Confusing carb question!!! Please help!

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dartkory

dartkory

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So long story short. I have a mildly built up 318 (10:1 comp, eddy heads air gap intake, comp 275deh cam around .484 lift so not huge) anyways, I was running a 600 cfm eddy carb, then went to a 670 street avenger and loved it, then sold it and while waiting to get my 650 electric choke dp, for ***** I put my buddies eddy 750 manual choke carb on. At first it would bog when flooring it but when I closed the choke a little it would scream!! I couldn't believe it. Then my dp came and I haven't been to impressed just a pain to tune so I'm gonna return it. But don't know what I should do! The 750 just seems a little much don't you think? Why would I have to close the choke a little? And all 4 carbs burned rich (no smoke at idle, but smoke at 6000) I just need some input, plus with the 750 i hate manual chokes because its a ***** to start in the morning. Thanks -kory
 
any and every carb needs to be adjust for the engine it is on and to the atmospheric conditions it is going to run in...

to take carb out of the box and say it does not impress you ...what did you expect...

the eddy 750 by closing the choke is telling you that it is too lean
 
Is the 750 vacuum secondarys or mechanical. If it is vacuum you need to use a stiffer spring in the secondarys. the 750 is a little big but the 670 should be better for your combo but will need tuned.
 
For ease and simplicity of it all....put the Electric choke 650 on....and jet it properly...and report back....It is a 4150 based 4777 650 double pumper right?...with choke and provisions?

I suggest going to a dyno tuning shop there in Portland... and having the A/F plotted... and tuned.

I think you'll love the results more than any of the other carbs you listed...for numerous simple reasons.

I have a 4777 650 double pumper with the choke tower milled...on the shelf awaiting some stuff...would love to hear more details about the jet sizes your running to run rich??

What Power Valve does it have, 5.5, or 6.5...or?

Got any pics?
 
chloros340 said:
Is the 750 vacuum secondarys or mechanical. If it is vacuum you need to use a stiffer spring in the secondarys. the 750 is a little big but the 670 should be better for your combo but will need tuned.
Click to expand...

He said it was a eddy 750 which are sort of vacuum controlled with really no adjustments available ..

the other issue with the double pumper is what kind of gearing and converter you have?

How about the engine timing and advance curve in the distributor.....everything is got to work together..
 
dartkory said:
then went to a 670 street avenger and loved it
Click to expand...

Not sure what to add here Kory......^^^^^^^^^^^^^^^^^^.

And to Tony......Get out of here man.....Maui is calling....FABO who....lol. Enjoy yourself :thumbup:.
 
It is raining....waiting to hit the beach in a few minutes
 
70aarcuda said:
He said it was a eddy 750 which are sort of vacuum controlled with really no adjustments available ..

the other issue with the double pumper is what kind of gearing and converter you have?

How about the engine timing and advance curve in the distributor.....everything is got to work together..
Click to expand...

sorry didn't see that
 
Conventional wisdom says that anything larger that 600 CFM is waaaay to big for a 318 right? You have just learned that conventional wisdom is a crock. You have already experienced a 750 that was too lean to run without the choke partially closed. For some reason 318s adore a 750 carb. I learned this back in the stone age (1973) when I was fooling around with a 318 Dodge van. Started off with a 600 Carter AFB per conventional wisdom and it was a dog. Ran better with the stock 2 barrel. Then tried a 650 Holley which was an improvement but not what I thought it should be given the expense involved. A co-worker was sending his new 750 vacuum secondary Holley back because he decided a mechanical secondary double pumper was what he wanted on his 383 Road Runner. Didn't have anything to lose so I bought it and slapped it on the van. Voila, once I got the jetting right it was instant raped ape. Settled on 1 step richer on the primaries and 2 steps leaner on the secondaries. That's been my starting point for a 318 since....
 
Thanks for all the great input so far! Lets see if I can answer all the questions. I have Tried to tune the 670 and the 650 dp but with no great change. Tried numerous jet and squirter changes which would help but could never compare to the 750. My car is an automatic with 2500 stall and 3.91's. timing is 16 initial, and 32 total. and the power valve is 3.5 due to my vacuum being around 8-9. And 70aarcuda, trust me I would never think a carb is ready to go out of the box, although the 750 felt that way other than the choke thing. And I put lighter springs in my distributor so it all comes in at I believe around 1500. Thanks again. -kory
 
[ame="http://www.youtube.com/watch?v=6QqISYlpu3E&sns=em"]http://www.youtube.com/watch?v=6QqISYlpu3E&sns=em[/ame]
I have never posted video so hopefully it works but here it is idling.
 
