JAPton blog

[Rockburner]

It might run ok at less than 1/4 throttle, but any more than that and it starts bogging down, won't fire at all, then after 2 or 3 deafening explosions from the exhaust it'll pick up and run well for about 10 seconds before it starts bogging down again.

Rinse and repeat again and again if I try to ride it anything more than 1/4 throttle (ish).

So... Back to to the tuning leaflets....

I still can't get my head around whether these symptoms are the carb set too rich, too weak, or something else completely.

The Amal booklet seems to suggest that issues with fitting in the exhaust are ignition related.... But that doesn't balance with the fact that the engine WILL run properly for a few seconds before it bogs again.

[Skub]

It sounds like it's getting some fuel,but not enough,though the backfire thing would make me think it's more an ignition fault.

[Rockburner]

It sounds like it's getting some fuel,but not enough,though the backfire thing would make me think it's more an ignition fault.

In this context, what does "ignition fault" even mean?

As I say, it'll run ok for a bit, then it seems as if something "builds up" and it stops firing, until the fuel in the exhaust detonates, and it clears up and runs again.... Until the "blockage" builds up again.

[Rockburner]

Well, I've still not figured out what's wrong with the JAPton. Did some checks last week and fuel flow is good ( more than half a litre per minute, which ought to be fine).

Raised the needle by one because i thought it might be a bit weak, and tried starting it up and although it started easily enough, its still spitting back and backfiring.

I'm beginning to think the ignition timing has slipped, so i took a cover over the magneto drive sprocket to check it.
Seemed fine so went to put the little cover back on, and bugger me if the sodding thread didn't strip.

GAH!

So I'm going to put the JAPton aside for a bit and concentrate on the other projects i need to get done before winter, and will very likely spend the winter stripping the thing down and learning more of its foibles.

[Rockburner]

I guess I ought to carry on here.

Re The Puch: the police have dropped the case due to lack of leads. The arrested scrote was released before they got a warrant to search his property so nothing was found and a few weeks later they cold-cased it. I've kept half an eye on ebay and FB, but nothing. It's either in a canal or disappeared into some local holiday camp's barn.

Re the JAPton - it's back, and I've been doing a little tinkering. Reduced the main jet to the next size down and fired it up in the workshop on Thursday evening, where it ran like a good un for 5 minutes* (albeit with some spitting in the carb at low throttle), but when I took it out on Friday evening for a road-test, after sealing the exhaust joint up properly, the bugger simply would not start. I kicked it for at least 10 minutes and got nothing but a few seconds of desultory spitting. Bloody thing.

I've a nasty feeling the timing may have slipped - there doesn't seem to be much compression (it's not a very high comp engine at the best of times, so it's difficult to really tell).

And the fecking kickstand has twisted on the starter again, so that needs sorting.....



* There's now a lovely aroma of Castrol-R all over the place.

[Rockburner]

I guess I ought to carry on here.

Re The Puch: the police have dropped the case due to lack of leads. The arrested scrote was released before they got a warrant to search his property so nothing was found and a few weeks later they cold-cased it. I've kept half an eye on ebay and FB, but nothing. It's either in a canal or disappeared into some local holiday camp's barn.

Twats.
The police and thieves.

I read on the news today that a farmer shot a couple of burglars, I gave a little cheer. No doubt someone will miss them but it won’t be me.

On the Japton, do you have the timing information to set it back properly?

I hope so! I've got the relevant books - but they never anticipated this particular conglomeration of parts: a 350 crank in a 500 engine. So there's a bit of guesswork but I should be able to get pretty close. IIRC I saw something recently that suggested inlet opens 44 degrees before TDC.... which seems very early to me! But I'll check it.

I want to check the coil and tinker with the carb a bit more tbh. Reducing the main jet size seemed to make a considerable difference to WOT, so I'm thinking that the needle/needle jet may be too open as well. (I think cleaning the carb upset it all a bit!)

[Rockburner]

I don't use degrees, I do it the easy way with a pencil down the spark plug hole, find TDC and mark it off, then IIRC on the Rudge it's supposed to open 13mm BTDC.

