Runaway 3120

rfwoodvt

rfwoodvt

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This side of eternity.
I've just finished rehabbing a Husky 3120 by putting in the following:
<ul type="square">[*]jug &amp; piston
[*]bearings and seals
[*] intake manifold and gaskets
[*] crank case gaskets
[/list]

She starts fine but idles a little fast even with the idle speed adjustment to the absolute minimum. Then once she warms up the idle speed picks up as if the partial throttle lock is on and won't kick down.

I've checked the throttle position and have pushed on the trottle plate arm to make sure it is all the way down but to no avail. The throttle itself travels the full range of motion and returns to closed throttle.

Generally when I get a high idle it is either because of a lean mixture or excess air getting in some how.

I've checked the carb seveal times and put in a new kit. The throttle plate looks to be seating fine and I'm pretty sure that the low speed mixture screw works by restricting idle circuit fuel as opposed to air.

Anyhow, once the engine is warm/hot she won't idle down at all like the partial throttle lock is stuck on.

I should also mention that she idle (even when cold) when the throttle is closed all the way.

Any suggestions as to what might be going on or where the air might be getting into the system?
 
Your sucking air some where but you know that , first try this , get yourself a can of WD-40 with the red straw that fits in the push lid on the can so you can pin point your spray, fire the saw up and spray around the saw , spray the carb gaskets between the carb and jug , gasket between the jug and crankcase , any where you think air is getting into the motor , now take your time and listen when you do this cause once the WD finds the air leak the motor will slow down or quit cause its now burning the WD as well , If you find nothing them I would guess its your crank seals
 
The way Ed described is how I find leaks too.

I wonder if you lipped inside out one of the seals on install. I did that on a 372 once. Check easy fix.
 
Have you checked that the high and low speed jets are in proper adjustment? A high speed jet set too lean will cause a saw that "runs away". Also a low speed jet that is too rich could cause the same problem. I am pretty sure a good starting point for adjustment jets is one full turn out from stop. I agree with the air theory and check, this is another thought to check before you lube up the entire saw. Good luck
 
There is no high speed jet in the 3120, unless you got one of the very first one .

One other thing I have seen is this , you said the idle screw was backed out , now take a very close look at the carb and make sure you did not back it out to far , Not sure on yours but about 1/2 the 3120 idle screws have a shoulder on the screw and if turned out to far the arm on the throttle lever will hit this shoulder and cause the saw to act like on fast idle
 
Had only some pblaster on hand so I sprayed a couple of places no real change in RPM but I'd get some white smoke. Smoke camea couple of seconds after spraying behind the clutch.

Ended up finding the plastic parts and brass gear on the oil pump shredded pulled that nad the crank seal was toast and the crank covered in melted plastic oil pump parts.

looks like the oil pump seized. I could move it with a screw driver but guess it was too stiff for the shaft to move it.. This also explains why that bearing had to be replaced during the initial rebuild last year.

Gonna put in a whole new oil pump and try again.
 
As long as you got the problem fixed , another thing I have seen and this is quite common on 3120's , the crank is drilled in the centre of the crankshalf , now they put a small piece of brass in the hole in the crank in by the wheel part of the crank, now I have seen them come out but if that happens when the motor is running its not a good thing but have seen them come out when people rebuild the bottomend , With the brass piece missing you now have a major air leak cause of the hole right threw the crank
 
It is for lube but the hole goes right threw the crank into the crankcase and if that brass piece is missing it will have a large air leak , sounds like your clutch unscrewed and retighten itself but got out of mess with your oil pump gear , this happens quite abit , On the race 3120's you better make sure that clutch is on real good cause it will do this in between cuts and have seen the clutch tighten back on where it seized the motor up,
 
If you want to check to see if the brass piece is in your crank, just pull your spark plug out and fill the crankcase full of mixed gas and watch, make sure you put enough fuel in to be higher than the centre of the crank , if the brass piece is gone it will leak bad, now I would say to pull the clutch off cause the gas is going to come out the hole in the crank in by the centre of the clutch, the hole the grease is to get the clutch bearing , Have seen guys think the crank seal is gone cause the clutch was still on the saw and looks like it was coming from the crankcase seal
 
Next question then is if it is missing is it a replacement part or do I have to do the whole durned crankshaft?

BTW, filling the crankcase with fuel mix sounds like a huge PITA. where is this plug supposedly located on the inside of the channel or outside by the clutch?
 
Putting fuel in is very easy , just make sure the piston is near the bottom of its stroke so the fuel can travel threw the transfer ports to the crankcase , if you have no leak then just flip the saw over and the fuel will come back out the sparkplug hole , let it drain for a while . If the brass piece is gone I donot believe you can buy them but I never really tried to buy them, I just plug the hole but thiese are on racesaws not on a saw that runs everyday . The hole that the fuel will come out of is the hole when you grease the clutch needle bearing for your clutch which is located pretty much centre of your drive gear area on your clutch so that is why I take the clutch off to see is the fuel is coming out the seal or the hole in the crank cause with the clutch on its pretty hard to be 100% sure
 
Put the new oilpump in today along with the seals, o-rings and other stuff that came with it and that solved it.

We now have an operational 3120!!!

The old oiler would seize up at temp and the worm drive would be forced into the seals.

Shoulda done this a couple years ago!!!
 
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