Snuffing out?

Information relating to the Matchless G85 500cc Heavyweight, AJS 7R, Matchless G45 and Matchless G50
SPRIDDLER
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Re: Snuffing out?

Post by SPRIDDLER »

I can't see how a mag would become temperamental only on hills......and not on the flat, unless its components were seriously overheating, but maybe a mag guru knows better.

What plug are you using? Is it definitely good? It could break down when hot, not necessarily causing a misfire but a weak spark, sparking between the centre electrode and any random point on the body rather than the earth electrode. I'd fit a new plug as a matter of course regardless of the age of the one in use.
Is it a good colour, not sooty or white? I wouldn't lean the mixture if you're not sure that it's too rich as you'd risk holing a piston or a seizure on your extended motorway ride. If anything, a lack of power on large throttle openings is usually a sign of a weak mixture - i.e. undersized main jet or wrong or slipped (dropped down) needle in the throttle slide clip. Have you removed a previously fitted air filter?
You can check the float level quite easily.
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bjorn
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Re: Snuffing out?

Post by bjorn »

Re Spriddler's:

"Since it has started happening to both bikes at more or less the same time it's likely that it's not ignition related.
Ignoring the remote possibility that both engines are overheating and nipping up..........."

Could it be that the bike(s) are actually overheating and nipping up? Have they both been rebored? By the same company? Are piston to cylinder clearances sufficient?

If a re-bored motor was otherwise running perfectly with good carburetion and ignition and it started to loose power uphill my first thought would be that it was nipping up/seizing, either due to too small piston to bore tolerance or faulty lubrication.

Hope you sort your problem.

regards
Bjørn
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robcurrie
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Re: Snuffing out?

Post by robcurrie »

Matchymarty, here are some things to check: non-resistor spark plug, non-resistor ht lead and plug cap. Make sure the connections on ht lead are good and that the insulation isn't leaking spark (check in dark at night). You could try closing the plug gap a bit and try it up the long hill to confirm if it is ignition related.

If it is fuel related it could be insufficient fuel flow due to restriction in the supply: blocked filter, gauze pickup blocked, bore of fittings or pipes too small and blocked fuel tank vent. I have seen figures for checking fuel flow mentioned somewhere.

Could there be something in the bottom of the tank that covers the pickup when going uphill? Have you tried opening both fuel taps when encountering the problem?

Rob C
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Re: Snuffing out?

Post by Matchymarty »

bjorn wrote:Re Spriddler's:

"Since it has started happening to both bikes at more or less the same time it's likely that it's not ignition related.
Ignoring the remote possibility that both engines are overheating and nipping up..........."

Could it be that the bike(s) are actually overheating and nipping up? Have they both been rebored? By the same company? Are piston to cylinder clearances sufficient?

If a re-bored motor was otherwise running perfectly with good carburetion and ignition and it started to loose power uphill my first thought would be that it was nipping up/seizing, either due to too small piston to bore tolerance or faulty lubrication.

Hope you sort your problem.

regards

Bjørn
Interesting. The '55, has recently been rebored, resleeved and new piston and rings with 5 thou clearance. I don't believe the bike exhibited this issue previous to the new piston. That said, the previous piston was 70 thou (yes you read that correctly) undersize. So no chance of it nipping up!

The '56, I have no details on internals, as I've only recently purchased it, and have not opened it up.

That said, given that if the bike is revved higher up the same hill, in a lower gear, and does not exhibit the issue, would that discount the nip up theory? I would have thought higher revs = more heat and more likelyhood of nip up?
SPRIDDLER
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Re: Snuffing out?

Post by SPRIDDLER »

There's a confusing 'wild card' in your problem in that both the '55 and the '56 seem to have the same issues which would indicate a similar cause for both.
This could surely be only two factors...
Weather, or Fuel used. Have you started using a fuel additive?

or as Bjorn said, both may have been rebored with inadequate piston clearance or have lubrication issues. The 5 thou clearance on the '55 should be o.k. (assuming that the rebore/resleeve was competently done). As a rule of thumb (where the clearance is unspecified by the manufacturer) on an unknown piston I have worked on a 'rough and ready' 1.5 thou clearance per inch of bore diameter, plus half a thou.
It seems unlikely that easing off the throttle or changing down would instantly clear any nipping up although th'engine would not be labouring so much.

It's the fact that both bikes seem to have the same problem that's confusing........
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clive
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Re: Snuffing out?

Post by clive »

Rob Harknett wrote:I sprayed a cap silver on one of my little Reliants years ago, I got about 15 miles . At the time about a mile into Hatfield forest. Car stoped. No fuel gauge. I was sure I had plenty of fuel. Took off the cap to try a dip stick in the tank. As soon as I removed the cap I could hear air being sucked in. Yes, paint blocked the cap hole. Your bike will not quickly stop as a warning if your oil cap gets the hole blocked.
Generally the oil caps on our bikes do not need to be vented as there is an internal overflow pipe which also acts as a vent. However if an unvented oil cap is used as a petrol cap ........

