Makita DCS 5121 ignition woes

[cloggy]

I've got a problem with the above. Starts fine cold. After 1/2 of a tank it starts to pop and cut out at high revs but starts immediately again. At 3/4 of a tank it cuts out and although will idle cuts out when throttle opened.  If I push it and keep trying it won't start at all till cold, some hours later. I've refilled but that makes no difference, neither does running the fuel cap slack.

I suppose this is the ignition unit, but don't want to put the same one in again. Noticed on ebay that there is more than one part number to work with this. Wondered , if I'm right if Shevey knows of and can supply an uprated part.

[billpierce]

Defs talk to shavey on here. He may have a used one also.

I would def check your compression and also check if you have a spark before such a purchase

[cloggy]

Loads of compression and as it starts but doesn't rev I've got some sort of spark. Got to get it really hot till it won't start at all to check for spark, but the first time it did it changing the plug made no difference. It's fine next day till it gets hot again. Last autumn it was popping and shutting off at high revs but always started first pull again. This year it initially does that till it gets even hotter. It also appears to be revving higher when it is running correctly.

[Stubby]

Low comp symptoms. When it gets hot tolerances open up  to the point were it won't support combustion .  Possibly ...

[shavey]

It does sound like ignition troubles but as Stubby says  it might be low compression; when hot

 

Couple of questions what year is the Saw , is it easy start there has been upgrades with coils and flywheels and these don’t match up with  older saws sometimes I’ve spent many hours trying to match up 

flywheels with new coils 

this family of saws has diffferent flywheels and coils to the profi range the coil number you need is 181-143-206

if you want any parts or help give me. A shout 

[spudulike]

Have you checked the gap between flywheel magnets and coil? Had a MS460 like this once.....gap too big!

[cloggy]

Thanks Shavey

It has consistent good compression, hot or cold. The problem seems entirely heat related. To me it seems when hot something is progressively breaking down. I will check the spark the next time I go through a tank

I'd already indentified that part number as being the replacement part. Significantly it is stated that it replaces .....205. I've had the saw three years and not done anything apart from filters and plug but it isn't my only one  and I just cut  firewood. It's  on it's third chain.  It's the lower tune model with less revs and an aluminium crankcase, at least according to all the specs I've read.

It was easy start, but that broke under warranty and it doesn't appear to be that system anymore; at least if it is it's never worked as easy start since I got it back. I think they just shoved another complete unit on.  

 

Edited July 20, 2018 by cloggy