VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 1931 Engine Miss

Hello All,

It has been a while since I posted on the forum, mostly because I have been out driving the `31 Special Sedan like crazy since the engine rebuild. However, the engine has developed a problem that has me perplexed and I thought I would reach out to the experts and see if I could catch a break.

The problem is: When accelerating under load (wide open throttle condition in second or third gear), the engine tends to sputter and miss step. Not so much like a backfire, but more like a chugging feeling (I might try and upload a Youtube vid to help describe the issue). I think (could be wrong) that it is some form of lean condition.

The car will accelerate, but seems to be down on power. It eventually gets to the desired speed, but much slower than I recall. The problem developed in a fairly rapid manner on my return drive from the Old Car Festival last year.

Things done to try and fix this (not in any particular order):
1.) Checked timing (set to 12 degrees (I know I could go to 18, but each time I blew a rod bearing it was when the engine was timed at 18)
2.) Replaced coil, and condenser. Performed tune-up (rotor, points, cap, re-gapped plugs). I get a bright blue spark from the wire end when I bring a screwdriver close to it.
3.) Replaced carburetor with a donor. I originally thought this was the issue as the previous one had a crack where the mounting flange met the tube of the carb. I removed the standpipe, choke cone, and venturi and replaced them with aluminum ones from the Filling Station. Followed JYD's recommendation to remove and replace (and reseat) the low speed jet. Float set to 3/4" per manual. Car idles so very sweetly with no miss that I can tell. Plenty of adjustment left on idle air bleed screw.
4.) Rebuilt fuel pump - Thinking it could be some form of fuel delivery issue. The lines on this car are very old (I believe original) so they might be candidates for repair/replacing next
5.) Checked valve lash. All valves were pretty darn close to spec at .006" and .008" (intake and exhaust). Checked manifold pressure with a vacuum gauge and it reads 16-17 inches of mercury (vacuum) at idle. The needle consistently fluctuated between those two numbers. Under open throttle condition the number drops to around 5 or so before recovering. At medium throttle conditions the number holds stead at 15 inches of mercury (vacuum). All these numbers were checked with the car in the garage, not driving.

The rest of the car's drive-line appears to be in working order. Oil pressure is good, no indication of over heating. No brakes dragging from what I can tell.

Any help or other thoughts, tips, or troubleshooting ideas would be greatly appreciated.

Thanks for reading in advance,

Respectfully submitted,

Rusty Berg
Formerly Indianapolis, IN now West Bloomfield, MI.

Did you check for a leak at the intake manifold? Spray something (ether, WD40 or motor oil) along the top where it bolts to the head. See if that changes the idle speed of the engine.

--bb

Bill,

Drat, knew I was going to forget to say something in the work I have done. I replaced the manifold gaskets (after lightly sanding the flanges to true them up slightly). I have sprayed carb cleaner at those points with no noticeable uptick in engine RPM.

Thanks for the thought,

Respectfully submitted,

Rusty Berg

Checked the condenser? Our 32 showed the same symptoms a year ago and I replaced the condenser and no worries since....Good luck with the car.

Mac

I assume you have a fuel filter and replaced during fuel pump rebuild.

Wonder if they were new or not...?

The vacuum needle should have a steady reading at idle. If it fluctuates back and forth rapidly at idle that would indicate a possible burned valve.

Hello All,

Thanks for the suggestions. I do have a filter on the system back at the tank since I am running a replacement hot rod tank and needed something to interface with the barb fitting. I replaced the filter, the hose to the filter, and the hose from the filter to the steel fuel line.

The burned valve scenario is something I fear might be possible, although I have tried to be very careful concerning valve lash on the engine. I would have thought that burned valves would have produced a more drastic fluctuation on the needle... Learn something new every day...

I have one last thing I want to try, I noticed today after looking at the fuel lines again, that there is a crack in the compression nut on the line from the fuel tank to the pump. My theory is that this causes the pump to not pull as well from the tank. It's a stretch but...

I intend to cut in a replacement to see if it will remedy the situation.

I guess if the fuel line thing doesn't work next step is to pull the head.

Many thanks to everyone for their ideas, I will try to post an update of what I find.

Respectfully submitted,

Rusty Berg

P.S. As an afterthought, for information purposes all the components used in the tune-up and ignition check were new replacements from the Filling Station. I have not replaced the plugs, but the condition of the strap and electrode looked good.

With a crack in the compression nut on the fuel line you could be sucking air.

My experience is an apparent loss of power without popping or backfire is normally ignition related. In most cases due to points being dirty or burned. It can be due to weak condenser or even coil. Sorta like turning off ignition at higher speeds. It can also be over fueling or too rich a mixture. Typically lean conditions produce a popping or backfire.

Hello All,

I would like to thank everyone again for your support as I've been working through this issue. I apologize for not getting back sooner, but work/life commitments have not allowed me any time out in the shop to troubleshoot until now.

I think at this point I've pretty much got it licked!

As I was working on the distributor, I noticed (and previously stated) that the compression nut on the fuel line had a crack. I can now confirm that this is very much most likely the issue as I was able to see that when I rapidly accelerated the motor from idle and then quickly stepped around the door to see the fuel pump, a fine stream of bubbles would move into the sediment bowl. I've got the parts on hand to repair the line, now I just need to find more time to fix it.

Thanks again to everyone,

Happy motoring!

Respectfully submitted,

Rusty Berg

Thanks for the update!