Tecumseh Model: HMSK105, Spec: 159908C carb issues

[jwales]

I have an MTD snowblower with the Tecumseh engine. owner bought a replacement carb (from China). Took the old one off (and threw away ) and put the new one on. He said it would not run (either carb) so assumption was old carb was bad . I have checked compression and spark. Both appear to be good. Govenor rods appear to be located in the correct positions on throttle lever and carb.

Closed the idle mixture and hi speed screws in all the way and started at 1.25 turns out. It started but was running rough (barely running). Started with the idle screw and was not having any success in getting it to stabilize. opened up hi speed on carb bottom and did get it running at a more appropriate RPM in full throttle position. But when I tried slowing the throttle lever down the engine did not change (it did not reduce down to "idle" speed). It stayed at the same RPM until I turned it off. Ran out of time to do anything else, but looking for thoughts when I get back at it.

My first intent is to remove the bowl and idle and hi speed screws and clean as necessary (even though a new carb). Reinstall and start at 1.25 turns out on both screws. As far as adjustments should I be starting with one over the other to get running smooth? Is there something in addition to the carb adjustments I should be looking at? It seemed weird that the engine would not idle down for me moving the throttle lever....

Thanks.

[38racing]

Is it the old L head engine. They have a spring mechanism on the throttle lever that interacts with the governor lever. This forum has a thread with video links to the setup.
https://www.mytractorforum.com/44-small ... hm100.html

[jwales]

Thanks for the links 38! I am going to work on it tonight. If I remember correctly I think the governor rods are all connected in the same locations as in the u tube. I will surely play with the adjustment screw on the throttle lever to see if that makes a difference.

[jwales]

So I gave it another go last night trying to get this snow blower to run. I connected to the link 38 has in his post. I reviewed all linkages from the governor to the carb and vertical throttle lever and they are correct (or the same) to what the u tube showed. When the vertical throttle is in the low speed zone (just above shut off) there is free play both ways when pushing the governor rods. When in full throttle there is some tension from the spring in the throttle mechanism. So I believe the governor rods are in correct setting based on this.

With lo and hi speed mixture screws set at 1.25 turns out I started it up again. It started but I had to leave it on partial choke for a while and at full throttle it was not running at the correct RPM (closer to what I would expect in the idle/ low speed range). When I reduced the throttle lever it would quit. Fired it up again and began trying to adjust fuel mixtures and no improvement. I also tried adjust the star screw on the throttle linkage for governor adjustment and could not get it to full power/RPM. I also pushed on the governor rods to open up the throttle on the carb. It would begin to rev up but still seemd link it was loading up/fowling.

The engine was to warm and I ran out of time last night, but tonight I plan on removing the carb and disassembling to see if there is something off or dirty (not sure what else to check). This was a new re[placement carb from china but had many good ratings as a "plug n play". This blower does not have many hours on it and looks brand new.

Any additional ideas would be appreciated. Thanks.

[Skywatcher]

Hi J.

Experience has taught me that these Chinese clone carburetors need to be dismantled and have all the metal shavings cleaned out of the various circuits before installing or attempting to adjust. The Chinese laborers working on the production line for 75¢ per hour probably don't even know what they're assembling, yet alone how critical it is for the carburetor body and various parts to be properly cleaned before final assembly.

I have found aluminum shavings stuck in the inlet between the needle and seat and brass shavings stuck in the bowl screw main jet. I've also seen torn or cut O-rings and pinched gaskets in brand new, fresh out of the box carburetors. I'm not saying this is your problem, however it is something to keep in mind whenever you're dealing with Chinese cloned products. All the best,

Sky

[bobodu]

Had one that gave me fits....turns out the timing was off.

[jwales]

Hmmm. So maybe the flywheel shear pin is damaged or coil needs to be set. The unit is very clean but I suppose he could have jammed something into the auger which could have caused some dmamage. I will look at that after I go through the carb.

Thanks.

[bobodu]

I just lookup your up....the one that caused me problems had points.

[jwales]

So I did-assembled the carb, ran wires through several of the holes, clean in the US cleaner. Installed and I can get it running with the throttle in hi/ wide open but it is running a little higher than idle speed only. Hi and lo speeds set at 1.25 turns out. I adjust lo open from 1.25 and no changes to engine. If I move throttle down it quits. With throttle on full and closing lo it quits at around .75 turn open. If I try and open the hi needle I can not get a change in throttle/rpm and it quits when I reduce throttle. On full throttle and running, if I adjust the star screw (turn in) I can get rom’s up to what might be close to correct rpm. When I move throttle down no change, does not idle down. All the time the engine is running in either condition it sounds like it is laboring/hesitating. Almost like it wants to backfire. I am thinking I should try a static setting of the govenor and maybe check flywheel key???

[Skywatcher]

Hi Again J.

This is starting to sound like you have more than just carburetor problems. Does this engine have the external solid state ignition coil, or the points and condenser under the flywheel? (Partstree indicates this to be a an external solid state ignition with an alternator under the flywheel for the light). Generally the flywheel keys don't shear on these engines with the cast iron flywheels. However, if they do shear, the crankshaft tends to slip in the flywheel retarding the ignition.

The other thing I'd want to check is the valve clearances. The Tecumseh manual calls for .008" to .012" clearance on both valves for the L-head engines. You may also have an air leak between the carburetor and the cylinder block. Make sure that both ends of the intake elbow, the intake port on the cylinder block and the mounting flange of the carburetor are completely flat and clean. Use all new gaskets to eliminate as many variables as possible. Let us know what you find out,

Sky