inline 6 carb. question
 

I am installing a Clifford intake and headers on my 250 inline. I was planning on using a Holley 390 but they are pretty spendy. There is an Edelbrock 500 cfm on the parts board. I have heard of a few guys using them. Anybody have an opinion. Stock cam and so forth. Thanks

Re: inline 6 carb. question
 

500 is big for an otherwise stock 250, why switch to a 4-barrel with no other upgrades? With a cam and headers it would be OK, but not on an otherwise stocker.

Re: inline 6 carb. question
 

I have a 1403 on my 250 with a stock cam. I messed with the jetting and came to the realization that the stock settings were the best. Just bolt it on, set the idle and mixture and go!

Re: inline 6 carb. question
 

That's what I wanted to hear Brad. Thanks. Are you using a water heated intake? I have a Clifford but it has no water passage. I was thinking of trying it without. I can add it later if needed.

Re: inline 6 carb. question
 

Brad, how does it work? I know the theory behind volume vs CFM and a 750 is too big for a 350 and I have used them without issue, so a 500 is too big for a 250, but in this case, the 250 is bone stock whereas my 350's were hopped up. I don't doubt it would work, just how well, and would a 325 work better? I have a 250 with a 4-barrel intake, and a 500 carb, but I plan to stab a cam in it and a header and maybe a turbo too, so I guess I wonder if MPG and driveablity wouldn't justify the smaller carb?

Re: inline 6 carb. question
 

The Holley 390 carb might work better assuming it was optimally adjusted, but that's pretty tricky to do whereas the 1403 works right out of the box.

Re: inline 6 carb. question
 

I've messed with inlines for quite a few years now.Not the later 230-292 Chevy types but the older GMC 302 inline 6.
The last one I built recently was a 302 with a moderate cam(215 degrees at .050. lift),tube headers,9.25 actual compression ,water heated Clifford 4 bbl intake.This combo makes about 230 hp at 4500 rpm,maybe 320 lbs. of torque at 3000 rpm .I found through a lot of road testing and carb rejetting that a 400 cfm carb is all this engine needs.Larger cfm carbs din't help performance.This engine is in a 2900 lbs 37 Chevy truck with 5 speed.
I also found that this engine needs a richer full throttle mixture than a typical V-8,especially at the torque peak around 3000 rpm.As the engine winds up near peak power the mixture could be a little leaner,not exactly possible with typical 4 bbls,so it's a compromise.
I don't know if my experience can apply to the later inline 6's but it should be somewhat similar.
I would say a larger carb works better at higher rpm's. For street driving with 250 cubic inches ,5000 rpm maximum,350 cfm should be fine.It's best in my opinion to use a smaller carb gving better throttle response and economy at the rpm range normally seen and give up a little on top end that's rarely seen.The Clifford intake has fairly large runners and under carb plenum making the carb bigger than it is so to speak.
It's your engine,tune it the way you want is the only way to know for sure.

Re: inline 6 carb. question
 

Here are some pics of how I routed my heated intake. I'm really not sure if it's needed but I figured I'd hook it up anyway, due to living in the PacNW. It's an older model intake before they had the box under the manifold and I had a box welded on directly underneath the carb (it's probably the same older style that you have it sounds like). I've thought about running copper lines instead of the heater hose, but haven't gotten around to it yet.

Re: inline 6 carb. question
 

Hey Brad, I like your clutch rod. Looks familiar.:lol:
Dave -- I used to run the 390 Holley on a .030-over 292 with Offenhauser intake and Clifford headers. It lasted about 25 years. But when I rebuilt, the Holley wouldn't set up any more, so I got an Edelbrock 1404. The 2005 build was the original '68 292 block, also bored .030 over, but with bigger intake valves, Crane 260H cam and the same intake and headers.
Carter used to make a 400 CFM version of the AFB carb, but when Edelbrock took over marketing of this style carb, the smallest CFM 'Performer' they sell is the 500. Don't be afraid of the numbers. The secondary valve system is a demand type design. It flows only as much fuel/air as the engine vacuum demands.
Personally, I prefer the Carter/Edelbrock design for its ease of tuning and rebuilding. Holleys are great when set up right, but I'm no rocket scientist.

Re: inline 6 carb. question
 

Brad, I think I will go with the box under the manifold like you did.
I found a good deal on a Holley 390 so I am going to give that a shot. I'll let you know how it comes out if I ever get it back togehter :)

Re: inline 6 carb. question
 

Any updates on this topic? Im about finished with my 250 rebuild. Still not sure which Carb to use?

No need for aggressive, its a Sunday Cruiser Blazer. Just want something easy and reliable. Im leaning towards the Edelbrock 1406 just because I have had a few of them in the past...

