TVT691 A couple of problems

PTmowerMech

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640221 Carbs. Bought new, installed but walked away from it for a long time to work on other stuff. A year later, there was dirt dobbers nest in the small air hole that goes from the front of the carb to the bowl. I busted the dirt, sprayed cab cleaner in it, but couldn't get it cleaned so I blew air through it. Something shot out of it. Don't know if it was the dirt dobber egg, or something that was supposed to be in the carb. The second carb. I cupped my hand over the end, to catch what ever blew out, and it blew through my fingers and got lost as well.
Question is, is there something important in there, that's gonna cause me to just replace both carbs? (the carbs are expensive)

Also, do they make metal bowls for these? All I'm finding are the plastic ones.

Compression is about 120 on each side. I got fire on both coils. but only one cylinder will run using carb cleaner or gas.

Any advice will be appreciated. This is the only 2 cylinder Tecumseh I've ever worked on.
 

PTmowerMech

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I have the same motor in my racer. These motors are torque monsters. Anyway I don't have the original carbs on mine I use 2 of the 17hp carbs. Here is a good breakdown for the motor that should help you.


http://www.smallenginesuppliers.com/html/engine-specs/tecumseh/Tecumseh_V-Twin_Engines_Service_Information.pdf

Thanks for the reply. In the pic I don't see anything going through the "atmospheric vent." So it must've been just the dirt dobber egg. At the moment, I think I can just replace the bowl cheaper than I can replace both carbs.
But, I would like to know the part numbers for the carbs you use. The ones I have on here, cost me over $250 for the pair.

BTW, the fuel pump is pumping. BUT, when I'm turning it over, with the fuel lines disconnected, fuel doesn't squirt out both ends. I'm wondering if that's normal for this. Obviously is pumping. But I have no way of checked to see if it's pumping enough.
 

MowLife

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The carbs are for 17 hp single ohv but bolt up to the twins. They have a bigger bore than the stock twin carbs and will drink some more fuel. 640072 is part number. Synchronizing them is required of course. I purchased the motor with them already installed by previous owner. Solenoids are disabled on them.
 

bertsmobile1

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Thanks for the reply. In the pic I don't see anything going through the "atmospheric vent." So it must've been just the dirt dobber egg. At the moment, I think I can just replace the bowl cheaper than I can replace both carbs.
But, I would like to know the part numbers for the carbs you use. The ones I have on here, cost me over $250 for the pair.

BTW, the fuel pump is pumping. BUT, when I'm turning it over, with the fuel lines disconnected, fuel doesn't squirt out both ends. I'm wondering if that's normal for this. Obviously is pumping. But I have no way of checked to see if it's pumping enough.
Squirt out of BOTH ends ?
Fuel pump has 3 lines
Fuel in
Fuel out
Impulse .

The fuel out has a check valve on it so fuel can only pass one way.
Some of the better ones had a check valve on the inlet as well.
So the side that has 2 inlets is the in side
the tube on the top is the impulse line & pushes & pulls a diaphragm that does the pumping.
On the outside is a sintered bronze filter to allow the air on the other side of the diaphragm to get in & out
These get clogged and reduce the efficiency of the pump.
 

PTmowerMech

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Squirt out of BOTH ends ?
Fuel pump has 3 lines
Fuel in
Fuel out
Impulse .

The fuel out has a check valve on it so fuel can only pass one way.
Some of the better ones had a check valve on the inlet as well.
So the side that has 2 inlets is the in side
the tube on the top is the impulse line & pushes & pulls a diaphragm that does the pumping.
On the outside is a sintered bronze filter to allow the air on the other side of the diaphragm to get in & out
These get clogged and reduce the efficiency of the pump.
What do you suggest cleaning the bronze filter with? I'm skeptical about compressed air or carb cleaner. Sea foam spray isn't too harsh. How about that?
Or replacing the pump all together? What's your suggestion?
 

ILENGINE

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old toothbrush would be fine. it isn't that critical like some other things. Just not packed full of dirt and other stuff.
 

