Cota 247 Running Lean and Overheating

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Eventually got it going with the 15 minute old B7HS and it felt really good - lot's of low down response with no lag so i gave it another 15 minutes up and down our steep hill climb and it ran well and idled well - here is the same plug after this run - it still looks a bit lean to me . I will take it for a fair dinkum ride tomorrow and see how it goes.

[David Lahey]

Neither plug photo shows any indication of the motor running lean.
In both photos the gap looks too wide. Looks like 1.0mm, should be 0.5mm. Having too big a gap has no effect on motor heat output, but it might run better with the right gap.

[TriCub]

Hey David.
I don't like to disagree with you but the first one looks lean to me . The earth electrode change of colour is the part that looks lean to me. It's been getting to hot. Although a photo is never as good as looking at the real thing. I agree with the plug gap being to wide though. Better get back to packing planes for tommorrow.

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Must be camera distortion the plug gap was 0.55 so not that far out.

I took it for a ride and as usual started out well - about 2kms from home I went down a gully and took the wrong route (as is my want) she stalled and wouldn't start. I removed the plug - it was bone dry and had spark I left it for 10 minutes to cool down - no way . I replaced the plug with a spare and when I was just about to give up - I turned the fuel off and gave it one last kick and she fired. I managed to get half way when I stopped to open a gate - she died and would not restart. I pushed and freewheeled the last 1.5 kms trying to clutch it on long downhill runs - not a hope. So I parked it in a neighbours yard I then went out for 3 hours came back and 2nd kick it started - I rode it home played with idle mix started a test ride - maybe 100 metres and it just died as if I turned off the ignition. I removed the plug and it was bone dry and sparking. The inline fuel filter was full and tickler spitting happily .

What model Mikuni should I be looking for - and does anyone have something to sell?

[brownie]

Hi Andrew,
I have a mikuni flange mount carby that you can try off a sherpa t 325 give me a ring if you want to see how that goes.
Ross

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I had a call from a guy called Peter from ACT who has a web site http://www.mymontesa.com/ I had contacted him to try and source some rings for the 247. He seems a terrific guy and a Montesa nut with 6 bikes.

When chatting to him it occurred that one of the few parts of the carbie that I hadn't returned to original was the needle. I mentioned that the new needle supplied by AMAL as part of the kit was thicker than the original but I thought that was probably just wear on the old one. Peter pointed out that the needle should be marked with a U - when I check it isn't it is marked with a single groove and so is not the correct needle (yet another incorrect part in the kit) - so I have replaced the new needle for the old needle and took the bike for a 20 minute slow run around my hills. The bike stalled a couple of times (my fault as usual) and it started after 3 or 4 kicks on both occasions. I made sure the engine was fully warmed and turned her off - and she restarted easily :)

It's dark and so I can't get a reliable close up of the plug but it now looks slightly less gray - moving towards a brown tinge but still slightly leanish. Only a proper ride will tell. BTW - I completely drained and cleaned the tank and the tap and found no residue or dirt.

However I am now back to virtually the original carbie and as to be expected I now have the original flat spot in the top end - I mean really flat. But I am confident that I can work that problem out. Stay tuned

[TriCub]

You may find that your drilled out main jet may be to big now that you have the correct needle back in it .

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Well tested today and the original dead top end was back but it behaved ok for about 30 minutes then it started to idle faster , I stopped and checked plug , still pretty lean - after that was clutch start or nothing so not progress. I give up on the Amal I will now try Mikuni

[cemoto2]

Hello Andrew, I got this info. off a Montesa web site some time ago regarding fitting a Mikuni carby to a 247 Cota. They used a 24mm. carby with a 110 main, 2.5 slide, 4F10 needle, 2.0 float needle, 04 212 needle jet with float height of 17-19mm. If you go with the Mikuni the info. might help. With your Amal your slide is not worn too much in the main body of the carby? Regards Graeme.

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So I fitted the Mikuni lent to me by Ross Brown, rigged up an air filter and it started second kick - took a little while to set the idle and mixture and then rode around the garden ( 2.5 acres ) . It felt different but good (as always) felt like smoother power delivery but plenty where it was needed, popping front wheel easily etc. I was riding for maybe 5 minutes turned a corner and it was again as if the kill switch was on (which it wasn't) and it didn't want to restart.

Same old story plug was dry still looks a bit lean.

Something I have noticed before and recently is the exhaust manifold works its way loose and leaks a bit of oil. Its not always noticeable and I think may coincide with when I bolted the expansion chamber to the frame - there was a but mount there but it wasn't bolted when I got it. I was thinking about this as the original header is separate to the chamber joined by a silicon coupling but in mine it is welded. Maybe the vibration of the solid mounting has affected the manifold join.

I know this could cause the problem I have but it seems it doesn't explain why it won't restart after the manifold is retightened. It appears the last few threads are buggered now as when I tighten and tighten it slips loose again. I have already replaced the copper gasket but I removed all and added a bit muffler putty and around exhaust port then refitted gasket and pipe but the slipping still happens. I can add a second gasket (with some putty between) do you think this would have any detrimental affect on things?