Re: inline 6 carb. question
 

The 1406 is a 600 CFM carb. More than you really need for a street L6. I run a 1404 [500 CFM] on my overbored 292. [296 CI w/ .030 over]
Very happy with it.
I prefer manual chokes. A 1405 w/ manual choke is the same 600 CFM carb as the 1406 with electric choke. I run one of those [actually a Carter AFB 9605S] on the 350 V8 in my '71 Jimmy 4x4.
I think the 1403 is the electric choke version of the 1404 500 CFM.

Re: inline 6 carb. question
 

Thank you for this, I really appreciate your comments...

Now I know this seems silly, but.... The 1406 has a "Black" version. It would go well with the color combo Im trying to go with...

Is the 600 CFM going to be harmful, cause any problems or be just a plain old bad choice for the L6?

Thanks again!!

Re: inline 6 carb. question
 

OK, So you've got a 250. right? Why do you want a carb that's made for a 350?
Drag racing? Going uphill both ways?
They used to say Less is More about carburetors.
I once tried a 780 CFM 4150 Holley doublepumper on the V8 350 in my GMC K/1500 Jimmy. Ran great on the freeway, but would stall out after getting off the offramp. Finally it ''sucked valves'' -- the pistons on #6 and #7 smashed their sparkplugs. 350s normally run 600, 625, 650 max, carbs. I wound up replacing that engine.
Now you may not get into much trouble with a vacuum secondary type carb like the Quadrajet or Carter AFB -- since it only draws as much Air Fuel mixture as it can use. But a 600 CFM carb on a 250 is too much IMO.
An Edelbrock tech rep once told me ''You can put the smallest jets you can find on a 600 CFM carb, but it's still gonna flow 600 CFM.''
''Because it's black'' is an unsound reason, mechanically. Who's gonna notice, anyway?

Re: inline 6 carb. question
 

yes, I specifically said the color of the Carb was silly question.

I didn't completely understand the whole difference between the 500 and the 600 CFM so I felt it did not hurt to ask. I still dont completely understand but I can see its just best to stick with the 500 cfm...

Thanks

Re: inline 6 carb. question
 

This.

I had a manual choke 390 on my 250 with Clifford cam, headers, HEI, and Clifford intake. I had to mess with springs and jets quite a bit.

Re: inline 6 carb. question
 

If I'm not mistaken, the Holley 4160 #8007, 390 CFM, is sold with electric choke. It has to be converted to manual choke. It was the recommended carb by Clifford when I first upgraded my 292 in 1978. [Now they recommend a 350 CFM 2-Bbl for whatever reason.] I ran the 390 Holley for about 25 years, but after an engine rebuild, it would not set up right, so I got an Edelbrock 1404 [500 CFM] since no 400 CFM AFB design was available.
Holleys are problematic, in my opinion. They had to be babied, and tweaked with every weather change [and Arizona has a wide climatic range]. The worst offender was the Power Valve which would blow out with any big backfire. Replacing it required a $10 throwaway part. Lots of tiny little parts that each needed careful initial adjustment.
I usually needed a Holley expert friend to pull off a tuneup. Bribery usually included beer and pizza, but sometimes involved cash. The Carter AFB design, I found, I could handle myself, being a lot simpler, and not susceptible to backfire blowout.
No carburator, regardless of catalog advertizing claims, is a simple bolt-on-and-drive-away device straight out of the box. But the AFB design is closer.

Re: inline 6 carb. question
 

I did finally get this truck on the road a few years back with the 390 Holley, Langston cast iron headers and Clifford intake. Ran like a bat out of hell but never got it to idle worth beans and had issues with exhaust gaskets blowing out. Pulled that out and now have a 383 stroker in it. The 250 was real tired and I didn't want to do internal upgrades.

Re: inline 6 carb. question
 

I would like to delete the Manual Fuel Pump and switch to the Electric. Any recommendations on the setup I should run with?

Re: inline 6 carb. question
 

Why?
Electric pump involves a lot more than just bolting it in. You might also need a fuel regulator, return line to the tank etc.
What carb you got.

Re: inline 6 carb. question
 

Hi Brad, would you know the part # to the cap and rotor kit you have set -up.i have mine set-up with the hei also.thanks

Re: inline 6 carb. question
 

Brad,
Do you mind sending pictures or explain where the two hoses on the Heater Box go to? Do both hook into the "Lower Thermostat Housing"? I bought a Upper and lower thermostat housing from 12bolt.com. There are 2 spots in the bottom and 1 on top?

Thanks

Re: inline 6 carb. question
 

Brad has his hooked up wrong.
Flow is from thermo housing to bottom of heater core, top of core back to water pump.

Re: inline 6 carb. question
 

Brad is a really nice guy, and one of the few board members I've actually met, but he sold his truck years ago and has not been active since.

Re: inline 6 carb. question
 

I do not have a heater core? No AC or Heater (at the moment). I did find a picture of a guy running from the Water pump to the Heater Plate, then from Heater plate to the bottom thermo housing.

Would that sound right?