Engine Starting Problems


Old 06-17-03, 02:08 PM
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Unhappy Tecumseh 50 Centura problem

Hi folks,

I have a Tecumseh 50 centura on a rotary mower purchased two years ago.
This year after about a month the mower stopped - wouldn't start again.
It had a good spark. I cleaned the carb using the excellent description in a previous post in this group. Still no joy

After all the usual troubleshooting I numbered the bolts and removed the head. I found both valves, cylinder and the headcaked with gunge. I clean as best i could, and reassembled. Last year i may have accidentally added two stroke oil/fuel 1:50.

It now starts but the revs are about 3 times that before, although it does repond to the hi-lo settings. I re-did the carb following the instructions exactly with due attention to the throttle linkages - but it still does the same - make mowing the lawn three times quicker though :-) - any ideas?
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Old 06-18-03, 12:35 AM
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Hello scotsman!

Sounds like either the linkages to the carb are incorrect, or the governor spring is too tight for some reason. Running it at high rpm will ruin the engine, so don't let it run long like this.
Old 06-18-03, 01:44 AM
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Hi Cheese, I checked out the linkages and they are as
described in http://www.angelfire.com/mb2/visitme...tecumseh.html.
The engine is very difficult to start - as many as ten pulls
at the recommended high speed setting and two squirts (once only) of the cold start bulb before it races off and i bring it back under control with the throttle control. I checked that at the lowest throttle setting the butterfly on the carb is all the
way closed. When running at the lowest throttle setting, engine is rough and uneven.
Old 06-18-03, 01:52 AM
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A fuel mixture problem would probably cause this. The engine might be running to lean causing it to rev high the run rough at idle. You could try adjusting the needle valve in both dirrections until it smooths out.
Old 06-19-03, 05:54 AM
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I checked out the carb again and it is supplying fuel, in fact the fuel pools in the intake manifold after numerous attemps at trying to start the thing.
It's also now begining to kick-back occasionally when trying to start it

Do you think I should take the engine apart and look for mechanical trouble like a partially broken key, bend rod or something?

All advice gratefully received..........before i go crazy or get lost in the ever growing jungle that was once the lawn!
Old 06-19-03, 07:48 PM
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Now we're getting closer to the problem, lol.

Kicking back is mainly caused by two things...a loose or missing blade, or a sheared flywheel key. If the blade is tight, remove the flywheel shroud and pull the flywheel nut off. From there, you will be able to see the key. If it is sheared, or partially sheared, get a puller and pull the flywheel and replace the key.
Old 06-20-03, 07:19 AM
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Had a look at the key today and it seems fine. Sits in a recess on the flyweel and butts up against a machined-out shoulder on the crankfshaft.
I took the head off again to check the timing - it appears to me to be about 35 - 40 degrees before TDC, I thought this was a lot, but being "pointless" it may take a while for the EHT to build for the plug. Didn't see anything else unusual. Valves open at the right time and there are cleanish.
I did note that the self tapping screw holding the governor lever was stripped. This probably caused the over speed I had earlier. changed it for a nut and bolt.

Stuck it all back together again - and now I have it started after about three pulls. It runs at the rightish revs now but is still rough - it also spits and coughs black smoke from the muffler when I go from idle to max.

Thanks guys for the replies.........
Old 06-20-03, 07:52 PM
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Is your air filter really dirty, or soaked with oil? It sounds like you are running too rich, due to either carb problems, or a restricted air filter.
Old 06-21-03, 07:03 PM
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Tec Engine

What kind of compression reading do you have with
this engine ?? Have you, by chance, hit anything with
this mower BEFORE all this started ?? In worse case
scenarios, the small crankshaft gear can MOVE on the
crank, putting the engine out of time slightly. The "kicking
back" comment you made seems to indicate you have a
"timing issue". If key is not sheared, and is CORRECT KEY
(611004 Tec part #), then the gear might have moved.
With piston @ TDC on the compression stroke, cam and
crank timing marks should be aligned at around 2-2:30
o'clock as it would appear on a clock face. If anywhere
else....the crank gear is your problem. I've seen mechanics
"slop some JB Weld" all around the base of the gear after
they got everything back in time. The only REAL WAY to
know you've corrected this problem is replace the crank.
Just speculating here....hopefully, is nothing nearly this bad.

Old 06-23-03, 02:28 PM
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Yes it is likely that the engine is running rich, the plug was black after only a few minutes running. The carb is so simple i.e. not many parts, that I can see nothing wrong. How do I stop it inhaling too much fuel? All carb parts are spotless and the holes in the bowl nut are clear the only other bit is a plastic insert that protrudes into the carb barrel just infront of the butterfly. Could I have lost a bit in dissassembly? Any exploded diagrams for this carb anywhere?

I didn't hit anything with the mower prior to this problem, as I said before the only thing I goofed up on is using 1:50 oil/fuel (2 storke mix) by mistake. The compression tester shows bewteen 60 and 80 psi (after I clean up the valves) .

Are the timing marks visible on the fly wheel and a stationary part anywhere?

Another thing I've noticed is the revs are not much different from throttle min/max - and certainly lower than I remember.
Thanks guys!
Old 06-23-03, 02:45 PM
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The plastic main nozzle, or emulsion tube as Tecumseh
calls it, has (2) rubber O-rings on it, same part # 632547.
If you ever took the nozzle out, the UPPER O-ring will almost
always stick to the bottomside of the carb's venturi, or
carb throat, where it seals the nozzle from where it protrudes
up into the carb throat. 60-80 lbs is about MINIMAL PSI for
the engine to run, and you would normally want to see around
80-90 at start-up. This could also point to a possible timing
issue that throws the valve timing off just enough to cause a
slight drop in compression readings. As I said before, the
moved crankshaft gear is a rare occurence, but it CAN happen.
There are visible timing marks on the small crankshaft gear,
and the camshaft. The hole drilled into one side of the cam face
is where the timing mark will be there, and this makes it easy
to find that way.


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