Yep. There's an addition to that where you mark it once, then rotate the engine back the other way to the next (previous?) TDC, mark that, and then genuine TDC is halfway between the marks. (if I understand what I've read correctly).

It seems very forgiving because although I'm as careful as I can be it's not exactly microscopic accuracy.

With the old singles I think there's a lot of "tolerance" in the system.

I also start it the easy way, flood the carb, put it in gear, wheel it backwards until it's just before TDC (because the compression won't let it go back anymore), pop it into neutral and it fires first kick every time.

The JAPton is easy enough to kick over compression, (there's a valve-lifter) and it generally easy to start, this is one of the reasons I think something has slipped.

A fuel issue I had with starting was because the petrol seemed to leave a very thin layer of varnish in the carb when it evaporated that was invisible but very successfully blocked stuff up. So now I drain the float bowls any time I'm going to be leaving it more than a day not being used.

hm probably a good idea, I do tend to use the very low ethanol fuels (Shell 98 Supreme iirc).

Oh and once I bought very legit looking spark plugs off eBay that turned out to be fake NGKs, they worked but were rubbish and it was hard to start and ran like a dog. I bought new ones and it instantly cured it. The fakes were very good fakes but next to proper ones you could tell.

I've got a couple of new ones, (the one in there is new), bought from a reputable website, never had much luck with ebay so I tend to avoid it.

[Rockburner]

Yep. There's an addition to that where you mark it once, then rotate the engine back the other way to the next (previous?) TDC, mark that, and then genuine TDC is halfway between the marks. (if I understand what I've read correctly).

I'm not sure I'm following what you mean?

TDC, as I understand it, is literally when the piston is sat at the top of it's stroke and furthest from the crankshaft, if you're doing it with the head off then it's obviously very easy because you can see when it stops rising, but I find it very easy with a pencil (or dowel or something that you can easily mark) down the bore because (if you rotate the engine very slowly) as soon as the pencil stops moving then you know you're at TDC.

A couple of checks to ensure you really have marked the pencil at TDC, then I mark the pencil exactly where I need the contacts to close and then I rotate to the correct position and set the points with a fag paper or something. As I said IIRC on the Rudge it's 13mm from TDC, but I've tried it a millimetre or so either way and it seems very forgiving, plus I've got a manual ignition retard/advance on the handlebars as well.

I found all this stuff quite intimidating when I first got into it, but it's pretty straightforward as long as everything is working and in tolerance.
I've heard about blokes stripping magnetos at the side of the road and fixing them like Macgyver but fortunately I've never had to try.

It was something I read, I need to find it again. I think it was just a more "accurate" way of finding TDC.

What are you measuring the 13mm on? is it 13mm around the outside of the primary chain gear or something? (because obviously that will translate to a degrees angle and will be dependant on what the diameter of the circular thing is). Or is it 13mm of travel back down the cylinder by the piston?

The JAPton has a BTH Mag with a sealed electronic "points" modernisation - so theoretically I just need to get the mag timed correctly it's drive chain - I "think" I've got some details for this, but need to double check them again. My Dad didn't keep the receipts for anything so I've no idea who supplied this modified mag, but there's a few people who do the modification so I might be able to ask around if I can't find the details.

It could be that the valve-timing has slipped instead/as well - I think it's going to be a full strip down time. It's a pretty simple engine when all is said, there aren't even any gaskets anywhere (apart from the main head gasket!)

[Rockburner]

When I eventually refurbished the Rudge I sent the head off to have new seats put in and new guides, the bloke that did it is in his sixties and he said it was the most worn out head he'd ever seen, the guides were non-existent and it had started wearing into the actual head, the stems were rattling around in there.

The cam lobe was worn really badly too, there is a little stem between the lobe and pushrod and that was worn terribly as well.
(I'm using Mini Cooper pushrods so I could put balls on the valve arm and have the ball/cup arrangement)

Once I had it apart I was amazed that it was even running at all to be honest and it really shows how bulletproof these old single cylinder engines are, they can be worn to a shocking degree and it will still get you home.

I "think" the head I've got here had phospher-bronze valve-guides fitted - but I'm not 100% sure - I KNOW Dad had the valve guides done on something, but he also had a 1930 HRD Vincent, with a similar J.A.P. engine and it might have been that engine that was updated. (I think a lot of his notes in the J.A.P. engine book refer to that engine - not mine.)

