IH400

New User
I have a 400 diesel that idles very slow on gas, about 500 RPM.
How do you get it to idle faster without a throttle?
Thanks for any help anyone can give. Bill W
 
You can change the airgap under the fixed throttle plate. I can't remember if you increase or decrease the gap. Doing a search on here will tell you which way to go.
 
increasing air gap increases rpm. they usually ldle slow on startup as warmed up the idle increases.
 
Do you have to remove the carburetor to get the air valve?

And I too cannot figure out which way to turn it or how much?
Thanks for any help. Bill W
 
Thanks, but mine idles so slow that the starter turns the motor over faster than when it is running, and it often stop when I let of the starter.
 
yes have to remove and split carb. i know on the old wd40 you can adjust air valve . but on these newer ones just not quite sure if there is an adjustment. the gap has to be increased for more air to enter for faster idle. it is a round disc and the air gap is less than 1/8". am going to check on adjustment of these.
 
they need a lot of choke till warmed up, usually 1/2 way out till warmed up. then the engine will pickup speed and you push choke in. the 650 has an extra valve on the carb for more fuel for startups and once running warm you just turn the fuel valve in and the engine runs at a good speed.
 
I had a similar trouble with a 450 diesel I bought about 15 years ago. Found that the timing was way late on mine. I advanced the distributor timing and now mine runs plenty fast at cold idle and maybe even a little too fast at hot idle on gas. Mine ran very slow, smoked a lot, and was hard to keep running. Now it starts right up and runs maybe 800 RPM until I switch it to diesel. Something else for you to check or try. Al
 
Air gap should be 3/32" - 7/64". Larger gap = higher RPM.

Early MD carburetors had an adjustable air valve (remove a cotter pin and turn a collar up/down) However later production (SMD, SMTAD, 400D, etc) are supposedly "non-adjustable". However a clever mechanic should be able to get around it.
 
Rustred, You are right about the choke on the 400s and 450s. You have to try to keep it in just the right position until they warm up for 30 seconds or so. My 650-D has the fuel control valve adjuster rod and adjusting it rather than the choke seems to help a lot on cold starts. Takes a little experience to get the hang of starting these IH diesels. Al
 
Thanks for all the input.
I think my timing might be off a little too, because it smokes a lot until it warms up.
Which way do you tune the distributor to advance the timing?
I put new points in it and I had trouble getting the gap on the points at the top. They might be a little wide. Would that make the timing a little slow?
 
Thanks for all the info.
I think my timing might be off as the tractor smokes a lot till it warms up, and then still runs slow.
How hard is it to advance the distributor a little or to know the timing is set right?
I also put new points in it and had a little problem getting the gap set right. won't this change the timing a little?
 
Wide gap makes timing earlier. What I would recommend is to turn the engine over by hand up to the timing mark on the front pulley. It is hard to see but one is there unless it got rubbed off. Then I would look at the points and they should just be starting to open in the normal direction of rotation of distributor. That will give you top dead center for starting and a reference point that you can always come back to if you so desire. Then I would start the engine, loosen dist and turn it for best rpm's. Shut it down and see where the timing is now. It may be close to top dead center or it may be off, who knows. Note it will run faster with a spark that is too far advanced but will not start as good so it is a compromise. I like to set them at top dead center static timing,(not running).
 
I really just timed mine by ear. When it was running on gas, I just rotated the distributor a bit and was amazed how much the RPM went up and how smooth it ran. I just set it so it idled about 800 with little or no choke. It still starts right up so must be pretty close. That was about 15 years ago and I have not touched it since. Remember, the distributor turns backwards on these diesels. Al
 

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