Carburetor fun...

Trapdoor2

Trapdoor2

Senior Member
The Coupe came with two Tillotson carbs, the one it was running on is an "X" and the one in the "parts box" is an "F". I haven't been happy with the X as it is leaky...and it doesn't run to my expectations. I learned pretty quickly to shut the fuel off and run the bowl dry every time I shut her down for the day. If I forget, it will drip out on the pans and my garage will smell like raw fuel. :(

Of course, I wanted a Zenith. The Tillotson F needs a new lower, as somebody obviously cranked down hard with an Air Maze screw and the throat is ovalized enough that the choke butterfly doesn't close properly. I'm not terribly interested in the F but if I run across a donor, I may rebuild it.

In the meantime, I purchased a Marvel Schebler. I've rebuilt several MS carbs used on light aircraft and they have always run smoothly. The one I bought had been cleaned up but no rebuild done. So, I ordered a rebuild kit from Renner's, found all the good info here (downloaded all the pix, etc.) and tore it down...

Well, I attempted to tear it down. The main jet is stuck and the screw slot is buggered badly. Not much I can do there...it is really deep. I fished around to verify all the passages are clean...I'm leaving it in. Getting the float valve seat out was a trial. I could see it was corroded, the needle was too. I finally found a big enough ratchet-screwdriver bit (1/2" wide at Harbor Fright) that I could grind the blade to fit. I had to needle-file the seat slot to clean it up (it was buggered up too)...but it came out, grudgingly. I replaced everything I could and I set the float height per the instructions that Renner's supplies (and I used one of their float height tubes). The two halves needed no flattening and it went right back together...now it has a viton-tipped float needle. Maybe it won't leak!

All this took some time...and I found a Zenith. The seller said the fuel inlet threads were leaky, so I got it cheap. I know these fittings and know that they do not seal on the threads. I figured I have some soft aluminum seal washers around here somewhere (I did pressure testing with 6000psi helium back in the 80s).

Thankfully, I had seen the seal seat grinding bit on Snyder's, so I ordered one of those. I ground the seal seat this morning by hand using a hurdy-gurdy. Worked like a charm. The actual ID of the hole was corroded a bit, so I took a very light cut with a 45 degree chamfer bit to clean that edge up. The Zenith is so easy to work on, I cleaned it up and checked all the passages...looks like it has been rebuilt recently so it went right back together.

The Tillotson X got disassembled this morning...the one I was running on. It has the same ovalized throat problem that the F has. I got the two halves apart and the float fell out in my hand. Solder joint had failed. I think it was bouncing around in the float bowl just held in by clearances. :eek: The previous owner had a rebuild kit, so I swapped out everything for new...but now I gotta fix that float (or find a replacement).

Anyway, the Coupe now has a M-S in place and a Zenith as backup. I'm still working on cleaning up the transmission area, so maybe I'll get to test out the new carb(s) this week.
 
I've run everything you mention and I think I like best Tilly X. Marvel is good, probably better than Zenith, but X is just like clockwork - when it runs right.

And perhaps that is the key.

Also - what works for you. Your methodology and care seem top-notch.

You'll end up like many of us with a line of Model A carburetors on the shelf - waiting.

https://modela.org/other_carbs.html

Joe K
 
Soldering the float should be fairly easy if everything is clean. I used a float from a Pontiac Tempest to replace a bad one in my tillotson X.
 
I have repaired floats for myself and others without solder. I figured that is tank sealer keeps fuel in, it will keep it out so I dipped the float in some, let it dry and all was well. Unlike solder, this method does not make any appreciable difference to the buoyancy of the float.
 
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I have been fiddling around with my B carb. Set the float with a jar. Put a gasket under the power jet, and that helped. Been trying to get the hang of the air-fuel mixture screw. I was taught 1 1/2 turns out, and make sure the spring doesn't bottom out before it TOUCHES the seat. Adjust a bit in, or out from there. The GAV has to be open about 1/4 turn before the thing runs decent though. Hope I can figure it out soon. Carbs can be stubburn sometimes I guess.
 
Ok, finally got the transmission plug out to check the oil level. Somebody screwed that puppy in with a breaker-bar! Oil level is just right and it looks and feels good. I'm leaving it alone. Put the plug back in with less grunt. 11/16" 12-point works nicely on that big square plug (3 yrs ago, I gave away my Dad's 8-pt. socket set. After rotting unused in the bottom of a rusty toolbox for 40yrs, who knew I'd need 'em?).

