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My New 1975 Montesa Cota 247 (Pics) Hot Starting Problems. It's My First Two Stroke.


handmadematt
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Float level or needle valve leaking / blocked.

You reckon? Resulting in a rich mixture meaning an easily flooding engine? That's certainly what it feels like to me.

Since opening and closing the carb so many times the gasket's given out and needs replacing. The bowl does leak a bit now now when tipped up. It's not overflowing though because the over flow pipe has never exhibited a flow.

This is certainly worth investigating.

It's the route I've felt to be a problem but so far I've been convinced on here to focus on the electrics.

We'll see.

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Do we know how old this carb is, i think i would of bought it a nice new one about a week ago.

In motion sell them.

I don't know how old it is exactly but the previous owner had fitted it and he owned the bike for six years.

It all looks in good condition though with certainly no damage.

amal can still supply the orginal type carb it is on there web site www.amalcarb.co.uk

Interesting, although when I select model and make of my bike, the carb it recommends is listed as a four stroke.

I'd prefer to identify the problem with the existing carb and fix it to be honest. It'll be much cheaper obviously.

Thanks again for everyones input.

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I have a 76' 348 Cota. 2 things come to mind :

#1/ Even a new coil can be defective. And 30 years ago, I had the very same problem on a 2 stroke bike....and a 504 Peugeot car. Always easy start when cold, but very unlucky when warm. Sometimes I had to wait 5, 10 or 15 minutes. It ended up each time being a faulty coil. It is worth trying another coil ( and always good to have a spare anyways ! ).

#2/ As said by others here, the Mikuni carbs can act " weird ". On my Kawasaki KT250, the bike works just fine, but when off, fuel will seep past the bowl gasket, even with a new float valve and the proper float height. One thing you could try is to shut off the gas supply when the bike dies while ridding it. And try to restart it like that. If it does, it could mean fuel is going into the intake when the engine is off.

As far as the wires cut and exposed, some models came with lights. Maybe when the lights were removed, the owner back then just cut off the wires ? Anyhow, that should be cleaned up.

BTW, your bike seems very nice and I would like to see more close-up photos if possible when you get a chance !

Terry

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Hi Terry mate, thanks for the reply. They are great bikes hey!?

It is worth trying another coil ( and always good to have a spare anyways ! ).

I think you're right. I'm going to get one when the supplier re-opens.

One thing you could try is to shut off the gas supply when the bike dies while ridding it and try to restart it like that. If it does, it could mean fuel is going into the intake when the engine is off.

That's a good idea. It might help with diagnosis.

...your bike seems very nice and I would like to see more close-up photos if possible when you get a chance !

Cheers bud. I'll post some up later today or tomorrow.

Thanks again.

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one way i use to determin wether spark or carb trouble is to use a strobe light on the plug lead it will light up when the plug sparks but if it isnt sparking under compression it wont light up ,so if its lighting up when hot trying to start it you know its not the spark but if it floods up bad after a few attempts that could wipe the spark out ,generally ive found that when they spark they fire up easily

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...BTW, your bike seems very nice and I would like to see more close-up photos if possible when you get a chance !

Terry

I managed to snap this one for you mate. She's a bit dirty around the engine but that's what they're made for!

2012-12-30134517182324_zpsa509f12b.jpg

one way i use to determin wether spark or carb trouble is to use a strobe light on the plug lead it will light up when the plug sparks but if it isnt sparking under compression it wont light up.

This is a great idea. (Today I couldn't even start the engine besides one kick where she splutter for ten seconds before dropping out and dying.)

So, I connected up my timing strobe with the plug out but earthed with a piece of wire. I got multiple fast flashes every time when spinning the engine over by hand. (Which was relatively easy with the plug out.) When the plug was back in though the strobe would only flash briefly once every other kick or so. So I think some of you may be right about the plug failing inside the cylinder. In the morning I'm going to repeat my strobe experiment and if I get the same results I'm going to remove the carb and repeat. If I can confirm that the spark is failing inside the cylinder even with the carb disconnected then it is the compression that's snubbing out a weak spark. If by some chance the plug does fire properly inside the cylinder without the carb then I can investigate a potential problem with fuelling/ flooding and fouling of the plug.

It's fascinating because the motorcycle works by running multiple independent systems which must all harmonise and work together to produce a functioning engine. Ignition, air and fuel for example. In my case each one of these systems is working correctly when independently inspected. They are all observed to function but that synergy is not happening. When combined, these systems are not harmonising to produce the desired result. A bit of mystery and a bit of fun in the workshop. I guess this is what I signed up for and this is what I get.

...If the plug fails tomorrow under compression with the carb off then I'll finally try a new coil. Here's hoping.

Thanks again.

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