My engine runs like chit after it is reved high

[GsxrMike]

350 carbed
no computer

If I rev my engine with no load to like 4500-5000rpm it runs like chit for about 20 seconds after. It is almost like I lost spark in a cylinder or two. Any ideas?

 

[mosesburb]

Check to make sure the weights under the rotor in the distributor are moving freely along with the advance plate they attach to. An easy way to check it is to pull the dist cap, grab the rotor, turn it and let go of it. If the advance plate is free it will spring back once you let go of it. If it does not move at all (can't turn it, or very difficult to move) the advance mechanism is locked or sticking to the driven shaft and full disassembly is required to free it up and re-lube it. Check the vacuum advance while you are in there.

 

[pauly383]

timing waaaaaaay advanced . Do you have the right balancer and timing tab combo ?

The small balancer gets the tab near middle of cover , the large balancer has the tab more off to the side .

My current truggy motor had this problem until I swapped balancers and timed it right .

 

[4X4HIGH]

Could also be that you floated valves and the lifters need to reset themselves. Basically over reving the engine makes the lifters pump up more than normal and causes the valves to be open (float) when they shouldn't be which causes a drop in cylinder pressure (loss of compression) which feels like a few dead cylinders.

 

[GsxrMike]

I think the valves may be floating a bit. The dizzy is newer and I have the initial timing set at 12* and I know both advances are working ok. Is there anything I can do to fix the valve float?

 

[smalltruckbigcid]

New springs or don't rev it so high...unless its on its last legs then its just time to start over

 

[GsxrMike]

Well the motor is fresh but I have no idea what it is in it. I know it has 1.94 intake valves, 1.60 exhaust, hydro-roller cam (no specs), but I know nothing of the bottom end. I only know what I know because I ran the casting # off the heads and I had to pull the intake to remove a broken bolt and I saw the cam. How would I go about selecting the correct springs with no info? And if I went with a stiffer spring would that wear out my valve train faster? Thanks guys!

 

[4X4HIGH]

Roller cams require more spring pressure because of the very quick acceleration rate of the lifter. The proper springs should allow easy 5500-6000 rpm's but much more than that and you should highly think about a rev kit (secondary set of springs between the lifters and underside of the heads to hold the lifters on the cam).