Mantis 4stroke deluxe tiller won't start

[Rolo]

Hi all,
Hope your all staying well. I really hope you can provide me with some advise on how I can get my neighbours tiller running. He has a Mantis 4 stroke deluxe tiller, with gx25 engine (GCAPT 1156494). I think 2-3years old.
He took out of winter storage, of course emptied fuel before putting into storage, filled up with fresh fuel and it started and ran fine. Switched off and Left it til usage next day, now won't start. And when it does eventually start will run on choke, but soon as you open up the lever for more air etc cuts out.
Very frustrating.
So he passed it onto me as I have repaired petrol mowers etc before with most success.
So in other words once started from cold and I try to move the lever off choke and it will cut out. Will also cut out when warm, if left on choke.

So far :

I have checked the kill switch is set to 1, so is on.


Pull off the kill switch wire from coil connection, and tried to start, won't start.


I have flushed the fuel tank, installed new fuel filter and rubber grommet, fuel lines look fine, got new fuel petrol in tank. Installed new primer bulb.


I have stripped, cleaned and rebuilt carb with new diaphragms/gaskets, new needle and lever, from the Walbro K10-WYB Carburetor Repair Rebuild Overhaul Kit for gx25 engine.


I cleaned out the jet in carb, was not blocked.


Cleaned filters in carb, they were fine I think.


Air filter is fine, but still won't start even if removed.


Replaced spark plug with new.


Adjusted the throttle linkage to have minimum 7mm thread from top nut. As described on mantis website.


I even looked at the clutch housing and was protruding near 5mm so is ok.

I just don't get why it won't start?! So frustrating. I haven't checked the coil, as not sure how many ohms to check for?? The spark plug does indeed spark, brightly now as is new.
Would this coil be the problem? It's the only thing not replaced with new I guess.

Anyway I would really appreciate your help and any advice.

Thankyou.

 

[DirtMechanic]

So the ability to run on choke is the clue. Restricting air (choking) balances the combustion, Opening it gives too much air and it dies of fuel starvation because it thins the air fuel charge. I would revisit the carb with welders tip files for orifice cleaning.

So you rebuilt the carb, but not the impulse line nor the case seal. Both of these are used to control positive and negative pressures from the case. The impulse circuit powers the fuel pump.

 

[oneeye]

I only used Premixed fuels that were 94 octane with my 2 cycle engines because when I mixed my own I always had problems. When I had problems with my 4 cycle engines I used Trufuel 4 cycle TF3 racing fuel. I could always get em started using these high octane fuels. They are expensive but well worth the money.

 

[Rolo]

Thanks for your replies chaps. Racing fuel eh? Hmmm Sounds like fun lol.
Unfortunately we don't get that over here in Uk, closest is probably Shell V power or Bp Ultimate, both high octane.
Anyway like DirtMechanic, had a feeling was fuelling issues.
So I went over the jets passageways in the carb again and there must of been the smallest of dirt in there, bout size of a gnats cock, so flushed it out.
And now runs a charm, ohh that sweet music of a nicely running engine
Thanks & all the best. Stay safe.

 

[DirtMechanic]

Thanks for your replies chaps. Racing fuel eh? Hmmm Sounds like fun lol.
Unfortunately we don't get that over here in Uk, closest is probably Shell V power or Bp Ultimate, both high octane.
Anyway like DirtMechanic, had a feeling was fuelling issues.
So I went over the jets passageways in the carb again and there must of been the smallest of dirt in there, bout size of a gnats cock, so flushed it out.
And now runs a charm, ohh that sweet music of a nicely running engine
Thanks & all the best. Stay safe.

Not the first time I have seen impossibly small particles do that, as the plastic tank filters are not as fine as the inline paper type on industrial engines. Be sure to make the torque of the carb mounting bolts even tighter after you run it to full temperature an have let it cool for one day. Air control is always helped by very tight bolts on those vibrating 2 cycle engines. Tune it wet\rich for no load full speed for lubrication reasons and you are all set. I run the mid grade gas in all my small engines. Its not just that I want more torque and cooling, but also the additives seem to help cleanliness and longevity when unused. Same for the oils, as the better grades such as Stihl makes are more ashless, cleaner and have better lubricity such that less may be used. More gas is more power, as the oil does not burn but does occupy some small volume in the fuel charge being ignited. I fully intend that the machine does as much of the work as possible.