LT-1 Replacement Carb Suggestion

[GaryH]

I've had a chance to put some miles on my 71 Vette the last few weeks. The original 4801 carb is dumping fuel. I've gone through it and I think it has a warped metering body or other internal prob. I'd like to stick it in a box for the next owner and put on a new Holley. Any suggestions on what number Holley carb I could get that will have a rear metering body, is the proper color and will allow connection of all the vacuum lines? The 3310 looks the closest but has no rear metering body. I'm not worried about a choke.

[VintageMusclecar]

Gary;

Where exactly is it dumping fuel?

Warped castings are an issue with older carbs, but it's not a big deal to correct and is s.o.p. for me when I go through them. It shouldn't be any problem to make your original carb right again. I'd be glad to help if you'd like.

Eric

[GaryH]

That depends on when you look at it. It usually acts up after I jump on it. But by the time I get pulled over it stops doing it. Last night while setting the floats it started to dump out the rear venturis then it started squirting out the accelerator pump jets. Strange. It only does it when it's hot. I'm familiar with vapor lock issues but it's just not hot enough yet to be that. The engine is running cool and under hood temps are pretty reasonable. I think it's had this problem for a while as the previous owner had removed the gas cap gasket, to vent the tank, in hopes it was an issue with the canister purge system. The carb itself looks like brand new and may have had some type of professional reconditioning at some time. I'd appreciate any input you can give me

[VintageMusclecar]

Gary;

That is a strange problem, esp. being intermittent. Does it ever do this just while driving, or is it only after you've jumped on it? Have you tried jumping on it a little bit before the engine is completely up to full temp, and if so, did it do it then? (trying to determine if it's 100% heat-related)

It almost sounds like you have an intermittent issue with either a/the float(s) sticking, or needle & seat(s) on the way out, but being heat related is throwing me off a little bit.

Do you know anyone with a good carb that you could borrow? Even a generic 3310 would suffice as a temporary mule to see if that isolates the problem.

Eric

[GaryH]

It won't do it if it's not completely warmed up, Eric. It has to be driven at least 5-10 miles first. When it's cold it runs great. The hotter the weather the worse it is. I took it out this morning to let a friend drive it and it ran great. It's chilly today and we didn't go far though. The only thing that seems a little odd is, in order to set the float level I have to have the needle/seat screwed down so far that the adjusting nut is barely catching the top of it. It was like that prior to the rebuild also. Are there different length needle/seats? The floats seem fine and they are not full of fuel. I'm pretty certian it's a carb issue. I'll ask around my car club and see if anyone has a carb I can borrow to see if that fixes it though. Let me know your thoughts on the needle/seat height.

[VintageMusclecar]

When you went through the carb, what brand of a kit did you use? Did you replace the floats? If so, are they brass, plastic, or nitrophyl?

On a Holley needle & seat, usually 2-3 threads showing above the float bowl will put the fuel level at or just below the sight plug.

Keep me posted.

[GaryH]

It was a Holley kit for the 3310. I purchased two 8.5 power valves and the blue bowl gaskets separately. I matched all the holes in the new gaskets with the old ones and they all appeared to be correct. I did not replace the floats. They are brass and appear original. I'm lucky if there is more than a thread or two sticking above the bowl on the needle & seat. You have me thinking I should pop this back apart and double check things on the floats and try some different needle and seats....

[VintageMusclecar]

Gary;

For no more than what they cost, go get a new pair of HOLLEY .110" needle & seats (stay away from the generic rebuilder jobs, esp. the Borg-Warner styles!) and a pair of new brass floats. When you re-assemble the float bowls, baseline the floats by inverting the bowl and running the floats down until the top of the float is at the bottom of the float hinge screws. That usually gets them very close.

Make sure the floats operate freely and don't stick or have any tight spots. Sometimes you might have to gently "tweak" the float hanger "ears" to get everything to set just right.

Also, while you've got it apart, check the metering block surfaces on the main body of the carb and see if they've ever been machined flat.

Keep me posted.
Eric

[GaryH]

Eric, I just got done pulling the carb. I took out the 8.5's and installed a 6.5 in the front and a 7.5 in back. That's the only ones I had laying around. I studied the floats and they look great. The hangers are square and do not appear to have ever been bent for any reason. I reassembled and reset the floats. Something is definitely amiss there. I have to crank the needle down almost to the point that it's flush with the top of the carb in order to set it correctly. That's both front and rear. I took it out for a ride and it's better. It likes the 6.5 in the front. I have better response and it pulls better at light to medium throttle. For the first time since I've had the car it had a consistent idle every time I came to a stop. Skies were threatening so I didn't go far but it is improved. I'll pick up a set of needle and seats tomorrow and see if they are any different. If not, I'll take it back apart and replace the floats and adjust as you suggested. With your help maybe I can get this squared away Thanks for taking some time out on this Easter Sunday and helping!

[VintageMusclecar]

Gary;

I'd still replace the needles & seats as well as the floats just to eliminate them as a possible cause. If you can't find them locally for a decent price, let me know.

Glad to help.

Eric