Carb rebuild? Distributor cap?

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Larry B
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Re: Carb rebuild? Distributor cap?

Postby Larry B » Fri May 17, 2019 10:20 pm

Pull the plugs. Put a socket and ratchet on the front crank pulley bolt. Timing marks are on the other side of the engine from the distributor. (brilliant design) Put your finger in the #1 plug hole and crank engine (look at fan to turn proper direction) you will feel pressure when coming up on the compression stroke. There are 2 timing marks on the pulley. First one is TDC, second one is 16 degrees BTDC. This is the mark for the advance. Always crank in direction of rotation, don't backup to the timing mark. You want to keep backlash out of the gears when you static time it.
The engine is a flathead design. Valves in block. Spark plug not over the piston like an OHV engine.

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Dale Finch
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Re: Carb rebuild? Distributor cap?

Postby Dale Finch » Fri May 17, 2019 10:41 pm

The best trick I was shown at a cubfest for finding TDC uses a cork in the #1 plug hole, and slowly handcranking the engine until it pops, then adjusting so the pointer is on the notch of the pulley. The hardest part of this procedure is finding the cork on the other side of the room/yard!!! :lol: :lol:

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Re: Carb rebuild? Distributor cap?

Postby cody96ss » Fri May 17, 2019 10:46 pm

I went with the balloon method...idk...it worked...haha.
Not the clearest photo, but you get the idea...
balloon.jpg
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Re: Carb rebuild? Distributor cap?

Postby cody96ss » Sat May 18, 2019 12:10 am

Larry B wrote:Ok. Here is my checkout for the ignition system. Some of this may seem obvious but it check most things.

Remove the distributor cap and bump engine till points are closed.
Connect a plug wire from the coil tower and other end to a spark checker or hold it 1/4" from ground.
With key on manually open the points and check for spark. If you can get 1/4" spark in air you have enough spark to run the engine. If won't jump 1/4" gap check point resistance, battery voltage at + terminal of coil, bad condenser, bad coil.
Assuming you have good spark. Position engine with #1 cylinder at TDC on the compression stroke. Remove the distributor cap and loosen both distributor hold down bolts. Turn on the key. Rotate the distributor slightly clockwise till the points are closed. Connect a plug wire to the tower of the ignition coil and other end to a spark plug and ground the shell of the plug. Slowly rotate the distributor counterclockwise till the points open and the plug sparks. Tighten the distributor hold down bolts. The engine is now static timed at TDC. Whatever tower on the cap the rotor points to will be #1. Install cap and wires. Double check firing order 1-3-4-2 distributor turns clockwise. Point gap .020. Install a NEW set of Champion D18Y plugs with .025 gap.
This will start and run the tractor. Still need to check with a timing light and the advance.
Give it a shot of starting fluid and try to start. Should run for a couple seconds.


OK, DONE. Everything set as you explained. I only have one distributor hold down bolt, but I doubt that's a big deal. Autolite plugs @ .024", point as close to .020" as I can get. Getting a nice pop from the coil now. Fixed the gas leaking from the carb by the way... just disassembled, cleaned, and reassembled.

I recorded the results... same as the day I brought it home...
https://www.youtube.com/watch?v=2PF_cmx0scg

When I take the plug out should there be any dampness? It's completely dry and the cast plate below the plug in the head is dry with some carbon on it. I'm moving on to fuel issues... How would I figure out if fuel is coming out of the carb? I'm decently sure that fuel is getting to the carb effeciently enough. I've cleaned the tank and fuel bowl tube with compressed air... Bowl of carb has fuel in it - when I loosen the drain plug clean gas pours out... If I crank it without the starting fluid, I get absolutely ZERO, but with the ether, it does fire a little... I'm wondering if it's getting nothing for fuel and that's why it can't pick itself up.

THUS FAR: Cleaned fuel tank, bowl, and carb: ohmed all plug wires: replaced plugs - .024": set stating timing: cleaned and set points to .020"ish: replaced coil with used (tested good - actually shocked the crap out of me): air filter ok: replaced upper radiator hose: flushed cooling system:
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Re: Carb rebuild? Distributor cap?

