MF35 Engine Loses Power

Crawford151

New User
I have a 1964 MF35 with what I believe to be a Continental Z134 (4 cylinder), engine. The problem I'm having is after running the tractor for awhile (30 minutes to 1 hour), the engine begins to backfire through the exhaust and loses power. The backfires at first are barely noticeable "pops" coming from the exhaust. However, after that starts, when I shut the tractor off I get a burst of flame coming from the exhaust. Also, when I was bush hogging (a pasture with 12"-18" tall grass), before the engine started "popping", the engine would get bogged down (a 500-600 RPM drop), several times during each pass. But after the "popping" started, the engine would bog down with a 700-1000 RPM drop, and never climb back up to the RPM I had started with. However, previous seasons, the tractor would do the same field without any decrease in power, regardless of how high the grass was.

Over the winter I performed the following to the tractor:

1. Complete fluid exchange (oil, hydraulic fluid, coolant);
2. Replaced the hydraulic pump;
3. Rebuilt the carburetor, (not sure if my settings are now correct);
4. Replaced a missing spring on the governor and adjusted it;
5. Replaced the friction pad on the throttle;
6. Installed a "tee" in the fuel line with a return back to the tank, (someone had told me the engine was vapor locking, and this would cure it);
7. Replaced the clutch, pressure plate and throw-out bearing;
8. Installed a high-temp coil;
9. Full tuneup (plugs, condenser, wires, points, rotor & cap);
10. Replaced the speedometer cable;
11. Replaced the oil pressure line; and
12. Adjusted the valves.

Anyway, I would really appreciate any help with this problem. The only thing I can think of is the carburetor setting is too rich and fuel is building up in the exhaust manifold. But I need a second opinion, even it's to only tell me how to properly adjust the carburetor.

Thanks for taking the time to read this post and I look forward to your input.
 
If it backfires it's electrical. Check your points. Set at 23. Some say they have trouble with some new points and condenser but I've never had that problem. Sparex points. Adjust carburetor--the small screw is 1/4 turn(air) large screw(gas) is 1 1/2 turns. This will get you running then you may have to adjust. If it hesitate's when you open throttle wide open adjust large screw open a little. Some time the small may have to be turned down. Just fine tune it.
 
Back fire is one of a couple of things. Running lean will cause it so if choking it help it is likely to be set to lean. Or you have a bad new condenser. I have not change a condenser in over a decade due to bad condensers being common now days. Or your points are set wrong or you have the timing off. Any one or a combo of these can cause your problem
 
I had the same/similar problem on a 65 Continental gas. Turned out to be the long idle screw in the bottle of the carb was turning due to vibration. I replaced the tiny O-ring which by compression holds the screw in place ...my problem went away. Not sure if it is the same carb. and perhaps that O-ring was replaced when your carb was overhauled.
 
(quoted from post at 10:31:10 05/27/18)
12. Adjusted the valves.

If you get them a little too close, when it heats up and things expand it may not be letting one or some of the valves close completely. I never want my valves to be too quiet.
 
UPDATE: Changed the condenser, made sure points were at .023 and timed the engine. Ran great after that...until the weather turned really hot again (90+). And today it's the same old BS. Started bush hogging (92 degrees when I started), ran about an hour and then started popping through the exhaust and slowly began to lose power. Within 5 minutes I had to shut down the PTO just to keep the tractor running to get it back to the shop. Strange thing though, when I pulled it into the shop and brought the throttle down to idle, it purred like a kitten. But opened up the throttle completely and it was only turning at about 1400 RPM, with no attachments running, and backfiring through the exhaust like crazy.

I am completely dumbfounded. Any help would be very much appreciated. And thanks to those who have responded so far.
 
Where did you get the points, and condenser from, the cheap ones that you find at most places aren't very good, like the condenser which sounds like what your problem is. Does your tractor have the clip on distributor cap, or the one that is held on with 2 screws.
 

UPDATE: Tractor ran fine the remaining part of 2018 (after taking everyone's advice - thanks to everyone who helped), and the first part of this year, until last week.

Had been bush hogging (field 24" and higher), for about an hour and a half when it started losing power. However, did not notice any pops coming from the exhaust this time. Would bog down to 400 - 600 RPMs, and I would have to engage the clutch, completely disabling the bushhog, to let the RPMs build back up. But each time I went through this procedure, the engine RPMs would max out at 50 - 100 RPMs less than it did the previous time.

Finally brought it back to the barn to let it cool down over night. The engine temp by this time was approaching 280 degrees. So hot the engine was smoking. Checked the coolant and it was full, with no bubbles, which indicates no air was getting into the system. The following day I changed the attachment to a 72" finish mower, to cut an area which had regular grass about 6" in height. After about 10 minutes of cutting it started doing the same thing as the previous day, with a new twist. The pasture has a slight upgrade to it (less than 2 degrees), and when making an uphill pass the engine would bog down so much it barely pulled itself along, even with the PTO disengaged. Headed back to the barn again, at full throttle (which is normally around 2500 RPMs with PTO disengaged), but the RPMs would get no higher than 1,000 - 1,200.

I am really at a loss as to what could be going on. Please help!
 
Something if starving the engine of gas.

In all the work performed I don't see anywhere cleaning the fuel tank, petcock, fuel bowl, and flushing the fuel line, cleaning the screen at the 90 deg. elbow.

Seems like under load, or going uphill some sediments maybe moving in the tank blocking the fuel inlet enough to starve the fuel bowl, how large if the bubble at the top of the fuel bowl? Ideally there should almost be no bubble and you should see the flow of fuel.
 

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