Rollo Croftmaster

[roatavator]

My new toy collected yesterday. When she’s cleaned up I’ll post some better photos.

• This topic was modified 2 years, 5 months ago by roatavator.

[andyfrost]

Peter , it’s just not noisey enough….. but very nice.

[roatavator]

Yes Andy, much quieter. But at least I can run it up whenever I like without feeling guilty about the neighbours.
However I still have a SIMAR to keep them amused!
Next plan is a winch for the truck; I’ve chickened out of driving it up!
I’ve got to sort out the throttle which doesn’t work at the moment. Cable goes into a barrel mechanism the other end of which is in contact with the governor. I’m confused as to open the throttle causes the cable to pull at the point it enters the barrel but to increase revs it needs to push on the governor at the other end. I’m thinking I’ll have to have it apart as no adjustments work.

[andyfrost]

Peter , you’ll get there , the various throttle systems on JAPs are all fairly straightforward.

Andy.

[trusty220]

On all of the JAP engines that I’ve worked on I’ve found that they tend to be designed to run at governed engine speed. I’ll have to look it up but that would normally be a high idle speed of around 2500rpm (I’m working from memory, so don’t shout at me if it’s wrong!).

To achieve a tick-over speed the throttle cable is used to override the governor lever and effectively pushes the lever so that the throttle butterfly closes. When you want to increase revs you are effectively releasing the governor arm which allows the throttle butterfly to open- you don’t open the butterfly, the governor does it in an effort to achieve it’s governed speed.

It sounds complicated but it’s really very simple, it just works differently.

[roatavator]

Yes Geoff. I’ve been fiddling with it today and come to the same conclusion. Effectively the throttle cable has to push against the governor lever to achieve running speed, when you close the throttle for idle the spring on the governor closes the butterfly.
The throttle cable enters one end of a barrel which is secured to the machine. Inside the barrel is a spring pushing on a small cylindrical plate, the plate pushes on another spring which acts on a rod in contact with the governor lever. It’s clear someone has had a fiddle with it in the past. I’ve managed to get the bits inside the barrel to move freely but I can’t even with many adjustments of the spring tensions get enough thrust on the rod to open the butterfly. Or at least I can but then there’s insufficient tension in the governor spring to return the butterfly to idle when you close the throttle. I’m getting a bit stumped. I’ll try and post some photos once I’ve reduced them.

[roatavator]

So here’s the set-up. The first photo shows the cable entering the barrel. The second photo shows where the barrel is in relation to the governor.
On reflection I think that the thrust on the rod at the other end of the barrel is provided not so much by thrust from the cable, but by the spring located between the cable end of the barrel and the plate in contact with the rod. If that’s the case it would imply that the problem is basically that the spring has weakened. Does this sound reasonable?

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[andyfrost]

Peter , any chance of a pic of your govenor weight housing assembly.
Can you manually rev the engine and feel the govenor working??

Andy.

[roatavator]

Oh yes Andy. It revs fine if you move the governor lever. It’s just that the thrust from the rod onto the governor lever is insufficient.

[roatavator]

This may explain better. Here I’ve removed the barrel which screws into the green collar I’ve indicated. At the other end of the collar you can see the end of the governor lever the rod acts on.

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[roatavator]

And here’s the barrel with the rod poking out with the big spring behind

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[roatavator]

Finally here’s the view ins the barrel, the end of the throttle cable is visible. Behind the circular washer is a second spring. I reckon it’s this spring which provides the thrust on to the rod and this has weakened so there’s insufficient force to move the governor lever.

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[andyfrost]

That seems to appear the wrong strength govenor spring.

Andy.

[roatavator]

Could be Andy but I’ve tried increasing the governor spring tension (you can change the position it’s secured to the air cleaner housing) but then can’t get enough push from the cable. I figure if the spring pushing on the end of cable were stronger it would then be possible to adjust the governor spring to suit. I’m guessing with the too weak cable spring friction is coming into play.

[wristpin]

Just a thought.
Hunting may be caused by wear / maladjustment of the governor or it may be the governor reacting to another cause such as a restricted maladjusted fuel supply. The simplest test for that is to partially close the choke. If it smooths out the hunting it points to wards a carburettor issue rather than a governor one.

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