WOT/Loud and slow

pjamin10

New Member
Feb 18, 2019
9
3
3
24
Hello,
I am working on improving my motor bike currently. It is very reliable and will always start. Last summer I could easily go 35 mph at WOT but now I have trouble doing anything above 12 mph. I am not sure what is going on but these are my symptoms and what I have done to try and fix it.

Symptoms:
Low RPMs sound good and push the bike forward well. Anything above the lower third of my RPM range my bike gets slow and sounds extremely loud. It sounds as if the combustion is trying to push hard but the bike RPMs drop dramatically. If I keep my throttle at WOT I will actually start slowing down as I ride. My Spark plug is super wet and dark.

What I have done to try and fix it:
I have checked for oil leaking out of the jug/piston/exhaust/intake gaskets. I did find a leak on the front of the jug/case gasket, so I replaced it solving that leak, still having my normal problems though. I place my jet pin to the leanest setting with the C clamp and I still have a wet spark plug.

It seems as if when I open my throttle all the way the air/fuel mixture is to rich but I am unsure of how else to make it leaner with the jet pin dropped all the way down.
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Eugene Laurens

New Member
Apr 26, 2020
1
0
1
34
Hello,
I am working on improving my motor bike currently. It is very reliable and will always start. Last summer I could easily go 35 mph at WOT but now I have trouble doing anything above 12 mph. I am not sure what is going on but these are my symptoms and what I have done to try and fix it.

Symptoms:
Low RPMs sound good and push the bike forward well. Anything above the lower third of my RPM range my bike gets slow and sounds extremely loud. It sounds as if the combustion is trying to push hard but the bike RPMs drop dramatically. If I keep my throttle at WOT I will actually start slowing down as I ride. My Spark plug is super wet and dark.

What I have done to try and fix it:
I have checked for oil leaking out of the jug/piston/exhaust/intake gaskets. I did find a leak on the front of the jug/case gasket, so I replaced it solving that leak, still having my normal problems though. I place my jet pin to the leanest setting with the C clamp and I still have a wet spark plug.

It seems as if when I open my throttle all the way the air/fuel mixture is to rich but I am unsure of how else to make it leaner with the jet pin dropped all the way down.
View attachment 104361 View attachment 104361 View attachment 104362 View attachment 104363 View attachment 104364 View attachment 104365 View attachment 104366
I could be wrong but it sounds like you need a new muffler. The baffle is corroded inside not letting all your exhaust through
Hello,
I am working on improving my motor bike currently. It is very reliable and will always start. Last summer I could easily go 35 mph at WOT but now I have trouble doing anything above 12 mph. I am not sure what is going on but these are my symptoms and what I have done to try and fix it.

Symptoms:
Low RPMs sound good and push the bike forward well. Anything above the lower third of my RPM range my bike gets slow and sounds extremely loud. It sounds as if the combustion is trying to push hard but the bike RPMs drop dramatically. If I keep my throttle at WOT I will actually start slowing down as I ride. My Spark plug is super wet and dark.

What I have done to try and fix it:
I have checked for oil leaking out of the jug/piston/exhaust/intake gaskets. I did find a leak on the front of the jug/case gasket, so I replaced it solving that leak, still having my normal problems though. I place my jet pin to the leanest setting with the C clamp and I still have a wet spark plug.

It seems as if when I open my throttle all the way the air/fuel mixture is to rich but I am unsure of how else to make it leaner with the jet pin dropped all the way down.
View attachment 104361 View attachment 104361 View attachment 104362 View attachment 104363 View attachment 104364 View attachment 104365 View attachment 104366
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,129
163
63
Santa Barbara, CA
Hey, welcome! Nice build

--> Check for a blown head gasket. Start the bike and put your hand down around the head and see if you can feel any air shooting out when you rev the engine, you could be losing compression. Head nuts should be torqued at about 15 foot pounds.

--> Remove and clean your carb with carb cleaner spray let it dry, put it together and try it again. Also, see if it will run good without the air filter, they can get blocked over time sometimes.
 
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pjamin10

New Member
Feb 18, 2019
9
3
3
24
Hey, welcome! Nice build

--> Check for a blown head gasket. Start the bike and put your hand down around the head and see if you can feel any air shooting out when you rev the engine, you could be losing compression. Head nuts should be torqued at about 15 foot pounds.

--> Remove and clean your carb with carb cleaner spray let it dry, put it together and try it again. Also, see if it will run good without the air filter, they can get blocked over time sometimes.
Thank you for the response and the compliment!

When I ordered my motor I didn't realize this but is a one piece head/jug so there is no head seal. There is a seal at the bottom of the jug and I just replaced it. I will feel for leakage still and check the carb out. I feel like it is lack of compression though too, not sure where though.
 

Tyler6357

Well-Known Member
Mar 15, 2012
1,129
163
63
Santa Barbara, CA
Oh, Okay, I didn't realize that. Hmmmm, compression

--> you should check your crank seals. Open up your mag cover and check it for any sign of oil in there, it should be clean. There is also another seal on the clutch side.

--> Maybe a broken piston ring?

--> Check for air leaks at the carb/intake manifold and the intake manifold/intake port connections. One trick is to spray soapy water on the connection start it up and look for bubbles.

--> Also, if you haven't already, you should try it with a different spark plug, just to eliminate that as a possibility.

--> If you want to get leaner you can purchase a smaller jet. The stock jet is 5mm #70, you could try a #65. But if it was running good with the jet you had and then stopped it makes me suspect a carb problem, it's flooding out. Replacement carbs are about $11 or you could upgrade to an HT carb for about $20. However, I would try the other things first before you purchase any parts.

https://www.ebay.com/itm/Carburetor...664510?hash=item3d6ffa117e:g:YL0AAOSwvdFcMsEI

https://www.ebay.com/itm/Red-Racin-...262151?hash=item1c9b84e507:g:P0kAAOSwTEJaODNf
 

pjamin10

New Member
Feb 18, 2019
9
3
3
24
Hey guys thanks for all you help,
It was what I believed to be the least likely solution. The air filter was gummed up! I thought it wouldn't be possible because of how little filter there was! Definitly was the issue, I took it off and was able to zoom up to 35 mph again!
Was afraid my engine was shot so thank you!
 
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Tyler6357

Well-Known Member
Mar 15, 2012
1,129
163
63
Santa Barbara, CA
Hey guys thanks for all you help,
It was what I believed to be the least likely solution. The air filter was gummed up! I thought it wouldn't be possible because of how little filter there was! Definitly was the issue, I took it off and was able to zoom up to 35 mph again!
Was afraid my engine was shot so thank you!
Sweet! That happens sometimes with those kind of air filters, just replace and you're good to go.
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,843
235
63
up north now
You've got plenty of room, I'd get a real filter with some surface area on it, or clean the one you have with every fill up.