301 gas issues

WE have a 715 combine with a 301 gas in it. It has started to miss when the engine gets warm. We have replaced points, condenser, coil, plugs, wires, wire to coil, cleaned carb and checked fuel pump. what could be causing this. It starts fine and runs till the engine temperature warms up. We are pullng our hair out.

Your problem is real simple change the grade of gas. It needs 93 octane . Old engines do not like new gas. when these engines were new they were designed to run on the regular gas of the day. Most gas stations and gas delivered to the farm was no less then 93 and for the most part 95 octane . 87 octane is designed to to meet emissions in cars and light trucks of today it burns fast and hot , alot hotter then the 93 does. My friends and i still run a lot of old gas powered equipment and as long as we run the 93 we get along just fine . your octane requirements are in the Org. owners manual .

I don't ever disagree with Tractor Vet, ever.

However, just don't think fuel is your problem.

Adjust those valves; they are sooooo darned particular 'bout their adjustment and things have worn a bit over the years.

Valves have (for all intents and purposes) moved "up" in their guide travel as the valve face wears and now they are running too tight.

Engine gets hot; clearances close.

Just an alternative view, be it right or wrong.

Allan

(quoted from post at 08:18:40 10/18/11) I don't ever disagree with Tractor Vet, ever.

However, just don't think fuel is your problem.

Adjust those valves; they are sooooo darned particular 'bout their adjustment and things have worn a bit over the years.

Valves have (for all intents and purposes) moved "up" in their guide travel as the valve face wears and now they are running too tight.

Engine gets hot; clearances close.

Just an alternative view, be it right or wrong.

Allan

Click to expand...

Yep, that's the first thing that came to my mind.

It ain't the valves, If anything it may be the timing. And that spec. i do not have . They will run when ya can throw a cat between the rocker arm and the valve stem . I went thru this gas issue even on my old Massey 300 . I was tryen to be cheap and save a couple cents on fuel . with the 87 in it she would run way over 200 degrees on a cold morning with no power checked everything and replaced the water pump pulled the rad and had it rodded out and flow tested . Went to get gas one morning and the station was out of reg. so i spent the extra 20 cents for the high test and it ran all day at 190 and it got real warm that day had no power issues and even used a bit less gas . And on the Farmall tractors they need the better grade fuel as with the combines . Myself i would get the timing spec.'s and check that and there is no doubt on the fuel issue here as when working that engine is working at full load and the 87 will pre ignite and cause and issue . If you are doing nothing then you may and i say again you may get buy with the lower grade BUT are you willing to take a chance of seezen a piston ?? I have a collection of them and i do not get my rocks off fixen them . We run the bag off the two 706's we have over the past couple weeks between hauling silage and grinding feed . And if ya don't think dragging a BIG silage wagon don't stress them think again, at between 28-30000 lbs loaded.

I think fuel is the problem... But, did you replace the distributor cap? It might be cracked and isn't a problem until warm. At night, pitch black, darker than dark, start it up and look for arcing. Check the whole ignition system. Get it warmed up to duplicate what is happening in the daytime. Wayne

Had a new spark plug that had and intermittent miss when warm once.
Was not in a 301.

I'd check you intake gasket.

My answer to everything: adjust the valves.

It wouldn't be my first guyess, but since you've done so much already, I'd say it's time to rule it out.

The valves warm up and their length alters slightly. If everything is worn so much that there's no gap, it could run fine cold, then warm up and start giving you trouble with valves not seating completely.

just read through some of the other answers here - the problem isn't if the gap between the rocker and the valve isn't to spec - I agree, that the gap could be huge and it'd still run (worn lifters).

The problem is when the valves themselves wear into the head and there's NO gap at all between the stem and the lifter. Then they can't close tightly - especially once they warm up and expand. Then they can actually leak a little causing all sorts of trouble.

Again - bit of a long shot - but easy and free to test, so I say why not just rule it out.

sorry - between the valve stem and the rocker! not lifter.

I had a similar problem with our 715 gas 301. Tried all the fixes you have done. Eventually is started to miss and stop. Finally took the distributor apart and found it was worn out and shorting. Replaced unit with a rebuilt and it solved the problem.

Check the in take manifold gasket, I had one that when the engine got warm it would leak and
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Clif