JD 60 carb adjustments

620 John

Member
I was working on a guy's model 60 and was trying to get the carb set correctly. The problem I had was telling where the idle mixture screws (duplex carb) should have been set at. I shorted out the ignition on one cylinder and screwed in the mixture screw all the way in on the cylinder that was still running. I also had the load screw turned all the way in. Somehow this thing was still running with both screws turned in and no choke on. I pulled the throttle arm back as far as I could without the engine dying and adjusted the idle mixture to get the slowest rpm. I did the same thing for the other cylinder. When I was done with the idle mixture I adjusted the load screw for good throttle acceleration. Overall the tractor doen't run too bad, it can idle fairly slow and take throttle pretty good, but still wants to spit and sputter a little at all throttle positions. Pulling the choke does NOT make it run any better. I think some of the rough running could be due to valves but I'm not sure. He also has electronic ignition installed with new coil, dist cap, wires, etc.

I know the book says to check rpm of each cylinder when adjusting the mixture but I do mine a little differently. With it running on one cylinder I just turn the idle mixture screw in until the engine about dies and back it out a quarter turn or so and do the same on the other side. This seems to work pretty good for me.

So my two question are how would it still run with the screws turned in all the way and what else could be causing it to spit and sputter??

Thanks in advance and sorry for the long post.
 
Have you verified that the advance mechanism in the
Distributor is working properly?
With the engine stopped, remove the distributor cap
and find out if the rotor bug is springy.
If the bug doesn?t rotate and spring back, the cam that
the bug fits onto may be stuck in one position.
 
There are more than one idle port hole in the throttle bore. Only one has a needle to adjust it but even with it in, the other ones still supply idle fuel. They all feed from the same isle passage. The big screw on bottom is NOT a load adjustment. It has two fixed jets inside to regulate that. The big screw is a minute adjustment to supplement the main jets and fine adjust for differences in altitude. Set at 2 1/4 turns out and unless you live in Denver , CO or New Orleans , LA you won't need to touch. Spit & sputter could be way too many things to diagnose on here.
 
Those idle screws you start with them 1 1/2 turns out. Or now where every you are at to get it running. The basic idea is to get both cylinders running at the same speed at idle. You have to have the throttle plates closed enough to idle around 300 rpm this way fuel will only come in through the idle ports. You short out one side then adjust the other side to run at it's fastest idle speed. Then do the other side. Then you are to adjust the fastest running cyl. down to the same speed as the slowest one by leaning it by screwing the needle in.
 
Thanks for the help and clarification. I'll see what I can do next time I'm around the tractor. This one kinda threw me off because it acts differently than the 620's I've worked on. I think the little bit of rough running could be beyond the adjustments. Like I said before it takes throttle pretty good, it can idle pretty slow, and hardly gallops. It will probably clear up under load like most other 2 cylinders that I've been around do. I know a good work out would be good for this 60.
 

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