Installed all the floorboards. Much easier now that I know how they fit, of course. Everything I could reach under the boards has been cleaned and wiped down. Very little rust in this car beyond the muffler.

As soon as I had the carpet back in, I pulled her out and did the first test with the Marvel-Schebler. Took a few cranks to get the float bowl full. She did not want to run at all with the GAV all the way in...1/4 turn open seems to be the sweet spot.

I used the hand throttle to keep her running at high-idle until I could set the idle screw. I'm not very happy with my el-cheapo Amazon inductive tach...not that I expected much for cheap. It seems to indicate 500-600 rpm as low as I could comfortably set her. I suspect it may be doubling...but meh. As long as she runs and sounds good I'm not gonna worry.

So, I've been out circling the block tonight...pull her into the driveway, inspect, give her a tweak, circle the block again. Stopped and talked to the neighbors...she just ticked away while we talked...but she started a random "bump" during idle. Kind of like one cylinder will hit just a little harder occasionally. Even the neighbor heard it. Not a backfire, just a quiet random bump.

No leaks! Clean as a whistle. I'm sure I'll find the right combination as I continue playing with the idle screw, GAV, etc. Naturally, I'll play with it for a while and then install the Zenith and see how it does. I ordered a new float for the Tillotson from Mike's, I'll re-solder the old one for a backup.
 
Gene F said:
I have been fiddling around with my B carb. Set the float with a jar. Put a gasket under the power jet, and that helped. Been trying to get the hang of the air-fuel mixture screw. I was taught 1 1/2 turns out, and make sure the spring doesn't bottom out before it TOUCHES the seat. Adjust a bit in, or out from there. The GAV has to be open about 1/4 turn before the thing runs decent though. Hope I can figure it out soon. Carbs can be stubborn sometimes I guess.
Click to expand...

Hello Gene, why didn't your power jet have a gasket under it ?
The power jet is the smallest jet in the bottom of the float bowl.

What did you set the fuel level in the bowl to, distance from gasket surface to fuel level?

Idle air fuel screw at 1-1/2 turns out from seated is too lean for todays fuels, I would bet that it will idle and perform better at 3/4 to 1 turn out from seated.

Also curious is your GAV changing how the engine runs when its idling or only when going down the road?
 
So...I'm still attempting to get the MS carb to work properly. It runs normally but idle is a little lumpier than I would like. The worst part is that it is hard starting. It absolutely will not run at all with the GAV closed and won't start (cold) until I have it open at least 1/2 turn. Even then, it will only run for a few seconds and then quit. It will do that a couple of times before it finally decides to run. Occasionally it will pop and snap before settling down. Once it has decided to run, it starts easily and runs normally.

It seems to act like it is starved for fuel when cold (70F, she's in the garage when she's not on the road). I've checked that there is good flow to the carb. Float level is per the MS instructions. The only jet I couldn't replace is the main. No vacuum leaks. I may have to drill that main jet to get it out...which I can do, just don't want to.

I'm about to do a three-carb comparison. MS v Zenith v Tillotson. The only gripe I have with the MS is the starting issue.

Any thoughts? Recommendations? Things to try?
 
Remember when adjusting the idle mixture on a Marvel, it is opposite a Zenith or Tilley. Turning the idle mixture screw out enrichens the mixture where as on the others that would lean out the mixture.
 
Y-Blockhead said:
Remember when adjusting the idle mixture on a Marvel, it is opposite a Zenith or Tilley. Turning the idle mixture screw out enrichens the mixture where as on the others that would lean out the mixture.
Click to expand...
I need to revisit that. I don't really pay much attention to which way does what on the idle screw, I simply work it back and forth until I find the best running setting...and by the time I've got it set, the engine is at temp. Might need to run it on the richer side (1/4 turn?) of the window to help cold-starting. I'll try that tomorrow.
 
To me the Marvel is a "cold-blooded carb".
By this I mean, I have to open the GAV, 1 full turn in winter, 40 degrees outside, to get the car to start. After 10 to 15 seconds of it running, I can start to close the GAV back to about 1/4 turn open. The engine will smooth out and run great. It just needs this extra fuel for start-up. The rest of the year on a cold start I open the GAV 1/2 turn. When it warms up, I can run with the GSV closed. Both cars have Vintage Precision 160-degree thermostat.
For me, the Marvel is the best of the 3 carbs you have.
Your mileage will vary.
 
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