Perkins 4.108 Idle Speed Adjustment

[Astral Blue]

When my boat was repowered with a Perkins 4.108, the initial idle speed was too fast. The tachometer was reading close to 1500. I disconnected the throttle cable from the lever on the injector pump and adjusted the connection to the last notch, which brought the lever to the lowest speed possible, which was about 800. This is still higher than I would like, but I can live with it.

Over the past few months, the idling speed has gradually increased. It is back to near 1500 again. The lever does not seem to have more room to go back further.

Can someone point me toward the right direction as to what to check and what to look for? Thanks in advance...

[stargazerpnw]

Make sure throttle cable pushing back to idle stop screw on pump. You can adjust idle with this bolt/screw

[KrazySailing]

IF I remember rightly there's an adjustment screw on the top ot the injector pump. I'd suggest a check the operator's and maintenance manuals for detailed instructions. Manuals are available online. I'd send a photocopy of mine, but it went with the boat.

[Astral Blue]

Thanks for the information. I was suspecting there would be a screw somewhere on the injector pump to make this adjustment. I do have the workshop manual for this engine, but it's at the boat. I will check it next time I'm there.

[Dynamo1181]

You have two adjustment screws that will effect the idle. The first is the throttle stop that can be seen as a stop againt the end of the throttle shaft near the spring or cable connection. The other as previously mentioned is the "anti stall adjustment. This is on top of the pump. I am going on memory as I dont have my manual handy, but this is screwed in untill you see an increase in idle speed. You then turn back one half turn and lock down. Then adjust the throttle stop to about 725 rpms.
A

[Astral Blue]

Originally Posted by Dynamo1181

You have two adjustment screws that will effect the idle. The first is the throttle stop that can be seen as a stop againt the end of the throttle shaft near the spring or cable connection. The other as previously mentioned is the "anti stall adjustment. This is on top of the pump. I am going on memory as I dont have my manual handy, but this is screwed in untill you see an increase in idle speed. You then turn back one half turn and lock down. Then adjust the throttle stop to about 725 rpms.
A

I went to the boat today and got to work. I began by taking out the manual and reading about the anti stall adjustment. After reading the workshop manual, I became encouraged that it was a simple adjustment...until I took a look at the engine and noticed the anti stall bolt and retaining nut being located directly under the exhaust manifold!

The only way to access this are is to remove the manifold. It's interesting to note the workshop manual assumes this screw can be easily adjusted and recommends that several settings be tried before the correct setting can be determined. Perhaps if I had hands the size of my five year old son's, it wouldn't be so much of a problem.

Long story short, I removed the manifold, which included removing the coolant reservoir and exhaust mixing elbow. I examined the condition of the bolt and saw it was rusted and bent. I ended up removing it completely. I can compensate for it's absense by making adjustments to the throttle cable.

Now I can idle my engine at 750 with no problem at all. Thanks again for all the advice!

[Dynamo1181]

I have the "new" 4108 with a Bowman manifold. I can assure you that adjusting the anti stall screw is easier than removing the manifold bolts! Granted it does take small wrenches and etreme dextirity but doable. Anyway glad your fix works.
Alan
4108 with 7000hrs, 24 yrs and like new.

[LifesBetterWhenYoureBeating]

I've recently bought a boat with a 4.108 and it currently idles at around 400 RPMs. I've been told that is too low but couldn't find in the manual any recommendations for idle speed, so I'm curious what made you go with 750?

[mrcarson]

750rev's probably the Factory recommended. My 42ft Pugh had a 3 pot.
Pour some oil down the throttle cable too to lube it. They can bind.
They are cheap to maintain though. A gasket kit for my 2 pot Yanmar. cost same as full rings/shells/Gasket kit for the Perky. Rattly old things that they are.
I usually idled my small engines at 500rev's. Kept oil flowing and ALt charging.
The big Fial was 47 from memory and 340 flat out. All 15 pots on here.