Dolmar 112 continualy goes from rich to lean

[Butch(OH)]

OK carburetor men, care to help out a novice? I just completely rebuilt a 110 Dolmar that had lean siezed. New crank bearings and seals, cylinder and piston kit, and gasket kit for the Tillotson HK-21A. I have rebult a few carbs meaning blowing them out, gaskets, setting the needle height to spec, diaphrams etc but realy dont know ding how the things actualy do what they do. Not having a manual with initial settings I set both needles at 1 turn off the seat. The saw started very easily and the idle needed to be leaned justa tad and the high speed opened up. Id guess they are set at 3/4 out for the idle and 1 1/4 our for the high speed at this moment. You can start the saw and it ides perfectly, crack the throttle and it accelerates smoothly and comes right back to idle now here is the hitch. Put it in a cut (where it has great power) coming out of the cut it four strokes a bit but when you let off, one time the idle will be a smooth sounding higher RPM idle and when you try the throttle it hessitates, leaned out right?. A few seconds later the thing will idle normaly. Put it back in the cut and it has power like it should, four strokes a bit coming out of the cut but then trys to die. Playing with the throttle will keep it running but it is four stroking and smoking blue, Rich right? Will return to normal acting idle after playing with it maybe 15 seconds. Never know which way it will be coming out of a cut, rich or lean. Cleaned the vent and even took it out and ran the hose out the side just to try it, no differance. Installed a clear line to the carb and no bubbles. Filter is new, fuel is fresh. Squirted carb cleaner around all the intake gaskets and idle does not change. I am stumped.

 

[Gearhead1]

Butch, that's a difficult problem to diagnose without having the saw in my hands. Do you have a carburetor from another saw you can swap on to make a test? I have come across some (maybe 1 in 200) of these tiny 2-cycle carbs that won't run right no matter how much rebuilding effort you put into them. When I switched another carb onto the piece of equipment, it solved the problem right away.

 

[cuttinscott]

OK carburetor men, care to help out a novice? I just completely rebuilt a 112 Dolmar that had lean siezed. New crank bearings and seals, cylinder and piston kit, and gasket kit for the Tillotson HK-21A.

Butch the Till HK carbs are very tempermental the plastic module body that houses the metering lever is prone to worping pressure check the carb while dipping in a can of fuel look for body leaks

part #s till carb 112 150 002 module body # 112 150 450 alternate carb Bing 48B102 #114 152 000
Scott

 

[Butch(OH)]

Well, I am working on a parts 112 deal with another member. Dont know if the carb is rebuildable or not. I wish I could find some iterchange information for the 2 cyle carb manfs. I would swap it for a new Zama or Walbro. I have a parts list but am afraid to ask Dolmar, they are quite proud of parts for the older saws. I can make any linkages I need but dont have a clue which carb will be right for the motor and slide in place of the Tillotson.

 

[galde]

Dolmar 112 carb problem

I have seen this behavior with saws whose carb adjustment needles don't hold their adjustments due probably to vibration and contact with the cover openings through which they pass. I clean the threads with brake cleaner and apply a non-permanent thread locker to the male thread near the outer portion of the thread only, so the thread locker doesn't get to the seat of the carb. If you can see the slot of the screw, observe to see if it moves away from the correct setting after running the saw.

 

[Lakeside53]

I'm no Dolmar expert, but it sounds like you have an air leak... Have you done a pressure and vacuum test on the motor after assembly? It's the only way you can rule out everything BUT the carb...

I see this behavior on Stihls and it is invariably a leaky intake boot or crank seal.

 

[Butch(OH)]

Thanks for the suggestions will check things out.

 

[Freakingstang]

I'm no Dolmar expert, but it sounds like you have an air leak... Have you done a pressure and vacuum test on the motor after assembly? It's the only way you can rule out everything BUT the carb...

I see this behavior on Stihls and it is invariably a leaky intake boot or crank seal.

Ok, I am familar with a vacuum from the car background, but am new to these little boogars! Is there a link where I can learn of vac testing a motor for leaks? How about the carb, or is it one step? I have an 015av that I am working on that i believe has an air leak at the crankseal, but I can;t tell for sure.

 

[Lakeside53]

Ok, I am familar with a vacuum from the car background, but am new to these little boogars! Is there a link where I can learn of vac testing a motor for leaks? How about the carb, or is it one step? I have an 015av that I am working on that i believe has an air leak at the crankseal, but I can;t tell for sure.

Download one of the Stihl Service manuals from www.giftsofwood.com. The 026 manual (as an example) has the pressure/vac test procedure in Section 5.3

 

[Freakingstang]

thanks, it is very appreciated


Steve

 

[Kneejerk Bombas]

Thanks for the suggestions will check things out.

The first thing I'd look at is the intake boot.

 

[cuttinscott]

The first thing I'd look at is the intake boot.

This saw has no intake boot it has a manifold block. Very common for the Till HK series carb to have a body leak please check that.

Scott

 

[Dolmar_Tech_Mgr]

FYI, the Tillotson, HK's have been discontinued for many years and when this happened we switched the 112 over to a Bing carburetor. The 112 was discontinued in the late 80's and we no longer sell the Bing carburetor. Stihl used this same carburetor on the 038 (I Think) for a little time and it may be available from them but I do believe Stihl has discontinued that part too. Bing may be a source for that carburetor. I too agree that there sounds to be an air leak.