ashes0

Hey there folks! Been a while since I've been here but much much work has been done on my car including an engine build.

It was an L-48 350 original to my 79 with factory 4-speed.

I went with a mild lift cam, 210cc Intake Port, 64cc Chamber, 2.02/1.6 Stainless Valves Aluminum Heads and a new pro comp air intake.

Wound up just needing to hone cylinders and turning the crank so I left the bottom end of the motor stock.

I'm not sure on the power, but feels great, much more powerful than stock.

Now I decided to ditch the q-jet (Could not for the life of me get it to quit backfiring) which I initially was getting 12-13 MPG with on the stock build and go with a shiny brand new electric choke Edelbrock 600 CFM 1406.

I'm now sitting on a humbling 9 MPG average consistently over 5 tanks of gas with highway traveling and some with just city flooring between lights. It makes little difference. I've put maybe just over 1000 miles on this motor, and while I do push my car relatively hard I'm pretty sure I can do better than this.

I have read countless threads on ignition timing and believe I've set it right, I went ahead and got a new distributor which really helped out my throttle response but doesn't seem to have affected my MPG.

I set my total timing at 36 degrees (without vacum plugged in.) and adjusted my vacum canister to bring me to 52 degrees total timing. Initial timing is about 18 degress. I put in weaker timing advance curve springs to see if that helped, no dice as far as I can measure.

There is a smell of gasoline at WOT but I'm not sure if its an exhaust leak or not. No gas leaks that I can find...

So what next?

billla

In this process, did you replace the fuel pump as well?

We'll assume for the moment the timing is right - or right enough

First check is float level and ensuring the needle/seat isn't sticking or otherwise held open.

ashes0

The pump was not replaced during rebuild but had been a few months prior so its relatively new.

Shouldn't the carb be set right as it is new? Oh well, guess I'll be tearing into it sooner or later.

billla

What pump was put on?

They should be good out of the box...but sometimes, they're not

Sayfoo

Have you checked that the choke is opening fully?

billla

Good call and quick to do.

Ironcross

put the Rochester back on!

73ss

Most likely the carb is jetted to rich. That's the problem with an out of the box carb. They are set up to cover a wide variety of engine combos. Great article in this months car craft mag in the "whats your problem". Talks about this very thing. Is the oil getting dark quickly due to the excess fuel? As far as the q-jet backfiring, Most likely lean. Was the acc pump working?

Shark Racer

How would they set a carburetor right new? That's worse than trying to diagnose a car noise over the phone.

A motor has a wide range of fueling demands and a carburetor has many adjustments to try to cover those conditions. You need to spend some time tuning the carb to the motor. As 73ss said, it's likely jetted too rich. It's much safer to jet rich than lean, although too rich and you'll start wearing out the cylinder walls from a condition called "bore wash". You can also flood the crank case with fuel.

I'll gladly take your quadrajet if you don't want it anymore.

billla

Well, most of the street carbs come pretty close for most mild 350s....at least close enough such that he should be seeing better mileage. I think it's something more fundamental.

Robert H

Edelbrock has a pretty good guide on tuning their carbs. I would suggest that you buy the "tuning kit" for the 1406, and follow the procedure that Edelbrock outlines. It may not get as good as the Q-Jet though for a couple of reasons. If you were getting back-firing with the Q-Jet, if may have been lean, which would help MPG a bit, and kind of the whole point of the Q-Jet design is that the primary side is small to provide better mpg, and the secondaries stay closed until they are really needed. However--I have an 81 Vette that I put a GM performance ZZ383 in, with a 350 trans, and a 3:55 differential, and it gets about 13-14 with a Edelbrock 800CFM carb, so I think you have something not right, and it should be able to be improved.

garygnu

what are your vacuum readings ?sounds like you are running too rich .what carb are you using ?check your power valve.

Indiancreek

What do your plugs look like?

ashes0

This is something I've never fully understood. Where do I check vacum and what with? And what values am I looking for? How is it related?

I'm using the edelbrock 1406 600 CFM e-choke

As far as the choke goes, its electric and I tested to make sure it is getting 12 volts so I'm assuming its working.

Just ordered the tuning kit with all the springs and meetering rods and jets.

AirborneSilva

I'll be watching this to see how you fare. I just put a new crate motor in mine, have the same carb as you, without a choke, don't need it here, and I'm not getting good MPG's either. I haven't actually checked but I sure put a lot of gas in the tank it seems

Sayfoo

Doesn't mean it is working and FULLY opening.
Super easy to check. Just take off the air cleaner as soon as it gets to normal operating temp and look to make sure it is totally open.
I would also try to determine when the secondarys are opening. Want to make sure that they only open when you punch it, not at steady cruise or moderate acceleration.
Ignition/timing next.

SIXFOOTER

Here is a vac gauge.
http://www.jegs.com/i/Proform/778/67410/10002/-1
It gets connected to manifold vacuume. It comes with pretty good documentation, tells what to look for. The gauge will tell you a variety of things, leaking manifold, high or low etc.
The gauge is used to tune the fuel air ratio useing the f/a mix screws on the carb.
The carb you have will never perform as well as the 750 quadrajet you had.
My money would be on learing how to tune it.

iokepakai

Can't help you much with your Edelbrock carb.Read they are really sensitive to fuel pressure... Here's my story with fuel mileage.Previous owner installed a Holley S/A carb,couldn't get that carb to run right no matter what I tried .Rebuild it,set float level,adjust,change metering blocks everything I could think of I tried. Finally said screw it! Bought a new Summit 600 cfm carb less than 300.00.Bolted it on ,check float levels,adjust idle and mixture done! Carb looks great & been running awesome since February.This is a really nice street carb and the price is reasonable.It has annular booster and uses mostly Holley parts.Getting 20 mpg hiway with my ROD trans.Here's the write up on the carb.Good Luck,Hope you get it sorted out.

http://forums.corvetteforum.com/c3-t...or-review.html

Matt Gruber

maybe my story from 5 yrs ago will help?
http://community-2.webtv.net/MATTGRU/carb

ashes0

Just a bit of follow up here, got the edelbrock tuning kit however it only included over sized jets for enriching your fuel mixture so the best I could do with that kit was use a larger metering rod as per instruction.

Tried that out left it like that for a week, no real results or difference I can see yet. I went out and got me vacum/fuel pressure guage and found that I was frequently getting 7-9 PSI. This apparently is considered too much for these edelbrocks to handle so I got a fuel pressure regulator and hooked it in. After realizing I needed to put the filter before the regulator in the fuel line, I hooked it in and set it to 5 PSI. (Confirmed it was actually 5 PSI by hooking in the guage between regulator and carb.) With the lean metering rod and this I seem to be getting a lack of power on WOT and bogging down on engine. I may switch back to the stock metering rod to see if I can isolate fuel pressure as the cause.