102 still not running

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Lyndasbottom
Posts: 8
Joined: Mon Oct 05, 2009 12:08 pm
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102 still not running

Post by Lyndasbottom »

I mistakenly started this topic in the general discussion section. I have a 1955/56 102 s/n AC46369 fitted with an Amal 416 carb. I bought it from a guy who said he hadn't used it over the winter and didn't need it any more. Following advice from John, I put in a new plug and HT lead, reset points to 20 thou and some fresh 10:1 fuel. This got me to where it would start, albeit unreliably, but wouldn't run without the choke closed. After some more advice via the forum and John I have thoroughly cleaned out the fuel tank, fuel pipe and carb and changed the mix to 16:1. I can now start it on second or third pull without the choke but it will only run if I hold down the carb float tickler. If I don't do this it backfires through the carb. I've done a compression check and get 50+ PSI. I'm starting to think that the age/wear of the engine is such that it can't provide enough "suck" to draw the heavier fuel mix through the 416 which was designed for 25:1. I'm thinking along these lines because I put about half a litre of fresh petrol in the tank to flush out the 10:1 mix and tried to start it just to see what would happen and it ran pretty well. The 10:1 mix is very heavy which would explain why it wouldn't run without the choke and it is a lot easier to start with the 16:1 mix. I'm tempted to try a 25:1 to test my theory but aware that this may not be good for the engine. I've cleaned the carb to the point that you could eat your dinner on it. Have to say I'm getting to the point of tossing the thing in a skip :evil: . Appreciate any views before I consider more investment in the shape of the correct carb for the engine.
chris
Posts: 547
Joined: Mon Mar 06, 2006 3:13 am
Location: clontarf aus

Re: 102 still not running

Post by chris »

I would get the proper 2 jet amal carb for it,I have 2 old AD's at home with the right carb and they start easy and run well, I much prefer the 102's to the later models,
although I do like the century models
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Waggles
Posts: 252
Joined: Wed Mar 05, 2008 10:27 am
Location: Essex, UK

Re: 102 still not running

Post by Waggles »

Think it isn't a case of not enough 'suck' but its the needle in the 416 carbie. 25:1 mix is much richer ( in fuel ) so the mixture has to be leaned off in order to run correctly, as you say the 416 is designed to run on 25:1 so has been set to run much leaner hence why you are getting these weak mixture symptoms on the weaker 10:1 mix.

If you were to run on 25:1 it would probably run OK BUT DON'T DO IT!! your bearings much prefer 10:1 and will show their disgust if you starve them! On an engine of this age its best to respect it with 10:1 for all parts anyway.

In theory a needle change in the 416 to richen the mixture would work but I doubt such needles exist ( but don't actually know that ) so I am afraid my vote would be for getting the correct carb as well.
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Charles uk
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Location: Maidenhead Berks UK

Re: 102 still not running

Post by Charles uk »

The needle retaining clip should be in the lowest groove on the needle for 10:1, is it?
Make it idiot proof and someone will make a better idiot.
Lyndasbottom
Posts: 8
Joined: Mon Oct 05, 2009 12:08 pm
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Re: 102 still not running

Post by Lyndasbottom »

Thanks for all the replies. I have the retaining clip on the lowest groove. You all seem to confirm my thought that the 416 isn't really happy with heavier fuel mixes. However, I had a chat with an old friend who reminded me that we used to do our own re-jetting on motorbikes many years ago. So having in my possession some very small drill bits I have experimented with the 416 jet. The existing jet is somewhere between 0.9 and 0.95mm diameter as the 0.9 will go through and the 0.95 won't. Using finger power alone I was able to drill through the jet with the 0.95mm bit. Having made sure it was clean I put it all back together and using the 16:1 mix (as recommended by John) hey presto a running engine. A bit of twiddling on the cable and it will sit quite happily ticking away to itself and rev as needed. As this was such a minor change (I remember doing some very oversize jets on bikes) I'm going to see how it behaves over the winter. I haven't had a chance to try a 10:1 mix yet. Probably still go for the right carb in the new year.
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