JAPton blog

[Rockburner]

This thing is beginning to confuse me.

Dropped the needle in the carb today, from (iirc) 2nd notch, to lowest notch, and it's still dying at 1/2- full throttle opening, after a short time, just about when it starts getting properly hot. Before that its ok (ish)

I thought it was getting rich, but dropping the needle had virtually no effect, although it was struggling a tad at WOT, so it might be a touch lean when on the main jet?

Plug didn't look any different when i pulled it out after getting home. I cleaned it up before going out.

One slightly worrying thing is that when i pulled the plug out before the ride, it was smothered in oil...
I'm now worried a valve stem seal has gone.

I need to lower the oil feed to the head, its supposed to be 1 drop every 5 seconds at tick over.... Its currently twice that! That might be due to running R30 instead of R40, but i wouldn't think they're hugely different.

[Rockburner]

Sodding crap fibre washers!

I hate the bloody things.

Took the jet block off the carb this evening to check the fuel flow through, (to be sure the tank is breathing properly), it's fine e, but the sodding brand new fibre washer from Burlens will NOT seal again. It's gone hard already.

I thought fibre washers were meant to be reusable, at least a few times, this one ain't!

[Rockburner]

Use it as a template, cut it out of cardboard.

I've got an A4 sized sheet of Viton, going to try that.

I also found some NOS Amal fibre washers on ebay, so will try them too if they're any good when they arrive.

[Rockburner]

Been doing doing some thinking over the weekend and I'm pretty convinced that the mag is dying.

The symptoms fit: after 5 mins on the road the bike just dies and will only "run" at low speed, and struggles to tick over, but once cooled down a bit, it will fire up fine again.

Got a couple of leads of restorers so need to make some phone calls on Monday.

Even if it turns out to be something else as well, knowing the mag is good will be one less thing to confuse matters.

[cheb]

What goes wrong with them?

[Rockburner]

What goes wrong with them?

The windings break and you get arcing inside them.

[cheb]

OK. Not a home fix by a long stretch then.

[Mr. Dazzle]

The Bonnie had very similar symptoms when the ignition was iffy. Turned out to the leads and caps, it ain't got a Mag of course. Probably worth doing the lot while you're in there.

[cheb]

The Bonnie had very similar symptoms when the ignition was iffy. Turned out to the leads and caps, it ain't got a Mag of course. Probably worth doing the lot while you're in there.

Single shot like a Coffman starter and then reload?

[Rockburner]

So, stripping the carb again in preparation for an ultrasonic bath (a friend has one), and the sodding curse of fibre washers strikes again...

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[Rockburner]

Yay! Carb cleaner and a bit of hot air.... (And some careful scraping with the old dental picks...)

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Also stripped the Puch carb down, it still had clean oil in the bowl!

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[Rockburner]

So, while the Puch is awaiting bits, I turned back to the JAPton and, remembering roughly where I was, I stuck some petrol in the tank and opened the taps.

No leaks was the first win!

I tickled it up but instead of fuel coming out of the tickler, it eventually started dribbling from the manifold, bit odd, but the fuel is flowing.

Kicked it a few times and eventually it fired up, bit rough, but some small adjustments fixed that.

Opening the throttle though and there's a lot of spitting and backfiring, flames from the open bell mouth. Not good. I'm now worried that the inlet valve isn't shutting correctly, with the throttle fully open you can look down the manifold and see the flame front!

Nevertheless I took some time to adjust the oil feed to the head which wasn't running, now running at (roughly) a drop every 5 seconds on tickover, just like the book says.

I'm going to try a smaller main jet in case it's just a case of over-fuelling, but if it's still backfiring I'm going to have to have another look at the valves.

[Horse]

Zeus book

Still have mine. 1976 'Metric' edition

I don't know anyone who's actually bought one of those, yet everyone has one.

And I still have my British Thornton slide rule too

[Skub]

Zeus book

Still have mine. 1976 'Metric' edition

I don't know anyone who's actually bought one of those, yet everyone has one.

It was a necessary part of the toolkit when I began serving my time. I still have mine (it's a mite dilapidated) and occasionally refer to it for drill sizes and tapping info.

[Rockburner]

So - while waiting for a tyre fitter who's prepared to have a go at a 12" wheel.......


I tinkered with the JAPton last night.

It's all back together but wasn't running properly - lots of spitting back and backfiring in the exhaust.

