VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 1929 LQ Fire Truck Power Issue

I'm working on my recently purchased 1929 Fire Truck. Just finished a full service job, changing all fluids, tune-up, brake adjustment, etc. While it is a 1929 chassis, the engine is a 1930 engine which has been fitted with a later downdraft manifold. Despite good compression, timing at 18 degrees BTC, plugs gapped to .040, valves adjusted, the truck runs great at idle and low speeds but is way, way too lean at mid-throttle, popping back through the carburetor and unable to handle any sort of grade. If I can get it up to fairly high engine speed, it actually runs and pulls reasonably well, but as soon as any sort of load comes on in mid-range engine speeds it will wind down and stall out. It's clear to me that the problem is a very lean mixture at high loads and low to mid engine speeds.

But why?

First, the truck had a Carter YF Model 964-S carburetor installed. I disassembled and cleaned it, checked the accelerator pump operation and set both the float level and pump stroke per the Carter manual. Put it back on, no improvement. I decided that it may just have the wrong CFM range for the engine. I have no idea what this 964-S application is, but I know it's NOT a 1930 Chevy Engine.

Next step: I replaced the YF carburetor with a newly rebuilt W-! I have in reserve for my '32 cars. No change whatsoever, which surprised me.

Now the question is what should be the next step(s)?

My plan of action from here is:

(1) Return the hodgepodge fuel piping system to original, eliminating the fuel shutoff valve under the tank, the various hoses, clamps, unions, extra filters, etc. (Just in case something is obstructing the flow)
(2) Rebuild a fuel pump core I have on hand and change out the fuel pump. (Maybe it's pumping, but not putting out sufficient pressure / flow to keep up with demand)
(3) Remove the manifolds and replace with a set of '30 manifolds and an RJH-08 carburetor I have on hand. (Back to original configuration, and new intake sleeves, gaskets, etc to preclude a vacuum leak)

Before I go through all of that, does anyone have any thoughts on what I may have missed? Gene? Chipper? Skip? Others?


All the Best,

Chip

Have you checked the breather on your gas cap?
It would be worth bypassing the fuel line to make sure that the flow isn't restricted before you swap all the parts, also debris around the fuel pickup could cause similar symptoms..

Before you go any further, I would suggest doing a compression check on each cylinder and compare the readings per cylinder. Years ago reproduction Teflon head gaskets were sold on the market and they never worked because the gaskets would burn through between cylinders. With the defective Teflon head gaskets the symptoms were very similar to what you are describing concerning your 1929 fire truck. If your compression test proves okay I would go back to the correct manifold with the Carter updraft carburetor and also perform number 1 and 2 that you mentioned in your post.

Thanks guys -- I'll recheck the compression, backflush the suction line for the fuel pump and check that the vent in the cap is OK. It will be several days, though -- pretty busy. Thanks for the ideas. Any other thoughts?

All the Best, Chip

When the engine loses power does it "pop" and "spit" or just begins to slow down and lose power? I am thinking the opposite of lean. Not being there to see what it does makes diagnosis difficult.

I also have a thought that it might be valve timing with it being a tooth or two off.

If compression test shows all cylinders to be about the same then leaking headgasket is less likely.

Thanks Chipper: Yes, it does pop and spit....I'm pretty darned certain that the mixture is too lean under heavy loads, which is why I'm moving in the direction of the carburetor being starved when the fuel flow increases.

I'll give you guys an update in a week or so. Time to do yard work, honeydew lists, etc to avoid going into the penalty box!

Thanks to all of you for good ideas....... will advise.

All the Best, Chip

With the popping and spitting I agree that is likely is lean fuel mixture. But it also brings valve timing higher up the likely list. Yes valve timing not ignition timing. Let us know what you find.

Well, we had a great Independence Day Celebration, did a few honeydews, and I'm back on the trail. I checked compression: All cylinders 78psi +/- 2 psi. Checked for clogged fuel piping, all clear. THEN I checked the fuel cap vent. Plugged up tighter than a tick with dirt, corrosion, and debris! No airflow whatsoever and the threads are a tight fit in the tank neck. I think that may be the issue -- and our man "down under" - Chevrolet6 - may have nailed it. I cleaned out the vent hole in the cap, had a good look around the inside of the fuel tank (pretty bad, but nothing blocking the fuel inlet -- added to work list) and I'm ready for another test run as soon as the rain stops here. Maybe it's solved, maybe not, but I'm pretty optimistic.

If the problem's not solved, I'll move on to replacing condenser, then coil. To be clear, I'll put a condenser and a set of points in it anyway, but I want to know exactly what was causing the problem.

Thanks again to all who responded, and I'll keep working through your list of ideas until it's fixed.....I'll let you know how it works out.

All the Best, Chip

Just a suggestion for the short term: place a fairly strong magnet under the gas tank near the fuel outlet. Rust particles will be attracted to the magnet and not flow into the gas line.

;-) Dean

That's a great idea, Dean. Thanks!