The old A has it in for me

kopeck

Member
I've written about my '47 A a couple of times on here recently. I've received plenty of good advice but nothing seems to be curing my A's miss. You can see where I've been here:

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=883199

Since that thread I purchased another Zenith, cleaned it up my self and then bit the bullet and sent the parts out to have a pro look over, install new throttle bushing and reassemble.

The results are pretty much the same. Idles like crap/can barley keep it running and starting can be tricky too. WOT is usable but still seems kind of "strained" and there's still a miss.

It still feels like fuel to me but I'm out of ideas. At this point I've:

Tried 3 different carbs, none of which made it "right".
Tried running with the air cleaner disconnected
Tried the propane test to look for leaks

Each cylinder has 94 lbs (give or take a pound) of compression with the engine warmed up.

I've checked the valve lash and everything is set to spec.

New point and condenser (H-4 Mag), tried a different set of wires and 2 news sets of plugs.

At this point it almost seems like it has to be ignition related. The H-4 makes good blue spark when I turn it over by hand. I've toyed with getting a battery ignition for it for a while, I think they run a bit better then the H-4s BUT it still should run well with the mag.

Any more wisdom?

Thanks,

K
 
Spark a blue/white in color and jump a 1/4 inch gap or more on ALL 4 plug wires????? Gap at the points on all 4 lobes the same as in 0.013 with in 0.001 of each other?? If the bushings in that mag are bad and the gap is not close on all 4 lobes a miss is often caused by the mag being in need of rebuilding. Not often a carb causes a miss but common for spark or vales to do so
 
You can't time a mag with a timing light but I would
hook one up to it and see if that spark is jumping
around all over the place, meaning different degrees
on pulley. I would make a few reference marks to see
what it is doing as I realize there are no marks on
pulley. I imagine you have given it the air leak
test on manifold with a propane torch, W-D 40 or
something else similar.
 
Sorry for the frustration, I know what it is like chasing problems like these. When I bought my H the governor kept searching, I cleaned it, replaced it, rebuilt carb twice, rebuilt distributor, adjusted timing, plugs, wires.
Ended up pulling the head off, it was just plain worn out. Had the head redone, new pistons and rings, did the trick!
Good luck!
 
(quoted from post at 11:19:25 10/31/12) Sorry for the frustration, I know what it is like chasing problems like these. When I bought my H the governor kept searching, I cleaned it, replaced it, rebuilt carb twice, rebuilt distributor, adjusted timing, plugs, wires.
Ended up pulling the head off, it was just plain worn out. Had the head redone, new pistons and rings, did the trick!
Good luck!

Minus the ignition I wondering if this might be the case.

I can hold the throttle shaft (the one between the governor and the carb) stationary it it still misses. I'm willing to bet the governor could use some attention but I don't think it's at fault.

About 10 years ago I had the head done and I put new rings in it. I was at the time using it on a Woods belly mower and it drove it fine. I doubt I've put 30 hours on it in the last 10 years.

The missing/shuddering is new, started about a year ago but I've only had time to start playing with it recently.

It was always very easy to start by hand now it's really hard. It does start fairly easily using the starter but you really can't let it idle to much or it stalls.

I did get it to register 93-94 PSI warm but cold it was 10 psi less then that. Maybe it is time it's bite the bullet and go through the whole engine. The good news is at least the head should be set.

K
 
(quoted from post at 10:50:50 10/31/12) You can't time a mag with a timing light but I would
hook one up to it and see if that spark is jumping
around all over the place, meaning different degrees
on pulley. I would make a few reference marks to see
what it is doing as I realize there are no marks on
pulley. I imagine you have given it the air leak
test on manifold with a propane torch, W-D 40 or
something else similar.

I can try that I suppose. Just get it to TDC, make a mark and go from there.

Yeah I did the propane test, no luck.

K
 
(quoted from post at 11:39:24 10/31/12)
Vaccuum leak. Either the manifold gaskets, or the manifold is cracked internally.

I'm guessing if it's cracked internally then the propane test wouldn't work?

K
 
Couple of thoughts to add to the others - do you have a good flow of gas if you disconnect the carb. Old tanks can have stuff plug up the outlet to the tank. Steel gas lines can corrode making too small an opening for a good flow. Also - does the tractor smoke. When its running rough does opening the choke part way help. If you have a manifold leak a partial choke will make it run better but will also make it smoke. Also are the plugs fowling after it runs for awhile. Just some thoughts.
 
(quoted from post at 11:49:08 10/31/12) Couple of thoughts to add to the others - do you have a good flow of gas if you disconnect the carb. Old tanks can have stuff plug up the outlet to the tank. Steel gas lines can corrode making too small an opening for a good flow. Also - does the tractor smoke. When its running rough does opening the choke part way help. If you have a manifold leak a partial choke will make it run better but will also make it smoke. Also are the plugs fowling after it runs for awhile. Just some thoughts.

I just replaced the strainer/bowl unit and that didn't help. I blew the line out last time I had it off (when I replaced the fuel strainer). It seems like a good flow.

It doesn't smoke and it doesn't seem to fouling any plugs BUT I don't run it all that long so I'm not so sure if that means a ton. I did try to run it with partial choke and couldn't find any place that really helped. That being said if I had to guess I would say it's running more lean then rich, it hasn't back fired or anything but it's not smokey that I can see.

