2 X 4 Carb. Problem

[Joe Fisher]

I posted this question a while ago and I would like your thoughts.
I built a 283 .040 over, 151 hyd. cam, stock heads, pocket ported, port matched and multi angle valve job. The 2 x 4 set-up is a correct 270Hp unit.
The two front plugs, 1 and 2, were constantly fouling. I checked all the common problems, compression, valve adjustment, spark, timimg, I used hotter plugs, Autolite 86's, everything is new. There are no vacuum leaks, no flooding, no fuel drip while running. The engine starts immediately, no matter
how long it sits. The jets, metering rods and idle jets are stock.

What I finally did was cut a piece of aluminum flashing, and put it under the front carb.
Since then I have not fouled a plug and the engine runs great. I even participated in the Stars & Stripes tour into NYC on a 105 degree day and it ran flawless.

It was suggested on this board to call Bob Knutz, so today I did. I told him I got his name from this board and heard great things about him. I told him my engine set up and when I mentioned the 151 cam, he said that that was my problem, it was not correct for a 283. I explained what I did and asked
if the 270HP jetting was too rich and should I go to the 245Hp smaller jetting. He again said to get rid of the 151 cam. I asked if I could purchase the jets fom him and he said no.
So I thanked him and hung up. I was a little surprised that he kept blaming the cam and not the carb. jetting.
Sorry for the long story. Your thoughts and anyone know where I can purchase smaller jeting and larger
metering rods?

[Duke W.]

Re: 2 X 4 Carb. Problem

I don't think it's the cam. The 151 is very close in overall duration to the Duntov used in the 270, but the exhaust lobe is advanced a bit and the inlet retarded a hair for less overlap. The inlet/exhaust lobe centerlines are 108/112 for the Duntov and 110/118 for the 151, The lobe separation angle is just the arithmetic average of the two so the Duntov is 110; 114 for the 151.

Because of the less effective overlap the 151 will pull a few more inches of manifold vacuum at any given idle speed, and since idle and off idle fuel is metered based on manifold vacuum it might run a bit rich with the 151 relative to the Duntov with the same idle mixture settings, but it can probaby be tuned to work reasonably well by leaning the mixture screws a quarter to half turn.

I understand the 245 carbs were set up a bit different, but in '63 the 300 manual tranmission and 340 SHP engine used the identical AFB. It always amazed me, but that's how flexible the AFB was. It could work with a mild cam or a "3/4 race" cam as we used call the Duntov.

The 2x4 WCFB setup is known to run rich and have a propensity to foul plugs, and I think John Hinckley can give you some tips on how to keep them tuned.

Duke

[John H.]

Re: 2 X 4 Carb. Problem

I found there were two key issues on my '57 270 to keep it idling smoothly and to kill its hunger for plugs. The front (secondary) carb is strictly an idling device 99% of the time, and its throttle plate needs to be fully closed to make sure it's not drawing idle fuel through the transfer slots, which will foul the front plugs. This is adjusted by bending a tang on the primary throttle shaft lever on the driver's side of the linkage which bottoms out on the carb casting (no stop-screw adjustment). The other issue is plugs - it would foul any standard-length plug (like AC R44's or R45's or equivalent) one after another. Fouling pretty much ceased when I switched to extended-tip plugs like AC R45S or Champion RJ14YC's. Ignore the Owner's Manual and Shop Manual plug recommendations for 43's, as they're WAY too cold; they were superceded by a running change in production to 46's due to massive customer complaints of plug fouling, but that never made it into the Shop Manuals.

Another issue is secondary carb linkage adjustment/action - where the actuating rod slides through the two bent ears on the secondary carb lever, it tends to bind, preventing the carb from returning to full-closed position; I reamed out the holes slightly in the "ears", made sure they were exactly perpendicular to the actuating rod, polished that portion of the rod itself, and coated it with a light film of Lubriplate, and it never bound up again. It also helps to use two gaskets under each carb to elevate them slightly; with one gasket, the primary throttle shaft arm on the passenger side tends to ground out on the top of the intake manifold runner, which will also hold the primary throttle plates partially open.

The engine runs 99% of the time on the rear (primary) carb, and the design of the manifold makes for lousy mixture distribution from the rear carb to the front cylinders, so idle and the primaries are jetted on the rich side to avoid leaning-out at #1 and #2; this results in richer overall idle mixture than you have with a 1x4 setup, with lots of unburned hyrdrocarbon aroma - nature of the beast.

2x4's are fun, but they DO require periodic attention - just part of the "2x4 experience".

[James F.]

Re: 2 X 4 Carb. Problem

Joe,
You have an interesting post.Not sure why aluminum flashing would cure your plug fouling. Maybe you could double gasket the carb to manifold, which is what '56 2 X 4 owners are called to do. Changing Jets: Should you desire, you can figure out the hole area of your present jets and then check and pick an available AFB jet which has a smaller hole area. Lot of work. WCFB are made to easily change rods. I suggest you contact Chuck Smith (818) 222-5757 and order two pair of 1356 rods. These rods are for '56 2X4 BBL. They lean out the carbs. Chuck may as well have other suggestions. Regards,

[Joe Fisher]

Re: 2 X 4 Carb. Problem

Jim,
I put the aluminum flashing, with no holes, under the front carburetor, between the carburetor and the gasket.
So now I run 100% on the rear carb.
John,
I am running #86 Autolite plugs, equivalent to R46S. I did have the front throttles completely closed, but I noticed that the transfer slots were still exposed.
I was thinking of use a smaller idle jet in the front and a .031" in the rear.
Duke,
Thanks for the info. My manifold vacuum is 15" at idle.
I know these can be a pain, but I wouldn't trade them for anything.
I will keep at it and will keep you informed.

[Kris Schmalenberg]

Re: 2 X 4 Carb. Problem

I find it a little bit odd that Bob just blamed your cam. I have a 270 HP 283 in my 58 and when Bob rebuilt my carbs HE suggested that I calibrate them to the 245 HP specs. One other thing I did was to set the idle mixture screws properly with a vacuum guage and then lean each screw out the same amount. Keep leaning them out a little bit at a time until you notice a driveability problem on the road. This will give a rough shop idle but it will be super smooth on the road. I used to have a problem every time I stopped at a light but now things are great. Using a heat sheild under the carbs is also a great idea. Good luck!

[Robert Willis]

Re: 2 X 4 Carb. Problem

My 57 has a 151 cam in it and 1st design WCFB carbs and I have no problems at all. I had a problem like that once after the plugs got some miles on them but I just went one heat range hotter to offset the 3.08 rear and low RPM useage.