Carb Tech Questions '72 IH "Brick" Pickup

[plottek]

Recently, I drove my cold natured '72 345 to a local mechanic to replace my 2 bbl setup with a 4 bbl reblt holly and have new exhaust manifold gaskets installed. After a month, they can't seem to get it to run, again. It will idle just fine with the choke completely closed, but when gas is applied or the manual choke taken off, it just dies. Compression is fine; fuel pump is a 3-4 lbs constant; timing advance appears to be working; the "ole timer" that rebuilt the carb has gone over it twice and found everything to be working properly inside the carb; and the timing is slightly advanced.

The mechanic admits that, although he remembers carb systems, he has had more experience with fuel injection over the past several years. My carb man thinks there is a vacuum leak somewhere. The mechanic thinks the distributor May be bad, although it advances when gas is applied.

I would appreciate any insight that you guys might have with this situation. The mechanic has just given up and is willing to have me tow the truck home.

Thanks,

fred from alabama

 

[RobertC]

More information would be useful:

what manifold was used?

What list number / model Holley carb?

Sounds like a vacuum leak to me... I assume your mechanic knows to spray starter fluid / berryman's around the base of the carb / intake manifold?

Also, the intake manifold has "plugs" in the bottom.

Did somebody check that they were there; not rusted out; no "holes"?

 

[plottek]

Didn't think there were manifolds out there that would not match the motor. The bolt pattern did match perfectly, though. We sprayed around the carb base and didn't see any signs of a vacuum leak. We did not check for rusty plug in the manifold prior to installing because it appeared to be in very good condition...no rust anywhere.(but it could have been "dressed" up...the guy that sold it to me was pretty knowledgeable and seemed trustworthy.)

we'll check for leaks around the mani tomorrow. Right now the carb guy and mechanic are pointing at each other.

Thanks. Fred

 

[RobertC]

The question is not whether it "bolted up" --

it is where / which IH engine did the manifold come from (other than a trustworthy fellow)?

392? / 73 and older? / 74 - 75? / smog engine? / non smog engine? / late 70's Scout II 345 engine?

Might not be pertinent, but it might be useful to michael mayben who will be doing the real diagnosis...

He will also need the Holley list number / model... / part number from the airhorn of the Holley carb...

 

[Michael Mayben]

There are quite a few variations of any version of an sv intake manifold...but a 345 and 392 manifold will interchange on the heads. A 266/304 intake will not fit on a 345/392 due to major difference in block deck height.

Some manifolds have a very different intake "plenum" area and only a few carbs will fit without some re-work. A later "egr" intake will allow any carb to be mounted (within reason).

And is the manifold you installed a "square bore" version or a spread bore version and you used a carb adapter? If ya don't know the details of the manifold post some nice pics of the top so I can see what ya got.

I must know the carb list number taken from the air horn stamping so I can determine what it's root application is. These carbs are decidedly not "all the same"!!

I'm moving this thread to "carb tech" so it will be more easily searchable in the future...thanks for joining up with us!

 

[plottek]

I am working on getting sn's as you suggested. In the meantime, how would I know which carb to get if I need to purchase another Holley? Is there a database that would tell me the correct match for the engine block sn if I can locate it?

Thanks, fred

 

[Michael Mayben]

I am working on getting sn's as you suggested. In the meantime, how would I know which carb to get if I need to purchase another Holley? Is there a database that would tell me the correct match for the engine block sn if I can locate it?

Thanks, fred

The perfect carb for a 345/392 squarebore manifold install is a Holley list 80457 with electric choke. Also by far the least expensive due to it's popularity. It's very close to "right" regarding it's setup out of the box.

That recommendation is a carb that is near identical to what was oem on many 392 motors in pickups and travelalls, only a bit more "adapted" for aftermarket replacement use.

The other popular Holley 4v mixer is the list 1850, those come fitted with manual choke but can be converted to electric choke also. The pout of the box setup is not quite as "right" as the 80457 and will require a jet change, a power valve change, and maybe an accel pump cam change to dial in onna 345. That of course adds to initial expense as compared to the 80457 that is near perfect.

All this is based upon a typical "baseline" altitude of sea level through about 4,000ft.

All IH service manuals have specification tables that give nice carb setup data that is relative only to the Holley list numbers which were oem and shown in that table. Yes, we sometimes come across nice used cores of many different list Holley carbs that we can recondition into perfect mixers for those customers who are looking for "original" for whatever reason. Those oem list numbers have not been available for sale new in over 20 years...though some dealers/some parts distributors might have some around. But a new 20 year old carb that has set will need a complete overhaul, no matter how it was cared for!

This past year, Holley performance has released some new production of some of the popular "muscle car" carb list numbers for the crowd that plays with those rides. These are not "re-pops" but new production of the original carb systems. But they are very pricey and there are no IH app versions of those carbs in that very small market! But for a z28, or some Ford rigs, those are a super deal!

 

[plottek]

Apparently, the carb that I have May require a jet change as you have indicated. The list no on the carb is 1850-1. Right below is 0357. I had this one rebuilt by an old timer at advance auto (who does this rebuild stuff on the side).

The manifold has a number stamped on it 151539.

Today, we smoke-tested through the pcv valve in the valve cover and found no vacuum leaks. Looking down into the carb when idling and then accelerating, there is a steady stream of raw gas, which indicates to me that the accelerator pump is working. But, open the choke for more air and it just stops running.

The timing is set at 20 degrees adv, at 400 rpm, warm. The vacuum advance is worn out and needs to be replaced.

Perhaps the jets need to be replaced.

Fred from alabama