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Author Topic:   High rpm miss
JohnG
Dirt Maniac

Total posts: 137
posted September 11, 2005 04:17 PM  
Ran a new motor this weekend that I swapped for last week.

It ran to 6700 rpm, and had a high end flutter, miss etc. Sounded like it was floating the valves to me for sure, but the guy I got it from ran it to 6900 that night supposedly so it doesnt seem likely.

I am going to call the machinest who built it for the spring pressure.

Jetting was perfect.

It has pro heads I ran 36 degrees of timing which is what he had it marked at also. But I know as you get better heads you run less timing for example vortecs work best around 32.

could the extra timing cause it?? carb was a diff carb than Ive ran lately but its never had a problem, same ignition etc.

Xtreme12x
Dirt Forum Champ
Total posts: 874
posted September 11, 2005 04:30 PM  
Carb or ignition...

sc1 racing
Dirt Freak

Total posts: 419
posted September 12, 2005 02:27 PM  
i would say carb or possibly valves need to be adjusted.

JohnG
Dirt Maniac

Total posts: 137
posted September 12, 2005 04:18 PM  
ok,

valves were adjusted that night. .020 cold.

I put in oil restricotors I drilled out to 1/16, stock type roller tip rockers. the rockers started to discolor a little allready.

and the lash was tightened to half or less.

I was told by my machinest to run the restrictors, Im going to drill them to 1\8 now.

And replace cap rotor just in case.

too tight of lash shouldnt do anything high rpm wise should it, its a tight lash cam.

Xtreme12x
Dirt Forum Champ
Total posts: 874
posted September 12, 2005 06:26 PM  
It is a fuel or ignition problem.

sc1 racing
Dirt Freak

Total posts: 419
posted September 12, 2005 08:43 PM  
the rockers to tight will cause a high rpm miss. and i would do away with the restricters all together.whatever the cam manufacter says set the valves on stick to it. i always can tell when my valves are off at high rpms. they will get a flutter in the engine like its tring to float the valves..also always set carb. exspecially if its a holley and temp changes..

JohnG
Dirt Maniac

Total posts: 137
posted September 13, 2005 07:29 PM  
sc1, I agree on doing away with the restrictors but my machinest says he puts them in all the hobby motors he builds also??

Ive been running my motors without any but I also had some rod brg problems in two with hv pumps and no restrictors.

Im trying to find a comprimize and maybe just drill them out to 1\8.

on my two new motors Im running a m55a pump std vol high pressure at his recomendation.

sc1 racing
Dirt Freak

Total posts: 419
posted September 14, 2005 07:34 PM  
man if your rockers are changing colors they wont last long. id hate to see what the cam looks like. only thing they will change colors from is to much heat and that means valves to tight, and not enough oil flow.. think id fire my machinist..hope it works for you though..

ryan
Dirt Forum Champ
Total posts: 776
posted September 15, 2005 09:20 PM  
It the rockers are turning blue you have got too much spring pressure been there done that.

A. Bighurry
Dirt Full Roller

Total posts: 35
posted September 24, 2005 11:44 PM  
If the rockers are turning color it's because of heat for whatever reason (probably not enough oil to the top of the motor). Heat will also kill your valve springs.

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