High idling

henk · Post by **henk** » Mon Apr 05, 2010 9:57 am

Hello,

I’ve been wondering and searching many times for the reason why my major idles at about 800 to 850 rpm’s. The valve at the inlet manifold is set in the right position. I notice that the two pipe going from the inlet manifold to the pump are different sizes. The lowest on the manifold, that is the one behind on the pump is smaller. Could that be the reason?

Foxen · Post by **Foxen** » Mon Apr 05, 2010 10:03 am

The pipes are in order(they changed them to be different sizes sometime but I don't remember when, probably because someone fitted them the wrong way when they were the same size)

Have you tried to turn the big screw in the vacuum governor housing? The one that's facing frontwards? That one is for correcting eventual idling speed problems like "hunting" and such, if you've set a good idle speed on the throttle plate you can fine tune the idle speed with that screw, if it doesn't hunt when idling tho, I'd rather tune the idle speed down more with the throttle instead...

henk · Post by **henk** » Mon Apr 05, 2010 6:08 pm

Foxen,

I've tried tuning that screw with no effect.
My though is that the vacuum must be in balance when idling and with different sizes the balance will be different.
I will try loosen up the connection from te small pipe to the pump and see what happens when I give a bit of false air.

Foxen · Post by **Foxen** » Mon Apr 05, 2010 8:19 pm

henk wrote:Foxen,

I've tried tuning that screw with no effect.
My though is that the vacuum must be in balance when idling and with different sizes the balance will be different.
I will try loosen up the connection from te small pipe to the pump and see what happens when I give a bit of false air.

The small pipe is only a "leak off" pipe that allows a small amount of air to leak in behind the diaphragm via a small valve that is adjusted with the big screw, if what had happened on mine has happened on yours I suspect that this problem you have could occur(high idling and turning the big screw has no effect).

If you feel like it, screw off the diaphragm housing, loosen the circlip and gently pull the diaphragm out and see if the small conical piston that's pressed into the nut on the bolt going through the diaphragm has fallen out? It had on mine and the housing was half full och a mixture of engine oil, diesel and water :/

Post by **Brian** » Mon Apr 05, 2010 10:02 pm

The vacuum pipe size was changed to an equal size on later tractors but this was only to help with "hunting".

At the rear of the pump, behind the stop control is a threaded adjuster screw. Try adjusting that one turn at a time.

Foxen · Post by **Foxen** » Tue Apr 06, 2010 7:56 am

That's strange as here in Sweden there are equal size pipes on all FMD's that I've seen(56-57) and my SMD has different sizes just like two other SMD's that reside not very far from where I live...? How come?

Post by **Brian** » Tue Apr 06, 2010 5:42 pm

Perhaps the modification did not reach Sweden. The early Majors had two the same size that went under the thermostat housing. The Modified engine then had the large and small pipes fitted that went infront of the valve cover and this went through to the Power Major and early Super.

When "hunting" problems occurred the pipes were changed to two the same size again. We changed them when we did overhauls as a matter of course.

Foxen · Post by **Foxen** » Tue Apr 06, 2010 7:23 pm

Ah... Mine had the two of different size in front of the valve cover but they were in bad shape so I replaced them with sturdy and reinforced rubber hose... not recommended I suppose but better than half rusted through and in the way for my fiddling, they will probably last my lifetime anyway...

henk · Post by **henk** » Tue Apr 06, 2010 8:20 pm

Tried to adjust the idling by the screw on the back, but nothing happens. Loosen up the small pipe a bit and the rpm went up. Put some grease around the pipe connections to see if it leaks somewhere in or out but all was well.
Tried the adjustment on the front earlier and that made no difference to.

Is there some adjustment at the part between the diaphragm housing and the pump housing that houses the lever that connects the diaphragm and the regulator in the pump?

Foxen · Post by **Foxen** » Tue Apr 06, 2010 8:27 pm

henk wrote:Tried to adjust the idling by the screw on the back, but nothing happens. Loosen up the small pipe a bit and the rpm went up. Put some grease around the pipe connections to see if it leaks somewhere in or out but all was well.
Tried the adjustment on the front earlier and that made no difference to.

Is there some adjustment at the part between the diaphragm housing and the pump housing that houses the lever that connects the diaphragm and the regulator in the pump?

None that I know of, but if nothing else has helped, loosen the four bolts around the diaphragm unit and disassemble it to make sure the small plunger in the nut inside hasn't fallen out, as said in an earlier post, mine had... Btw, are you sure your throttle plate looks ok and doesn't "wander" from side to side, ie, lots of axial play in the throttle shaft? There is a picture in my thread on the wiki very far down that shows what my old throttle plate looked like...

henk · Post by **henk** » Tue Apr 06, 2010 8:44 pm

Foxen,

I've checked the diaphragm unit two years ago because I thought it was leaking. There were some things wrong but after repair the result was the same. The throttle plate looks all right to me, but I check it tomorrow.

By the way, your getting along well with your job.

Foxen · Post by **Foxen** » Tue Apr 06, 2010 9:00 pm

Thanks henk

I got a bit further today but I won't be posting about that until tomorrow when I've "recuperated" a bit... I feel half-dead right now, brake work always seem to get more complicated than you think when you decide to do something about it

Gman · Post by **Gman** » Tue Apr 06, 2010 9:51 pm

Hey Henk: Have you checked to be sure the butterfly in the air intake is working properly, since my power major throttle lever connects to this. I believe this controls the air intake and therefore the rpm. Just a thought and no one has mentioned this.