K
 
(quoted from post at 11:45:50 10/31/12) Fine-tuning the timing does wonders for random misses in my experience.

I've had the mag all over the place, advanced retarded you name it.

I was kind of surprised at how little effect had on the engine running over all.

K
 
Hi.

I had a miss in a Cockshutt 80 that I worked on for about 3 years. The engine ran ok under load, but at idle or no load there was a miss. I changed out the mag to a distributor and the miss was gone. I never suspected the mag because the tractor started good and there was a nice blue spark from the mag. The problem was in the impluse. It was really dirty and one coil on the spring was broken. I thimk the problems in the impluse caused the engine to get out of time. No bad enough for it not to run, but enough to develop a miss. I think the H4 mag is a good mag. it just might need some tlc. Good luck

Cheers

Russ
 
(quoted from post at 20:06:23 10/31/12)
(quoted from post at 11:45:50 10/31/12) Fine-tuning the timing does wonders for random misses in my experience.

I've had the mag all over the place, advanced retarded you name it.

I was kind of surprised at how little effect had on the engine running over all.

K

I had a strange experience like this, kind of reminded me of yours. Here it is:
I replaced the head gasket. It needed a new one badly. I went ahead and adjusted the valves on her, because it wont run right until you do. Turns out I forgot to bolt down the rocker arm assembly and just slapped the valve cover over it. She had good compression...for about as much time as it took to run a test. After that she started missing. Couldnt figure out what the hell happened. Someone mentioned to me to just take the valve cover off and look...well, the picture easily describes what I saw. She was only running on #2 and #3. I properly bolted down the rocker arm assy and she runs like a champ now.
Bottom line, if all else fails, just pull the valve cover off and run it, see what the valves are doing.
11917.jpg
 
Short attention span here, so I may have missed it in what you typed -

but have you checked the timing? Should be timed to snap between 1 and 5 degrees after tdc/compression stroke on 1. But use a light to see if it's advancing once it gets running.

Also - I've never seen it myself, but I believe the mag bushings can get worn and cause a little wobble - might want to check that. Maybe somebody else can chime in on that.

And I know this might sound too basic - but it really sounds more like you've got your plug wires routed incorrectly. cross two cylinders and it can run exactly how you described (I'm not too proud to admit that there's a reason I know this)

With new points - be sure to clean them up with very fine sandpaper - they often come with a coating on the faces that will keep them from operation properly. Just a real quick cleanup don't go crazy.
 
Wouldn't a vacuum gauge prove or disprove a leak? If you can eliminate that possibility and you've swapped carbs with the same result, I'd rule out carburetor problems. Anyway it sounds like we're all throwing darts so I'll throw a couple. First, yes you can check the timing with a light, you just need a 12 volt source to power the light. You may not learn much because the advance is beyond any marks anywhere. What you can learn is if the spark is occurring at the same time every time or if it's erratic.
I've had similar problems with different machines and the solutions were all different. My 140 Farmall taught me to adjust valves one cylinder at a time. For some reason getting it on TDC and doing the valves that the IT manual says you can do, didn't work well for me. Since then, one cylinder at a time. If you could borrow a distributor from another tractor and wire that up, you could potentially eliminate spark and timing from the list of possible problems. You may have cracked cylinder head allowing one cylinders exhaust to interfere with the adjoining cylinder's intake. As mentioned before, an internal crack in the manifold will do the same thing.
 
You said: "It seems like a good flow.".
How did you observe that? I'd remove the drain plug from the carb bowl and collect the gas in a container. Measure the amount after letting the gas flow for 15 minutes; should be at least a gallon. That amount may be regarded as "being available" to the jets. So, if the flow from the drain plug from the carb bowl is sufficient, the problem of lean running could be in the jets.
Other thoughts:
1) Is the venturi mounted properly?
2) Is there sufficient vacuum? Remove the pipe plug from the manifold (just above the flange to which the carb mounts) and screw a barb fitting in. Attach a transparent U-tube and fill with water. I must confess that I do not know how much vacuum it should register, but you could take this measurement form your B (or others may chime in...).
HTH, Hendrik
 
Only thing I can add is cap and rotor for the mag aren't on your
list of things you tried. Like old suggested check for spark at
all plugs.
 
Check for slop in the mag shaft bushings. Also looseness in the rotor on the shaft. Worn mag bushings will make setting the points almost impossible. Each time the shaft moves vertically for any reason, the point adjustment will change and a miss to occur. A a loose rotor to the shaft will cause a change in timing. I have seen a paper shim in the rotor to shaft make a world of difference in the engine running smoothly.
 
New cap and rotor as well.

The wires are right, I've had them off and on so many times that I think I could do it in my sleep.

I did throw the timing light on it and didn't see anything off on the pattern. I didn't check the advance, I could though as my timing light does have an advance feature.

So if I threw the vac gauge on the manifold what should I expect for a reading?

K
 
H4 mags have ball bearings not bushings. I have yet to see them go bad. I pack them with lite grease whenever I take one apart. I would try a different condenser. I would like to put the old one on my tester & check it out.
 
(quoted from post at 02:33:19 11/01/12) H4 mags have ball bearings not bushings. I have yet to see them go bad. I pack them with lite grease whenever I take one apart. I would try a different condenser. I would like to put the old one on my tester & check it out.

That is a great suggestion and I actually had a miss on my A in the past because of a bad condenser. And the condenser was brand new too.
 

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