Technical The Rochester 4GC on my 283 needs rejetting I guess...

The 283 in my ´34 has ran about 500 miles since I built it. It´s been bored to .030 , zero decked,steel shim head gaskets, ported and surfaced power pack heads ( a little over 10:1 CR), portmatched stock 4 bbl manifold and a mild cam (212°/212°@.050lift). It has the stock 4GC Rochester carb that it came with from the factory. It idles perfectly smooth, runs and performs great at cruising speeds and normal acceleration. Under full throttle it gets angrier at 2800 and really bites at 3500rpm. Problem is that I think it´s leaning (?) out to the point it bogs and pops at 4000 rpm and above. I feel like it really starves of fuel at about 3700-3800 rpm. It is worse when the weather is cold, once it´s warmer the bog comes in later, but I can feel the lack of power and the plugs are white. With an Edelbrock carb I´d go 2 steps richer with the metering rods and main jets and go from there, but I have no experience with the 4GC other than I rebuilt it once. Maybe one or two of you have an idea what jets I should order and start with ?
Oh yes, timing is set at 10° with a max 34° at 3200 rpm.

 

I doubt that the jetting is the problem....

 

I hoped you´d chime in, Jim. Where would you start?

 

What fuel pump?

 

I'd start with fuel supply, then look into the ignition system, and then maybe see if it has enough valve spring, etc.

 

I got a stock replacement carter pump from rockauto .

 

A lot of bad history from that pump. Do as @squirrel mentioned.

 

Do you have more information and pictures of your cam? I’ve got a pair of 283s and power pack heads and am planning something similar, and would appreciate any feedback on the cam.

 

Hmm, good ideas… I‘ve already played with the ignition system enough to say that‘s most likely not the issue… now that I‘ve said that loud, I‘m sure there is a bad pertronix or coil in my future But I have a feeling that fuel supply or valve float are more likely…. I figured the cam was mild enough to get away with stock style springs….but I have a history of being wrong, just ask my wife

 

I was wrong, the cam is 204°/214°@.050 wit 112° LSA and .420/.442" lift
https://www.edelbrock.com/performer...BNBcaTfMsrRwc8FW0KCkYQatdmHqWMP1sUJYhPcHXN**6
Lately I´m trying to find unused old cam kits that have been on a shelf for a couple of decades, because I trust the old lifters more than the new ones. This was the case with this cam kit. I figured this one was mild enough for a 283 with a little effort put in. I´m very happy it runs pretty stout for such a little engine.

 

... up to 4 grand.

 

OK, that´s new to me. I´ve had good luck with carter before. Ihave a clear fuel filter on the car, maybe I can set up a camera to check if it runs dry under acceleration. I can not produce the symptom by just revving the engine with no load. It´ll go to 6 grand just fine.

 

Thanks. I’m planning to use a hydraulic roller cam for the same reason. Just wanted to see what your cam specs are. That sounds like the cams I’ve been looking at for duration and LSA. Those heads are pretty much maxed out for flow after 0.400 lift, so no reason to go bigger on lift.

 

Bought 3 carters for Chevy 350. All bad. Had to go the the auto supply brand.

 

A fuel pressure gauge is usually more helpful for this. Clear filters often have a lot of empty space in them when the engine is running, so it's hard to tell exactly what's going on.

 

I agree, 9 times out of 10 it’s either fuel or ignition. I’d start with ignition. Do you know where the dizzy is coming in at full advance? If you have access to a distributor machined that would go a long ways in setting up on the ignition. As far as fuel go out on a country road and make a full throttle p***. At the end shut the motor off and pull over to the side of the road.Don’t idle the engine. After you’ve stopped pop the hood and pull a couple of plugs. Look for the coloration of the plugs. ***uming you don’t have an oil issue Light tan you are in the ballpark. The darker the richer your mixture is

 

Could be the spring under the arm on the fuel pump be boken? I've seen it before, worth checking!
Can you borow a GOOD fuel pump from a buddy, then do a couple test runs? I'm thinking a defective pump. Carter SBC pumps are curently made in CHINA... a buddy had one fail out of the box, another guy 2 bad ones! Their reputation has gone to hell.

