Generic gasoline engine tuning question

[studor]

You really do need a manual - the problem as you describe it could be everything from a stuck advance on the distributor to a governor out of adjustment to a carb issue.
What engine is in it and what carb? Lots of times there are crossovers with other tractor makes and often dealers will order parts for other makes for you rather than go the hundred miles.

 

[284 International]

According to what I've got, the engine make is Toyo-Kogyo (Mazda) model M471G The carburetor is by Nihon Kikakki, 18.6mm downdraft style. I haven't been able to find any cross-references for compatible parts.

 

[BeeferMan]

Too much fuel is not as common as not enough as there are lots of things that can reduce fuel flow, not to many that can cause too much. But in this case it sounds like too much fuel (to air). First thing I'd check is to make sure the choke is fully open...

 

[Jim Thompson]

284,
Curious if you've made any progress on this?
Jim

 

[SPYDERLK]

From all this I can think of only a couple good possibilities:
1] You have a little puddle of water under the main jet that doesnt quite reach it at idle, but gets sucked up to it as soon as you throttle up.
2] Your distributor cap is bad - when cylinder pressure goes up it is harder to spark a plug and the spark will take erroneous routes. Hence the popping.

To check for #1, get the engine reving good and then slam on the choke. Assuming you have the regular type choke that acts by obstructing the intake, this will suck some of the water out and should improve things. [This will not work with an enrichener type "choke".] If it improves its dry gas additive time .
To check for #2, clean the inside of your cap with alcohol and let dry thoroughly.

I dont think you have a significant rich condition or you would notice some black in the exhaust and smell the unburnt gas.
larry

 

[284 International]

I have made some minimal progress on this issue. I disassembled the carburetor and cleaned out the main and pilot jets, cleaned the float valve seat, and just generally sprayed the inside of the carburetor out. Everything looked clean and in good shape, and no gunk or varnish or anything came out.

I also discovered why, sometimes, there's a slight smell of gasoline when the tractor is running: The fuel pump diaphragm has dried out, and sometimes leaked a little fuel. However, after disassembling it to correct this, the gasket broke, so now it sprays a LOT of fuel. Since I'd rather not die in tractor fire, I ended up installing a low pressure electric fuel pump. On the positive side, the tractor now fires up almost instantly, since there's instantaneous fuel pressure to the carburetor. On the negative side, my tractor sounds like my '71 Nova drag car with a humming electric pump....

I cleaned the points and checked in the distributor cap, everything looked very clean and in good shape. I *think* I've ordered a replacement set of points, condenser, and a new coil that should all work from NAPA; we will see. It still doesn't feel like an ignition problem.

In experimenting more, and comparing the symptoms to prior experience, it feels a lot like an engine does that doesn't get enough fuel from the accelerator pump when the throttle is opened. It feels fuel starved, I think, when the throttle is opened. I think the slightly sooty exhaust and black plugs are from extended idle-rpm operation, and may be misleading as the actual problem (Since it doesn't like to run at rpm above idle very much, until it has been slowly worked up to it over 30 seconds or so.)

 

[Jim Thompson]

I'm not familiar with the exact engine that you have. Does it have an adjustable distributor where you might increase the timing.

Did you think to check the float level. With the carb inverted, it should be pretty near parallel to the top of the carb. I always shake the float while I have it off to insure that it isn't leaking.

If it fires off instantly, then the points are probably good. I would look closer at fuel and timing/ advance.

Jim

 

[SPYDERLK]

Once upon a time I had a set of new points that we installed at the same time we put in a cam chain. The engine idled fine but did crazy stuff if you tried to rev it. After disassembly to double check cam timing we finally put a timing light on it and found the spark going intermittent when reved. Put in the old points and it was fine! :confused2:. With the popping his problem definitely could be spark related.
larry

 

[Jim Thompson]

It absolutely could be spark related and the points could be bad. I never say never and I never say always when dealing with this sort of problem. My statement regarding the points was a best guess based upon past experience with ignition systems from the 50's, 60, and 70's. I am dealing with my perception of probabilities. I personally have not seen a properly installed and tested set of points behave in this manner. I have seen poor high rpm performance resulting from a weak spring but, not at low to mid rpm.

Sorry if I misled anyone.

 

[284 International]

The points that arrived do not fit, but the guy at Napa assures me he will get the right ones. It still "feels" like a fueling issue, running too lean, but the sooty black plugs imply otherwise, and sometimes it stutters briefly when at higher rpm, which very well could be an ignition issue. When quickly stabbing the throttle, the stumbling is improved by activating the choke. That appears to be improved and a little different after putting in an electric fuel pump. I'm still at a loss as to what else to try. Thanks again for all the tips and ideas.