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Ren - The Ed¹ said :-
"I suspect the plugs (Champion N4C) may be on the hard side?" - what do you mean on the hard side Ian? I'm guessing too hot/cold?
03/04/2025 07:58:11 UTC
Ian Soady¹ said :-
Hard = cold. Generally a high performance engine needs hard plugs to resist high temperatures, a tourer softer as temperatures may not be as high but the softer plugs burn off deposits better.
But I'm beginning to doubt my logic.....
03/04/2025 10:29:43 UTC
ROD¹ said :-
Ian, in my experience, not starting when hot is usually a rich mixture. I will not try to teach my grandmother how to suck eggs, but I would start with a valve clearance check, and then look at the carbs.
03/04/2025 11:51:57 UTC
Ian Soady¹ said :-
Many thanks Rod. It is a puzzler. Valve clearances checked (twice). Only one carb - thank goodness. In fact, I've been trying again and it seems it needs a VERY rich mixture to start - air slide fully down and tickled as well. I've also discovered that if instead of holding the starter button down, I release it after a couple of engine revs, it seems to start better - possibly because the ignition black box is seeing full voltage instead of the 10.5 or so it gets when cranking as the starter motor takes so much.
These things are sent to try us......
03/04/2025 12:00:27 UTC
nab301 said :-
Ian , I'm curious how old all the wiring is and whether you're suffering voltage drop due to the age of the cables in the loom and starter motor circuit?
As for the poor starting I had the opposite problem with my Enfield recently , ie cold starting, the bike does have an electric start facility but all the bits are removed... in the end I went back to basics with idle mixture screws (at one stage a senior moment must have had me thinking it was an airscrew rather than an idle mixture volume screw) and also the throttle slide was occasionally sticking open slightly with the engine not running , once sorted the bike fired first kick from cold although I'll need to repeat that a couple of times before I can be certain!
Nigel
07/04/2025 15:11:44 UTC
Ian Soady¹ said :-
I've completely rewired the bike Nigel, as it came with the usual bodged array of rubbish. I've used 1 sqmm thinwall cable throughout (rated at 16.5 amps which is way over what is needed) apart from the main earth and starter cables which are 10 sq mm - probably a bit over the top. I still have this theory that as the starter circuit cables are so massive, the starter is taking more current than it's perhaps designed for so not leaving enough for ignition. I have measured the voltage going to the BB black box and it drops to 10.4 or so when cranking.
I think I've also misled myself about the mixture for starting. It actually doesn't seem to care provided I use my new technique of brief bursts rather than churning over continuously.
What larks eh?
07/04/2025 17:00:40 UTC
Glyn said :-
I’m waiting for paint to finish the TZR so thought it was time to take another look at the Fantic 241 engine. I’d never actually given up but had certainly lost interest. The bike had backfired and sheared the woodruff key on the flywheel as it span round and appeared to cold weld itself to the crankshaft. 2 new pullers had been destroyed prior to the engine being delivered for my help. I’d applied as much heat as I thought was reasonable but still could not part the two. The engine was pretty much worthless at this point because the cases could not be split with the flywheel on the shaft. So I decided to use a 41mm holesaw and cut through 1” of flywheel until the outside came off. At this point I could see the coils and using a hacksaw blade only, made four cuts along the length of the remaining lump of flywheel trying not to damage the crank. Eventually it came off.
12/04/2025 20:31:10 UTC
Glyn said :-
Flywheel with 41mm holesaw and cut cut .
12/04/2025 20:33:28 UTC
Ian Soady¹ said :-
Well done Glyn. The only thing worse than a taper fit that won't grip is one that won't come off. My ploy of leaving the (incorrect) key out of the Electra starter sprocket assembly seems to be working well after dozens of starts and attempted starts.
Was that an ordinary holesaw you used as the ones I have seem made for wood and I don't think would cope with steel.
13/04/2025 09:57:04 UTC
Glyn said :-
Yes Ian it was a metal holesaw, well 2 actually and they're both ruined now. Whilst researching tapered fit flywheels, I read that the key is only there to locate the flywheel in the correct position for the timing only. The tapered fit has to be torqued up to 70 Nm and that alone stops the flywheel spinning on the shaft. I think I read that you suggested the taper fit needs to be lapped together with the flywheel. I can understand that perfectly, such a lapped joint would also make it easier to remove as there is a ccontinous contact area. I didn't mention it but the remains of the woodruff key were very difficult to remove from the keyway in the shaft. Time and effort paid off in the end.
