273 carb probs!!!

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rickdick78

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Hey guys, anybody have good advice on a good size carb for a 273 with a mild summit 6900 cam? Ive got a 600 cfm edel on there now, and i just feel like its way too big. I cant get it to run right.
Im really wanting an easy driver with good fuel economy more than a power house. Id rather drive it everyday!! Any suggestions??
 
I think a 600 is about what you want. Maybe the carb needs a tune or rebuild.

Im a Holley guy. If it were my car, I would stick an 1850 on it and call it done.
 
Hmm what size carb is an 1850? Im almost sure that my prob is a carb tuning prob, im not good at it and it is a very precise adjustment that i am just not that experienced in.
Ive been reading all the archive threads on carb tuning and its spinning my head. Ive read about 5 diffrent techniques that i havent tryed yet.
Any one live in the queens/brklyn area that would be willing to lend a hand to a dedicated beginner???
 
rickdick78 said:
Hey guys, anybody have good advice on a good size carb for a 273 with a mild summit 6900 cam? Ive got a 600 cfm edel on there now, and i just feel like its way too big. I cant get it to run right.
Im really wanting an easy driver with good fuel economy more than a power house. Id rather drive it everyday!! Any suggestions??
Click to expand...

That is the carb you want.
If ya keep yer foot outta it it is economical.
Floor it and it will cost ya! LOL

Anyway, eddy 600, (This is the stock replacement carb) love it for small block mopar. Make sure you use the proper spacer for your intake set up. Yes running a spacer makes a big difference for eddy on mopar.
Check the link for eddy tech videos. VERY helpful!!
http://www.edelbrock.com/automotive_new/misc/tech_center/install/tech_vids.shtml

You could also try going to the fuel section here on FABO;
http://www.forabodiesonly.com/mopar/forumdisplay.php?f=58

Good Luck!
John8)
 
Holley does make a 390 that I use on a stock 318 with duel exhaust and it runs well. Lots of power to pass and get up to speed on highway. I don't drag but I would imagine it would die at top end. Also I think I need a heat spacer, fuel boils on shut down.
 
rickdick78 said:
Hmm what size carb is an 1850? Im almost sure that my prob is a carb tuning prob, im not good at it and it is a very precise adjustment that i am just not that experienced in.
Ive been reading all the archive threads on carb tuning and its spinning my head. Ive read about 5 diffrent techniques that i havent tryed yet.
Any one live in the queens/brklyn area that would be willing to lend a hand to a dedicated beginner???
Click to expand...

Sorry, an 1850 is a Holley 600, vacuum secondary.
 
1403 Edelbrock Carburetor, Performer, 500 cfm, 4-Barrel, Square Bore, Electric Choke, Single Inlet

This is what I usually put on a relatively stock 273 or 318. It also fits the original 273 4 barrel manifold.
 
Yea i thought about going to a 500 cfm. Seams to make more sense, but ill keep at it with the 600.Hopefully i can get going. Id be real interested to try one of those holley 390. Might be fun to mess with one of those.
My biggest prob with the carb on there are the hard starts. Im sure that my ignition is working well but it takes a few trys. Frustrating!
 
If you have the service manual for your car, it will give you all the original Carter jetting and fuel metering specs for the 273 commando. My research says a 600 on a 273 is too much carb and depending on your intake setup may not give enough velocity through the carburator/intake runners to operate properly. JM$00.02 :)
 
I think 600 cfm is too big unless you plan to spin >5000 rpm. A 390 or 450 cfm would likely be better and should give better mileage and driveability. The 450 cfm I know of is the Holley Economaster (4360, I recall). It is a spread-bore pattern, so the factory manifold would need an adapter. Perhaps another spread-bores like a Thermoquad or Quadrajet would give good low end and all the top end you need. I have one of each to try on my 273.

While at it, the Offy Dual Port manifold is interesting. I bought one to try on my 383.
 
66fs said:
1403 Edelbrock Carburetor, Performer, 500 cfm, 4-Barrel, Square Bore, Electric Choke, Single Inlet

This is what I usually put on a relatively stock 273 or 318. It also fits the original 273 4 barrel manifold.
Click to expand...


I agree with this 100%. The stock Carter carb cfm size was 500 cfm.
 
Hey Rick I am not a big fan of Holleys but since the only eddy I could find was a 500 cfm I tried the 390. Holley has a great website that explained how they work with vacuum secondary's. They are saying you should not feel a kick that they should only open when manifold pressure requires it so a 600 will not open or should not open until it is needed which on a stock small block it will be screaming, a stock tranny will shift before then so top end is the only time this will happen.So that said it makes sense that the fuel in the secondary bowl will dry up and refill before you ever use it in every day driving so going smaller make sense and still looks good when you open the hood. Mine starts great cold and very short term after shut down. I can smell fuel after shut down that is why I think I have a fuel boiling problem flooding engine very hard to start if it sits or 5 10 min. they make a spacer for this which I am going to try next season. Wow that was long winded lol.
Check Holley web site good info.
 
