55.2-59 Apache running too rich

[chevyfiftynine]

I have a 58 Apache step side, column change 235 with twin Rochester B carbs and Offenhauser inlet manifold. Ever since I've had the truck it has always run too rich. It starts and runs fine, but the plugs are always black. These are the things I've done recently to try to fix it but with no success -
1. Checked fuel pressure from electric pump 2. Adjusted float levels 3. Fitted two new carb kits 4. Got recon back carb to match front.
5. Checked operation of choke. 6. Removed air filters and replaced with aluminium mesh to let more air in 7. Reduced jet sizes from 50 to 46.
The jets are down 4 sizes already, but is it possible that they should drop another 4? I can't think of anything else to try.

[dsraven]

it would be good to know what the cfm flow rate of each carb is, maybe you are over carbed for the engine and rpm you run at mostly. look online for a set up guide for the carb model you have. also check the heat range of the plugs you are using. maybe go a step hotter in the plug heat range and see if that helps. check the coil output. adjust the valves and timing, check distributor centrifugal and vacuum timing advance mechanisms, set base and max advance etc etc.

[mr48chev]

Read though this thread on Stovebolt talking https://www.stovebolt.com/ubbthreads...er=897644about a Rochester B running rich.

It might help you double check a couple of things.

I found out the hard way a long time ago that you always save the old gaskets or what is left of them and match them to the new gaskets out of the kit to make sure you are using the correct one when the kit gives you choices and then make sure that the right holes and passages are exposed. That may or may not be the issue but it is something to consider.

If it works close to perfect except for being rich it still may be that you have more fuel flowing than the engine can handle and need to go down on jet size.

[chevyfiftynine]

Thanks for your replies. When I kept taking the carbs off and putting them on again I broke a couple of gaskets and replaced them with non-identical ones that were in the carb kits that I got a while ago. The truck runs well, but I wonder if I've used the wrong gaskets. It has an electric pump and the fuel runs through the mechanical one. I know the pump pressure is okay, but is it possible it would deliver less fuel if I went back to the original? There must be some limiting device between the pump and carbs to reduce the amount of fuel being delivered, although I've never heard of one. Maybe a tube that narrows to slow down the volume? Another thought is that maybe the fuel is being increased in volume by running through the mechanical pump. The distributor is electronic and hasn't given me any trouble, and the coil is built in.

[dsraven]

if you have an electric pump then run a bypass for the mechanical pump. all you have done there is make it harder for the electrical pump to move the fuel, like a head pressure to overcome for the electric pump. the other thing that can be happening is the electric pump and the mechanical pump in tandem are putting out too much pressure for the carb inlet valve to keep back, causing a leakage that overfills the float bowls. I would do a pressure check on the system right at the carbs and see what you have. possibly install a pressure regulator in the line before the carbs.
if you have an electronic distributor it will likely also have a mechanical advance in there with centrifugal weights and spring. there are recurve kits available and block plates to limit the total advance. it is pretty common to have a centrifugal weight system that is sticking or seized. although electronic it still requires maintenance and since it is likely a "one fits all" scenario for the engine it might be good to know what the advance curve looks like. maybe not exactly what it could be for max performance of your engine since it has dual carbs etc. when recurving a distributor the shop would want to know cam, intake, carb set up, exhaust system type, any other internal mods done. not saying it is wrong, just saying it is something to check.

[dsraven]

also, with the dizzie, check the coil for heat spots, a good ground circuit, dizzie shaft wear, mechanical advance, vac advance if applicable, rotor integrity, cap contact integrity etc. plug wires, plugs, etc. you should have a good hot spark on a spark tester. when you get it all figured out swap in a new set of plugs. rich mixture can play havoc with the porcelain insulators and cause misfires down the road.
I would do a complete tune up including all the stuff talked about earlier because it all has an effect on performance, carb tuning and timing advance adjustments.

[chevyfiftynine]

Thanks for reply - I'll check the dizzie to start with, and also all the HT leads which haven't been renewed for years, and get a new set of plugs too. I'll try by-passing the mechanical pump, and it would be good to know if the old pump still works and what difference it makes to the fuel intake. I don't know why the fuel line didn't go straight to the carbs and not routed through the old pump. It'll be interesting to see what happens. I'll let you know.