MowLife

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Probably easier to get another pump. I replaced mine for 18 bucks from my local mower shop.
 

bertsmobile1

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I spray them with degreaser then use a tooth brush.
Not much gets through them.
Dust accumulates on the outside and blocks them off

The pump will still work with it blocked but at a lower capacity.

having said that the pump can shift about 20 times the volume of fuel per minute than can pass through the main jet.
The bulk of pump problems are people hooking them up wrong, usually backwards.
 

PTmowerMech

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Well I got everything ironed out, and working. Fired it up, and worked like a champ. I can't say I'm happy with this one speed stanley mower though. But that's beside the problem.

For two week, this engine ran great with the new carbs. Today, i fired it up, and it's surging. Low idle, high idle doesn't matter. I tried choking it a little at a time, and nothing changed. Except at a certain point, it chokes it up and tries to die. (like it's supposed to)
At high idle, it not only surges, but coughs quite a bit. Almost a backfire.
A few times, when I go from high idle to low idle pretty quick, the surging would stop. In fact, i let it idle (without the surging) for about 10 minutes. I increased the idle a little at a time, until it started surging again.
From that point on, it never stopped surging, no matter what I did.

I've put all new fuel lines and filter on it, along with a new air filter. (didn't replace the fuel pump),
 

bertsmobile1

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Put your finger on the throttle rod and see if it will hold a constant speed then slowly increase the speed.
Listen to the engine to see if it starves or is running rich.
Also try new spark plugs..
When I do this i Put an inline red spark tester on the plug wire.
This will enable you to see if you are getting a proper spark or not.
Also try saturating the area between the carb & the inlet and see if it sucks the WD 40 into the engine.
You will get speed changes and white smoke if it is sucking .
 

PTmowerMech

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Put your finger on the throttle rod and see if it will hold a constant speed then slowly increase the speed.
Listen to the engine to see if it starves or is running rich.
Also try new spark plugs..
When I do this i Put an inline red spark tester on the plug wire.
This will enable you to see if you are getting a proper spark or not.
Also try saturating the area between the carb & the inlet and see if it sucks the WD 40 into the engine.
You will get speed changes and white smoke if it is sucking .
It does hold a constant RPM. Although I didn't try it a low rpm. Only mid for a few seconds and increased it a little at a time.
The cheapo temp reader (harbor freight) shows both cylinders are about 400 just out of the head. Not sure the accuracy of the reader, but surely the reader wouldn't be off the same amount on both sides.
IIRC, there are new plugs in it.
That's all I can specifically remember right now. Will check the gaskets, (WD40) tomorrow.

I was told my old small engine guy, years ago, that these carbs have to be set to match each other. I don't see any settings on these carbs. Except the low idle screw.

BTW, could surging come from a slow pulse rate from the fuel pump?
 

bertsmobile1

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Volume wise the pump can move about 10 times the fuel per minute that the carbs can.

By holding a constant speed I am talking for a bit longer than a few seconds


We have to work out if you have a fuel supply problem, a spark problem or a governor problem.

So you start the mower put your finger on the governor rod to prevent the governor controlling the throttle.
You then hold it at idle for a few MINUTES then gradually increase the throttle till you get to full revs.

If the fuel supply is insufficint then the engine will stall out lean.
If it runs just fine at all speeds then there is a problem with the governor.
If it misses a little then fires & blows a little black smoke then misses again you have a problem with the ignition.

Same story with the spark tester.
If the ehgine is running fine then starts to miss and the flashing is erratic you have a spark problem.

And as for both cylinders being being the same temperatures , if the kill wire or one of the kill switches is faulty and making a ground, the engine will miss on both cylinders.

There are a variety of tests that can be done.
We don't ask you to do them because we like to make you run round like a headless chook.
We ask you to do these things so from the results we can work out what is actually wrong with your engine.

Remember we are here on the end of a computer screen & in my case 1/2 way round the world away.
If I was there drinking your beer I could tell you what is wrong by the way it runs & misses by what it sounds like & smells like.

If you can not be bothered then go play hunches and replace things at random, sooner or latter you will get lucky .
 
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