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New motor won't perform above 1/8 throttle


chrispy56

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Kenny, I have tried nearly all safe jetting combinations recomended by the builder and others on this forum with similar engine configurations.

Carbs are new.

No, I don't have any other carbs. What possibilities could make new carbs bad?

 

I did do a static pressure test on the cooling system

Pressurized to 15psi and the pressure bled down to 13psi then held 13psi for nearly 24 hrs. Pressurized to 15 again and now there is no pressure drop

I don't know what to make of that.

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15 psi is over the pressure rating of the cap. They are usually rated 10 psi or 15psi so yours is working fine if it held approx 13psi. I have seen some goofy things like mouse nest built in the pipe do what you are saying. Fuel delivery issue could be from the tank or pingle/shutoff. Make sure fuel pours out the fuel lines well if taken off the carbs, check for a good ground from motor to frame , try different wiring harness , check all plugs in harness. I hope you get it figured out soon , sounds like you have been working very hard on it.

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I'm having same issue with my HJR engine. Kevin did a 4mil with pump gas doms and I put it together over the winter. I have t5 exhaust,28mm pwk  Jetting about same as yours. I will need to look to be sure, Went by what Kevin told me to start at. Vforce 4 reeds, Hotrods 4 mill crank. Will start on 1-2 kicks and idles fine. If you rev it seems fine. Take off, once you get to mid range falls flat on its face. Sputters runs like shit, pull in the clutch and rev it up it will start to pull. Will run better on top, but does not feel like a 4 mill. My dads stock banshee with t5 exhaust will smoke me. I only ride at Pismo dunes, but you cant even ride it if our not on the top end all the time. I tried switching,stators cdi etc with my dads banshee, nothing changes. My frame was painted and I sanded the grounds down to the bear metal. Should I try running another ground for my engine? Was wondering if that could be the problem?

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Could be many things. Poor jetting, poor dome design?? Ect.. Try and really fatten up the needles. See if that helps. A couple yrs ago i had a similar problem that i now know was a dome problem. I had to go with a goofy needle to even get it to run half ass.

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  • 3 weeks later...

Sorry for the delayed response, I just wanted to be certain before responding.

 

Turned out to be the orings between the domes and cylinders(the brown ones). They had somehow deteriorated on the combustion side and the cooling side. I retorqued after the first few heat cycles so I'm not sure what caused this failure. Cooling system pressure test didn't really point to leaking orings either.

 

At any rate, runs great now, just needs a little fine tuning.

 

Thanks everyone for your input and sugestions. Much appreciated.

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  • 3 weeks later...

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