1948 JD A. - No Power

[wigfimml]

Completely overhauled a 1948 JD A over the past 5 years. Complete meaning engine sleeved, crankshaft resplined, transmission reworked, new valves, NOS governor gear and pinion, magneto, carburetor etc. Started it for the first time over the weekend. It started right up and runs very smooth but notice it has very little power. Power is less than running only on one cylinder although this is clearly running on both. Say would have trouble going up a small incline in first.

I suspect the carburetor, as the load screw seems to have no effect although I am only idling under no load. As I remember you could set the idle screw in and the tractor would still run but rough and surge as it get gas through the load channel. This is not the case here, as the idle screw gets set in the tractor just slows and fstoops running. If this channel is blocked would the symptoms be as I described?

If not what else could possibly let it run so well at idle but severely limit its power. Timing, Valve lash, governor, magneto?

Thanks in advance for any advice.

 

[Ben.So.Tex.]

Take your oil bath off and see if it runs better, if it does your air intake stack may be plugged with mud dobber's

 

[wigfimml]

Simple to check I suppose but really not a chance of that. Air intake was completely cleaned and painted. Was also one of the last things on in a clean garage.

 

[MrJDMan80]

I would start by checking your timing. Easy to do. If that is proper then make sure you spark is strong. Next, inspect the carb.
Tim

 

[buickanddeere]

Complete overhaul include a re-ground cam and followers? New valve springs?

 

[Mike M]

Run it above idle but not all the way open.

Now you should be able to have one carb. adjustment open at a time and it still run.

Close the load it will run on idle circuit,open load and then close the idle it should run on the load.

idle appox 1 3/4 -2 turn open
load appox 3/4 -1 turn open sometimes more ?

If it does not pass this test you need to clean the carb. passages until it does.

If it does pass make sure your throttle linkage does not bind and the RPM's at no load "fast idle" are set where they are to be at.
If you set the "fast idle" at the load setting it will really effect power on these.

 

[wigfimml]

Yes and yes

 

[wigfimml]

Thanks, This is exactly what I was looking for. It is what I thought should happen but was not trusting my recall. I'll repeat this over next weekend and try this again. I possibly did not have it at a high enough idle.

If it still cannot run on just the load open on the carburetor, I 'll try a second one that I have lying around. I'm reluctant to open the Carburetor as it was sent out and professionally rebuilt. It's also another reason I was thinking it was more apt to be something I did, which comprises 90% of the other stuff. However, the carburetor did sit over 4 years since it was rebuilt, but did sit clean and dry all that time.

If the weather next weekend is good I'll post back the results.
Thanks again

 

[41B-boy]

Yes, please do report back after you nail down the cause. I"m encouraged by the straightforward and thoughtful suggestion by mike. I"ll be using his suggestions on my stubborn '41B.
Thanks, Bob

 

[wigfimml]

Sorry the last reply to your post was misplaced here. Yes the camshaft and followers were sent out and re-ground. The original head did not pass pressure leak test so the head was replaced with one that did. This replacement head was all re-worked machined with new valves and guide valves. This was all done by what I and think most would consider a very reputable and qualified machine shop.
Again, there was an extensive rework on this tractor. I as a relative novice assembled all this. So My first thought is that I missed something. Which could mean a bad valve lash adjustment, governor/throttle linkage or mistimed gears, timing ext. My symptoms are a very smooth constant quiet running tractor, relativly easy to start with no power. This is leading me to the Carb. but was open to looking at anything easy to check first.

 

[Hayrack]

Ran into something similar a few years back on an A I bought. It ran well but couldn't pull itself across the yard and had just had a major overhaul. Turned out the cam was out of time. I would check your timing gears and make sure everything is correct. The gears were timed correct but the gear was bolted on the cam a wrong and was a third of a turn out of time. Good luck!!!

 

[Harold Oelke]

If your carb was badly rusted there two passages in there that must be drilled out with special aircraft drill bitts as no amount of cleaning with air etc. will remomve rust. If these passages arnt drilled out and then blown out the engine will run just as you described. Been there many times. --------Harold

 

[Mike Aylward]

In addition to the other good information you received I would check the governor to carburetor adjustment but more importantly I would replace the governor spring if it has never been done. I make it a point to do so on any tractor I get in here that I do not know the history of. I have a low-houred original 70 that ran well but was sluggish and a real "pooch" when I got it. I installed a new governor spring and it woke back up. The governor linkage was fine tuned at the same time. Something to consider. Mike

 

[wigfimml]

(quoted from post at 14:39:42 10/29/13) Ran into something similar a few years back on an A I bought. It ran well but couldn't pull itself across the yard and had just had a major overhaul. Turned out the cam was out of time. I would check your timing gears and make sure everything is correct. The gears were timed correct but the gear was bolted on the cam a wrong and was a third of a turn out of time. Good luck!!!

I am hoping someting like this would be in the last resort. Curious, If it was out by that much would'nt the valves be so out of time that a compression check might tip you off.

 

[wigfimml]

duplicate

 

[wigfimml]

(quoted from post at 14:48:20 10/29/13) If your carb was badly rusted there two passages in there that must be drilled out with special aircraft drill bitts as no amount of cleaning with air etc. will remomve rust. If these passages arnt drilled out and then blown out the engine will run just as you described. Been there many times. --------Harold

I had two carburetors, the worst one I sent out to be rebuilt by one of the professional shops. It was pretty bad as it has sat for a long time. That one is now on the tractor. The better one at the time, was the last one on the tractor and it did run but rough and certainly had more power than it does now, and I still have it. So I plan to do the procedure first recommended by Mike. Since I’m quite sure it will fail running on the load only, afterwards I’ll swap the carbs and see if there is any significant change in power.
But before I do this I’ll re-look at the timing as others suggested as best I can without removing all the covers. I actually may have some or all the pictures documenting where I lined up the gears and all was well when I checked the magneto/spark with compression stroke and flywheel marks. I’ll even check the compression just because, and see if it points to something. When all is said and done I have to take the responsibility good or bad for the timing/governor/throttle issues. The carburetor I sent out.

 

[wigfimml]

(quoted from post at 17:57:48 10/29/13) In addition to the other good information you received I would check the governor to carburetor adjustment but more importantly I would replace the governor spring if it has never been done. I make it a point to do so on any tractor I get in here that I do not know the history of. I have a low-houred original 70 that ran well but was sluggish and a real "pooch" when I got it. I installed a new governor spring and it woke back up. The governor linkage was fine tuned at the same time. Something to consider. Mike

Thats an interesting thought. The spring is original and has never been replaced (Tractor has been in familiy all its life). Now it ran gad, but had more power than it does now before rebuild. Is there something I can do to check this before I just replace it?