Carb Issues with 64 704

[1964 704 20]

Hi All, I am having some repeated issues with a 64 704 that I purchased a while ago. Thanks for all the assistance in the past.

 

It will start and idle just fine, and used to throttle up and down using the throttle cable from dash without any problems for the first 10-15 minutes of operation, then it would throttle down and almost die, if I gave it throttle at this point, it would die and backfire. I had already cleaned the carb with new needle valve, float was adjusted properly, and has new gaskets. The electricals (points/condenser/plug) are new. The fuel pump diaphragm was replaced precautionary as well.

 

It was recommended that I adjust the high and low speed idle screws (I'm guessing they meant the main fuel mixture and the idle fuel adjustment screws). I pulled both screws out of the carb (made reference to how many turns it took) cleaned out the holes in the carb with carb cleaner and cleaned off the needles as well. Installed back in carb and adjusted per the Kohler manual. The gas tank was cleaned recently, and an inline fuel filter was installed as well.

 

Now it only starts at idle, and when increasing the idle from the carb, it wants to die immediately, unless I coax it a bit and very slowly increase the revs at the carb and it will throttle up and stay that way for a while. If I pull the throttle cable from the dash it will die and backfire, if I push the throttle back in, it will start right back up at a slow idle, but will not want to increase it's revs. It smells as if it's running a bit rich, but accoarding to the Kohler Manual, I had the motor at full throttle and backed main fuel mixture screw off until it wanted to die, and then re-adjusted the main fuel mixture screw until it was idling smoothly. The Idle fuel adjustment screw was adjusted per the manual as well.

 

Still same problem, will die if I give it throttle.

 

I really want to start using this old horse and any suggestions/guidance would be greatly appreciated.

 

Thanks,

 

Dan

[buckrancher 2,672]

are the small holes in the main fuel needle clear?

[1964 704 20]

Thanks Buckrancher, I will check the main fuel needle (the smaller of the two correct?) the larger needle (Idle adjuster) has several holes in it that are clear. There is one hole toward the bottom pointed end that does not go all the way through though.

[buckrancher 2,672]

if you have a carter carb the main fuel needle ( long one with small holes in side of needle) is the one that screws down in from the top of the carb by the throttle control

should be around 3 turns out from bottom

low speed mix screw should be around 1 1/2 turns out from bottom this one is on the side of the carb

Edited August 13, 2013 by buckrancher

[1964 704 20]

Attached is a picture of the Carb, not sure what brand it is. I checked the top screw as you suggested, it's the long one with it looks like 4 holes in the top that go all the way through, one in the middle that goes all the way through and one on the bottom towards the pointed end that does not go through. I readjusted them and will see what happens. I attempted to load the pic, not sure if it worked.

Thanks for the help.

[squonk 38,844]

Another thing is the fuel pump actually pumping? I replaced the pump dia. on my 704 and it still didn't work. The tractor would run fine on more than 1/2 tank but get below that and it would start acting up..

[1964 704 20]

Thanks for the fuel pump thought Squonk, now that you mention it, that could be part of the problem. The pump is working, it spits out fuel when I crank it over with the fuel line disconnected from the carb. How did you determine that the fuel pump was not working? and how did you fix your problem?

[squonk 38,844]

It quit on me one day and the tank was about 1/2 way down.. I had spark and the carb had just been rebuilt by an old pro. I decided to add gas and it started right up. I used it again and when it acted up it was at 1/2 tank again. I got another vacuum pump at a show and sent to Then & Now automotive. This was 3 yrs ago. It worked great afterward but recently it has started to run a bit funny again at 1/2 tank. FILL ER UP !!

[1964 704 20]

Buckrancher, thanks for the tip on adjusting the carb, it worked! I was able to throttle up and down now without any hesitation.

 

It ran fine for about 10 mins at high throttle, then did what it has been doing and would not run above idle.

 

Squonk, thanks for the fuel pump tip, I actually disconnected the fuel line while it was running and a steady stream of fuel was coming right out, it sputtered a little bit, reconnected the fuel line and it kept running. I also tested the pump out while cranking, and it would spit out fuel as it was cranking, so I am guessing that the fuel pump is working.

 

One Item I will look into is the needle valve for the float. I remember when I removed it to replace it with the new one, that it was missing it's rubber tip, I think I cleaned out the hole where it goes, but there may be some crud stuck in there. To me it seems like a fuel starvation issue, once it is cold it will start right up and run great for about 10 mins, and then slowly start dieing. With all the other things that you folks have helped me diagnose, I am hoping it is something simple like a  maladjusted float or crud where the needle valve goes.

 

Thanks for all the suggestions, this is a great forum.

 

Dan

[buckrancher 2,672]

where is your fuel line routed from the gas tank?

[1964 704 20]

The fuel comes from the petcock to the fuel line to an inline clear fuel filter, to the side of the motor above the belt guard and below the muffler and attached to the fuel pump via the 11mm nut that threads into the fuel pump that the rubber fuel line attaches to it.

