1951 OC3-42 Smokes On Acceleration, Smooth Under Load

GlenT · December 15, 2014, 12:53:26 AM

I am slowly getting the old OC3 fixed up but need some ideas.

So far I have replaced the magneto with a rebuilt XB4000 Distributor (XH1113 mag. look alike). The timing is right on and the advance works well.

Replaced the spark plugs with AC R45S and the spark plug wires (copper core).

Overhauled the Marvel carburetor.

Today I took it out for a run after putting the overhauled carb. on and it ran well but sure does smoke on acceleration. It is running way rich. When I say it ran well, it seems to do fine (doesn't miss) going up my hill or whenever there is a load but, at any speed without a load (not in gear) there is random missing every second or two (a mechanic friend used to call this slobbering). After checking the new plugs, they were all full of soot after only a half hour or so. The smoking is on acceleration and isn't nearly as bad at a steady RPM. I think the smoking is from an overly rich condition rather than from worn or stuck rings (good compression). The smoke is mainly black with a little blue.

Nothing has helped the OC-3 that I have done.

While it was still warm, I pulled the plugs, gave it full throttle, and did a compression test. All four cylinders were between 115 and 120 PSI. I have a reduction starter on the engine so it did crank quite fast with no plugs in it.

I didn't check the carb. float for leaks but did set it to the standard 1/4" above the gasket. I soaked the carb. with the jets out for two days in carb. cleaner and blew it out with compressed air well. This carb. does not have the adjustable main metering jet. Would a leaky float cause the engine to "slobber" while running with no load? I would think a leaky float would cause a flooded condition.

There is very little blowby watching the oil filler tube. I can just barely see a little smoke sitting in the tube but there is no noticeable puffing.

I replaced the 10W-30 oil with Mobil Delvac 15W-40 just to see if the smoking would be reduced with heavier oil and it wasn't.

So, things I have thought about checking now is the carb. float for leaks but I can't think of anything else. I thought maybe I had bad rings or valves but the good compression test rules that out, right? I didn't check whether the carb. was the correct Marvel. I have read here that it should be a TSX 403 or 406. I assume mine is a 403 since I can't adjust the main metering jet. Would valve guides cause the random miss with no load and sooty plugs (all 4 plugs)? I used to have a Chevy 283 and 327 and both would smoke on acceleration because the valve guides were worn which was a common problem with those engines.

Anyway, I'd appreciate any help figuring out why the engine is running rich and smoking on acceleration.

Blake Malkamaki · December 15, 2014, 02:30:37 AM

Black smoke is too rich. I bet you have the wrong carburetor. You could jet it down, but it would take a lot of tinkering to get it right, whereas and adjustable main jet would be easy. What is your elevation?

Blake

Doug424 · December 15, 2014, 03:50:48 AM

I agree it's a jet problem. You might have the wrong carb, a lot of different carbs will fit that engine. Even having the right carb going by the model # still doesn't guarantee you have the right main jet size. I've cured problems like that by taking out the jet, filling the hole with solder and re drilling it to a smaller size. The jet should have a number on, at least most that I've worked on do. If you take the carb apart, see if the jet has a number on, or if you have wire gage drills, see what size fits. You could then compare that to another OC-3 carb. I have a lot of them, but I think most of mine have adjustable main jets. The fact that yours doesn't have that, makes me think someone put the wrong carb on your engine.

Jack in NB · December 15, 2014, 09:24:42 PM

Hi Glen -

Might be worth a try to lower the float level 1/8" or so first. That in effect leans the mixture.

Another possibility is a restricted air cleaner or duct, although you probably cleaned that up thoroughly in your earlier work.

GlenT · December 15, 2014, 11:37:49 PM

Good idea Jack. I checked today and the carb. is a TSX 403 and the main jet is a #130. I'll try lowering the float. The carb. is off now. I plan on giving it a good workout to try and loosen the compression rings also. If all else fails, I'll give it a ring job (hopefully that is all that is needed) this Spring. I'm thinking the cylinders are in pretty good shape with 115 - 120 PSI compression on all cylinders. I thought the compression rings usually wore out long before the oil rings but I don't know much about the Hercules engines.

Blake Malkamaki · December 16, 2014, 01:17:39 AM

What makes you think the rings are shot?

Doug424 · December 16, 2014, 03:17:24 AM

Thats not a bad compression reading. Does it have blow by? You might just be wasting money doing a ring job on it. There is a spec for the float level, I would check that before I just lower it. If you are getting sooty plugs, not oil fouled plugs it's excess fuel that's causing it, not bad rings.

GlenT · December 17, 2014, 01:06:24 AM

Blake and Doug, I think you are probably right on the rings not being a problem but it may just be wishful thinking on my part. The plugs were just sooty. Does anyone know if the main jet is supposed to be a #130? That number was stamped on the little jet and does the metering of the fuel and there is no adjustment on the TSX-403. I'm wondering if the wrong jet is in the carb.? There is very little blowby. I watched the oil filler tube while the engine was running and could just see a very little smoke that seemed to be sitting there and not puffing.

Blake Malkamaki · December 17, 2014, 01:21:12 AM

They probably make an adjustable main jet for that carb. Call http://w-t-p.com and see if they have one.

Doug424 · December 17, 2014, 08:40:53 AM

I'll look at some of my extra carbs to compare, but as I recall most Marvels I have from the OC-3's have adjustable mains.

GlenT · December 18, 2014, 02:13:05 PM

Thanks Doug. One site said the TSX406 was for distillate. Was it also used for gas?

Jack in NB · December 18, 2014, 08:39:34 PM

Mine over the years have had both 403's and 406's, all running gas. The 403 had no high speed adjustment; the 406's have needles to adjust both idle and high speed mixtures. My current one uses the 406.

GlenT · December 18, 2014, 11:21:31 PM

Thanks Jack. Now the search for a 406?

Doug424 · December 21, 2014, 04:42:07 PM

I checked all my carbs and the all the ones that were, or on HG's and OC-3's have the adjustable main jet. I'm thinking someone changed yours. Best thing you can do is get the right one. I do have an extra Marvel with an adjustable main, it's from a Case VAC. Different #, but basically the same carb from an engine with a displacement close to what the IXB is. If you can't find the exact one, this one would work.

GlenT · December 22, 2014, 12:44:35 AM

Thanks Doug, I'll keep your offer in mind. A machinist friend is getting a power needle from a friend of his. I don't know what it from but I'm thinking an Allis or Farmall with a Marvel carb. We are thinking the plug on top of the carb. where carbs. like the 406 have the power needle, could be knocked out and the power needle could be put in the 403. There are threads under the 403 plug and there is a jet where the needle would seat. Without the power needle, the jet hole regulates the mixture but with the power needle, the hole is adjustably (word?) shut down and the mixture is regulated.
Anyway, that is what we are hoping will happen??
Does the Case VAC carb. have the throttle and choke on the same side as the 403? The Allis carbs. have them on the opposite side.
Thanks again.