Hi guys,
i have a 350 with a 2 barrel carb at the moment and the carb is fubar so i'm taking the opportunity to swap it for a 4 barrel manifold that i have on another newer engine. Trouble is the 4 barerel seems to have a lot more going on with EGR and i guess smog kit installed onto it. Would anyone have a diagram showing what's what on the 4 barrel and advice on what i can get rid of and how.
Sorry if its a bit of a basic question, i'm an enthusiastic amateur so i tend to learn as i go along with these things.
Thanks in advance :-)

 

Will see what I can find.
When you get done you should notice a mileage improvement because a 4bbl breathes better than a 2bbl. The only time the secondaries open is when the pedal is floored. and there were many that the secondaries never opened because the only time the pedal was floored was when starting.

Make sure the 4bbl was update to handle unleaded fuel. (different material used on float needle) otherwise the neoprene would swell and produce a low float level = problems.

I don't remember just what addl pieces were on a 4bbl that influenced EGR, shouldn't be any.

 

Thanks Hanky,
Ive attached a noted picture of what i have. the notes list what i think i know and a few question on parts i don't :-)
Hopefully its clear


I will try and get some casting numbers so we all know what year the manifold is. The best i could see today is 18436672 actually on the intake manifold but i will try and be 100% on that tomorrow.
I do have a 4 barrel Holley with an electric choke that i was thinking to use but my plan for now is to get this manifold and carb working as it all came off a Buick my theory is that it will be easier to get working.

John

 

The numbers you posted appear to be the engine firing order.
You labeled 3 what's this is
One is the EGR valve, another is the choke pull off, and the last is a float bowel vent.
I have rebuilt many carbs like this and should be able to help you out. Lots of people complained about those carbs , most likely because they didn't know how to adjust or repair them. It would be a smart move to get hold of a rebuild kit they are pretty much the same. The literature in the kit will provide the specific adjustments that apply to each series and that is determined by the 6 digit # on the side of the float bowl. I may still have the Delco parts and service manual for them.
I enjoyed rebuilding them because they required critical adjustments, but when done correctly and in the proper sequence the vehicle performed like it was supposed to and ran like a charm ! You can do certain ball park adjustments on the rebuild bench, but fine tuning was done on the vehicle from choke settings to idle mixture adjustments.

 

Thanks again Hanky, your a star. I can't believe i didn't spot that the number was a firing order - DOH !
As you have expected i'm sure, a couple more questions.
- Where would the float bowl vent be attached to, is it fuel that comes out or just the displacement of air ?
- the" Vacuum port to 3 places" that i have since found out is a EFE/EGR switch had the highest on the side connector broken off and the pipe loose that is from the EGR valve, i have simply put it onto a free connector below it but that now begs two questions, is moving it to the different port still going to work correctly ( i.e. does the switch turn on different ports at different times) and what was the port below it for ? can i simply block it off ?
I've gotta be pushing your knowledge of the fine detail on this so sorry about that but i'll be damn impressed if you do know or can find out .

John, in the UK by the way

 

Hi John,
Glad to be of any help, my pleasure.
The bowl vent just went out to the atmosphere.
The vacuum "tree" as they were known were controlled by engine temp and had one port to which was fed manifold vacuum.
when the temp rose high enough the vacuum was allowed to now pass through and operated the EGR valve. The main purpose was to control NOx emissions.
Most of the time the EGR operation was disabled because it caused some hesitation. If you can't locate a replacement vacuum tree , let me know and I will see if I can locate one.You don't really need it to make the engine run nicely..

The first or top port of the tree was I believe where the vacuum was fed in, the second one down went to the EGR valve and the lower one was a vent to release the vacuum from the EGR when manifold vacuum came up. The EGR valve is supposed to be closed at idle (high vacuum) and load increased and vacuum dropped some was allowed to open the EGR valve. This goes back a ways for me , but I will check to make sure I gave you correct info.

 

OK, Totally impressed now Hanky. Thank you so much, i'll be doing the transplant over the next day or so. With this new information i'm confident it will go well.

John

 

OK, full of confidence i made a start on the swap of the 4 barrel manifold from my spare engine ( approx late 70's at a guess ) to my 68 engine which was previously a 2 barrel manifold. Got to the point of actually fitting the replacement and i eventually worked out why it wouldn't sit right. Turns out there is a locating pin at both front and back on the engine however the 4 barrel manifold does not have a rear hole that locates over it. See pic attached.
So now do i simply remove the locating pin or is this trying to tell me that this manifold is a no no to fit. the valley gaskets all match and all else looks to be in the correct place so i'm suspecting the answer is simply remove the locating pin but i need advice to be sure.

 

John,
I don't know the answer to this problem.
I would suspect the years the manifolds came from could have some bearing on the answer.
I will look through my literature to see if I can come up with a satisfactory answer.

 

Thanks Hanky,
i had a look on TA Performance at it does look like their replacement manifolds don't have that location hole either.
Just as i thought i had it all sorted !!