Box Stock

Stock appearing build help

J

JJDEkartracer46

New member
I attempted to build a stock appearing predator and it looses power when i'm on the track around 5300 rpm. It seems like it is loosing fuel so I am not sure if it needs a fuel pump or is jetted improperly. This is what I have done to the motor and it still has the top mount fuel tank.

nr racing marine cam 280 lift
longer arc rod .020
shaved & ported head .050
28lb springs
arc flywheel 32 timing
gutted exhaust
stock air box with more flow
.650 nr racing carb

any help would be greatly appreciated and do you think a fuel pump would help
 
yes the cap is vented and I knew the cam was only good for power between 2000-5500 rpm but we can only turn 6 so it I thought this cam might work
 
Fuel flow issues are possible . Hard to verify though .
Its also possible that its incorrectly jetted .
Too rich can cause an issue .
 
we pulled it on a dyno and it ran good but then it died just like on the track when its under a load. We tried different jets but it always did the same thing. I'm just not sure if a fuel pump is needed with this type of build
 
appreciate all your help I have a header ran threw the stock muffler box so it still looks stock and the air box is a lot more open than stock im lost
 
JJDEkartracer46 said:
we pulled it on a dyno and it ran good but then it died just like on the track when its under a load. We tried different jets but it always did the same thing. I'm just not sure if a fuel pump is needed with this type of build
Click to expand...
Does it actually die ? Does it fall off then come back too life ?
 
That is such a mismatched bunch of parts and machine work that it could be one thing or a combination of things. have you considered (starting with easy things first) yanking the stock air box off to see if it made a difference? Put a real exhaust pipe to see? I saw no mention of jets or changes in jets to see if it helped. And thats a lot of energy robbing valve spring to run such a low rpm. I doubt the springs directly have caused you this problem but something like a 22# spring will make it a bit more free. Dyno time is wasted money if you aren't going to use it to correct problems. A stopwatch will tell you what youve got.
 
With stock looking airbox and exhaust ,and 6000 limit , why would you want that much spring pressure ?? Remeber for every action theres a reaction
 
What I have found on these type builds is to flatten out the motor on the mout no more than 7 degrees or completely flat is even better. Also fill the tank until you can add another oz. If the fuel is below the strainer in the tank it is low on fuel. Sometimes I even have to remove the strainer that is inside of the tank. They are really finicky and will suck the bowl dry quickly
 
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