an older model motor that takes a lot of running in - if it were just too rich, one can ride uphill and move throttle around to find a sweet spot where it starts to sound more like a 2-stroke

 

[FurryOnTheInside]

Unfortunately I don't have a compression gauge or know anyone who does so I can't test foe that

It would be great to know, for comparison purposes.
However if you have one of the cheap and sloppy engines from eBay it could have excessively wide piston to head clearance, and you may be able to infer that it has a lower compression than desirable. Measure the clearance by squishing a piece of 2mm soft solder. A sloppy eBay engine like mine could still take a reduction in the clearance from 1.2mm (ridiculously high) down to 0.55mm without any problems of piston strike.

The aluminium gasket isn't very reusable. Removing the head to check for signs of a leak might actually cause a leak!

I was able to reduce the volume (of the compressed charge) by a whopping 1.13cc simply by using the twisted Teflon tape gasket which is 0.65mm thinner than the stock aluminium gasket.
Raising compression does increase the power and torque of the engine a lot. There is a safe limit of course, and an engine can self destruct through predetonation caused by too much compression at high RPM but I don't imagine that it's easy to get beyond the safe limit with a sloppy eBay engine.. Particularly if you believe that a lack of compression is causing the issue with the poor torque levels and the wet plug.

 

[FurryOnTheInside]

you may have gotten an older model motor that takes a lot of running in - if it were just too rich, one can ride uphill and move throttle around to find a sweet spot where it starts to sound more like a 2-stroke

Yeah rich condition runs smoother uphill and accelerating, and four strokes when there is less load. This doesn't seem to fit the OP's description of the issues.

 

[James Owens]

you may have gotten an older model motor that takes a lot of running in - if it were just too rich, one can ride uphill and move throttle around to find a sweet spot where it starts to sound more like a 2-stroke

That may be I suppose, I don't have much of a frame of reference since this is only my second motor

It would be great to know, for comparison purposes.
However if you have one of the cheap and sloppy engines from eBay it could have excessively wide piston to head clearance, and you may be able to infer that it has a lower compression than desirable. Measure the clearance by squishing a piece of 2mm soft solder. A sloppy eBay engine like mine could still take a reduction in the clearance from 1.2mm (ridiculously high) down to 0.55mm without any problems of piston strike.

The aluminium gasket isn't very reusable. Removing the head to check for signs of a leak might actually cause a leak!

I was able to reduce the volume (of the compressed charge) by a whopping 1.13cc simply by using the twisted Teflon tape gasket which is 0.65mm thinner than the stock aluminium gasket.
Raising compression does increase the power and torque of the engine a lot. There is a safe limit of course, and an engine can self destruct through predetonation caused by too much compression at high RPM but I don't imagine that it's easy to get beyond the safe limit with a sloppy eBay engine.. Particularly if you believe that a lack of compression is causing the issue with the poor torque levels and the wet plug.

Unfortunately I don't have a caliper to measure and don't have the money to buy one at the moment (broke college student, spent my budget on a new torque wrench since my old one caused the death of the last motor).


I guess the biggest concern I have is that this engine is drastically different from my last one on its first run. I would say this one has maybe a third of the power. I would understand if it were just slightly different, but it's not even comparable.



I will give the Teflon gasket a try and see if it helps. If not, I guess I will wait until the base gaskets I ordered come in and just swap out the cylinder, head and piston and see that that does.

 

[FurryOnTheInside]

It's difficult to know if that would be a wise move, without having a way to measure the clearance.
You need to know there is in fact excess clearance in the first place, and that there will be sufficient clearance to be safe once the engine is hot.
The piston could strike the head when the engine warms up and shatter the bearings.

I would wait, put up with the crappy low power until you can get a few basic measurements.

 

[crassius]

older motors have very smooth cylinder walls, while newer ones have noticeable crosshatching marks on walls, but it is best to look before starting the motor - older motors will run in OK, but it takes a while