sbc 350 stumbles?

when i drive around town. normal speed 40-45 drives nice. then when i want to punch it it stumbles.when car is in park runs bitchen and rev it up no problems or stumbleing seems like only happens under a load.and when i keep my foot in the pedal it doesnt clear up.....

engine is mild 350 with h.e.i with a 600 holley
carb was removed from my buddys chevele and installed the next day in my car so its not the carb.could it be the hei?
checked the fuel lines and they are clean and new.
has a new electric fuel pump.

 

My guess would be spark plug wires...they can run fine no load and crap out under load...

 

they are taylor's that are new

 

Sounds almost like your spark advance is failing, and letting the spark angle slip back to no load or worse.

 

this is the first hei i have had.what part would cause that to happen?

 

I don't know maybe vaccume hose failure, get out the timing light and chalk, revit up etc. Kinda sorta sounds like you're "running out of spark".

 

just put a new vacume hose from the vacume advance..at idle it is 12 degree's

 

I'd try a #25 or #26 pump squirter on the carb first.

 

motor not getting enough fuel??

 

Another thing you might want to try is to hook up the dist. vacuum advance hose to a manifold vacuum port. Some folks mess up and hook it up to the port on the primary metering block.

 

It could have a bigger pump squirter. You can't tell unless you remove it.

 

I think it's 8 degrees BTDC for a 350???

 

i have it hooked up to the metering plate.will that really cause my engine to stumble?

 

Yep! On the front of the carb, there's a capped off vacuum port on the throttle plate. Hook up the vacuum advance hose to that port and cap the port on the metering block. Then take it for a ride and let us know how it worked.

 

tried that one also. no difference when i drove it..

 

Must be something else.... Did you try and re-adjust your timing?? Set it with a timing light @ 8 degrees BTDC.

 

will try that in the morning.thanks

 

What are you using for a fuel pressure regulator? What PSI? You should be getting at least 5 psi under load.

Make sure plug wires are "snapped" onto plugs tight. If not tight, give the ends a squeeze with pliers until you can feel them snap onto plugs. Do same at distributor end.

Check fuel level in float bowl. Adjust needle and seat until fuel JUST drips out of site plug hole while running. Keep a rag under hole on intake and have a fire extiguisher close by. A friend in the car to kill engine, or a kill switch under hood would also be a great idea.

 

Also, I'm not far away. If you need a hand with it, I could come by. I'll be going to Corona in the morning and on my way home around 1 or so.

 

Thanks guy!

 

not running a regulator useing a electric fuel pump says 4-7 psi.can i get your number?

 

PM sent

 

Please post what the problem was when everything is repaired. Thanks!!

 

People; There is no vacuum advance when you stomp on the go pedal!

 

When you say it "stumbles" do you mean that it just starts running lousy/sputters or does it fall flat on it's face. If it pretty much falls flat on it's face and won't recover until you pull back on the pedal, you could be running out of fuel. If that's the case, check/change the fuel filter and, if that's doesn't help, check the pickup screen in the tank.

 

kind of hard to explain driving at a normal speed around town its fine when i step on the gas full throttle starts to stumble and wont pick up.cant even gradualy step on the pedal seems like anything around 40 and over it cuts out and runs like crap when i back out of it drives up to a certain speed

 

Your initial timing is way out. How are you setting it.

 

With or without the advance connected. It should be with it disconnected andthe fitting on the carb plugged at the time. 12 degrees with it disconnected should work on that engine even though 8 is the factory setting.

Is the advance on the distributor working. If you suck on the hose or put a vacuum pump on it do you get a resistance? It may have a bad diaphragm.
If it is a used HEI are the advance weights free to move or are they sticking on the pins?

Check your fuel line to the carb to make sure that the line isn't kinked or twisted so that it restricts fuel. If you changed any fittings make sure that the fittings have full flow and aren't restricting fuel flow.

Never say never. In moving the carb around and turning it upside down you may have dislodged a chunk of dirt or crud that is plugging a passageway in the carb if you can't find something else. Also these carbs usually need to be jetted to match the engine that they are installed on.

If it just goes flat when you poke it it's probably with the accelerator pump, if it dies about 80 or so feet after you poke it it's most likely a restriction in the fuel lines and the bowls are running out of gas until you let up on it and the pump fills the bowls back up.

 

tested the vacume advance and it is working.also was timed with everything plugged up then after lines were hooked up..

 

when i first got it running it did the same thing with the fuel can. then put a real gas tank.and still did it