chevy 235 missing at high rpms

hey guys just looking for some advice. heres what i have going on. i have a 53' chevy with the original 235. it is missing and nosing over at 15mph 1st gear,30mph, 2nd gear and will only get up too about 45-50 in 3rd. heres the list of everything i have tried . the entire electrical system is new...points, plugs, dizzy, rotor, cap,wires, all of it. i have put an electronic fuel pump on it and replaced the entire fuel line including adding a fuel cell. the carb. looks good but i have only had the car less than a year. i got a rebuild kit for the carb but am a little hesitant on doing it just because i havent done one before. i have had all my freinds look at it and we are all baffled. i have found a dual intake and second carb for it. i have wanted to do that to it since i got it. could that fix it? im planning on taking it to the autorama show in cincy this weekend and really dont want to have to drive 45mph all the way there from columbus! thanks guys

 

I'm assuming it idles and free revs fine? It does sound like a fuel starvation problem, possibly a clog before the needle and seat? It also could be a restriction in the exhaust.

 

If it doesn't run well BEFORE you put dual carbs on it, you're sure to have a headache after you put them on.

What did you gap the points to?

What fuel pressure is your electric fuel pump putting out?

Why change from the mechanical pump? You know it was made to work with the rest of the system.

It sounds like a fuel supply issue to me.

Shawn

 

Have you done a compression test? and adjusted the valves? and check to make sure they're all opening all the way? no broken springs?

What do you have for an air filter?

what is the choke doing?

 

Did you change the coil?

 

If you have a cable choke? try choking it just a bit when it is doing that.
If it makes it run fine, you may need to go a bit bigger on the mainjet.
I rejetted a 48 Ply 2 months ago .

 

ok. it runs and idles fine up to that point.
the electric fuel pump was on it when i got it ( he actually had 2 on it !!) i have tried both separate and have no change in the problem
it has an automatic choke
the coil is new
the air filter is a small after market one. i have an original but dont have the filament
i have not checked the valves
the exhaust is just the manifold down tube into a glass pack with a turn out and i did raplace the doughnut ring
i will say when i got it it barely ran and after doing all of this i have got it running great except at those speeds. i drive it around town all the time and it does fine. i just dont take it on the highway.
i too think it is ultimately a fuel issue just because i have got it to run better for just a day or so after messing with the carb but then it just goes right back to how it was.

 

You could do a flow check by running the pump with the line to the carb disconnected and into a bottle (just be safe about it). Also, have you looked to see if the flap deal on the exhaust manifold might be stuck shut? As I mentioned before, a restricted exhaust will keep an engine from revving. I have seen it happen with plugged cats on late models. I'm thinking it might be something as simple as a low float level though.

 

try hooking a dwell meter to the coil, like when you install new points, then rev it up, watch what dwell is doing. i ran into 1 situation where the points mounting plate was loose causing dwell and timing to be off when vacuum advance activated. also recheck condenser