Got it running, and spent about an hour going back and forth between the ancient Monobloc "Notes" leaflet (Dad had some photocopies so at least I wasn't getting the original filthy!)* Eventually got my head around it and realised that the damn thing was running "weak" in the mid-range and so pulled the needle up a notch (the first thing I'd done was lower it a notch to the "top" notch, it refused to run on that setting). Now it's in the middle of the needle's range its actually running pretty well (once it's hot). The occasional spit back or backfire, but I think I can live with that for now. (I know that the end-can is a bit loose and that will be contributing to the backfiring in the exhaust).

Happy bunny!

During the course of the session I'd spotted a couple of nuts that had fallen on the floor - one was an engine bolt that (in hindsight) I know was loose - the primary chase mounting lug is held in place by it and I'd simply forgotten it was loose.
The other was the nut off the forward connection for the gear linkage.... it's a nyloc, but I discovered that Dad had cut the bolt for it down so short that the threads aren't actually engaging the nylon locking collar! ( ffs). Couldn't be arsed at that point to root around for a better bolt so I just pushed the nut on upside down. Hardly ideal but it'll do to hold it all together while I figure out another issue.

I was wiping some oil off the top of the crankcase when I discovered something that terrifies me...



That bolt, the one between the push-rod tubes, is loose, and it won't go tight.

It just revolves.

Now - I may be wrong.... but, to me, that indicates that there's a friggin NUT on the other side of the case, that is loose, and is hanging on the threads of the bolt.



I may be wrong, and the loose bolt is caused by the threads on either the bolt or the casing being thoroughly knackered.

But - either way, the mininum work needed before I can do anything with the bike is to strip the entire right side of the engine away to check what's going on in the timing box.

I can't take a chance on the probability of a nut dropping into the timing box.

So - The JAPton is unlikely to see tarmac again this side of Easter, simply because I know that I've never done any of this stuff before and I'll be taking things very slow and thoroughly checking it all, and researching how it all works. Oddly, for all the tinkering I've done over the years, this is the first time I've ever had to actually do the timing on anything.

I also seem to have been thrown off / barred from the JAP Engine Facebook group I was on - so also need to find a J.A.P. specialist source of further information.


Dagnabbit.







* I must get a copy of that leaflet blown up and laminated. I did the same with the exploded diagram for the carb and it's an invaluable reference sheet).

[Rockburner]

Just a quick look at some photos online... and I can't figure out what the hole itself is for... it's NOT the location of the 5th stud on a 5-stud engine (J.A.P. engines came in 4 and 5-stud, and most of the components are interchangable). The 5th stud on the 5-stud engine on the plug side : Here's a photo showing an engine with the 5th stud on the same side as the plug - all the timing gear is on the other side.

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[Rockburner]

oh yeah - there's one other weird thing happening in the JAPton:

On the Monobloc carb, although I've cleaned it all up, when I use the tickler to push the float down, it "works" - but the fuel doesn't overflow through the ticker - it eventually overflows out of the bellmouth! (or possibly a tiny hole in the inlet manifold).

The tickler is simply a metal tube, closed at the top end, but with a small hole on the side about a mm down from the top. The bottom of the tube is squared off, but not closed up, and it's completely clean - it's not blocked in anyway.

The top of the float - which the tickler pushes down on, is rounded, so there's no "flat plane" on which the end of the tickler could possibly "seal".

So I'm highly confused as to why the fuel isn't exiting out of the tickler!

[Taipan]

If its the same as the one below, then it looks like the tickler pushes the float down but the fuel would likely flow out of number 24 as its lower and that would be where you're thinking its coming from? Possibly indicating the needle valve (seal) is worn?

[Rockburner]

If its the same as the one below, then it looks like the tickler pushes the float down but the fuel would likely flow out of number 24 as its lower and that would be where you're thinking its coming from? Possibly indicating the needle valve (seal) is worn?

24 is the feed IN.....


Oh - and the float, float- needle and pretty much everything else replaceable is new.

but - I am now wondering if an internal seal is not in place correctly...

[Taipan]

If its the same as the one below, then it looks like the tickler pushes the float down but the fuel would likely flow out of number 24 as its lower and that would be where you're thinking its coming from? Possibly indicating the needle valve (seal) is worn?

24 is the feed IN.....


Oh - and the float, float- needle and pretty much everything else replaceable is new.

but - I am now wondering if an internal seal is not in place correctly...

I'm not familiar with these carbs, but do have memories of stinking fingers from petrol coming out of ticklers. So it seems odd that its leaking out somewhere before that happens, but as you've just replaced something lower down than the tickler, I guess the golden rule of going back to where you last worked applies then....