Low power, Brand new Engines?

[Jason Kotchey]

Help! (I'm sure you get that a lot! lol). I"m having a problem with 2, 80cc engines. I have purchased 5 on ebay (different sellers) and 3 of the 5 work great 2 struggle to get up to 15mph where the other 3 run up to 30mph. The 2 in question run and Idle great! I've tried switching motors to different bikes, changing stators, Magnets, CDI, spark plugs, Carbs., Banana muffler ( the muffler helped a little), ETC. I have checked the cylinder bore and confirmed its a 80cc engine. I'm running out of options to try to get better speed and power out of it. Any suggestions?.

 

[heligonka]

Help! (I'm sure you get that a lot! lol). I"m having a problem with 2, 80cc engines. I have purchased 5 on ebay (different sellers) and 3 of the 5 work great 2 struggle to get up to 15mph where the other 3 run up to 30mph. The 2 in question run and Idle great! I've tried switching motors to different bikes, changing stators, Magnets, CDI, spark plugs, Carbs., Banana muffler ( the muffler helped a little), ETC. I have checked the cylinder bore and confirmed its a 80cc engine. I'm running out of options to try to get better speed and power out of it. Any suggestions?.

It is impossible to determine the cc's of displacement by measuring the bore of the piston. Displacement is determined by knowing the Bore and the Stroke of the engine.

 

[Jason Kotchey]

I measured the stroke and bore of the engine. I also noticed the marking on the connecting rod is labeled zae50..

 

[FNTPuck]

Help! (I'm sure you get that a lot! lol). I"m having a problem with 2, 80cc engines. I have purchased 5 on ebay (different sellers) and 3 of the 5 work great 2 struggle to get up to 15mph where the other 3 run up to 30mph. The 2 in question run and Idle great! I've tried switching motors to different bikes, changing stators, Magnets, CDI, spark plugs, Carbs., Banana muffler ( the muffler helped a little), ETC. I have checked the cylinder bore and confirmed its a 80cc engine. I'm running out of options to try to get better speed and power out of it. Any suggestions?.

None of the engines are 80cc...as stated, you need the stroke as well to calculate displacement but that is not the issue here.

Before troubleshooting, we would first need to know what they are doing. Are they bogging at 15mph? Vibrating like crazy? 4stroking?

I would normally aim towards the carb just by the vauge description since I have seen the jets vary from batch to batch, but you say that you have swapped them already so that shouldn't be it. If you switched the whole motors and the issue moved to the other bikes, that would also eliminate a clogged or faulty petcock filter or fuel filter which would have been my next guess.

Please be a bit more descriptive, or even post a video if you can.

 

[crassius]

some older motors did not have much of a hone on the cylinders - these take much longer for the rings to seat (I've seen some take 80 miles, some never did) - you may have hit a seller getting rid of old ones

otherwise, check that ports were properly machined out in cylinders, and be sure a compression gauge gives a decent reading

 

[Jason Kotchey]

Okay, I did a compression test It seemed to be around 50psi. I.m enclosing a video of the results of the test.the pressure built and held the pressure fine. also im enclosing some bore and stroke measurements bore was 47ish and the stroke was 38ish approx. 67cc. (enclosed pics of measurements).. Tomorrw Ill mount the engine and take some video. FNTPuck, I would say minimal 4stroking. normal vibration, I would say possible bogging! It acts like it just dosent have enough power to get it past 15mph. I can pedal assist the engine at that speed and it just cant rev up enough to go any faster. The compression video is too big to send I put it on Youtube.

 

[Street Ryderz]

How many gasket's are between the cylinder and case? Did you change the piston at any point?

 

[Jason Kotchey]

Just one. and 1 head gasket. Never changed piston (arrow on piston pointing toward exhaust port.). Only about 30 miles on engine.

 

[Street Ryderz]

Just one. and 1 head gasket. Never changed piston (arrow on piston pointing toward exhaust port.). Only about 30 miles on engine.

Those pictures show that the piston pin location (type) may be wrong,is the fourth pic above with the piston at T.D.C. ?

 

[Jason Kotchey]

No when at TDC the piston crown is above the cylinder a little.