Irregular running of MF-35

From other postings I get the feeling that it may be caused by either restricted fuelflow or by vacuum problem in the intake beyond the carb. As I checked and tightend the manifold I do not suspect this to be a problem but I suspect a feedback line.

There is a feedback line from the valve cover into the intake manifold just above the carb.

Can somebody explain it's function (I think it is a pressure relief issue) and could this be related to the problems I'm seeing. I lifted the cover and the valves (tops) etc. seem to be in pretty good shape (for an inexperienced mechanic).

Could the engine be sucking in air through the valve cover seal or maybe even used air through the valve guides through this feedback? How would I check this?

regards.

Link
ml

Bill Stanley

I tried it again yesterday evening and it started a little hard as it died of fuel starvation (empty tank) the day before (I still have to get used to it's appetite for fuel!). Again it was running smoothly with the choke almost fully pulled (if you pull it fully it will override the governor and the revs go way up!. I sprayed the areas around the intake manifold and the connection of the ventline with ether to see whether the revs would go up but it did not.

When it was warm I eased the choke in and it made all the noises you described Greg (popping, banging like backfiring). The revs also started to oscilate as the governor was trying to get a steady RPM. I managed to push the choke in completly this time.

After a short period of "whobbling and banging" it settled down and started to run better and I slowly turned the low speed needle in 1/2 a turn and was running smoothly though a little fast. When I increased the revs (pulled the "gas" lever it picked up, immediately started making the same pops and bangs again and stalled out. I was too late to rescue it by closing the choke again.

By the way. The exhaust is not smoky at all (not blue not black, not white).

By then it was time to pay some attention to my wife so I had to leave it at that :-) (Boy these old tractors do have a tendency to keep you occupied!)

I will try to remove the vent line and plug it (not very easy as I have to remove the tank to loosen it at the top) Any more tips and tricks I can try before I go on a short break next week?

This has become confusing. What's wrong with disconnecting at the manifold which is right out in plain view, plugging the hole and testing the engine. Anything longer than five minutes on this test and someone is wasting time.

Bill Stanley

Good luck, keep us posted.

Greg

First off, the line you are describing sounds like it is a "positive crankcase ventilation" system and it is used to carry crankcase fumes and smoke back to the carb to be reburned. If that line is leaking, it shouldn't be causing your problems because the leak will be in front of the carb, so it won't lean your engine out. If this line is plugged, it could cause your engine to smoke more and would use more oil.

What puzzles me about your posting is that all the all fuel, or petrol/kerosene engines that I have ever driven use a small tank that is filled with gasoline only to start the engine on. The gasoline is used because it starts very quickly. The intake manifold runs through, or around the exhaust manifold to heat the kerosene up before it enters the engine. It sounds to me like you aren't using the gasoline to start your engine on. What you normally do is start the engine on gas/petrol and then after it has run for just a few minutes (5 minutes is plenty long) you shut off the petcock for the petrol and switch to the kerosene. If you do this it will run very well. I have an old green tractor that is gasoline only, but when we were farming it and would run low on gas, we could use kerosene or diesel in it but just like you, we had to choke the fool out of it to get it to run. We would have to run the tractor at full choke for a long time until the engine got heated up enough to finally run on the kerosene. Believe it or not, you have to choke an engine a whole lot more to get it to start on straight kerosene or diesel than you do with gas. Look around on your tractor and see if you don't have a small (1 or 2 gallon) spare fuel tank. If you do, put gasoline in it and see if your tractor won't run a lot better. If this is the case, start the tractor on this small tank and then switch to the larger tank with kerosene in it. Be SURE (very important) to shut off the gasoline tank before you open the kerosene petcock or else your gas tank will fill with kerosene and you'll be right back where you started.

Good luck.

The line looks like a positve crankcase vent but then for the upper part of the engine and it does get in the manifold AFTER the carb. That is what's bothering me. I'm using straight high octane with lead replacer to start and run the engine all the time. I have two tanks (a smaller inside the bigger one) and filled both of them with the gasoline. I suspect that the bigger one was contaminated with dried up kerosine (paraffin?) which may have clogged the carb when it was resolved by the gasoline.

You are right that the intake manifold is connected to the exhaust manifold which will it heat up. May this be a problem for the straight gasoline mixture getting too hot before entering the engine?

My Massey 35 which runs on gasoline has a plug in the location you describe in the manifold. Take the line off and hold a block of wood or rag to seal the hole and see how it runs. Doesn't cost anything to try.

We do not use a lead replacer in the US.

Bill Stanley

I'm not too sure about the gasoline getting too hot by going through the exhaust manifold. I know a lot of folks around here with the old kerosene burners just run them on straight gasoline now. I don't think that's your problem. It should start and run on straight petrol--it's just that it probably won't have the same horsepower with petrol than it would with kerosene.

I'm really puzzled about the line comming from your valve cover to your manifold. If this line goes into the manifold after the air and fuel is mixed in the carb, then it could very well be your problem. When you start the tractor and try to push the choke in, does it pop and bang and sound like it's backfiring?? If it is doing this, then you are getting an air leak and the engine is leaning out way too much. If the engine just dies after you try pushing in the choke, or sputters without all the banging and popping, you could have some trash in the carb. What you may try is to take the line off that goes from the valve cover to the manifold (I was thinking that the line went from the valve cover to the air breather--upstream from the carb). Take this line off and plug the fitting with a cap or cover that is very tight (air tight) and see if the engine runs any better. If after plugging the hole in the manifold the engine doesn't run any better, most likely your problem is in the carb. If plugging the line helps your engine you've found the source of your problem.

Good luck...keep us posted

You describe a condition where the engine is not getting enough fuel through the low speed circuitry. First and easiest thing to try is to adjust the low speed screw on the carburetor (the smaller screw). Second would be to shut off the line temporarily.

The line you describe sounds like it might be intended to evacuate the vapor in the crankcase back into the manifold to be burned. I have seen the technique used on cars which had a lot of blow by at the rings to continuously remove combustion products from the crankcase. Does the crankcase have another vent tube? It probably does. If so the design deliberately leaks air into the manifold.

In any event any leaking air into the manifold from anywhere creates less vacuum at the carburetor. Maybe the design is to accommodate the 'kerosine' aspect of the engine.

Bill Stanley

You say I should begin with the low speed setting of the carb (the little needle) I tried to play with it but it seemed to haven little effect. How quickly does the engine respond to changes? Does it have to burn excess fuel first (in case of a rich mixture) or should it respond immediately? I read that I should start to close the needles and then back them out again one to one-and-a-half turn. Warm the engine up and then try to adjust it by turning them back in again until the engine starts to tumble and backfire but I do not have a clue to hw resposive the engine will be to these changes. Could you give an indication?

Thanks for the help. I can try to get you some pictures of the engine details If you like?

Thyge Taageskov
Denmark

Bill Stanley