A Question for the Brain Trust

super99

Well-known Member
My Oliver 1550 has been running great this summer. I rebuilt the carburetor and in order to accelerate without stumbling, I have to have the load screw opened 4 turns. I pulled the spark plugs and this is what they all look like.
cvphoto101005.jpg

According to the pictures I have seen, its running too rich, but If I close the load screw even 1/2 turn, it stumbles on acceleration unless I pull the choke out a little. I dont have any heavy loads to put it under to work it, but hopefully there will be some plow days coming up that I can work it some. It has Autolite 386 plugs set at.025 per the operator manual. I havent taken time to run a compression test yet. Is this normal for a non working tractor?
 
Ive seen that happen very often on light use and parade tractors.

Things that can help are 1) To use t stats or shutters etc to get and keep the temperature up OPERATE AT HIGHER TEMPERATURE,,,,,,,,,,,,2) Try a hotter plug like the Autolite 388,,,,,,,,,,,3) Run the carb on the lean side but just enough so it will take fuel and run okay under those light loads,,,,,,,,,,,,,,,4) Make sure the air filtering and inlet pipes etc are free and clear and the choke butterfly is opening fully,,,,,,,,,5) Insure the ignition and plugs points wires and condensor are in shape and the timing is accurate and NOT too slow

Hopefully others can add more tips to this

John T
 
Some carbs have only one adjustment screw.
Some carbs have high speed and low speed screw.
Some carbs the screw is backwards, turn in the screw on farmall and it goes rich. The farmall has only one screw. To lean the mix, I have the screw all the way out.
One screw on Jubilee is backwards too, the idle screw.
I agree, your plug is saying it's running rich.
I would have coated the carb gasket with RTV to make sure no leaks.
Good luck.
 
JT,
Agree, One time I had to run Jubilee with choke because the points were bad. Totally shot. Hard to start too. No power under load.
 
I haven't checked the temp with the infra red thermometer, but the guage runs in the middle of the scale, so I'm guessing it's OK. I've tried closing the main jet a half turn at a time. I've had it down to open 2 1/2 and it runs OK with no load, but if I drive up a hill, I have to pull the choke out to get to the top, so I open it back up. It has a new air filter and the system is clean and the butterfly is open all of the way. I haven't check the timing yet. It has new wires, cap, rotor, points and condenser, plugs were new 50 hours ago.
 
Looks like the main jet is a little rich. Acceleration is usually controlled mostly by the idle circuit and the knurled headed adjustment/screw needle which is usually found near the the top of the carburetor close to the outlet. This is often referred to as the low speed circuit adjustment also. There are usually 2 or 3 tiny holes in the carburetor body that are near the throttle butterfly. There may be at least one on the engine side of the butterfly to provide fuel for idle when the shutter is close. Air flow through the venturi will be very little at low speeds. As the engine starts accelerating these little holes provide fuel for that since there is not an acceleration pump or well provided. These holes are very small and are different sizes and most require a very small wire like a bread wrapper tie wire to clean out and are many times missed when cleaning the carburetor out. You should check them and if they are open you can spray cleaner or something into the idle adjusting screw hole and see it come out the tiny holes. The idle circuit needs to be adjusted correctly for both the idle speed and mixture. As you adjust the idle speed it will also change the main jet setting some so they need to both be adjusted probably several times to get it right. These adjustments are related and often one will affect the other one slightly. Most idle circuits run 1 &1/2 to 2 &1/2 turns open when correctly adjusted. This is not absolute truth though and yours may vary but the instruction manual should give an approximate setting for both. The main jet is best adjusted under a load.

Gene Davis Tennille, Ga.
 
I'll check and see where the idle screw is set, I don't remember off hand, but the little holes are open and I have the idle set at about 500 rpm's.
 
Mine does that till it warms up a bit. Haven't pulled plugs in a few years and I haven't used it for haying for three seasons now so I probably should check them. I find the idle mixture screw has very little effect on the low idle.
 

Yes, those plugs ARE a little sooty, but I wouldn't worry about it. I've seen worse and the tractor still ran just fine.
 
They look good to me, especially for not getting worked hard. Some of the soot could be oil. The insulator is perfect!

Set the carb to what runs best.

Not having an accelerator pump, it will have to be slightly rich to not stumble. Nature of the design.

Most updrafts, the idle mix screw adjusts air bleed, not fuel, so turning the idle screw in richens the mix, out leans it. But that adjustment will have very little effect on the overall mixture.

If it were mine, I would be very happy with the plug reading!
 
(quoted from post at 10:08:41 09/13/21) They look good to me, especially for not getting worked hard. Some of the soot could be oil. The insulator is perfect!

I agree, you read the insulator when reading plugs.
 
I agree with Gene Davis- the idle mixture has a lot to do with smooth acceleration. And also have seen points closing up cause a stumble, too. Mark.
 

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