Postby cody96ss » Sat May 18, 2019 12:50 am

Ok, I dumped a little gas in the intake and gave her a spurt of ether... Ran for about 10 seconds, idled itself up, then died...

Here's the video
https://www.youtube.com/watch?v=VgamDfNafLA

UPDATE: So I Jimmy Rigged a small funnel and a small diameter piece of hose and ran it down the intake hose and just into the carb. The idea of this is to not put gasoline straight onto the intake hose - which appears to be a coolant hose... I don't want to deteriorate it. Plus, it slowly let the fuel in as opposed to just dumping it in. I cranked, it started and ran for about 30 seconds, which is how long it took to empty the funnel of fuel. I could see the governor working back and forth and it seemed like it ran smooth. Didn't hear any knocks or slaps, so that's a positive. The glass fuel bowl is still full, so I'm lead to believe that it isn't pulling fuel for some reason. Onto that mess I go...
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Rick Spivey
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Re: Carb rebuild? Distributor cap?

Postby Rick Spivey » Sat May 18, 2019 5:27 am

You are definitely not getting fuel. I see you say you cleaned the carb, but my experience is that as simple as these things are, they must be perfectly clean to run properly. There are various small passageways that get blocked, open them up with (1) a soak in chem-dip or similar, (2) carb cleaner in aerosol can, (3) small copper wire, or (4) combinations of all 3 suggestions. Be gentle, but firm. Also insure the main jet is clear. The IH carb has idle circuit openings just above the butterfly valve, hard to see, but necessary to get a good idle. Also on the IH carb, the idle mixture screw is adjusting air flow, so "in" is rich. "out" will lean it up. I don't know squat about the Zenith carbs, but I'm sure patience and thoroughness count on those as well. Lastly check the carb inlet screen for blockage.
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Larry B
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Re: Carb rebuild? Distributor cap?

Postby Larry B » Sat May 18, 2019 6:04 am

Pull the fuel line off the carb and see if you get a steady stream on fuel. This is a gravity system so no pressure but should still get a steady stream of fuel. If that is good hook fuel line back up and remove the carb main jet. 1/2" wrench and jet is on lower right side of carb. Fuel should come out in a steady stream. If it doesn't check float and needle. Clean passages in main jet and put it back in. Try to start tractor at full throttle and choked. This bypasses the idle circuit. Tractor will want to start at WOT and choked any time it is a cold start. May want to take the air intake hose off the carb and make sure choke closes all the way. Make sure you are using new plugs. Wouldn't believe the difference they make starting the tractor.

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Re: Carb rebuild? Distributor cap?

Postby cody96ss » Sat May 18, 2019 5:58 pm

Did a full carb clean last night. There were in fact small passages and ports that needed some attention. Once I put it all together, fuel just dumped outta the thing. So I still have a float and/or gasket problem. Will order a rebuild kit and hope for next weekend...
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Re: Carb rebuild? Distributor cap?

Postby Rick Spivey » Sat May 18, 2019 7:11 pm

Not a Zenith expert (already said that), and not to insult your competence. But I find these small carbs are really sensitive to things being just right. Make sure the float lever is spot on for both upper and lower positions, and check to be sure float doesn't rub the bowl anywhere. When assembled and dry, you should be able to hear float open and close as you rotate carb right side up to upside down.These little guys are simple but very picky.
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Dale Finch
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Re: Carb rebuild? Distributor cap?

Postby Dale Finch » Sat May 18, 2019 7:35 pm

And double check for a common problem that causes a carb to leak...a sticking seat.

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Re: Carb rebuild? Distributor cap?