I have only just caught up with this thread and having read it from the beginning have the following thoughts,
The problem is happening on two bikes
Both bikes have recently had their petrol tanks repainted
Coincidence or did you do something to both bikes when refitting the tanks? We heard you used a rubber seal to stop leakage ( just fill less, works for me) the seal ought to be a thin cork or thick paper I think. In my experience rubber ends up being affected by the fuel. The symptoms you describe, problems when using full throttle uphill but intermittent, can certainly be caused by a speck of dirt in the cap below the main jet. As you open the throttle the muck gets sucked up and partially blocks the main jet. Throttle back and it falls down. If you fitted rubbers to both caps is it possible it is a bit of disintegrating rubber on both bikes? I know the filter as the petrol enters the carb should stop bits getting through but the muck only needs to be very small to cause this problem and seems to be able to pass through the filter.
clive
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Rob Harknett
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Re: Snuffing out?

Post by Rob Harknett »

Generally the oil caps on our bikes do not need to be vented as there is an internal overflow pipe which also acts as a vent. However if an unvented oil cap is used as a petrol cap ........ quote.

I am not that familiar with all years , 1935 to 1947 Matchless had the same cap for petrol and oil tanks. Those being what are referred to " Pie Crust " caps. AJS also used the Matchless caps on both tanks circa 1946/47. I assume using up old stock. These caps were internal expanding, they were able to breath. They were less likely to get blocked via the expanding mechanism, than the later push on and turn external fitting caps with a pin hole. I do still stick to advise I was given when I first got a motor bike. When the old boy across the road from where I lived, took on the job of checking my bike and teaching me how to look after it. Neighbours did that in those days. My father also used to tell me to go and ask Joe before I meddled with my bike. It was him that run a drill though holes in both my tank caps telling me to make sure they are always clear. He used to do it with a little drill tool that had a spiral stem. On the stem was a fitting you pushed up and down to turn the drill.
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clive
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Re: Snuffing out?

Post by clive »

We are discussing a 55 and 56 bike here Rob not living in the prewar crusty years.
clive
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Matchymarty
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Re: Snuffing out?

Post by Matchymarty »

clive wrote: Generally the oil caps on our bikes do not need to be vented as there is an internal overflow pipe which also acts as a vent. However if an unvented oil cap is used as a petrol cap ........

I have only just caught up with this thread and having read it from the beginning have the following thoughts,
The problem is happening on two bikes
Both bikes have recently had their petrol tanks repainted
Coincidence or did you do something to both bikes when refitting the tanks? We heard you used a rubber seal to stop leakage ( just fill less, works for me) the seal ought to be a thin cork or thick paper I think. In my experience rubber ends up being affected by the fuel. The symptoms you describe, problems when using full throttle uphill but intermittent, can certainly be caused by a speck of dirt in the cap below the main jet. As you open the throttle the muck gets sucked up and partially blocks the main jet. Throttle back and it falls down. If you fitted rubbers to both caps is it possible it is a bit of disintegrating rubber on both bikes? I know the filter as the petrol enters the carb should stop bits getting through but the muck only needs to be very small to cause this problem and seems to be able to pass through the filter.
The Problem has only occurred in a 'minor' way on the '56, and only once. I have not ridden the bike enough to test further, and likely will not due to other issues with it now (see other thread - hideous vibration, which caused broken oil line yesterday - now I'll have to park, and pull down - fuel tank also leaking again so ugh... :headbang: ) For Reference, the '56 has a firm rubber type fuel tank cap seal and I've never changed it, and an unvented oil tank cap. .

The '55 which snuffs the most, has a cork fuel tank cap seal, and a vented oil tank cap. Burns oil to the rate of 500ml per 100 miles, only 2500 miles since new piston, rings and cylinder sleeve. - suspect broken ring or something worse, and valve guides for oil consumption.

I've drained and cleaned the main jet cap several times, some times, it's clean, sometimes has small silt like muck, but doesn't seem to be blocking the main. Takes a fair bit to block a 260 main. I'm in the process of getting a filter to try exactly as you mention. I may rinse out the tank too, as it has a liner in it.

Now that you mention it, I wonder if it is the liner breaking down.... The liner has failed inside the '56 tank, as it is leaking again, and blowing the paint off.

Great. I wonder if it is and if it's reacting with the petrol and burning badly causing the oil consumption etc. I can't exactly remember when this snuffing started, but, I suspect it was after I got the tanks painted and lined inside!
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Re: Snuffing out?

Post by Matchymarty »

Could it be the Red-Kote tank liner dissolving in the fuel and causing burn issues?
The liner has failed in the '56 and tank is leaking again. I got the '55 tank lined with Red-Kote as a preventative measure. The fuel is coloured red, so I wonder... not to mention both bikes now blow loads of smoke that didn't use to ... ???
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