Fuel Spillover, again...

Sorry to bring this up again, but...

Getting ready to order the Holley Truck Avenger $$$ for my '63, 283 Chevy with a Carter 4bbl. Just wanna be sure of the problem before I, ouch, order.

Some steep hills it does great. Go a little steeper and it feels like it's running outta gas. Pump it a bunch and it keeps running, but barely. Fuel spillover? Is that what it feels like? And what exactly happens when the fuel spills over? Does it go in the air filter? Down the bowl? Could this be a fuel pressure problem?

The one I'm looking at is a 670cfm. Too big for a 283?

Thanks again.

 

Kinda ! In my misspent youth when building 283's we found that 500 cfm was about it for a good running engine. If you go bigger, 6 to 700cfm, it will work well only on a "built" engine. That is with at least 2.02 intake valves, good manifold and headers.

You might also consider Edelbrock carbs. They make one specifically for off road. And, there made by Webber.

 

I think Jim knows of what he speaks.

 

Thanks Jim. This motor is stock! Bone stock. The only recent work is the heads were redone to stock specs.

I've been all over Edelbrock's web page and have not found an off-road carb. Do know the model by chance.

Do you think this is a spillover problem?

 

I don't know the part #'s, but Edelbrock's off road carbs are called the Thunder AVS series.

 

Thanks Mike.

 

Was just checking out their site. Seems the Thunder AVS off road only comes in a 650cfm. Too big?

 

Crash 7 & Patrick: Patricks' correct about the venturi speed. I always thought the perfect stoichmetric ratio was 13.8, but that was "pre smog". The problem with a big cfm carb is--can you get enough venturi flow? Always better to error on the small side.

On the Edelbrocks, they make a 500 cfm carb--manual choke--that is not a "Thunder AVS". But the difference is some parts inside. It would be worth a call to Edelbrock and they can set you up with the correct parts to make it an AVS. They are very accomadating--that is their business!

Now, after saying all this, the last 283 I ran had a Holly 650cfm (I think) on it. But, I ran an old set of Vette heads with 192 intake valves, a 5 angle valve job, matched ports and an Edelbrock intake. I also ran stock W type exhaust maniforld. It worked fine, but the only improvement over the 500cfm was when I had my foot in it. It also got less mileage than the smaller carb, but 102 oct leaded premium was only 29.9 then. :twisted:

 

Maybe this site will help.
http://www.thedirtforum.com/cfmcalc.htm

Jeff

 

Hey Crash,
Have you ever considered running a TBI system? With a 283, it shouldn't be hard. It would definitely get rid of the problems running at steep angles.

mruta

 

The best carb I have run off-road was a Rochester Quadrajet mounted backwards on the intake manifold. Side hills and steep angles are not a problem - I have run with fuel injected rigs as well, and have had no problems going where they go -
Just takes a bit of messing around with the throttle linkage and carb spacer to get it all to fit right - but it works AWESOME!

 

A mechanic buddy of mine has a Q-jet I'm gonna try. Picked up a Edelbrock Performer spread bore intake to mount it on yesterday. Fingers crossed...

Thanks for all the ideas guys. TBI FI is tempting, but a little to $$$ right now.

I'll keep ya all posted.

1968Jeep - Why backwards?

 

Pat: I think you'll like the Q-Jet. I've been a big fan of them since my '67 396 Camero.

One thing to remember is to get a rebuild kit and set ALL the rods and other settings exactlly as specified in the rebuild kit. None, I repeat, NONE of them are correct from the factory. Other than that, GREAT CARB!

 

The FSJ guys really like the Quadrajet on an aftermarket manifold for the 360 and 401. Reputed to run at any angle. The best junk-yard carb available.

Don't know if it was here or on IFSJA - somebody pointed to the QuadraJet tuning articles by Lars. Tuning of the QJ is difficult for some people. The QJ supposedly works well if you take the time to understand how the tuning works and follow the procedures carefully.

 

That's the way I understand it too. Difficult to set up, but work great once done. Luckily my buddy work in a carb shop for a few years and has a lot of experience setting them up. He swears by them.

 

Pat: Their not difficult, just sort of complicated. You can adjust the secondaries with different meter rods and height and such.

Also, if I remember right--it's been a long time, there are a couple of brass block off plugs in the base of the carb body that can leak sometimes. Easy Fix--JB Weld them around the seating area--never happen again.

 

We'll my friend is just about done with the rebuilt. He went to look up the specs on where to set the floats. Turns out this thing came off a late 70s truck with a 454. $h1t!!! He had been told it was off mid 70s pass. car with a small block. Guess not.

I got on ebay first thing this morning and was able to win a bid on a Q-Jet from 84 Chevy van with a 305. $30 bucks with shipping. Hopefully it arrives as advertised. Still gonna put the Performer intake on tonight.

I new there was a reason I bought the adapter to run a square bore on it just in case.

 

Pat: Yea they do make some BIG ones. On my '67 396 Camero SS I had a 850 cfm one. And it Wasn't TOO BIG!

With that 305 Q-Jet you should be fine. They used those engines in Marine applications and IIRC they were about 500-600 cfm.

 

It's finally done. Got the freshly rebuilt Q-jet sitting on the new Performer. Had to get new vavle covers too since the oil fill was on the original intake and the stock covers had no holes. It was that or fill the oil through the dip stick hole. Ha! Also changed the distributer over to HEI. There's not enough room to put a the big stock HEI in there with the firewall so close so I got a conversion kit from Pertronix. Seems to work good. Everything runs great and looks good with the new goodies.

Headin' for the desert tomorrow for the weekend, see how it does on the hills. I hope we don't melt. 100+ all weekend with chance of thunderstorms.