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Ransome/MAG mower issue


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This is the beauty of these inexpensive and quick to use red neon plug caps that flash as HT passed thru.


I use them for checking HT in real world engine running actual conditions.


The ignition system may work for starting but what happens when engine is working hard meaning the ignition system has to work hard .


Bike, self contained CDI ignition system, non battery dependant, a modern take on a magneto if you will.


Great starter and runs well for a few miles, then seems to have either a fuel problem or a coil breaking down at about 5 k revs, surging, just will not rev over 5 k revs.


Struggle bike home, fit red neons, start and rev...flashes disappear when misfire starts, revs drop, flashes reappear, engine revs to 5k, misfire...repeat.


So loss of ignition at revs.


Dmm shows acv output of generator to CDI fall with revs ? And at about 5 k revs, acv output goes below about 28v AC.


So, Geny coils breaking down under load and heat.


Rate of change, acv rises, insulation break down....


Or clean carbs many many many many times as it's an ignition fault.


These neons save your hair and stop you getting dizzy...well worth the money.


A good bit of kit and very easy to use.  I also use them on petrol cars.....if needed.

Edited by Martin Harris - Moderator
Unacceptable language and defamatory statement removed.
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Vaporisation is a thought. If the petrol is a winter grade and has high ethanol content, it may have pushed the simple technology carburation too far. 

You could try some fresh premium E5 (or E0 if you can find it) fuel from a “named” garage rather than supermarket cheap stuff if that is what you’re using. 

Easy to prove if you can pour some cold water onto the carb without shock cooling the engine.  The fact that it revs on choke tends to discredit the ignition theories.  

Edited by Martin Harris - Moderator
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Thanks, lots to go at.

Neon/compression testers later this week.

Will also try cold water on the carb body for vapor lock

Higher octane petrol. Although runs fine for first 20 min.

One test/change at a time.

Just to clarify, once fault occurs it still starts and ticks over but won't rev even with partial choke and full choke kills it.

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Well yesterday didn't go exactly as planed ?

The compression tester wasn't available but we still went armed with the new neon HT checker, 5l of water/towel and fresh 98 octane fuel.  Plan was to run until fault arose, check HT with neon, if ok then cool carb with towel soaked in cold water. If still no joy replace fuel with fresh 98 oct. So only checking or changing 1 thing at a time.

Started 2nd pull ? worked fine for 20 minutes and were just waiting for the fault to develop - then bang and the cutting cylinder stopped rotating. Removing the side cover revealed that the drive chain had snapped - long string of expletive's.

The bolt holding the sprocket had come undone allowing it to come off which in turn meant the chain then got wedged on the drive roller mechanism and something had to let go.  You can see the very bottom link is splayed open.

Finished off with our self-propelled rotary and will now need to source a new chain and are still no closer to identifying the fault.1570470422_20210422_1758371.thumb.jpg.77477369d0c52ab04aa797fd0c83a506.jpg

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True Rich. However once we identified the broken chain it was driven off the patch and back to its container storage a couple of hundred meters away still without the fault raising its head and anyone  considered it could be still driven without actually cutting the grass. ?

Mind set was - broken - fix it then continue another day and get on with some flying.

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Brian, doubt icing as carb/silencer are on the same side and with the motor running for 20 min+ B4 fault carb is warm but not hot. Could try the wet towel heated on silencer then wrapped around carb if cold towel to test vapor locking failed.

Will look at bearingboys if we struggle locally ? 

Edited by Ace
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Hi, must say this; I used a number of sit on mowers some years ago.I had problems similar, was the safety switches that exist to make sure that you are seated, and other things re grass box etc. they may be simple but can malfunction. Does not seem applicable in this case but always a possibilty. Most faults usually came down to simple things



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