[buckrancher 2,672]

The fuel comes from the petcock to the fuel line to an inline clear fuel filter, to the side of the motor above the belt guard and below the muffler and attached to the fuel pump via the 11mm nut that threads into the fuel pump that the rubber fuel line attaches to it.

sounds good as long as whatever you are useing for a muffler is not to close to the fuel line and causing vaper lock

 

Brian

[1964 704 20]

I was wondering the same thing Brian. The muffler is routed correctly from what I have seen on other models of similar vintage. The previous owner put a piece of sheet metal below the muffler, but above the fuel line to mitigate vapor lock I believe. I also checked the fuel line while it had been running for quite a while, and it did not appear to get warm or be affected by the heat from the exhaust.

[WH nut 553]

Check the screen in the bottom of the tank. Remove the petcock to see.

[1964 704 20]

Thanks WH Nut,  The screen looks new and you can see through it. There is no blockage coming out of tank.

[buckrancher 2,672]

have you checked the fuel flow at the carb from the fuel pump when she will only run at idle?

 

brian

[1964 704 20]

When I disconnected the fuel line from the fuel pump to the carb at idle it would come out in a  steady stream (which in my opinion is enough fuel to fill the float bowl). With the engine stopped and when cranking over it would pulse out with the revolutions of the motor.

 

I was even able to disconnect the fuel line to the carb while it was running, the fuel would stream out like mentioned above, and then the motor would start to sputter, I reconnected the fuel line and it would idle normally.

 

It typically happens at around the 10 minute mark, and once I attempt to increase the throttle at the carb it would want to die and evenutally does When it does die, it backfires through the carb as well. When first started and for the first 5-8 mins, it revs freely without hesitation.

 

All of this testing has been with the tractor sitting in a shed for those 10 minutes. I am not riding it. Also, the muffler is correct for the model and year and installed correctly according to the Manual.

 

Thanks for the assistance Brian.

 

Dan

[buckrancher 2,672]

the ten minute thing bugs me I wonder outloud if the problem is the coil under the flywheel breaking down under heat

I've seen points do this idle only thing but right from startup

 

Brian

[1964 704 20]

It's got me baffled as well. the coil and the points are both new, if there was a problem with the electricals I would think like you said that it would be from the start, and not after 10 mins. You do have an interesting point though about the coil getting heated up. The motor has an aftermarket 110v electric starter that I plug an extension cord into to get it started, but I can't really see that creating any problems. 

 

I even wonder that while it sits in a 10x10 shed that maybe it is getting too hot, but the top of the engine shroud is not hot at that point and even when it does die, I am still able to get fuel to the carb.

 

Dan

[WH nut 553]

Have you changed condenser?

[1964 704 20]

Yes WH Nut, the condenser and points are brand new.

 

I just got off the phone with a guy that runs a mower repair business, he thinks that the engine is losing compression which is why it is dying after about 10 mins, and suggests a complete rebuild. I thought that when a motor loses compression, you typicall get oil blowby from the exhaust as in blue smoke. this is not the case with my motor. I did mention to him that the exhaust valve was sticking when I originally pulled the head to diagnose it, his comment was that if I did not properly grind the valve down it could cause this problem. And then proceeds to tell me that the rings are bad as well. I am not an expert, but this engine feels like it has adequate compression.

 

Any thoughts or suggestions are appreciated.

 

Dan

[Martin 2,130]

how did you take care of the valve sticking problem?

 

as far as the rings go, i would think that would show up as oil smoke from the exhaust. 

 

if you think its loosing compression when it gets hot and its not blowing smoke, maybe the valve is sticking open slightly.

 

im not discounting others theories on electrical (ignition) problems though......

 

is a compression check worth taking hot and cold to see whats up there? im not familiar with these engines whether they are acr or not, but you could still maybe see a reading difference from hot to cold if compression is the problem....

[1964 704 20]

Thanks for the response Martin. The stuck exhaust was pretty simple, sprayed a bunch of pb blaster on it, and very lightly tapped it a couple of times, and it popped right back into place. I then scraped the carbon off the head, piston and valves and cleaned everything off. I have pulled heads before and have cleaned like this in past with success.

 

I would agree with your assessment of the rings.

 

As for the valve sticking open, I will do a before and after compression test. I will check the compression when cold and see what the variance if any is when it is hot. I looked in the Kohler engine manual for cylindr compression ranges, but found none. Do you know what the compression should be?

 

All electrical components are new and from Kohler dealer.

 

Thanks again.

 

Dan

[Martin 2,130]

if you have a manual, it shows methods for checking compression with acr. not sure what manual version you have but my paper manual rev 5-73 has all the info you should need starting on page 9.1 under 'engine- general service' and then the next section on 'kohler acr' look at page 9.4 and it describes one method (never tried this).

[Anglo Traction 759]

Dan, I will only chip in with one other thing to check that has not been covered yet, if only to rule it out.  Just check your Fuel Cap on the Tank and make sure the vent is clear. If it blocks up, a vacuum occurs when the motor is running and will eventually starve of fuel.