[Rockburner]

....Or is it 13mm of travel back down the cylinder by the piston?

Yes, it's literally that simple, get the piston to TDC, then drop it back down 13mm, then set the points.

The 13mm will also be a certain number of degrees but I find it so much easier to do it with the pencil down the bore, rather than take the side cover off and use a degree wheel measuring device.

Ah - so on your engine 13mm will equate to an exact angle of rotation - sounds like a good way to make the job simpler - I'll have to take come careful measurements and see what the drop is on mine for the correct before TDC angles I need (valves and spark)

[Rockburner]

Yes, it's literally that simple, get the piston to TDC, then drop it back down 13mm, then set the points.

The 13mm will also be a certain number of degrees but I find it so much easier to do it with the pencil down the bore, rather than take the side cover off and use a degree wheel measuring device.

Ah - so on your engine 13mm will equate to an exact angle of rotation - sounds like a good way to make the job simpler - I'll have to take come careful measurements and see what the drop is on mine for the correct before TDC angles I need (valves and spark)

Yeah it's so much easier to do it that way and no less accurate.
You can buy a proper tool that measures it with great accuracy, it's like a vernier type scale that allows better accuracy than a pencil lol, but as I said it's very forgiving, in some engineering applications a quarter of a millimetre might as well be a mile, but not on the timing of TDC on an old 500cc single.

Need to see if I can get a vertical drop through the plug hole (it's angled at about 40 degrees off-line from the cylinder). I think I can.

[Pirahna]

The standard Rudge head (the Special not the Ulster) is a side plug, but I converted mine to a centre plug, I haven't had it on a dyno but people that have reckon it's worth a good few bhp. I have to use a small CR7 NGK spark plug, but it works a treat.

Is it dual spark or do you keep the old plug in to fill the hole?

[crust]

Yep. There's an addition to that where you mark it once, then rotate the engine back the other way to the next (previous?) TDC, mark that, and then genuine TDC is halfway between the marks. (if I understand what I've read correctly).

We used to do this on the Wasp Norton.

Replace the spark plug with one we'd made (drill though centre of plug and welded a rod through it) that would stop the piston.

Bolt on a degree disk and make a pointer with a bit of bent welding rod held under a case bolt. Rotate the crank one way until it was stopped by the plug, note the number of degrees, rotate it the other way, note the degree, divide the difference by two.

Remove plug, the rotate the crank back to the first number plus half the difference calculated above.

Sounds complicated but isn't, there'll be a you tube video, here's one >

[Rockburner]

The standard Rudge head (the Special not the Ulster) is a side plug, but I converted mine to a centre plug, I haven't had it on a dyno but people that have reckon it's worth a good few bhp. I have to use a small CR7 NGK spark plug, but it works a treat.

But my point is that it was easy to convert, because it has a centre bolt in there anyway that I just expanded with the right drill/thread - my assumption is that the centre bolt was there so you can measure the timing that way - doesn't your head have the same feature?

I'll have to have a look, but I don't think so. It's only a 2 valve head so there may not be room for a central plug.

This isn't mine, just a photo I found online.

[Rockburner]

Methinks the kickstart lever is toast.



The shaft splines seems good, luckily.

[cheb]

Is there anything special about it that makes it difficult to replace?

[Rockburner]

Is there anything special about it that makes it difficult to replace?

Shouldn't be, there aren't any original parts left, but the pattern parts from good suppliers are supposed to be good.

I'm reliably informed that it's a bog-standard pre-Commando Norton lever.

[Rockburner]

Small steps....




(but lots of swearing, damn that thing is tight!)

I only bought the lever itself and the pinch bolt, so I swapped the pedal-arm over from the old assembly and used loctite-blue on both the pedal-arm retaining bolt, and the pinch bolt.

I also realised that there's a hole bored down the end of the shaft which I obviously hadn't noticed before: at some point I'll go spelunking and see if it's got a decent thread in it....

[KungFooBob]

That gearchange assembly is... different.

[Rockburner]

That gearchange assembly is... different.

Fancy rearsets..... No idea where they're from.