Chevy 350 Surging, starving for fuel?

[ndemge]

'71 G30 1ton Van<br />4,000 miles on rebuild, rebuilt carb, new everything else.<br /><br />Pulling even a slight load, if you give it throttle it will surge, have to pull way back to slow rpm's to keep it steady.<br /><br />It seems like it is starving for fuel. Fuel lines look good, no kinks between pump and carb.<br /><br />This has slowly been getting worse and worse<br /><br />Anythoughts on what to troubleshoot?<br /><br />HEI ignition

 

[dolluper]

Re: Chevy 350 Surging, starving for fuel?

do a fuel pump presure test

 

[Barlow]

Re: Chevy 350 Surging, starving for fuel?

ndemdge - this might seem a pain in the arse to check .. but when was the last time the muffler was replaced or exhaust line checked .. <br /><br />if I'm right in saynig so '71 was before cadilytic(sp?) converters which was my first thought.. ??<br /><br />not sure other than that ..<br /><br />.. maybe the automatic transmission is taking a crap on ya too..??

 

[Xcusme]

Re: Chevy 350 Surging, starving for fuel?

Didn't those still have a heat riser at the exhaust manifold/exhaust pipe junction?? I remember having to spray 'bust rust' on it and sometimes use a few hammer blows to free it up. If rusted/stuck/frozen, you would have back pressure issues.

 

[waterone1@aol.com]

Re: Chevy 350 Surging, starving for fuel?

When was the last time the fuel filter was changed ?

 

[ndemge]

Re: Chevy 350 Surging, starving for fuel?

Xcusme<br />Good thought on the heat riser, it is still there, I'll check that out.<br /><br />waterone1 <br />4,000 miles, at time of engine/carb rebuild<br /><br />dolluper<br />.. I'll try this after checking the exhaust<br />Do you disconnect from the carb and hook to a pressure gauge and crank the starter, or a "T" while it's running? It's a brand new heavy duty pump.

 

[Bob_VT]

Re: Chevy 350 Surging, starving for fuel?

This almost sounds like the HEI module is starting to fail. I would check the fuel system before I swapped out anything. There is probably a small screen filter in the fuel line at the carb and those tend to block up quick.<br /><br />The G-30 is a 1 ton and some were not equipped with converters on the muffler.<br /><br />Bpb

 

[snapperbait]

Re: Chevy 350 Surging, starving for fuel?

Betcha got a vacum leak...<br /><br />Very carefully, with the engine at idle, spray a bit of starting fluid around the base of the carb gasket, intake manifold ports(where the intake meets the head), and other sources of vacuum... If the engine makes a noticable change in it's idle speed, then ya know what and where the problem is..

 

[ndemge]

Re: Chevy 350 Surging, starving for fuel?

starting fluid..... WD or liquid wrench work ?

 

[Xcusme]

Re: Chevy 350 Surging, starving for fuel?

Starting fluid?? Yikes!! I'd go with a can of carb spray with the plastic tube for a pin point spray.<br />The WD40(newer stuff=no propane propellent) or Liquid Wrench won't be volatile enough.

 

[SS MAYFLOAT]

Re: Chevy 350 Surging, starving for fuel?

Waterone might have the answer for you. A partially clogged filter will cause a steady decrease in performance. It will get worse as time goes on. Check that first.<br /><br />Does it take the gas slowly but not suddenly? If so, it could be your accelerator pump. With the engine off, remove the breather. Prop open the choke to look down into the carb. BE CAREFUL NOT TO DROP ANYTHING IN THERE! WHile looking in the carb, open the throttle. There should be two streams of gas squirting into the carb. If one does and not the other, you have a plugged port or jet. If it starts to squirt after you have moved the throttle a bit, it could be out of adjustment. It should start to squirt when you first start to open the throttle. If it doesn't squirt at all or very little, it very will could be the accelerator pump.<br /><br />In 1971, 1 ton vehicles were not mandated to have any pollution control devices.

 

[fatpratt1996]

Re: Chevy 350 Surging, starving for fuel?

I know this sounds dumb but are you sure the engine is surging or is it the transmission giving up on you? Does it only do it while pulling a trailor? Mine did this for a while. Tranny was blown.

 

[jimr]

Re: Chevy 350 Surging, starving for fuel?

will it rev up in park with no load? I would put a fuel filter on it and go from there. and make sure its in going the right way I have taken a bunch out that were put in backwards.

 

[dolluper]

Re: Chevy 350 Surging, starving for fuel?

what isn,t new on it would help us out alot,you might want to check your vaccum addvance unit on the distribator for hose off or not working, can you discribe what your calling surging [ping] shake rattle or roll [bucking]use a tee it's easier in the line

 

[waterone1@aol.com]

Re: Chevy 350 Surging, starving for fuel?

Another thought, besides the fuel filter (does it have two, one in the fuel line and another in the fuel inlet of the carb) would be if it has a four barrel. Are the secondaries opening too soon ?

 

[rwise]

Re: Chevy 350 Surging, starving for fuel?

and another thought would be the float set to low.<br />and another thought would be the vacum line to the distributor from the carb (via whatever) on the wrong port at the carb, easy to do, causes the advance and retard to work backward, timing at idle is correct and will rev without load but loaded it would could pitch and buck!<br />just a thought or two

 

[ndemge]

Re: Chevy 350 Surging, starving for fuel?

Will hopefully find time to play with it this weekend, thanks for all the thoughts on what to check.<br /><br />Accelerator pump is working, and no, if I'm under a load I really can't even just slowely get up to speed. (I had a problem with accelerator pump right after rebuild, had to really slowly build up rpm's, but got that fixed)<br /><br />I can be cruising down the highway, hit a slight incline and have to slow down because it will start bucking,...

 

[dolluper]

Re: Chevy 350 Surging, starving for fuel?

timing or air leak,if pump checks good ,heat riser operating,fuel fiter not colapsed, a timming lite will tell you if it's advancing properaly , check under cap for carbon tracks ,rotor too ,while your there pull rotor off make sure centifical advance is not binding and is free but tight moving and pick-up coil doesn't show any little burn on green wire or yellow ,you can ohem check it if all this fails one little fast trick with GM distributors is start the engine with the hold down bolt al ready loose ,plug vaccum advance hose ,crank timming ahead[be faster idling] tighten bolt go around the block if it runs with more power no ping the distributer shaft is binding will not advance properly ,replace shaft or free up /they like to seize on the bushings IF NOT air leaks

 

[Barlow]

Re: Chevy 350 Surging, starving for fuel?

ditto on the timing .. I'd still check the exhaust too.

 

[red10]

Re: Chevy 350 Surging, starving for fuel?

i'd check the muffler bearings or maybe put winter air in your tires