The 670 is way too big IMO and you probably noticed it feeling sluggish of idle and light throttle cruise.
A DP carb can be more tricky. It's a race carb and unless you have a real good tuning sense, or spend a day either at the chassis dyno or at a track rental running back to back runs, it will be harder to tune. You'll almost never see me recommend one for a street car as a result of that.
The 750 Edelbrock has smaller primaries which gave you the better response. Also there are two versions of that carb - one is configured permanently lean, the other is more rich all accross the board. The lean one is the cheaper one and from what I've seen usually the cuplrit of someone hating Edelbrocks...lol. As noted above - all carbs need tuning. As far as the Edelbrock goes - they should raise the price by $50 and include the strip kit in every box. You will need to replace the step up springs due to your vacuum level (again - in gear) and then get the fuel curve figured out. The bog is the wrong step up springs more than anything.
All that being said - If you run a Holley I'd run either the 570 Street Avenger Vacuum secondary, or the 600cfm vacuum secondary. The power valve is too low if you have 8" of vacuum idling in gear. Raise that up to a 5.5 or 6.5. You want it to stay closed at idle, but open when the engine comes under load.
If you go Edelbrock I'd get the 650cfm electric choke and order the strip kit at the same time. If you though the 750 was good - the 650 will be better.
 
Sounds good Idling Kory.....

:prayer:


and I have also had good luck with the Edelbrock 1406 650cfm carburetor with electric choke......like MOper said ^
 
No such thing as an 'Unconfused Carburetor',

I had some success with a 750 CFM on the 318, but in the long run it was too much for the Street.

Moper is 'right on', less is more...........
 
If it runs better with the choke partly closed its too lean

I'm a firm believer on using a heated intake with carbs unless you live in a very warm place--like Texas in the summertime. Carbs need some heat to help burn the fuel mixture.

Racing is different cause its not run at part throttle and most the times the engines have 13 to 1 compression--even then its just a few more HP you gain with a cold intake, its not worth the hassle on the street

If you pull the spark plugs I got a feeling you see they are fouled, clean them up and jet the carb up 2 jets sizes and go from there but overtime those plugs are likely to foul up again.

I like using the exhaust heat to warm up the intake, can make a world of difference for the better
 
Right now I'm running regular v-power plugs. Would running a hotter plug help at all? I'm mainly confused on why it blows the black smoke at top end so much, I mean its not like what you see coming from a diesel but its something I don't want to see at all. My buddy has a ford galaxy with a stock 390 (other than a little bigger cam) and when he was running the 750 he had it jetted up almost as much as it could go and there was never any smoke! I'm beginning to think it might be something mechanically wrong with my motor, even though all my compression is good! One time years ago I put a eddy 500 cfm carb on my engine and although it didn't blow smoke top end it completely dogged it. So are my only 2 options, blow smoke and haul ***, or don't blow smoke and not haul ***? Oh and one more thing, if its only rich top end do i still have to worry about my cylinders being washed out!?! thats one of the things that worries me the most. sorry forthe novel but Any help or input is appreciated! Thanks -kory
 
Hotter plugs might help--long as the motor doesn't knock

It could be too rich at WOT and too lean at part throttle. Its a new carb ?

If the motor ran good with the eddy 600 you could put it back on, the secondary air door weights need to be lighten up and it pick up some power. With the stall and gearing you have, you might just be able to remove the secondary air door on the 500 carb and give it a go. Can always put in back if it bogs too easily--which I don't believe it will. The top of the carb needs to come off and the secondary boosters need to be removed and out comes the air door

Eddy carbs get a bad rap cause folks don't tune them as good as the carbs can be tuned, IMO

Plus eddy carb boosters work best in small cfm, 500--600, the 750-800 are too big for the booster designs. No problem, just use two 500 or 600 carbs but most folks just get a holley carb cause it is cheaper and less hassle and works really good. Carter-Eddy carbs can be made to work well if you want to spend the time tuning them
 
Not near enough engine and stall converter for a 750 DP for sure. The main reason it boggs is the carb is too big. When you put a carb that's too large on an engine it doesn't get enough signal to the boosters to get the fuel flowing quickly. You can band-aid it by putting the biggest squirters and most aggressive pump cam on it you can find but like I said that's just a band-aid.

