What's on your bench today?

[MattyF]

Ok couple more questions mate how long would you leave it with caustic , tried battery acid and there is a few bits that seem welded just below the exhaust port

[spudulike]

Cool cheers Steve ,It's off a husky 240r brush cutter , was straight gassed I think ! I'll do that and chuck in a Meteor piston and see what happens.

 

On the second pic, next to the inlet port, near the bottom of the photo, is that some sort of wear/scuff or is it just the photo, missed it earlier!

[MattyF]

Yeah it's a big dirty score nearly all gone now,There's a few tiny lines I can't get out but I only have 240 and up in wet n dry so might try and get some brick acid and 100grit unless you would be happy to put a new piston in going by the last photo with those lumps just below the exhaust port?

[spudulike]

Yeah it's a big dirty score nearly all gone now,There's a few tiny lines I can't get out but I only have 240 and up in wet n dry so might try and get some brick acid and 100grit unless you would be happy to put a new piston in going by the last photo with those lumps just below the exhaust port?

 

The aluminium transfer MUST all be gone, if any is left it will take out the rings in seconds. You leave the solution on until it stops fizzing where you clean it, abrade it lightly and try some more. 20 - 30 mins is not unheard of. An hour on really bad stuff.

 

If the bore feels smooth with your fingertip, all is OK!

[harvey b davison]

Hi, can i please ask a question. This may sound dumb to some but i am very very green when it comes to repairs.

 

Can someone please explain how a spark plug works, and the ways in which in can fail and the various results of it failing.

 

I am still having problems with my makita 4300. I have fitted a new coil ( as told it needed one by the 'professionals', thats done nothing, i have ran it with all the gubbins removed from the exhaust,done nothing.

 

The saw starts up and runs fine for a few minutes, but then under throttle it starts sort of backfiring, not running right and even had a few sparks coming from the exhaust. If i turn the saw off, leave it a few minutes then i can start it it again as normal and then the same thing happens over and over again. I dont understand how or why it starts normally then goes haywire.

 

I know its 'only' a makita, but its the first trouble its given me and i would really like to get the saw up and running again, but also learn about the saw as well.

 

Sorry for the long post

 

Harvey.

[spudulike]

Hi, can i please ask a question. This may sound dumb to some but i am very very green when it comes to repairs.

 

Can someone please explain how a spark plug works, and the ways in which in can fail and the various results of it failing.

 

I am still having problems with my makita 4300. I have fitted a new coil ( as told it needed one by the 'professionals', thats done nothing, i have ran it with all the gubbins removed from the exhaust,done nothing.

 

The saw starts up and runs fine for a few minutes, but then under throttle it starts sort of backfiring, not running right and even had a few sparks coming from the exhaust. If i turn the saw off, leave it a few minutes then i can start it it again as normal and then the same thing happens over and over again. I dont understand how or why it starts normally then goes haywire.

 

I know its 'only' a makita, but its the first trouble its given me and i would really like to get the saw up and running again, but also learn about the saw as well.

 

Sorry for the long post

 

Harvey.

 

Plugs will either stop sparking or may start tracking through the insulator causing an intermittent spark. Backfiring will tend to be a heavilly retarded ignition, that is the saw is sparking on the downward stroke causing the detonation to bang out of the exhaust rather than to ignight in the combustion chamber.

 

The other thing that can happen is that fuel vapour can be retained in the exhaust and get ignighted by the exhaust gases.

 

Backfiring is generally caused by a sheared flywheel key, that is the only time I have ever had a backfire from a saw. It is possible that a faulty ignition coil with smart ignition advance gone wrong may cause it also.

[harvey b davison]

Plugs will either stop sparking or may start tracking through the insulator causing an intermittent spark.

 

Cheers spud, so if the plug started to track through the insulator, how would this affect the saw. What would it run like

[GardenKit]

Backfiring is generally caused by a sheared flywheel key, that is the only time I have ever had a backfire from a saw. It is possible that a faulty ignition coil with smart ignition advance gone wrong may cause it also.

 

I agree with you Spud. The only times I have had a true backfire have been all down to a loose flywheel with a sheared (or damaged) key.

 

The saw starts almost normally but as the crank accelerates the flywheel slips back and retards the spark.

 

But as the crank decelerates, the flywheel overruns and advances so that when the saw is switched off the crank is in a good position for a start.

 

I would check that before anything else.

 

And in response to Harveys question about the effects of a tracking plug, it simply means that the coils energy will track to earth within the plugs body rather than having to jump the gap.So either a weak spark or no spark at all.

[harvey b davison]

I agree with you Spud. The only times I have had a true backfire have been all down to a loose flywheel with a sheared (or damaged) key.

 

The saw starts almost normally but as the crank accelerates the flywheel slips back and retards the spark.

 

But as the crank decelerates, the flywheel overruns and advances so that when the saw is switched off the crank is in a good position for a start.

 

I would check that before anything else.

 

 

Cheers barry, How do i check the fly wheel, dont forget i am a total novice at this.

[GardenKit]

Cheers barry, How do i check the fly wheel, dont forget i am a total novice at this.

You really need to remove the flywheel to check the key and the taper for damage. If it has been damaged or worn it will need renewing.