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Old 08-08-2004, 09:54 PM   #1
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Default Need some help with engine mods......

Hey all,

I need some help with my engine, it's just a basic sport engine which came with my Ultima RB.



Anyway, i disassembled the carb to clean it out, and noticed that the barrel in the carb has a 4mm throat (!!). The inlet of the carb is 6mm....but the throat is tiny!!

I see this as a big restriction, and i plan to bore it out to 5-5.5mm......can anybody give me any tips or suggestions as to how i should go about this, and any problems i may get from doing it?? I'm also going to remove 1 head shim to try and raise compression, will i need a different glow plug if i do this??

I have added a tuned pipe, and matched andpolished the exhaust manifold. I also added a higher flow filter than the stock one, and oil and clean it regularly.

I am starting an offroad buggy club (we have an unused BMX track to race on) and i will be racing mainly agains other RTR's such as Evaders (.18 O.S.), and want to better my chances of keeping up.

Thanks in advance,

Jamie

Last edited by jamiekulhanek; 08-10-2004 at 12:30 AM.
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Old 08-08-2004, 09:56 PM   #2
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BTW its a kyosho GX15 CRG
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Old 08-17-2004, 04:38 AM   #3
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bump
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Old 08-18-2004, 07:58 AM   #4
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The carb hole is suppose to taper, if you drill it out to the same bore with no taper you will hurt performance. The taper is called a venturi, the air speed increases as it enters the carb becasue of this taper, leave it alone.

Sounds like you are about to mess up a good motor.
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Old 08-19-2004, 07:48 PM   #5
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The thing is it doesn't taper......it goes from 5.5mm, to 4mm (barrel)instantly, like a big step, then the bottom part of the throat between the engine and barrel is 4.5-5mm. so this means that the air accelerates through the barrel (4mm) then loses velocity when it goes into the tube leading to the crankcase.....

I haven't done anything yet.....
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Old 08-20-2004, 06:30 AM   #6
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Are you sure you are not missing the insert (restrictor)?
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Old 08-22-2004, 11:23 AM   #7
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There is no restrictor for this carb...
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