Atco rough running.

[peter]

Clive, or anyone else, I have an Atco problem.

ATCO Commodore B17HT Ser 2A L80022 No0082631/K.

On top of the carb is a heart or butterfly shaped flat switch operating the choke?

It has three positions middle is labelled "A" right is labelled "C" and I've forgotton what left is labelled.

It Starts ok on low throttle in A or C but not Left.
It runs in A until the throttle is opened up more than halfway then it dies.
It runs in C with the throttle wide open but sounds "sooty".

Idled fine in A for half an hour while I was letting a plot.

Throttle cable is damaged, but can operate to either extreme and it does not kill the engine in "off", I tried using my finger to poke the carb lever to the off end limit and it still did not die. In the end to kill it I pressed the tickler on the carb bowl.

Any guidance on carb settings?

Could anything else be wrong?

[Clive.]

Hello Peter,

Long time since I was pondering on things Commodore..they first appeared in about 1983... fitted with an Atco/Qualcast A114 engine(114cc)..which was a new model of engine in a similar style to the earlier A98.. The A114 had mechanical in sump governor wereas the A98 had an air vane governor acted on by the blow from flywheel.

A114 engine at first used a Dellorto carburettor...this may be what you have on you machine.??...Delortto carbs were better known fitted to Aspera and Tecnamotor...Italian engines..

I have a feeling that after much puzzling I realised that the A and C ref on the choke lever could in fact be an Italian ref.??.
.....Open=Apperto...Closed=Chiuso..??????

I seem to think though that A was one side and C the other with an unmarked centre position that should only be used during the warm up period....I say should be because many would only run in this centre position.!!...I have pet theory that it would seem that the draughting of the carb was not well matched to the engine??...I think the carb was not really being worked hard enough on a relatively slow engine speed when mowing a formal lawn???

The centre main jet tube on Dellorto used to block with grass and gum which would lead to weak running and again need mid choke to run at mowing revs. The centre vertical jet is brass and can be unscrewed for cleaning once the carb bowl nut is removed. The jet tube has a screwdriver slot..but being brass can easily be muffed up.!!

Setting for Delorto as standard was only by the side slow run mixture screw...and then the throttle stop screw.

Allow engine to warm up then adjust to optimum tickover.. There was then an idea, that appeared after running problems abounded, of a final setting of a quarter of a turn richer from optimum...can't remember if this is an air screw or a fuel screw ..but there are only 2 ways to try. A slightly lumpy tickover often had to be put up with to get the engine to perform under load and not cut out when put into cut/drive.

Some very troublesome set ups had a retro fitted adjustable main jet under the carb bowl...this jet replaced the standard fixed size jet and the adjusting screw fitting replacing the standard bowl nut

There was a fix at one time to gap the then J8C or J17Lm plug to massive 40 thou to cure more poor running...(only with Dellorto carb and early electronic ignition)

I learnt last year that this was later returned to 25 thou and a new plug recomended with regard to improved running with unleaded fuels....I was concerned about this plug recomendation at first as it was an extended nose type..but was assured that there was room for it.?..NGK type...number alludes me at present would expect a current agent would be familiar with this..

Now at this point you are going to say but my carb isn't Dellorto perhaps I should have checked that first .but I enjoyed typing it anyway..

Later A114 engines used a second type of electronic ignition...and a changed carb..Tilotson I think??...sadly I know absolutely nothing about them. Commodore must have finished about 1995??.. with Tilotoson carb from..either 1989 or was it 1991....haven't been asked lately so I have forgoten...

There should be a stop function at a throttle position below tickover on the handlebar lever..if ok the lever should make a horrible plasticky click as it goes to stop position..this allows a crank arm on the back of the engine to contact a screw head with wire from carb that is usually held from earth...sometimes this metal crank arm got bent slightly and did not contact the screw head..or it could be just the poorly cable cable preventing travel.??..again this bit refers to early ignition and Dellorto...

Nearly my bed time...must take a breath and stop typing

Clive.

[peter]

Clive, I will print and read in the shed with the offending machine. Cheers.

[Clive.]

Peter,
Please don't read it out loud in the shed...the offending machine might get all upset at my thoughts on early A114 engines

..and don't do the running/tuning in the shed...exhaust gases etc...

Genuinely..as well as the obvious health risk if run in shed....these types are best tuned on a grass area that absorbs any vibrations which otherwise could lead to false settings.

All the best,
Clive.