Postby cody96ss » Wed May 22, 2019 9:55 pm

Howdy Fellas! Update time!!! So instead of buying a gasket kit or anything I just bought a sheet of felpro gasket material and cut my own out for the carb and carb flange. I adjusted all of the screws back to 'factory' as I was unsure if they had ever been tweaked. I measured the floats according to the manual I found on here and assembled it all. Worked great! Except I was still dumping fuel on the floor. So I took off the 7/16" fitting and lightly tapped the floats up and down a few times and the leaking stopped. Maybe the gas lubes the needle for the bowl but it seemed to be ok. Started it up and it ran! Drove it for about 1 minute and it died. Got it restarted and parked it back in the garage and apparently the drive shook some sediment loose from the tank that I had not found in my previous cleaning.

Clutch is EXTREMELY touchy...

Also, the upper coolant hose connector leaks coolant... on a car it would be the thermostat housing, but I'm not sure if this has a thermostat. I tried to loosen the bolts but they are in there... I really don't want to snap one of those. I don't have a torch, so after I get the tank cleaned again I will let the tractor run for a bit to heat up the bolts and try them again. Can anyone tell me how hot this thing should run? I have a laser temp gun, so if someone could point me in the direction of some numbers I would greatly appreciate it. I haven't looked at the manuals for clutch adjustments, but that can't be that difficult, right? It seems like it is running hot and I definitely don't want to over heat it so I will be treading lightly until I can find some figures on running temps. Thanks for all the help!
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Re: Carb rebuild? Distributor cap?

Postby Dale Finch » Wed May 22, 2019 10:22 pm

Is the coolant leak from the outlet gasket at the head or the hose? Often the outlet area covered by the hose gets deeply pitted from corrosion and allows coolant to leak. If it's the hose area, you might try tightening the hose clamps, but you will probably need to remove the hose, and smooth the surface of the outlet where the hose seals. I have spread JB WELD on the outlet and sanded it smooth, painted it, then installed a new hose.

If it's leaking at the base of the outlet at the gasket, then you are right about being careful to not brake those 2 bolts, especially the forward one. That one is very difficult to access. Good luck!

Oh, and there is no thermostat.

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Re: Carb rebuild? Distributor cap?

Postby Eugene » Wed May 22, 2019 10:30 pm

In hot weather, tractors with thermosyphon cooling systems, will run somewhere around 200 F.

Edit: If it's not boiling over, good to go.
I have an excuse. CRS.

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Re: Carb rebuild? Distributor cap?

Postby cody96ss » Wed May 22, 2019 10:58 pm

Dale Finch wrote:Is the coolant leak from the outlet gasket at the head or the hose? Often the outlet area covered by the hose gets deeply pitted from corrosion and allows coolant to leak. If it's the hose area, you might try tightening the hose clamps, but you will probably need to remove the hose, and smooth the surface of the outlet where the hose seals. I have spread JB WELD on the outlet and sanded it smooth, painted it, then installed a new hose.

If it's leaking at the base of the outlet at the gasket, then you are right about being careful to not brake those 2 bolts, especially the forward one. That one is very difficult to access. Good luck!

Oh, and there is no thermostat.


It’s leaking from the seam at the head, I have already replaced the hose and sanded down the fitting.

As for the boiling over... coolant was coming out of the cap, but it’s old and I’m sure weak. It has the overflow hose ran down the side of the radiator but nothing was coming out of it... thinking about installing a Ball Jar on it to catch the overflow and act as a reservoir... I’ll be back at it tomorrow!
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Re: Carb rebuild? Distributor cap?

Postby Larry B » Wed May 22, 2019 11:09 pm

The cooling system is a thermosyphion system. There is no thermostat or water pump. Hot water rises from engine to upper part of radiator water is cooled by air pulled through radiator and cooled water sinks to bottom of radiator and flows back to engine through the bottom hose. I don't know what the max temp should be but as long as the radiator is not corroded up inside and the screen and fins are free of grass and the cap holds pressure it shouldn't overheat. Mine runs pretty hot when mowing. If it boils coolant it is too hot.
Clutch adjustment is .015-.020 gap between clutch plate and pressure plate with clutch fully depressed. Should have about 1.25" of pedal freeplay travel.


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