If it's blowing black smoke real bad on the top end it can wash the rings down and ruin them.

Although I think it's a little too big you probably need to get another 670 Avenger since you said you loved it.

As for putting in hotter plugs, you need the plugs that are the correct heat range for the engine, not plugs that are 1 or 2 sizes too big just to try and burn off the excess fuel being dumped down.

One last thing, a 3.5 PV is way too small for an engine with 8-9 inches of vacuum. I'd start with a 5.5 in it and see how it does.
 
dartkory said:
Right now I'm running regular v-power plugs. Would running a hotter plug help at all? I'm mainly confused on why it blows the black smoke at top end so much, I mean its not like what you see coming from a diesel but its something I don't want to see at all. My buddy has a ford galaxy with a stock 390 (other than a little bigger cam) and when he was running the 750 he had it jetted up almost as much as it could go and there was never any smoke!
Click to expand...

You cannot compare your small block cammed up 318 to a stock big block Ford. Your comparing apples to oranges. Not only is there the big cubic inch size difference they are a completely different design. All 390 Ford's I've had and worked on needed really large jets to run good. Plus they liked a ton of timing. Usually 40-42 degrees. My only thought to that is their not very efficient.
 
The 750 isn't a dp. And the 750 doesn't bog it just blows a little at top end. It's the 650 dp that bogs and blows more smoke then the 750 at top end. And not very efficient to say the least! Cause my 318 blows the doors off his big block 390! Mopwr!!! But I'm now thinking about getting a edelbrock 600 with the manual choke. But other than the jet sizes are there any differences between the 600 with the electric choke compared to the manual choke? Because the 1406 has been the worst carb on it yet. Well it was a hair better than the edelbrock 500 cfm.
 
Again you want to be careful - I'd go straight to the Edelbrock website - there are different versions of the same CFM rated carb. For the most part anything with an electric choke and AFB-based is base calibrated for economy. The 1406 is the economy calibrated 600cfm electric choke. The 1405 is the performance calibrated manual choke 600 AFB-based carb.
If you are looking at starting "from a clean slate" my first choice would be the 1806 Thunder AVS 650 cfm. It has the tunable secondary air door (handy for smaller engines) and the electric choke with a performance out-of-the-box calibration... And I'd order the strip kit....lol.
 
Not to throw a 'cog in the wheel',

But my friend experienced the same thing with the larger carburetor at Top End.

He removed the Air-Gap intake, as he believed it stayed too cool with the bigger
Carburetor. He changed intakes but kept the 750. No black smoke problems,
and only lost a shade off the E.T.
 
I tried the 1806 a while back and it felt about the same as the 1406. And 69cuda440, I went to the air gap from an rpm intake and both smoked top end. Did your friend put the performer back on? Cause I'd be worried about losing top end. These 318's need all the help they can. But I called the edelbrock tech line and Moper is right about the 1405 and 1406 being completely different other than just the choke and jets. So I guess I'm gonna be ordering the 1405 and see how it does, that's also what the rep suggested. After I get it on I'll repost to let everyone know how it turns out. Thanks again -kory
 
moper said:
Again you want to be careful - I'd go straight to the Edelbrock website - there are different versions of the same CFM rated carb. For the most part anything with an electric choke and AFB-based is base calibrated for economy. The 1406 is the economy calibrated 600cfm electric choke. The 1405 is the performance calibrated manual choke 600 AFB-based carb.
If you are looking at starting "from a clean slate" my first choice would be the 1806 Thunder AVS 650 cfm. It has the tunable secondary air door (handy for smaller engines) and the electric choke with a performance out-of-the-box calibration... And I'd order the strip kit....lol.
Click to expand...
Best answer yet. I would go with the 1806 on your set up and fine tune it.
 
1406 elec choke version is lean on a a warmed up 318, cruise surging is the common symptom.

Kory, if the carb u like is dead off the line lean and fat as Hell up top...then you just need to tune it. Fatten the primary and lean the secondary out....but in the end if you find its never quite right.....its because its too much carb 'or your skills are lacking , in which u shpuldnt be in denial of if so' . Sometimes what we think feels better...isn't really better when reflected in the et and 60ft.
 
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