Thread: 350 aggresive surging in gear with moderate throttle.

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well me and my friend are wrapping up his 94 s10 project. the 4cyl popped and we found a decent 350 for real cheap so we figured with put that instead. more work than we expected but its pretty much finsihed up. its paired with t5 and some basic edelbrock carb. we finally got it to run after a few days of frustration. it was all timing related. (ill admit we really dont know wtf were doing...) but anyway yea. its now set initially at 12. then jumps up a good bit when reved up. but not sure how high exactly since it then goes off the little chart thing on the balancer. but the timing seems perfect now. it idles dead smooth and starts instantly with no pumping the pedal. once its fully warmed up we get in to test it. if your very very light on the throttle and accelerate very slowly its fine. were talking barely a normal street start. but if you try to accelerate with like 1/2 inch of pedal travel it lurches foward, the falls on its face, and repeats a few times till you let off. it will actually lay rubber doing this, only it looks like this on the road - - - -
we thought it was a carb problem so we borrowed another stock 4 barrel, basically the same that we have it does the exact same thing. so what gives? any help is appreciated, thanks!

o yea, and while idleing you can free rev it all you want and its fine. its just when your actually trying to drive, even in just first gear so there shouldnt be much load on it.

i think 12 degrees if timing is a bit much for a stock 350 chevy, more like 6 - 8 BTDC is a more suitable starting point. also check your connections on your HEI, and check the fuel pump and fuel filter. also what size holley is it, if unknown get the numbers off the air horn and post them.

Try another distributor. The wires to the module sometimes crack, causing much the same lurching as the advance moves, making and breaking connection.

thanks. i thought 12 would be too much also. but we started around 5 and worked our way up slowly. it just kept on running better and better. until a little after 12 it started to sound wrong. 12 was were it idled the best and reved good with very little popping and backfiring. any lower it idled worse and would backfire more whenever you let off the gas. the surging also seemed to be even worse with less timging.

i think the edelbrock one is a 500cfm. the other i dont know, but im pretty sure it was just a stock one from an early 80's 350. they both did the exact same thing. you couldnt tell which one was on there by the way it ran.

will try to get a hold of another distributor to test. but this one looks ok, and we replace the cap and rotor. although it is old, so you may be right.

if that does not work out, does it have a solid mount or clam shell type motor mounts? if clam shell mounts maybe when the motor twists under load it is shorting out something somewhere. let us know when you figure it out, i am curios what the outcome is.

You installed a bigger pump/gas line for the 350?

How old is this 350? Could it be a worn out and stretched timing chain?

Maybe a broken vacuum hose to the distributor? Would be the easiest guess, sometimes it's the little things... I had exactly your problem and traced it to a cracked hose. you wouldn't even see the crack, but the moment you rev suddenly higher, vacuum gets higher fast (if your on ported vac), that's enough to drag a bit of air through the crack, f**k up your timing and get the engine into low revs again. when revving low the whole game starts over...
JMO, Max

How's your fuel pump?

Spray a little starter fluid around the intake and vac hoses @ idle. If it's a vac leak the idle speed will increase when you spray the leaky spot.

Hey laxman
The 94 S-10 would have had the fuel pump in the tank with fuel returning back to the tank. What needs to be done is to remove that fuel pump and install an electric pump behind and outside the tank. A fuel pump which produces 6-8 psi for your carb. Your original pump produces 45 psi and in order not to burn it out, it has to have fuel running through it at all times which returns back to the tank. If you installed a fuel pressure regulator lowering the pressure from 45 down to 7 psi with no provision for a continuous flow of fuel back to the tank, your fuel pump is stalling. This would mean that when the carb shuts off the flow of fuel because the float bowl is full, the pump would come to a stop, and then when the fuel is required and the pressure drops off, the pump can stat up again. At low rate of speed increase, I suppose that the pump can catch up in time, but when a higher rate of fuel is required, the bowl might well be empty prior to the flow starting again thus causing the surging that you speak of. That would be my first guess.

Your problem seems to be a lack of fuel. This could also be from a plugged fuel filter, as was already mentioned. It could also be that your tank is empty. It could also be that your inlet in the tank is too high off of the floor of the tank.(maybe you hooked up to the return line which is high off the bottom of the tank).

I would check for fuel flow at the carb with the engine off, and the hot wire to the distributor disconnected. just so that you don’t accidentally have a spark with the fuel line open. With the original system, the pump would come on for 3 seconds when you turn the key on. Then once you have oil pressure, the pump comes on again. I would eliminate that setup. Let us know how you make out.