Trials Australia Forums

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.

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.

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.

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?

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

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

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

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

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.

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?