The pump on my '57-283 went out a couple weeks ago. I asked around, seems that all the new mechanical pumps are from China or parts of Asia. Even the Edelbrock's are using Chinese components, and aren't lasting as long as they should. What USA pumps are available here, are EXPENSIVE!

Carbking and another gent recommended rebuild kits fom Then and Now Automotive in Weymouth, Maine. My pump had stamped-steel covers, wasn't rebuildable. A buddy donated a couple #4460 cores that have 10 screws. I'll rebuild both pumps, cary one in the trunk. The kits were $52.00, plus shipping.

GOOD idea for the fuel pessure gauge... any of us determined to stay with a mechanical pump might need to run one these days!

 

There’s a shop in Texas that sells obsolete parts. They seem to have everything. I got some main bearing for my Desoto hemi several years ago

 

I would look for NOS parts. Usually, with the Pertonix they either work or you nare stranded.

 

Yeah,that makes perfectly sense!
I would never have doubted the new fuel pump…

 

The distributor maxes out at 34*@ 3200 rpm. I did just that and all plugs are snowwhite, what made me think of a fuel supply problem….

 

Just saying A removable O2 gauge would save so much time ,
Most pump gas @ leat here in states New blend is so hard to read , I would say Snow White
Its severe Lean .
Look @ moldean tail pipes Black
& they computer controlled
with emission.
I think to add few more deg's of Btdc
To 14-16 ,
But not your issue, just a better running engine , total timing would need experiment with ..
I had a set of plugs one time
Bad @ about 4,000 rpms only ,

 

yeah, an O2 gauge is very helpful!

 

I am not convinced your issue is not ignition related, but after hundreds of "carburetor issue" customers that I solved by suggesting dropping in a points distributor for testing; I am a confirmed pertronix skeptic! If one is installed, it is the first item I test.

All of us can guess, but testing is the answer.

(1) Results with a known points distributor would confirm / deny the distributor, but not the coil.
(2) If the electronics are good, then fuel supply FIRST.
(2a) Fuel pressure gauge to see pressure at WOT during breakup.
(2b) If pressure is low, or non-existant, rebuild of stock pump, or better aftermarket.
(3) If both ignition and fuel pressure are good, then:
(3a) The 283 Rochesters came with fuel valve number 7012144 (0.098).
(3b) Fuel valves with higher flow: 7023809 (0.101), 7023013 (0.118)

Be very careful about jumping to the 7023013 if this is a street cruiser, as fuel leakage at idle / low RPM is a real possibility.

Jon

 

@carbking
Probably a dumb question to ask
& did not look up
The term & part a
Description of Fuel Valve ? Power V
Some call a coil a Igniter .
Push rod , push tube .

 

Probably lucky it doesn't want to go over 4 grand, ..with that zero deck and steel shim head gasket ;-)
What is the gasket thickness? Piston to wall?
Oh yeah, about jets..***uming it's a Power Pack 283 carb....Low 60s in the front and mid 60s in the rear, ***uming the power valve is stock and functioning.

 

19Eddy30,

Fuel valve a.k.a. needle and seat ***embly a.k.a. float valve.

Or the valve(s) controlled by the float(s) to regulate fuel flow into the carburetor.

And while I did not mention the term: power valve a.k.a. economizer valve.

Jon

 

If you have same type ****ty ethanol mixed gasoline as we have in finland, i suggest four numbers bigger jets.
I put xe262 cam in 390fe and it needed about 20% bigger jets to start functioning. Stock autolite carburetor.

 

Do you happen to have or could borrow any other known good carburetor ever a 2bbl with an addapter you could swap on and rule out ignition, valves ,timing and other problems in about a half hours time and then if you find it to be the carb it's already off for repair.

There is no color on the plugs and even with today's fuels that make it hard to read there should be something. That's generally not ignition or valves .

A inline fuel pressure guage is cheap and fast . Should know what your pump is putting out any way .
Restricted needle and seat , could also cause this.

 

Or if you can find an older 4 gas or cheap 5 gas ****yzer.