The Holley 650 double pumper, mechanical secondary carb i'm looking to swap for my Holley 600 single line vacuum carb does not have a choke. My current carb has a manual choke and i use it a good bit. I don't understand how a chokeless carb can perform well in the cold, but i'm tired of the hesitation in my vacuum secondaries...will the chokeless mechanical perform better?

 

I ran an Autolite 2100 with it's choke wired open for quite a few years. To start it I had to pump the gas pedal 15 or so times before even I cranked the engine over. Then I would just let it idle, very rough, until it was warmed up. Once it was warm it ran good. It was kind of a p.i.t.a. having to pump it that many times when the engine was cold just to start it. I eventually converted to an electric choke four-barrel carb.

 

I'm running my Courier with a chokeless Autolite as well now, I just have to pump the gas a couple times and hold it above idle for a few minutes.

 

i have my stock 2 barrel carb choke wired open as well i give it 2 or 3 pumps of the pedal and it fires up just need to give it alittle gas for a minute or so when its cold out but is fine for me

 

Brother man, unless you are planning on turning your truck engine up in the 5000 + rpm range, I'd suggest you look a little longer at the swap. Your engine can't handle it for daily driving. A lot of raw gas will be dumped out the tail pipe onto the hyway.




John

 

I was wondering if my motor was gonna handle it, my friend had a 351w with a 650 dp, he just downsized the jets and adjusted the linkage for the secondaries to come in and it was able to hold it. i guess by doing that he was actually probably running the equivalent of a 550. do you think that could work? also i have a fuel regulator on my truck and i was wondering if that would help anything?

Sam

 

Why does your vacuum carb have a hesitation?? It shouldn't unless it's set up incorrectly. Accel pump shot too big/small? Spring too light in secondary(opening too soon and not enough fuel will cause it to hesitate).

What motor? What gears? etc.

I can't see a DP helping on the street. They aren't designed for that application, if you don't have enough engine RPM it will still fall on it's face.

I've always took the choke plate off all my 600 Holleys. I only use the high idle cam to keep the RPM up til it's warmed up enough. Yes, I have to pump a couple times to get it to start, but beyond that it works flawlessly. Doesn't ever flood itself from leaving the plates closed too much.

 

If the only hesitation you have is with the secondaries, I'd work on that. Springs are cheap, even the quick change kit isn't that expensive. Choke does come in handy, especially in colder weather.

 

for a street truck going from vacuum secondaries to mechanical is only going to make things worse .
they sell a spring kit for the vacuum canister , allows you to tune when they kick in .
it's cheap i recommend this

 

also check out the quickfuel adjustable vacuum canister . i've been thinking about getting one of those .

 

i did not know you could custom tune that, and they hesitate when i got to burn out or get passed somebody driving to slow for my liking, or in other words when i give it heavy throttle. not straight smashing it, but feeding it pretty heavy

 

i have a 390 (.030 over), c6 bone stock tranny (for now) and a 3.25 rear end (which i absolutely hate).

 

Could need a bit more accel pump shot too.

Take a test. Pull the phillips screw out of the linkage on the secondaries(that attaches the vacuum diaphram to the throttle arm. Take it out and drive it. Does it still hesitate when you stomp on it? Then it's accel pump needs more shot. You can buy them with bigger holes, plus other cams that give it more duration.

Has this carb been played with before? Getting a used carb from an unknown source can lead to all kinds of issues since someone played with it and now it won't work on your motor. "Usually" new out of the box they are plug and play without having to screw with much.

Removing it out of the equation will allow you to pinpoint the problem. Maybe someone put a light spring in the secondaries and they are opening too soon(especially with your 3.25 gears) and allowing it to fall on it's face. With steeper gears, the motor will recover easier/quicker.

It's hard to tune a carb over the internet, but we'll try.

 

ill give that a shot and see what happens. i did get the carb from a "carb specialist" he had it on a 318 mopar and drove for 20 miles then took it off. supposedly thats all that was done to it, but you never know.

 

Let me guess, they sold it because it didn't run well? LOL!!!

With some tinkering, it should run well for you. Just have to find out the issues.