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[Entwood]

Qualcast Classic petrol 35S

Acquired this a couple of years ago, have no books/manuals whatever other than an exploded parts list downloaded from t'internet .. which is about as much use as tits on a bull ... I don't even think its the same engine ..

It was sold as a non-runner, but after cleaning the carb, changing the oil and a bit of lubrication it has started first time and run well for the last few years, and the last month as well .. until this week ... and especially today ....

Problem are .. it is reluctant to start, needs full choke, WOT and quite a few pulls, but once running it is then OK ... for 20 minutes or so, after which it needs more and more choke, and more and more throttle to continue to run, after another 10 minutes it stops completely. Leave to stand for 10 minutes and it runs for another 10 .....

It is obviously fuel related ... but I have cleaned the tank, new fuel line, checked the filter, blown through the jets, fresh fuel, cleaned everything so many times now it is getting silly.... removing the air filter makes no difference whatsoever....

Needle valve in the carb seems to be free, and when it stops pressing the fuel check valve shows fuel in the reservoir, so it looks like sufficient fuel simply does not flow through the jet, but by partially closing the choke helps for a while.....  all that does is increase the venturi effect across the jet if memory serves ..... so why does it slowly get worse ??

So, any one any ideas what the problem might be and what the fix is  

[Marks DTM Calib]

My money is still on the carb.

There are aquite a few small drillings which sit near the throttle butterfly in the closed position, these can get clogged up particularly if there was any fuel left in the carb over winter.

Its clearly a fuel issue as your limiting the air supply to richen the mixture to get it to run (e.g. not all the drillings are clear).

So check it again and clean it really well again checking carefuly the drillings in the carb barrel

[Entwood]

OK thanks .. I'll get the compressed air can out ... again !!!

Can't see much I can take apart to clean .. there only the one "screw" on the side that leads to any drillings, and the drillings from inside the float chamber...

ho hum ...

[Kevin Wood]

Agreed. The carbs are full of little drillings. I had one where one of the idle drillings was blocked. Engine ran fine at full bore, but wouldn't idle, just hunted on the speed regulator. Had rebuilt it a couple of times before I got a good diagram of all the passages in the carb and was able to check each of them was clear. The idle passage started running up the middle of the screw that fixes the float chamber on, then darted off half way up the thread into the carb body. You wouldn't know it was there on inspection, but once unblocked it was fine.

IIRC they are Tecumseh carbs, if you've got the same engine as me. I found a great web site that gave you complete rebuild instructions for every Tecumseh carb with pictures showing all the little orifices. Can't find it now, but will have a look later. Hopefully I've bookmarked it somewhere.

Also remember that the float chamber needs a vent into it, probably from the barrel upstream of the choke somewhere, otherwise it'll gradually suck down a vacuum and go lean giving the symptoms you describe.

[Marks DTM Calib]

OK thanks .. I'll get the compressed air can out ... again !!!

Can't see much I can take apart to clean .. there only the one "screw" on the side that leads to any drillings, and the drillings from inside the float chamber...

ho hum ...

Compressed air often wont shift it, a strand of copper wire (from mutistranded wire) is a good little tool for loosening muck in the fine drillings and is soft such that it wont damage them

[omega3000]

Last weekend there was much swearing of a couple of neighbors trying to start these petrol mower's  Most probably the same issue as all they were doing is pulling the start cord for hours on end  The points kept failing on my old villiers lawn mower  that was kick start 

[Marks DTM Calib]

It will be a CD ignition system on these later engines.

The usual cause is not running the carb dry at the end of the mowing season. 

[omega3000]

It will be a CD ignition system on these later engines.

The usual cause is not running the carb dry at the end of the mowing season. 

Aye  . Use to lift mine in back of car , boy was heavy .. probably why i got knackered back now 

[Kevin Wood]

I think it might have been this site that I found useful when unblocking my carb.

http://outdoorpowerinfo.com/repairs/tecumseh_carburetor_cleaning_repair.asp

[slowboy]

decking or gravel

[Taxi_Driver]

It will be a CD ignition system on these later engines.

The usual cause is not running the carb dry at the end of the mowing season. 

Thats interesting.....my Dad, in the days when he was capable of mowing a lawn had a Honda petrol mower.....he used to every last cut of the season, let it idle till it run out of petrol......after a few years it wouldnt start.....he took it to a lawn mower place that diagnosed a new carb needed.....he told them that he let it run out of fuel before he put it away for the winter....i remember they told him not to do that....leave it with carb full of petrol  Which he always did after that and never had a problem.....

My mower is a Stratton Briggs.... In the 10 years i had it....leave it with fuel in it all winter......every time i use it.....pump the 'easy start' about 5 times to flood the carb......full throttle and first pull it always starts  Tho it does only have full throttle or off.....no idle

Interested to know why the difference of opinion   

[Taxi_Driver]

Use your B&Q 10% pensioner discount card Mr E and go get a new one 

[omega3000]

It will be a CD ignition system on these later engines.

The usual cause is not running the carb dry at the end of the mowing season. 

Thats interesting.....my Dad, in the days when he was capable of mowing a lawn had a Honda petrol mower.....he used to every last cut of the season, let it idle till it run out of petrol......after a few years it wouldnt start.....he took it to a lawn mower place that diagnosed a new carb needed.....he told them that he let it run out of fuel before he put it away for the winter....i remember they told him not to do that....leave it with carb full of petrol  Which he always did after that and never had a problem.....

My mower is a Stratton Briggs.... In the 10 years i had it....leave it with fuel in it all winter......every time i use it.....pump the 'easy start' about 5 times to flood the carb......full throttle and first pull it always starts  Tho it does only have full throttle or off.....no idle

Interested to know why the difference of opinion   

  Does the engine glow red after a few minutes , poor air cooled machine 

[Marks DTM Calib]

It will be a CD ignition system on these later engines.

The usual cause is not running the carb dry at the end of the mowing season. 

Thats interesting.....my Dad, in the days when he was capable of mowing a lawn had a Honda petrol mower.....he used to every last cut of the season, let it idle till it run out of petrol......after a few years it wouldnt start.....he took it to a lawn mower place that diagnosed a new carb needed.....he told them that he let it run out of fuel before he put it away for the winter....i remember they told him not to do that....leave it with carb full of petrol  Which he always did after that and never had a problem.....

My mower is a Stratton Briggs.... In the 10 years i had it....leave it with fuel in it all winter......every time i use it.....pump the 'easy start' about 5 times to flood the carb......full throttle and first pull it always starts  Tho it does only have full throttle or off.....no idle

Interested to know why the difference of opinion   

Simple, the fuel bowls are vents on these carbs so the petrol evaporates over time and leaves a residue/varnish

[Entwood]

Late to this as some friends were round and only just left ...

Did what Mark suggested , stripped it down and cleaned every orifice I could find with a bit of wire from a 13 amp cable core  .. and bloody thin they are !! used some thicker stuff on the bigger holes ... loads of carb cleaner as well .... I hadn't spotted the two extremely small holes by the choke flap before .. so gave them a good soaking. Flushed the tank (again) with fresh petrol as well, and a new piece of fuel pipe.

Re-assembled, (and Kevins links actually told me stuff I didn't know about the fuel bowl positioning and needle valve orientation  )  stuck some more new fuel in .. and it started second pull !! Now responds well to throttle, and the choke works like it should !!  ran it for 20 minutes and no problems at all.

Will test it properly next week when I cut the grass next

Many thanks to both Mark and Kevin .. seems to be sorted for now ... time will tell

Many thanks to all