Idle screw, hp carb dellorto Sha clone

ycodryn

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Hello guys, I have a question for you. I bought a chinese engine (100cc but from what I heard is over rated so is maybe 80?) with a carb like nt one. With that carb idle screw was working as intended (11 turns in). I changed the carb with a hp one, but now the idle screw is all in and I have to tune the throttle screw to have a nice idle. With just the idle screw all in, the engine is not staying at idle speed, is dying. I'm new at this, is my first build. This means that the pilot jet is too small and is not having enough gas? Should I use the jet from the old carb (hope to have same thread size) ?
Edit: 20C outside, engine is starting without choke. If choke applied while running, engine dies.
Edit2: here is a picture with old and new carb. It seems to me that both have same clearence. So the idle screw on the hp carb is not raising enough?
 

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Greg58

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Just wondering why are you changing the carburetor? We always suggest that you wait till it’s broke in before making changes, then only change one thing at a time till you learn the engine. I’m still running a stock nt on a couple of bikes and they run well, I have a bofeng on my 75cc that runs well too.
 

Chainlube

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Just because it says "Performance" doesn't mean it's any good. I have had lots of issues with the HP carbs, mostly air leaks though.

Put the OE carb back on and see if there is an improvement.

But, both of those carbs look like they have way too high of slide to idle low at all, check the floats. The NT should be 21mm above the bowl base with seal removed.
 

ycodryn

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I really like the choke feature. Now I had a run with the bike, after the engine is getting hot, is dying without throttle. Tomorrow I will exchange the jet with the OE one.
 

ycodryn

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Exchanging the jet is not possible, the original one is wider then hp one. I have to find a set of jets before shimming the slide. Mine is straight, does not have any angle. Went again with it after checking the holes from needle, realign the needle, the jet, the float is straight, checking with cleaning fluid for leaks.. Now is idling better but is still dying after a ride of some 200m of 20% degree of road.
My question is who's fault is for this behavior of this Sha dellorto clone, the jet or the slide?
 

Karl Snarl

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Hello guys, I have a question for you. I bought a chinese engine (100cc but from what I heard is over rated so is maybe 80?) with a carb like nt one. With that carb idle screw was working as intended (11 turns in). I changed the carb with a hp one, but now the idle screw is all in and I have to tune the throttle screw to have a nice idle. With just the idle screw all in, the engine is not staying at idle speed, is dying. I'm new at this, is my first build. This means that the pilot jet is too small and is not having enough gas? Should I use the jet from the old carb (hope to have same thread size) ?
Edit: 20C outside, engine is starting without choke. If choke applied while running, engine dies.
Edit2: here is a picture with old and new carb. It seems to me that both have same clearence. So the idle screw on the hp carb is not raising enough?
You need to rejet the carb. Those sha knock off's are crap. they work great at top end and suck rich on the bottom, or they work great on the bottom and lean out on top. You have to mod the needle and slide to get the to work right. Go with a saw carb and grab an adaptor plate for better performance on both ends, and they add gobs of power, and fit in a tiny space. On a 40mm intake spacing you will have to drill the holes on the adaptor plate 2mm on each side out get them to fit right. A rat tail file and few strokes on one side of each hole is all it takes.
 

ycodryn

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Replaced the carb with the default one but made something to keep the air filter and I had a ride of 6km, same road, all went ok. I will keep it this way until I can find some jets to test it again. For slide mod, what number should I choose? Mine is #1.
 

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Karl Snarl

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Replaced the carb with the default one but made something to keep the air filter and I had a ride of 6km, same road, all went ok. I will keep it this way until I can find some jets to test it again. For slide mod, what number should I choose? Mine is #1.
A #2 or a #4 should work better. I'd personally try the #4 first.
 

ycodryn

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Thanks, next week I will grind it and try again. I liked better how engine performed with sha clone, beside idle ofc.
 
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