Tecumseh mower troubleshooting

[Mursal]

Don't start on your hair, until you get the mower sorted ............

 

[Navigator82]

Very long shot given the age of the thread, but here's hoping.

I have a Mountfield Empress with Tecumseh Bvs143 /Dellorto carb combo identical to the original poster.

Bought for peanuts as a non runner as a bit of a project. Got it home and stripped the crap out of the carb and diagnosed non runner as being due to fuel starvation, carb bowl was corroded and leaking like a sieve. I gave a quick clean and a temporary fix with some isopon in the bottom of the bowl, bolted back together and she ran fine on choke (had to manually wedge choke flap open), ran with choke removed but died after a few minutes which I put down to needing mixture adjusted. Fundamentals were good, not smokey or rattley.

With that I was happy that it was work spending a bit more time on (also had a broken height adjuster and choke linkage was broken) so brought it back in, fabicated a new choke linkage and did a deeper clean on the carb including the main central jet etc .

Bolted all back to get together and went outside to get it fired up and tinker with mixture, but lo and behold I can't get so much as a cough from it.

Valves are still free (checked at plug), I have a good spark, good compression, throttle linkage and governer linkage looks right , my choke bodge is doing what it needs to in terms of linkage and doesn't foul main throttle. After a lot of pulling the plug isn't wet which makes me think fuel starvation, but the carb bowl is full and and float bowl is free.

Anyone any ideas where to start or what I might have missed in the carb rebuild to cause lack of fuel pickup between bowl and inlet? Thanks (hopefully) in advance!

 

[Burnerman]

Remove the brass bolt at the bottom of the float chamber......it’s actually the main jet too, and relies on a hole cross drilled through it, and then passes fuel through it upwards into the emulsion tube.
Do check that its clear!
John

 

[Nige F]

If you don't have any joy - then winter comes - put the carb in a bottle of methylated spirit - it'll dissolve all the varnish - I left mine all over the winter, soaking. went like a good un next spring. OK for a project

 

[Navigator82]

Thanks both - took apart the carb again and cleaned it out - didn't see too much wrong but I did get a puff of something when I put the airline on the main jet.

Reassembled and we have a runner! Am not entirely sure what I'm at with trying to tune an idle, think I have something half passable and it's running off the choke, but occasionally it's doing a lot of bouncing (as in full open - nearly full closed) off the governer. Is this a case of adjusting the Idle screw and throttle limit screw?

Am chuffed tbh, 20 quid lawnmower will hopefully get a new lease of life on my postage stamp lawn!

 

[Burnerman]

Above the main jet is the emulsion tube with tiny drillings across its axis.....make sure they are clear.
You should be able to see through them (against the light) if all is well.
John

 

[Navigator82]

Above the main jet is the emulsion tube with tiny drillings across its axis.....make sure they are clear.
You should be able to see through them (against the light) if all is well.
John

Do you mean these?

 

[Burnerman]

Yep, that's the emulsion tube, main jet below it.
John

 

[Navigator82]

Yep, that's the emulsion tube, main jet below it.
John

Grand - main jet through the bore, 4 cross bore holes through the emulsion tube (learned something there!) and the main jet at are all visibly clear or were poked with fuse wire.

What is the principle of the governer spring, is its movement dictated by engine speed somehow ?

 

[Burnerman]

The engine governor system keeps the engine speed as constant as possible - typically between 3000 and 3600 RPM (full throttle). Obviously as the engine gets under load the revs drop, so the governor opens the throttle to compensate.
The governor system will either be a wind vane type - which is controlled by the cooling vanes on the flywheel (early side valves in particular)- or more commonly a bob weight governor driven by the engine camshaft at around 1/4 engine speed.
Both types have springs and rods to connect them, directly or otherwise to the throttle butterfly in the carb.
The springs are there to essentially damp out sudden movements by the governor.....a single cylinder engine can typically stall if its give full throttle all at once, so the springs dampen that to allow for a fractionally slower pick up. A twin or multi cylinder engine gets over this because of the extra power stroke.
Other springs are in place just to keep the governor rods in contact with the governor - which you can identify by a lever sticking out of the crankcase.
Its best not to play about with these springs - although they play a rather minor part some engines can get upset if they aren't there.
John