No top end power

Jaycee604

Active Member
Joined
Dec 7, 2021
Messages
190
Hey guys, me again. Just came across this problem and need some input. My engine (with the clutch pulled in) revs really crappy. Doesnt rev like my other two. Normally the bikes will shake a bit more and its very loud. But this has a boggy sound. Happens when i ride too. 1 to 25kmh seems to be fine but then sounds like it four strokes after and runs like ass. Im waiting for my new jug (because i think i ported this one wrong) and my expansion chamber (mz65 clone) but there was a point that it ran better. Its worse now. I just changed the exhaust, base and intake gaskets yeaterday. I used a rubber cork material. Im thinking i shouldnt have done that.

66 cc
Hc cdh power head
Pz20 carb (jet size unknown) played with the needle, made no difference
Ngk plug
44 tooth
Stock mag and cdi
Poo poo exhaust ( yes i know this is crap, was working fine with it before, this isnt the cause of my recent power loss)
 

DieselTech

Well-Known Member
Joined
Sep 18, 2021
Messages
4,119
I'm not sure on this , but I'm going to relate that to the cork gasket. I'm wondering since the cork gasket was used & its a lot thicker than a normal base gasket, & that you basically have altered you port timing & compression do to the increased gasket thickness. I'm not sure on this 1, but that's my thought on your issue. Possibly could be a air leak as well, but usually they try to rev to the moon with a air leak & clutch pulled in/disengaged.
 

Jaycee604

Active Member
Joined
Dec 7, 2021
Messages
190
I'm not sure on this , but I'm going to relate that to the cork gasket. I'm wondering since the cork gasket was used & its a lot thicker than a normal base gasket, & that you basically have altered you port timing & compression do to the increased gasket thickness. I'm not sure on this 1, but that's my thought on your
I'm not sure on this , but I'm going to relate that to the cork gasket. I'm wondering since the cork gasket was used & its a lot thicker than a normal base gasket, & that you basically have altered you port timing & compression do to the increased gasket thickness. I'm not sure on this 1, but that's my thought on your issue.
i just took off the jug. The brande new cork base gasket i put got smooshed so bad lol and got eaten away for some reason. It said id could have contact with gas. Anyway, heres a pic of it, hope this is the cause. Other pic is my new one
 

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DieselTech

Well-Known Member
Joined
Sep 18, 2021
Messages
4,119
I'm not sure on this , but I'm going to relate that to the cork gasket. I'm wondering since the cork gasket was used & its a lot thicker than a normal base gasket, & that you basically have altered you port timing & compression do to the increased gasket thickness. I'm not sure on this 1, but that's my thought on your

i just took off the jug. The brande new cork base gasket i put got smooshed so bad lol and got eaten away for some reason. It said id could have contact with gas. Anyway, heres a pic of it, hope this is the cause. Other pic is my new one
Houston I think we have found the issue. I would start there. Have you ever checked your squish clearance on your engine? I personally think setting squish clearance, should be the 1st performance mod performed/made. Squish also kinda determines what kinda of engine performance you can expect. Big squish clearance=low power less efficient engine, small squish clearance=big power more efficient engine. Optimal squish clearance is .7mm
 

Jaycee604

Active Member
Joined
Dec 7, 2021
Messages
190
Houston I think we have found the issue. I would start there. Have you ever checked your squish clearance on your engine? I personally think setting squish clearance, should be the 1st performance mod performed/made. Squish also kinda determines what kinda of engine performance you can expect. Big squish clearance=low power less efficient engine, small squish clearance=big power more efficient engine. Optimal squish clearance is .7mm
I only have a plastic version of that measuring device so i cant read the solder if i put it in to see the squish, nor do i have solder. I guess i should ask a friend if they have one. Unless i find an accurate one on amazon for cheap. Solder isnt cheap here either lol
 

Jaycee604

Active Member
Joined
Dec 7, 2021
Messages
190
I only have a plastic version of that measuring device so i cant read the solder if i put it in to see the squish, nor do i have solder. I guess i should ask a friend if they have one. Unless i find an accurate one on amazon for cheap. Solder isnt cheap here either lol
Also check this picture. Should my piston completly clear the exhaust ? I put two base gaskets to make it a little higher so the piston can fully clear the exhaust port
 

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DieselTech

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Sep 18, 2021
Messages
4,119
I've never seen 1 clear the port fully, your problem is that you used 2 base gaskets without correcting your squish clearance, big squish=low power. Plus it would result in a bogging engine because compression would be lower. I can help you along the way with this as others will to I'm sure. My 100cc steel sleeve engine is worse than that, & that thing will scare you riding it. It runs super strong, & I run 2 base gaskets, but with a properly set squish clearance.
 

Jaycee604

Active Member
Joined
Dec 7, 2021
Messages
190
I've never seen 1 clear the port fully, your problem is that you used 2 base gaskets without correcting your squish clearance, big squish=low power. Plus it would result in a bogging engine because compression would be lower. I can help you along the way with this as others will to I'm sure. My 100cc steel sleeve engine is worse than that, & that thing will scare you riding it. It runs super strong, & I run 2 base gaskets, but with a properly set squish clearance.
Keep in mind the picture where the piston clears the port all the way the engine isnt bolted down. I use the acorn nuts. Going to get reg ones soon
 

DieselTech

Well-Known Member
Joined
Sep 18, 2021
Messages
4,119
Keep in mind the picture where the piston clears the port all the way the engine isnt bolted down. I use the acorn nuts. Going to get reg ones soon
Mine is a little better than yours you posted on picture #2 of post#6.
 

Jaycee604

Active Member
Joined
Dec 7, 2021
Messages
190
Mine is a little better than yours you posted on picture #2 of post#6.
I found some regular bolts. Check pic. The piston clears the whole exhaust port once at the bottom. Should i just take off one gasket while my head is off?
 
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