Emiel · Post by **Emiel** » Tue Apr 06, 2010 10:06 pm

Henk,

A real stupid question from me. Is the proof meter giving the correct reading? And otherwise, there is nothing wrong with 800 rpm in my opinion.

Best regards

Emiel

henk · Post by **henk** » Wed Apr 07, 2010 7:01 am

Hello Emiel,

The proof meter is set with a battery screwdriver. And you can here it's idling to high. There's no problem for the engine, but at road runs I have to switch High Low to many times. And if it's suppose to run about 600 rpm I want it to run 600 rpm.

Gman · Post by **Gman** » Wed Apr 07, 2010 4:18 pm

Gman wrote:Hey Henk: Have you checked to be sure the butterfly in the air intake is working properly, since my power major throttle lever connects to this. I believe this controls the air intake and therefore the rpm. Just a thought and no one has mentioned this.

Hello Henk, I reread your first post and see you are ok on the air intake. My questions, is there only one way to get the rpm reading and what is the max rpm it should run? My power major idles fine at a low rpm and with full throttle she runs at a high rpm, I do not usually run her at full throttle for anything I do. She did not have a cable when I bought her years ago, was told it was a speed odometer cable, so I wasn't worried about how fast I was going. Anyway, good luck on yours.

henk · Post by **henk** » Thu Apr 08, 2010 10:26 pm

Gman,

It low rpm is around 600 and the highest would be around 1600 or 1800. Not sure.
Mine will run up to 2200.

Gman · Post by **Gman** » Fri Apr 09, 2010 1:40 pm

henk wrote:Gman,

It low rpm is around 600 and the highest would be around 1600 or 1800. Not sure.
Mine will run up to 2200.

Thanks Henk: I did a little reading last night of one of my manuals. Says you can check the accuracy of the proofmeter rpm off of pto rpm. I forgot to bring manual with me so do not remember the correct pto rpm, raised pto was lower than standard pto and I'm not sure how you check the pto rpm. I do remember proofmeter rpm according to this manual was 550 low and 1900 high. I guess I will have to get me a cable and see if my proofmeter works. Thanks for your help, it is greatly appreciated.

henk · Post by **henk** » Fri Apr 09, 2010 3:09 pm

Gman,

Be sure to get the right cable. They have different lengths and connections. I think the super is the easiest one to get.

Kim · Post by **Kim** » Sat Apr 10, 2010 2:59 am

You can check the engine RPM off the pto by using a mechanical tachometer. It consists of a shaft with a rubber grommet on the end of it that you hold against the end of the pto shaft and as it spins, you get a readout of actual RPMs. You then have to work backward through the gear reduction for the engine to PTO but it is accurate. I picked mine up very reasonably at a flea market but I'm sure an auto parts store can supply one. It will also work off a belt pulley or front of the crankshaft pulley if you can get the end of the tach in solid contact with it.

henk · Post by **henk** » Sat Apr 10, 2010 6:28 pm

Frans,

I have contacted the person you wrote me about. He told me the butterfly had to be completely closed when idling. Mine was still open.

This use to be the setting when it run 850 rpm's.

This morning I set the butterfly in the closed position and adjusted the throttle rod and started the engine. It ran about 500 rpm’s. So far so good. Adjusted the governor damper valve on the righthand of the diesel pump and set the revolutions at 600 rpm’s.

Now the strange thing. When I move the throttle up to increase the revolutions it will clime to 1100 rpm’s and than when still going up with the throttle the rotations fall down to 850 rpm’s and from that point going up all the way.

I assume that’s the reason the previous owner set the butterfly to rum 850 rpm’s.

What could be the reason of this strange result.
Adjusting the maximum fuel stop on the left hand of the diesel pump makes no different.

john.n · Post by **john.n** » Sat Apr 10, 2010 9:12 pm

just a theory....based on the injection pump on a dexta....but it works in more or less the same way
opening the throtle reduces the vacume in the govener, increasing the amount of fuel, so the engine revs up. once the engine revs the vacume is then increased reducing the amount of fuel injected so the engine revs drop. because the screw you describe is alowing the vacume in the govener to be lost through leak off, the governer is not functioning as quickly as it should?
any help? or am i totaly wrong?

henk · Post by **henk** » Sun Apr 11, 2010 1:03 pm

John.n,

Don't know the exact working of the system, so I don't understand all of the theory you are talking about. Lack of English languish will do the rest.
When is the vacuum the highest? Butterfly closed or open.
The spring at the diaphragm house will push the diaphragm towards the pump. I assume vacuum will suck it to the front and give more fuel.
Am I totally wrong?

Foxen · Post by **Foxen** » Sun Apr 11, 2010 3:27 pm

High vacuum will suck the diaphragm towards the front, just as pulling the stop will push the rod towards the front, thus giving less fuel... High vacuum occurs when the throttle plate is closed... Is your throttle plate firmly pressed into the shaft or can it "wobble" a bit? Mine was worn(pictures in the wiki) and could move slightly on the shaft, that will give rough control over engine revs... I swapped mine out for a less worn throttle shaft and plate and now it's easier to get a steady rpm...

henk · Post by **henk** » Sun Apr 11, 2010 3:49 pm

John.n

I've done some research on the internet and thanks to Anatefka I now know the fuel rod inside the pump is just working the other way around. Now I understand your theory.
I assume you are speaking about the screw with the damping valve at the end of the vacuum house.
The damping valve has been changed a few years back because it was broken. The shape of the previous one was a bit different. The result in idling however was still the same. 850 rpm.
I could try to screw it further out and see what happens.

Foxen,
The throttle plate is firmly pressed into the shaft of the inlet manifold.