carb problem

Joel · January 29, 2002

When I push on the gas part way, the truck acts as if its not getting much gas. Give it more or less and it responds. If its cold (180 and under) it will die if I don't throttle it.

Anyone know what the problem is? Do you think its the accelerator pump?

Joel

'74 Chevy 350 1/2 ton w/2 barrel holley, 150k+ miles

76BBSub · February 2, 2002

Two possible causes come to mind from what you have described...

The first, which you mentioned, is that the accelerator pump is not working. These are normally part of a rebuild kit, which is about $20 or so at the parts store. The easy way to check if it's working is to remove the air cleaner assembly, and, with the engine OFF, manually rotate the throttle and look for gas squirting out into the primary venturis. It should be a nice, continuous stream throughout the action of the throttle. If not, buy the kit and replace the pump. I would recommend cleaning out the fuel bowl and generally cleaning the carb while you have the top off.

Another possibility is that the power piston is stuck. The power piston reacts to vacuum to change the position of the metering rods in the jets. If it sticks your truck will run either too rich or too lean, depending on where it's stuck and the demands on the engine at any given time. This is pretty easy to check, too. Pull the top (you can do this while replacing the accelerator pump piston). I'm not familiar with your particular two-barrel, but in the center of the fuel bowl there should be a small hanger with the two primary metering rods hanging down into the jets at the bottom of the fuel bowl. At the center of the hanger is the power piston. Push lightly on the center of the hanger over the power piston, it should go down slightly, then rebound quickly when you release it. If it sticks, or doesn't move at all, gently pry the little cap at the top off of the piston and remove it. The rebuild kit may not have a new power piston spring or power piston, I can't recall, but you should be able to clean the bore and lightly polish the surface of the piston to remove and deposits or other gunk. Any carb that has sat for awhile with gas in it is likely to develop a sticky power piston.

Check those two things and let us know what you find.

Jeff

85gmc · February 3, 2002

I had the same prob with my rochester quadracrap if you have the money get a weiand stealth manifold and a 600 carter problem fixed plus you gain alot of tire smokin power Chris

Joel · February 4, 2002

Thanks for the info! I'll check it out hopefully today or tomorrow and will post what I find. The truck does seem to be running rich. At night I can see exhaust in the headlights behind me when accelerating. I also spent 99 bucks in fuel last month just driving to work, gym and arrands on the weekends.

Joel

95Yukon · February 4, 2002

Check your float level while you're in there and replace and reset the float height if the rebuild kit comes with one. Make sure it isn't sinking, which will make your engine run rich all the time.

Joel · February 5, 2002

It didn't come with a float but I have specs on what it should be set at. BTW, I originally quoted the carb was a rochester. It is not! Its a Holly 2 barrel.

Joel

76BBSub · February 13, 2002

Hmmm...well I've never disassembled a Holley 2BBl, but it should be about the same as the Rochester or MotorCraft. And the suggestions we made with reference to checking the float level, accelerator pump, power piston, etc should all still apply.

Hope ya get it squared away, although I also tend to agree that a nice aluminum intake and new 4BBL carb would solve it!

Jeff

ClipperSkipper · March 2, 2002

If it's a flat spot where the carburetor looks back at

you when you crack the throttle than you own an

Edelbrock Performer. If Rochester, probably leaking

through a gasket either in the air horn or throttle body;

this is easy to spot: With the engine idling, spray Gumout at specific places around the carb in order to isolate a vacuum leak. Pay specific attention to the linkage which runs

horizontally through the carb, the casting bores often

wear and create a huge leak.

If a Carter or any of the above...I use the best rebuilder

on the East Coast.