Perkins 4108 throttle problems

[chuck g]

My trusty Perkins diesel has had two persistent problems since the start of the current season:
(1) a very stiff throttle lever on my pedestal
(2) limited RPMs -- not going above ~ 1200 when in gear, vs 1800+ under way historically

A bit more info for any detectives who may be able to offer theories as to what's going on and how to improve the situation:
* Both problems are new this season and come on the heels of having my exhaust manifold replaced during the offseason
* I believe the engine runs at a much higher speed when in neutral than in gear -- although I need to check this (certainly sounds like it)
* At idle, the engine runs well below 1000 rpm, so there is some ability to control the throttle.
* I've checked the propeller shaft for obstructions and haven't found anything that might be slowing things down when in gear.
* The engine doesn't sound like it's laboring when in gear
* The throttle cable feeds through an old Yacht Specialities pedestal; I've sprayed the exposed portion of the cable extensively with both PB Blaster and Boeshield to improve lubrication. It's only marginally better.

A quick youtube video is posted here: https://mail.google.com/mail/u/0/#se...e9?projector=1

Thanks in advance for any theories or solutions you may have!

[tkeithlu]

What happens when you advance the throttle at the engine rather than at the end of the cable? That would isolate the problem to engine/drive train versus pedestal/cable.

[chuck g]

Haven't tried that but I will the next time I'm aboard... thanks for the suggestion!

[model 10]

The throttle linkage is bolted to the bottom of the exhaust manifold. They screwed it up.

[silverfern]

Hi
Disconnect the cable linkage at the injection pump. Check that it moves freely from idke to full throttle. If ok start the engine and operate slowly through to full throttle and back to idle. If ok then remove the throttle cable completly. Check it it for stiffness. Fill a container 50/50 diesel and kerosene and let it soak for a few days. This will be a tempory fix as at some point in time you will need to replace the cable with a new one

[latka]

Originally Posted by silverfern

Hi
Disconnect the cable linkage at the injection pump. Check that it moves freely from idke to full throttle. If ok start the engine and operate slowly through to full throttle and back to idle. If ok then remove the throttle cable completly. Check it it for stiffness. Fill a container 50/50 diesel and kerosene and let it soak for a few days. This will be a tempory fix as at some point in time you will need to replace the cable with a new one

And chech the pivot point of the throttle lever on the pedestal. Very common problem is slow binding over time. i dismantled mine and machined it on the lathe.

[Jesse]

Disconnect The cable from the throttle lever and check the lever operation for stiffness and length of travel. If it's normal reconnect it and disconnect the cable from the throttle arm on the injector pump and check for stiffness or limited travel again. If it is normal the only remaining component is the injector pump. The throttle arm should move freely with your fingertips, if it doesn't the pump should be rebuilt. The most likely problem is with the cable. it is also the least expensive and easiest to replace. Good luck

[chuck g]

I have determined that the throttle cable is advancing the throttle control to the limit set by the governor screw. Next up, I will try disconnecting the cable altogether and see what I learn from that. Thanks for the ideas and input.