706 choking out

Guys-
My 706 gas has decided to annoy me by choking out after running approx. 5 minutes or so. I"ve removed and cleaned the sediment bowl, disconnected the fuel line at the carb and checked for flowage, then hooked everything back up and it ran perfectly fine for a couple of days. Now we"re back to sputtering to death. If I pull the choke out I can squeak another couple of minutes out of her before she dies an inglorious death. Starts right back up again, but will only run a minute or so on restart and then does the swan song thing again. Does it need a bullet, or just another cash infusion?

Its probably because you"re not running high octane aviation gasoline in it. 87 octane makes the pistons swell up and your engine won"t run.....just ask some of the guys here...they"ll tell you. If you don"t believe me, just soak your pistons in a bucket of 87 octane gas and see if they"ll fit back in the cylinders.....yep, I"d say that"s your problem.

acts like there is something rolling around in the fuel tank, dirt, debris, soybean maybe, could even be dead earwig bugs. next time it stalls, drop the sediment bowl with a cup or something under there to catch the fuel and see if it slows to a dribble. if so something is in there.

First thing to try-let the gas cap be ajar. Could be the vent in the gas cap is not venting properly.

Float in carburetor not allowing enough fuel to flow into carburetor? I put a rebuilt carburetor on a truck engine several years ago.Truck would not get above 35 mph without dying out. Pull choke out and it would go a little farther. Set a minute and it would restart but continued to die out. Opened carburetor and bent the arm of float a little. Problem solved.

My 706 did the same thing. The gas tank had bits of rust in it that plugged the intake to the sediment bowl fitting. Even though the sediment bowl had little rust in it, the inlet was the problem.

Have a bucket ready and take out the entire sediment bowl assy from the tank. All the gas (and hopefully some of the rust) will come out. Look at the inlet of the fitting, there is a disk staked into the center. Under the disk are two slots the fuel enters the valve. This is where mine clogged. After two cleanings, I finally solved the problem by cutting the disk out and extending the inlet with a piece of copper tubing 1/4" dia by 1" long. This abandons the bottom 1" of your tank capacity. Apparently, the rust can't jump that high as I've had no more problems.

I understand the need for appropriate fuel. Research the issue, and you will find that the medium grades of today's fuel are equal to the old designation for that engine.

I for sure do not relate to your swelling of the pistons in a bucket of fuel. It is heat from preignition and improper combustion that overheats the aluminum pistons causing sezure.
Aluminum does not swell on exposure to fuel.
Do not take this as a flame, just info. JimN

Jim,

I do mean my comments as "tongue in cheek". Dry sense of humor or whatever.

As I mentioned in a previous post concerning this octane issue.......it isn"t the extra 20 cents a gallon that concerns me, buying hi-test over regular gas.

I just cannot understand why a low compression, 6 cylinder tractor engine needs a higher octane fuel. Furthermore, I cannot envision the heat expansion of aluminum pistons..to the point of seizure and/or scoring....due extra heat generated by a regular grade of gasoline.....alone.

Let"s assume....for the sake of this discussion alone.....that there was nothing but 87 octane available. What then? You just going to park it? Oh yes.....also assume there are no magic additives to boost the fuel"s octane. 87 is all there is and that"s as good as it gets. There is no pulling it apart and installing FORGED pistons...just cast aluminum.

I honestly wish I owned a 706 or similar and I"d see just how long it would survive on 87 octane.

I have a 706 gas, mine did this piston expansion and seized and scored my sleeves. I rebuilt this engine on 2 occasions because of this happening. I didn"t know about this tractor forum until I found a cure that works on my 706, I installed cooler plugs, it did have Champion D21s which a local tractor mechanic told me was to hot for this engine and 87 octane gas. I switched to a colder plug (Autolite can"t remember the #)and the tractor has not done it since. Just my experince, what it"s worth.
Bill

AHH that is the reality.
I feel that the temps found with 87 would be operational as well. A Triumph 750cc twin needs .010 piston clearance when cold. Its pistons swell .0085 when running under load.
Tractors run under full losd for hours at a time.
If they have preignition, or excess heat from poor cooling system operation, they will melt down. I do believe (in contrast to The Tractor Vet.) that the proof is in the detonation actually found in the engine, and the exhaust gas temp found. Gasohol also needs a bit more fuel to compensate for its reduced thermal content. JimN

Jan the piston in a 706 up around the rings are .019 to .020 smaller then the skirt and with .004 to .0045 skirt to wall clearance when working one with the 87 octane she will swell that top over .025 and will seeze her . As the 87 is way to hot at peck comb. as it is a really hot burn where as the 93 is a longer cooler burn . Also the org. pistons that came in them new were a forged piston that would take the heat away from the top faster and transmit is to the skirt faster and could take the heat better . Now days all ya get is the cast piston. Plus nobody uses these old tractors for WORK we are all suppose to go out and buy brand new DIESEL TRACTORS that have computer control . Took me long time to figure out my heat problem on my OLD GAS combine as i was tryen to be CHEAP and run the CHEAP stuff in her . Coould not keep the engine temp down below 220 , tryed everything first had the radator cleaned out then recore it with a bigger rad with and extra row of tube changed the thermostat twice still no help checked timing nothing i did was helping . Till one day i was out at a sale in Indiania and on the way out gas prices were 35 cents a gallon less then at home and it was harvest time for corn , i got the bright idea to buy a couple tanks at the sale and fill them on the way home . Got the tanks bought and stopped at the fuel stop to fill the truck and the tanks , well they had a pump that said FARM GAS and the octane rating on it was 94 and it was twenty cents cheaper then the 87 at home well i filled both tanks on the truck bed that was 325 gallon . Come home and filled the old Massey 300 and went to shelling , The old Massey dropped engine temp down to 180-185 and stayed there ran better . Got me thinking and got to checking in books as to fuel requirements for this pice of equipment and oh what do i find that this old Massey needed the higher OCTANE as she was built when the gas was higher then i started READING on the requirements on the 706's and what do i find that they NEED 93 in them . I had never given it much thought as i was usen HIGH TEST in mine way before i READ it. and I DID do tillage with mine . The bad part is that when REALLY worken any of the 6 cylinder they all need the good stuff . Since the hightest of today is not even close to the reg. grade of days gone by. Yes i am and old foggy and i did grow up in the day of hot cars and fast wimmen and back in the day of the big gas powered semis that burnt 105 octane gas and that was back whenthe 460 -560's were new then along came the 06's and the gas was better then today, If ya think i am joken here go buy a car from back in the 60-first part of the seventys don't care if it is a big hp motor or a ma and pa grocery getter and put the new and improved gas of today in it and see what happens . I have been building engines since 1963 from mild to wild and i can look at a engine and tell ya the what and why's it did what it did .

I agree 92+ octane runs cooler. I now understand your point. Mediocre pistons do no one any good. I am 59.5 and have built a host of engines from Maytag 2 stroke to nasty exotic race cars with four valve heads. If it is a function of bad pistons, then replacement with better would be worth it. But I don't own one, and there is no reason to get carried away. Jim

Hey guys-
Thanks for all the suggestions and comments. Very interesting stuff. I've never been a mechanic, nor have any illusions as to my skills with a wrench. But part of the "fun" of running these old tractors is not having to be a computer technician in order to tinker with them. I'm going to try cracking the gas cap open first, then go after cleaning out the gas tank/sediment bowl connection that several of you have advised if the gas cap isn't the problem. And I'm going to start burning higher octane fuel, if I can find it, when I get the old gal running again. I'll save the bullet for later.