I would not go by those charts. It is a good rule of thumb, but I've run a 750 CFM thermoquad on a 273 and it took every bit of it.

As for the original queston, The 600 seems to have a problem. I would take the top off and set the float level and drop. Check for contamination while you are in there. then adjust the choke till it closes when cold and is wide open when it reaches operating temperature.

Summit 6900 Cam and Lifters, Hydraulic Flat Tappet, Advertised Duration 262/272, Lift .420/.442, Chrysler, Small Block

I tried most carbs on a 273 and my least favorite was a Holley 1850. It was OK when it was tuned, but I always seemed to have to mess with it. Any carb with an adjustable air valve for the secondaries is a plus on the smaller engines. TQ, QJ, AVS
 
It,s more in this than just the carb.
For example, if you have a dual plane intake it’s possible to have larger carb.
I guess 500 cfm /single plane is equal to 550 – 600 cfm/dual plane, due to the vacuum generated and secondary opening/rpm.
One other important component according to vacuum is the cam. I’m not able to give a formula, but a sharper cam generates more vacuum.
So, if you put an Eddy 600 on a single inlet with a mild cam, there will be problems with the vacuum and secondary opening.
But if you use my recipe, Eddy D4B intake + Comp cam (duration @ .015 270/270, duration @ .050 224/224, lobe lift .313, valve lift .468/.468, lobe separation 110) the Eddy 1406 will work very nice on a 273.
My do it.
 
If you ever make it north to CT I can help you with it. I think the 600 is on the edge of too big. But, it should be able to run well with it. Hot starting issues may not have anything to do with carb sizing.
 
I've had 4 carbs and 4 intakes on my 273, non-commando compression specs 8.8:1, and that being a pretty conservative cam, I'd say go no bigger than the Holley 390 in any case.
 
rickdick78 said:
Hey guys, anybody have good advice on a good size carb for a 273 with a mild summit 6900 cam? Ive got a 600 cfm edel on there now, and i just feel like its way too big. I cant get it to run right.
Im really wanting an easy driver with good fuel economy more than a power house. Id rather drive it everyday!! Any suggestions??
Click to expand...

OK, lets get serious about this carb. What, exactly , isn't it doing that it should be doing, or, what is it doing that it shouldn't be doing? Be specific. The carb guru's here need to know all this to properly troubleshoot the problem.

The 600 on it should be in the ballpark, and probably just needs some adjustments to run right. Could be vacuum leaks, or even timing issues (carb's get blamed for all sorts of issues that aren't carb-related). 390,500, 600 aren't that different from each other. Now, if you were trying to get an 1150 Dominator to work on that 273, then you'd have some issues.
 
you said hard start, are you pumping the pedal a few times before you crank it? its cold out is the choke set correctly? also is accelerator pump working and if it is is it sending to much/ just right / not enough?

273 is a small v8 as suggested the smaller carb probably better for you but that you have should work.
 
66fs said:
I would not go by those charts. It is a good rule of thumb, but I've run a 750 CFM thermoquad on a 273 and it took every bit of it.

As for the original queston, The 600 seems to have a problem. I would take the top off and set the float level and drop. Check for contamination while you are in there. then adjust the choke till it closes when cold and is wide open when it reaches operating temperature.

Summit 6900 Cam and Lifters, Hydraulic Flat Tappet, Advertised Duration 262/272, Lift .420/.442, Chrysler, Small Block

I tried most carbs on a 273 and my least favorite was a Holley 1850. It was OK when it was tuned, but I always seemed to have to mess with it. Any carb with an adjustable air valve for the secondaries is a plus on the smaller engines. TQ, QJ, AVS
Click to expand...


I wouldn't go by those charts either....the factory thermoquads on 340's were 800 cfm.....Sounds to me you have a choke issue with hard starting...."then adjust the choke till it closes when cold and is wide open when it reaches operating temperature" as stated X2
 
these charts are very conservative but there good for very flexible running. good economy throttle response and decent power. when i type response i don't mean power i mean no dead spots smooth flexible operation. just a reminder nascar truck division uses 390 carb and make huge power. 600 range. (although they would go bigger if the rules allowed them) they make big power because those engines are highly refined. but the point is you don't need large to make good power.
 
Djakken said:
It,s more in this than just the carb.
For example, if you have a dual plane intake its possible to have larger carb.
I guess 500 cfm /single plane is equal to 550 600 cfm/dual plane, due to the vacuum generated and secondary opening/rpm.
One other important component according to vacuum is the cam. Im not able to give a formula, but a sharper cam generates more vacuum.
So, if you put an Eddy 600 on a single inlet with a mild cam, there will be problems with the vacuum and secondary opening.
But if you use my recipe, Eddy D4B intake + Comp cam (duration @ .015 270/270, duration @ .050 224/224, lobe lift .313, valve lift .468/.468, lobe separation 110) the Eddy 1406 will work very nice on a 273.
My do it.
Click to expand...
I love this breakdown! What about a dual plane LD4B, w/ a 600cfm Eddy 1406, but on a stock mild cam / base model, 180hp 273 Engine? How will that run? Would it be worth the effort?
 
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