this last weekend i was racing at my local 3/8 mile oval ashpalt track in the pure stock class.  i was leading the race and at about 5000rpm the engine went FLAT.  no pull no rpm gain.  and my water temp went from 180 degrees to 210 degrees.  thing felt very strong all the way to 5k but after that it was dead flat.  my initial thought is that the float stuck in the carb and was allowing the engine to suck the bowl dry and lean then engine out, hence the temp spike.  we use a q jet carb by the way.  i've been told the problem may be ignition related but i don't ever remember having an ignition issue that increased the water temp. any thoughts of ideas would be greatly appriciated.

thanks,
flying14  

first, does it have this problem with no load, light load, or only heavy loads?  if you can get it over 5 k without trouble with no load, it may be fuel supply related.  If it cuts out at 5 k or so regaurdless of the load, then check the valve springs.  

sitting in the pits i can take it up to 6400 without issue.  so it's definatly load related.  

flying14:
sitting in the pits i can take it up to 6400 without issue.  so it's definatly load related.

hey flying14
 Yea sounds like a fuel flow problem to me. could be a simple fuel filter clogged.  i recommend a fuel flow rate test. dont know if that would cause a temp spike tho. unless the lower rpm caused a lower coolant flow also  

Yeah, but sitting in the pits, the motor's not under load.

I'm thinking this is more of a valvespring issue than fuel supply. Sounds like your springs are worn out, or can't handle the RPM range you're running in. What class do you race, what heads cam do you run, what springs are you limited to?  

He's not having trouble in the pits either.

Get a fuel pressure gauge, put it where you can see it while hotlapping.  if it doesn't dip to 0, you're good there.  

You may also want to check your ignition components, sometimes spark plugs can do funny things like that too when they're in marginal condition.  

well i don't think it's a problem with the valve springs considering they are brand new z springs at i believe 115 pounds of seat pressure don't quote me on that though.  in the first part of the race it was fine i was able to run right up to 6k.  but after 8 laps it died.  i took the car down the road today and went right out to 6200 without problem.  i'm beginning to lean towards an ignition issue.  we are going to rebuild the carb though, just for good measure.  

We are having same issue here. Car pulls just fine for a couple laps, then 'stumbles' coming off turn getting back into throttle. Fixed fuel pickup tube colapsing and was fine for next race. Went through ignition,(volts into dist. to plugs) everything checks out fine. Any ideas???  

i had the same prob in my purestock and it turned out to be a dirty passage in the carb from gunk fixed it and one the four car dash the next night car would pull till 5 g and then fall flat on its face also running q jet