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Gerg

7117 predator re-power tested

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Gerg

I have two mowing's on the 7117 Predator re-power and here are the test results:

1st mowing

1- halfway through the first mowing I had some excess heat coming from the muffler that started boiling the gas.

solved - Installed pusher fan on front of engine and put fiberglass insulation behind the muffler overtop the engine. There is now no heat on the hood behind the muffler, gas tank or battery, here are some photos showing what I did.  

2- Had puffs of smoke coming out of the exhaust pipe.

solved - I had over filled the crankcase, removed some oil and it seems to have corrected the problem.

2nd mowing

Ran great, I have a lot of thick water grass in one area to mow which was a good test for power. I am having one issue - the engine runs real lean throughout its speed range and there are no mixture adjustments, It seems to run good on partial choke. If anyone has any ideas on the lean issue please let me know.

Thanks Greg  

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SimpleOrange

That lean fuel mixture is probably the reason your exhaust is hotter than usual.

 Replace the OEM jet  with an after market specially made to fix the lean fuel mixture.

 

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fishnwiz

Excessive heat can be a killer on any engine. Are you concerned at all that the fiberglass bating will stem air flow and increase heat buildup of the air circulating around the engine? 

 What about trying to use a autobody heat shield peel and stick material used on the flooring of muscle and high performance cars instead of the fiberglass as that should help with air circulation and deflect instead of holding your heat around the engine itself?

 Hopefully the lean fuel mixture fix will remedy your over temp issues.

Good luck.

Edited by fishnwiz

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bruker1

I like the fan idea and I think it should take care of the heat.

 

Not too sure about the pink insulation though...I'm getting itchy just looking at the picture.

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SimpleOrange

Gerg how high above sea level are you. Looks to me the Preditor engine is shipped with a carburettor with fixed jetting to run at sea level.

Higher altitude would cause the factory stock engine as shipped to run lean.

altitude.png

Edited by SimpleOrange

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rich_kildow

This thread shows where the adjustment caps are for the jets.  It would probably be worth seeing if it can be moved a bit more rich.  I'd worry about that insulation choking off airflow to the engine, but I really do like the fan idea.

 

https://simpletractors.com/forums/topic/60563-22hp-predator/?tab=comments#comment-483857

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PhanDad
2 hours ago, SimpleOrange said:

Higher altitude would cause the factory stock engine as shipped to run lean.

I believe it's the other way around.

A fixed jet will deliver the same volumetric amount of fuel regardless of outside conditions.  However air at altitude is less dense and has less oxygen and the engine will run richer.  (This is why carburetor equipped small  aircraft have a "mixture" control to lean the fuel mixture as you increase altitude.) 

 

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Gerg

I am about 600 feet above sea level, so I would think the standard jets would work but they don't. I was worried about air flow to the carb but as it turns out the air cleaner intake is to the rear of the tractor and there is no obstruction from the insulation, besides if there was it would probably be running rich. I checked and double checked the insulation to see if it was moving around and it doesn't. I didn't fasten the insulation down for a good reason, I park the tractor outside and remove it at the end of use. If I didn't remove it, the mice would think it was a supermarket (my cat cant keep up with them). I would like to get the lean problem cured, maybe I can remove the insulation permanently.

It did come with the high altitude jets and gaskets, if I knew what to drill them out to I could use them. I suppose something could be plugging them up, I should take the carb apart and look. As a note, the first I ran the engine it didn't seem to have a lean problem, it occurred after about two hours use.

By the way the fan works great, most of the air blows through the grill, some blows to the ground out front of the tractor and some blows muffler heat through the vents in the hood.

Thanks Greg        

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SimpleOrange
2 hours ago, PhanDad said:

I believe it's the other way around.

A fixed jet will deliver the same volumetric amount of fuel regardless of outside conditions.  However air at altitude is less dense and has less oxygen and the engine will run richer.  (This is why carburetor equipped small  aircraft have a "mixture" control to lean the fuel mixture as you increase altitude.) 

 

All WWII fighter planes were turbo charged the Germans were the first to use fuel injected engines. Fuel injection eliminated carburettors which were prone to icing up.

Fuel injected planes allowed the Germans to fly at higher altitudes.

Naturally aspirated engines rely on atmospheric pressure to fill the void created in the cylinder on intake, the carburettor is nothing more that a fancy atomiser. You may remember that your early Briggs and Stratton push mower were the carburettor sat directly on top of the fuel tank with a siphon leading to the bottom of the fuel tank. There was no fuel pump.

Atmospheric air pressure at sea level is roughly 15 psi.

Edited by SimpleOrange

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SimpleOrange
2 hours ago, PhanDad said:

I believe it's the other way around.

A fixed jet will deliver the same volumetric amount of fuel regardless of outside conditions.  However air at altitude is less dense and has less oxygen and the engine will run richer.  (This is why carburetor equipped small  aircraft have a "mixture" control to lean the fuel mixture as you increase altitude.) 

 

Interesting.

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Gerg

I thought that with less oxygen content at high altitudes you would need smaller jets (less fuel) 

to maintain 14.5 to 1 fuel air ratio. no matter what size jets at high altitude power output is less unless you add a supercharger or turbocharger. Does anyone know where I can find jet sizes for this engine?

Thanks Greg 

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Richard Wright

I agree with Phan Dad. Gill, I think if you read the Honda bulletin again, you will agree. It indicates that you will get a too lean condition (and excess heat) if you've modified the carb with the HIGH altitude jets and then run it at a lower elevation.

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SimpleOrange
32 minutes ago, Richard Wright said:

I agree with Phan Dad. Gill, I think if you read the Honda bulletin again, you will agree. It indicates that you will get a too lean condition (and excess heat) if you've modified the carb with the HIGH altitude jets and then run it at a lower elevation.

Glad to have you guys set me straight on this matter, have to admit I did not read the Honda bulletin in full detail but I did google what Phandad commented on aircraft equiped with carbureted engines running lean at higher altitudes.

 

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Gerg

The engine has the standard low altitude jets in it now, so it should work. I did look at the extra high altitude jets that came with it, there are two sets, one set for 3000ft to 5000ft and the other for 5000ft to 8000ft. The lower altitude jets have a bigger hole than the higher ones, also the paperwork says if you leave the standards jets in at high altitudes the engine will run rich. I will have to do one of three things get bigger factory jets, drill out the ones I have to a size that I am not sure of yet or run partial choke at reduced horsepower. I'm just guessing but with the added fan and running partial choke its putting out 20 horsepower instead of 22 horsepower, which still acceptable and shouldn't harm the engine as long as I can maintain the 14.5 to 1 fuel air ratio, it would be kind of like NASCAR restrictor plate racing. Winter will be a completely different story (maybe I better fix it).

Thanks Greg          

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