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Old 12-21-2008, 04:05 PM   #1
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Default Engine suddenly revs up during break-in

I am having trouble breaking in a new truggy engine for my XRay XT8. It can be started with some trouble and idles fairly stable. After running idle for 1-2 minutes it suddenly revs up like crazy and I have to kill it. This problem is consistent and has repeated several times also after long cool down periods.

I am suspecting an air leak, but I cannot figure out where it should come from. The tank and fuel tubing is brand new and seems fine. The carb is fastened securely. I have not examined the engine itself for leaks.

I am also suspecting wrong needle settings, but I do not know where to start.

Engine: GRP .28 tuned truggy
Plug: GRP #5 conical (also tried with GRP #6)
Needle settings: I got lost. GRP does not inform the factory settings since each engine is adjusted individually. I have tried with 4-5 turns out with the HSN. LSN is a bit richer than flush.
Enviroment temperature: 22 degrees C

Thank you in advance,
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Old 12-21-2008, 04:16 PM   #2
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you can probably find the factory settings on the grp thread.... are there any bubbles in the fuel line?
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Old 12-21-2008, 06:18 PM   #3
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sounds like fuel shortage ...kinda strange ...settings for the motor should be this

hsn 3-1/2 turns out from bottom
lsn 6-1/2 turns out from bottom

this was determined by screwing the needles in and noting how many full turns it took before the needles bottom out .....this may be the cause as your lsn may be to lean if you are just counterclockwise from flush on the lsn ...i broke my .21 in the other day and thought i needed to lean the lsn from stock to get it running ...WRONG ,,,,,,,had to richen it back up ....

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Old 12-21-2008, 06:28 PM   #4
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im breaking in the same engine, but i havent had this problem
but my LSN is about 4 turns out from flush so it has plenty of fuel

i would say try and richen the bottom needle ( like Zixxer said ), and remember u have to turn in the idle screw as well
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Old 12-21-2008, 06:34 PM   #5
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Look very closely around the carb for fuel leaks and also around the front bearing. Take your tank off and plug one of the lines off with your finger and submerge the tank and blow into the other line, then switch lines and look around the cap for a leak. Ceck your exhaust gaskets and make sure that they are right..... I know if the o-rings aren't right where the pipe meets the manifold you can lose fuel pressure there... they can get swip swappy.I just had my GRP .21 leaking around the carb and I personally could not see it . Soup Nazi and Grouchy eyeballed and potentially saved my engine. I am gonna seal my carb w/ permatex per Soup Nazi's suggestion.
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Old 01-01-2009, 05:51 AM   #6
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Thanks guys! It was the LSN that was too low. I just finished breaking it in, and it's a blast :-)
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