Mikuni repairer needed - Northampton area

[stickleback]

Hi. My Mikuni has given up the ghost. Switching it on, it starts to go through its start up sequence, then blows the 30 amp fuse in the engine bay. I am useless at anything like this so I need to find someone who can repair it for me! Does any one know anyone?

 

Thanks.

[Albion]

Hi. My Mikuni has given up the ghost. Switching it on, it starts to go through its start up sequence, then blows the 30 amp fuse in the engine bay. I am useless at anything like this so I need to find someone who can repair it for me! Does any one know anyone?

 

Thanks.

I can tell you what the cause is most likely to be but if you haven't the confidence to dismantle and repair it yourself then it's best to get an engineer. You could try ringing Mikuni Home page and asking if they know of an agent in your area. They are usually very helpful on the phone in my experience.

Roger

Edited June 19, 2012 by Albion

[stickleback]

Roger, thanks for that. I would be interested to know what you think it might be, and I am going to call Mikuni as you suggest.

[Albion]

Roger, thanks for that. I would be interested to know what you think it might be, and I am going to call Mikuni as you suggest.

 

It will almost certainly be a carbon build-up shorting out the inter-turn windings of the glow plug. When this happens the system runs as normal until the glow plug is switched on. The carbon shorting across the glow plug element causes an increased current to flow which exceeds the fuse rating. I had exactly the same symptoms on an MX 40 of mine and I found the cause and the cure as a result the hard way.

 

OK, to prove whether I am right or not is quite easy even for a non-techie so follow this guide if you wish:-

 

Remove the glow plug

Shown here Parts diag and the plug itself is illustrated below the exploded diagram.

This involves pushing the rubber cap to one side and undoing the steel nut. Be careful to note where the steel and insulating (paxolin) washers go when you are removing the connecting cable. This is very important as the insulating washers prevent the two opposite polarity wires of the joined plug wiring terminals from touching and shorting out.

Now unscrew the glow plug from the glow plug holder (Item 5 in the exploded parts diagram).

If I am correct you should see, on the lower side of the heater coil wire windings, a black carbon build-up bridging the windings. If this isn't visible then forget all this and call in an engineer.

If it is visible you need to remove the carbon from the plug windings. You may get away with this with careful scraping but you may break the windings, in which case you need a new plug.

Remove the glow plug holder

This is the most important step, failure to do this will mean that your cleaned or renewed glow plug will fail again within no time.

Undo the fuel pipe attached to the holder and push away slightly to allow access. Undo the two retaining screws (items 34) and remove the holder. You should also buy a new gasket (item 7) and a new dished sealing washer (item 33) ready for when you reassemble.

Carefully examine the body of the glow plug holder where it pushes down into the body of the heater. You should see two (air swirl) holes but they, most likely, are completely plugged with carbon and may just appear to be two blackish round shadows. These holes should be cleaned out totally but beware of the angle of them. If in doubt start to clear them with a pin until you see the direction that they run and then finish cleaning them out totally by holding a suitably sized drill bit between your fingers and rotating to drill out the carbon. Ensure that the holes are completely cleared out back to full size.

 

Reassemble everything in the reverse order and test

 

 

What happens is that the swirl holes get plugged with carbon which then allows the injected fuel to run down the bottom surface of the glow plug windings instead of being swirled around to contact the whole plug. This causes the carbon to build-up on the plug and then the resistance is lowered, the current increases and the fuse blows.

Hope this helps.

Roger

Edited June 19, 2012 by Albion

[stickleback]

Roger, thanks for that very detailed explanation. Being rather ham fisted and liable to wreck it, I will use an engineer, and send this information to him - as a pointer. Many thanks.

[frangar]

You could try JIMMS

 

http://www.jimms.net/

 

07845 277 058

 

Based in South Leicestershire but he does travel.

 

Cheers

 

Gareth

[stickleback]

Hi Gareth. He's the one that Mikuni recommended and he's coming to look at it - thanks for the endorsement!