The Stovebolt Site Forums The Shop Area Engine Shop Apache running too rich

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.

There is a distinct possibility you will never get it to not run rich. Too much carb. There is probably over 1000 threads over the past 22-24 years on multiple carb problems. The old school guys will tell you to make a block off plate for one carb and just run on one. No one will know but you. Good luck.

'59, with Rochester B carbs, it's possible the airhorns are warped enough to leak the power system vacuum signal internally, which can cause the power valve to always be open, causing the carb(s) to run very rich. The power system adds fuel to that metered by the main jet, so that might explain why dropping the main jet sizes wasn't effective. You may have already checked, but airhorn flatness would be an item to investigate on both carbs, if not already done. Unfortunately, tightening the 4 hold down screws can just worsen the warp.

Are the two carbs from a 235? Old-school wisdom was to drop down to the smaller 216-spec carbs if running 2 on a 235. That also gives some good options for Carter W-1 or Stromberg BXOV-2 Chevy-spec carbs that were run on 216s. Those carbs have the smaller SAE2 flange, with 2-11/16 bolt spacing, so if your manifold is for the larger (SAE3) flange carbs used on the 235 with 2-15/16" bolt spacing, you would need to make some further changes.

Just some food for thought... hope this helps.

Too much carburetor = not enough gas

Block off the power valves. With that much carburetion, you'll never develop enough manifold vacuum to keep them closed, so the size of the main jets, or other means of mixture control will be irrelevant. Then the engine will backfire, stumble, hesitate, and otherwise be difficult to run at anything other than a steady cruise on a straight and level road, but you'll still have that dual carb eye candy to look at. Alternative- - - - -find two small Carter carbs for a CJ-2 Jeep 4 cylinder engine and run them instead of the Rochester B's. Then you'll only be slightly overcarbureted instead of having the equivalent of two toilets flushing gas into your engine.
Jerry

Thanks for your replies and useful suggestions. The truck had had some major engine mods when I got it such as stage 4 heads so it's quite sporty for 2 and a quarter tons. I think its original carb was kept and a second added, but I suspect the idea of just putting on a duplicate might be behind the over-carburation, but there's nothing to say the bodies aren't warped or some other damage. The 216's or Carters might be the answer, but that's an expensive option if it doesn't work. Maybe if I try blanking one off and seeing what difference it makes it might give me some idea of what's wrong. At least it runs okay, but the fuel cost is too high. I'll try some experiments and get back to you.

stage 4 heads

What does that consist of?

I have the same question.

"Stage 4 heads"- - - - - - -How do you get more than one head on a stovebolt six????????????
Jerry

'Head' singular. Stage IV Remanufacture. 1. Cleaned by thermal oven and steel shot abraded 2. Valve faces and stems ground 3. Valve seats ground 4. New bronze valve guide liners 5. New valve stem seals 6. VSI shims with new springs 7. Magnafluxed milled flat and vacuum tested 8. Hard seats installed.

That sounds like a conventional head reconditioning job from a quality machine shop. In the racing business, "Stage IV" in reference to a cylinder head usually involves porting, polishing, flow-marching ports, oversized valves, and a few other specialized procedures reserved for competition-only engines. If you do those things, and install a very radical grind racing camshaft, it might be possible to make two Rochester B's function close to effectively on a 235 engine, but only at wide open throttle. Even then, it would be difficult to get any sort of good performance and/or acceptable fuel economy during low speed or part throttle operation.
Jerry