13/04/2025 12:17:02 UTC
Glyn said :-
Maybe I’ve wasted a whole lot of time getting the Fantic apart. When I split the cases I found the crank is shot. Look at the upper shoulder that runs in the L/h main bearing. I think this is water damage from being stood. The bearing is also rusty. On the lower part of the shaft mainly at the back ( so not in picture) is another rust line where the seal sits. Oh deary me.
13/04/2025 15:43:54 UTC
Ian Soady¹ said :-
Ren will of course tell you not to waste your time on a 2 stroke. However, I sympathise. You can spend hours and days on something only to discover (as you have) that there is a further unsurmountable problem. I take it that it's not worth having it metal sprayed and remachined? How's the big end?
13/04/2025 16:13:18 UTC
Glyn said :-
It’s the challenge Ian. Whilst the Ed is a formidable alternative repair man I believe he prefers the challenge of how many socks he can get in a small hold-all with his super small tent. The Fantic bike itself is not that tidy so almost certainly not worth doing a major repair to the engine. Let’s face it, these things are designed to be thrown down steep hills and smashed against rocks whilst climbing impossible gradients. They are not meant to last! However, if I can find a man to metal spray ( I didn’t know such a thing existed) then I would certainly have a go. I’m currently appealing to the members of the owners club for used parts. There’s very little activity on the site so it’s unlikely that will come to anything. After replacing the gearbox on that Yam Dragstar this is a doddle to work on and very lightweight.
13/04/2025 18:53:44 UTC
Glyn said :-
I’ll bet there’s still some clever engineers out there who could take it all apart with a press and turn down a new shaft. Sadly, I don’t know any. Some one has suggested chrome plating and turning it down to the correct sizes. I’ve always wanted a lathe, and the skill to operate one. The shaft has a taper and thread, that’s probably not easy.
14/04/2025 08:01:23 UTC
Ren - The Ed¹ said :-
Holy moly that looks/sounds like a LOT of cutting Glyn. I certainly would not have the patience for that - but then I'm not retired and tinkering in my shed. If you've gotten the time then why not, I'm sure it was much more fun than watching daytime TV.
This does seem like a lot of effort for what is essentially a noisy horrible smelly 2-stroke. Ian has his odd Suzuki engine in a classic cycle thing. Why not stick a "fresher" motor in there? You could have endless fun working out alignments, mounting options, ignition systems and even build your own exhaust!
14/04/2025 08:12:40 UTC
Ian Soady¹ said :-
It's not a 2 stroke Ren it's a 4 stroke DRZ400. Glyn - I don't know where you are but there are still a few proper engineering shops about. We have a superb one here in Redditch - Nametab Engineering - but I suspect the owner is approaching retirement. He will tackle just about anything (was formerly an Ariel Arrow/Leader guru) and is surprisingly inexpensive.
14/04/2025 09:39:58 UTC
Ian Soady¹ said :-
Or.....
You might get away with turning the shaft down and fitting a speedi-sleeve.
But I take your point that it probably isn't worth it.
https://www.bearingboys.co.uk/Speedi-Sleeves-Shaft-Repair-3289-c...
14/04/2025 10:41:08 UTC
Glyn said :-
Thanks both. Would love to put a different engine in there but for 2 immediate problems; the swinging arm bearing is through the rear of the engine and the chain drive is on the right. Add that the entire bike weighs in at 97kg when most 4 stroke engines will be heavier that that. Perhaps I should drag that Honda CMX 125 out of the hedge that I posted a picture of recently. I will look up Nametab Ian, you never know your luck. The Fantics dont fetch a lot of money even complete and original. Not sure a Jap twin will render it illegal for use in classic off road events. You’ve got me thinking though Ren, it’s a different challenge and sure to interest Ian who loves things such as Triumph engines where Villiers lumps used to be.
14/04/2025 10:41:43 UTC
Glyn said :-
That Speedi Sleeve shaft repair looks interesting. However, I’ll still need to get the shaft out of the web to get it into a lathe which is going to require skills that are absent in me and a press that is absent in my garage.
14/04/2025 12:55:58 UTC
Ian Soady¹ said :-
You might be able to dismantle it by finding fine thread setscrews & nuts that will just fit between the flywheels and using them to jack them apart. As recommended in my 1948 copy of The Motorcyclists' Workshop. You don't have anything to lose.....
15/04/2025 10:01:11 UTC
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