cheap carb swap onto 3PG engine- Tecumseh carb works great- with lots of pics

[kyerik]

(I still need to make a choke linkage)

Tecumseh carb swap pros:

carb mounts with no modifications
BIGGEST PLUS= high speed mixture is fully adjustable! (and you still have a low speed mix adjustment screw)
spring loaded drain button on bowl to check for gas if the engine won't start and to drain water
Integrated air filter- so you can get rid of the large black air cleaner hose

Cons:
Requires making a new throttle and choke linkage
gas line must be rerouted (it simply attaches to the opposite side of the carb)


I bought a 91 marathon about a month ago and did the HEI module/coil conversion and put new crank seals and bearings in it, but it would still only run "fairly good" with the choke about 25% out (130 psi of compression). I also noticed that the throttle shaft "bushing" had a lot of slop in it- which served as a sizable air leak.

Being on a tight budget, I got to looking around at some other old carbs/engine I had laying around and noticed that I had a Tecumseh vertical shaft motor (3-4hp) that came off a craftsman tiller that had a similar float type carb with the same mount spacing (1 3/4") as my 91 marathon with 3PG.

I cleaned the carb out and found that it bolted in place nicely. I rigged up a throttle linkage (I still need to make a choke linkage).

The cart runs good at idle and drives great with lots of power and no backfiring. I love the fact that I can now tweak the high speed mixture.

The bore of the Tecumseh is 20 mm on the intake side and the mikuni is 18-19mm. The Tecumseh carb gasket seals the intake nicely.

Here are more pics:

Note the high speed mix adjustment screw and spring loaded bowl drain on the bottom of the Tecumseh carb

[amesmotorsports]

Sweet nice job

[LiL' rascal]

Just wondering, is that carb off a 4 stroke motor? I didn't know if a carb off a 4 stroke would work on a 2 stroke?

[kyerik]

Yes- it came off a 3 or 4 hp 4 stroke tiller engine.

Update- I rebuilt my weak fuel pump 1 week after this carb swap and then the carb began flooding. With some research I found that this is a common problem for carbs designed to be gravity fed. Having more than 1/2 psi of fuel pressure can overcome the float valve in the carb and cause it to flood. Rather than buying a super low pressure fuel regulator, I T-ed off the fuel hose going to the carb and ran the line back upstream of the fuel pump and put a small valve in this line to add a little bit of restriction- this way the fuel line going to the carb never builds much pressure. This fixed my flooding problem.