Mech

Yeah I'd seen that.. but as you say.. You need to ride it. And to read the plugs for changing the jets, you really need new or cleaned plugs. You'd have to ride full throttle for twenty minutes to change the color otherwise. It'll be fine mate.. Adjust the idle, then tune the needle slide, then see how it goes.. You're an observant guy... and won't bugger it from a lean main jet.

Well... I doubt it has a rev limiter as such.. not like modern cars do anyway. The induction will be the limit I think.. The manual may say otherwise. The trouble is that if they retard the timing to limit revs, the motor gets hot, and if they advance it to try and limit revs(while someone is holding the throttle wide open), it's not good for the bearings and rings. That's why they kill the ignition on modern cars and you get that horrible bucking and jerking as the rev limiter kicks in and out.. Nobody keeps trying to push them once that starts.. haha. If it's jetted for best economy/power balance, and you back off very slightly, the vacuum goes up for a second, and the mixture goes slightly richer than at a steady full throttle. If it was a bit rich to start, it will sound and feel rich, and if it was about right it will pull ever so slightly nicer. All that's a bit harder to sense with a diaphragm carby though.. But then, those carbies aren't really made for thrashing.. they are made to be user friendly. If you want performance, get a better carby. You could try it though and might be able to tell about the mixture.. It's the test I'd do. All that said.. I'd just assume that if the emulsion tube, slide needle, and emulsion air bleed are all right as per the book for your bike and altitude, and it runs nicely through the needle's range of control, then the standard main, for your altitude and bike, will be pretty right too.. We don't often use main jets to their limit. It should be quite safe.. unless you live in a desert or something and really do use full throttle in a high temp and for prolonged periods of time. If it pulls right through the power range with full throttle, and just slowly fades at the very top as revs build, it's probably fine, induction is limiting it. If it starts losing power as you open the throttle the last little bit, and it's before it's at full revs, then yeah, perhaps a bit more fuel is needed. Perhaps.. too much fuel, quite a bit too much fuel, will give similar symptoms. I'd ride and monitor it for a bit (and likely change the needle clip position).. before I changed main jets..

General rule is about 16 percent leaner for every 1000 foot of elevation.. There are a few ways of testing the main jet setting.. Full throttle blast along a long road or big hill, then pull clutch (pressing down on the shift lever should disengage the manual foot operated clutch) or throw into neutral, kill motor, then read plug colour. Or, and this is simpler, full throttle for a few seconds, then ease the throttle slightly and note whether it smooths out/pulls better and/or picks up a very few revs.

This mate... "Rpm’s fall and rise slowly as if fuel level drops and then catches up. ".. It's obvious now.. I've seen it before.. On cars and bikes. If anyone gets that symptom.. Remember this thread..

Ok. Well done.. Float vent would be an obvious one I guess.. in hindsight !! It's a concern to have to admit to having seen that before.. Dang... Memory and focus isn't what it used to be. And I was sitting here with that feeling that the answer was right on the tip of my tongue.. That I'd seen that exact symptom before..haha. And yeah, I guessed you must be some sort of mech to be using a vacuum gauge.. That's old school.. and a bit of a lost art. Never hurts to brainstorm though huh.. sometimes just talking it through helps our thought processes ( I wish).

If the pistons stuck because of sitting it might be ok.. usable even.. If it seized from overheating and then got parked.. not so much.. Soak it is something.. diesel even does a good job.. then pound it (the piston) a bit with a wooden hammer handle, or solid dowel and hammer (one pound).. It'll come free.. Free the rings in their grooves carefully then take them out and and clean it all and put that top end back together.. It will be good enough to test the rest of the bike.. Then you decide whether to do more repairs or not.. That's what I'd do. Ah.. Gwbarn beat me to it..

I was talking to my son last night over a beer, and he reckoned that if they are dry flywheels, the magnets come unstuck from sitting around.. he's had then deteriorate sitting on his parts shelf(my shelf really !). He reckons rust creeps in if they get cold and wet.. poor little things..

As Ulfthendar says, it would be a good idea to deglaze the drums.. rough emery tape or sandpaper.. 80 grit, and a bit of pressure.

Well the float needle and jet might be for something with a fuel pump.. and be too small for a gravity feed. And I suppose you'd have checked the slide is free and the diaphragm's good and working. I've been baffled before with cv carbies not revving, and it's eventually been because they had no, or not enough air cleaner restriction.. They have to have a bit. And sorry to mention it but... on the slide needle, if it had two plastic washers, one top and one below, are you sure they didn't get muddled.. they are sometimes/often different thickness.. but some few thou.. About a needle clips worth maybe.. The problem sounds like it's in the needle's range of operation.. How about the air bleed to the emulsion tube ? Was that changable ? "Rpm’s fall and rise slowly as if fuel level drops and then catches up. ".. Hmmm.

Ok.. one question.. When you say it will not maintain revs, do you mean steady revs, or, that it dies away after some short time.. or something else ? Blocked tank vent ? Any emission gear on that bike ? Charcoal canister ? Vacuum release diaphragm on side of carby ? I don't really know these machines at all.. haha.

If it's over advanced it would probably "hunt" at light load and light or medium steady throttle.. Just a slight surge sort of thing.. Pulling the choke on improving things makes me think it will be carby, not electric.. but that would apply to the advanced thing too.. Check the voltage at the battery to start with. It should be about 12.5 not running and about 13.5 idling, 14.5 at revs. It should be able to maintain the 13.5 with the lights on and a few revs. The voltage shouldn't go over about 14.7. If you have a timing light check the ignition timing is set the specs, and then watch as you rev it a little and make sure it advances the timing.. Check the exhaust isn't blocked. If the air filter is meant to be oiled, make sure it is. Err... I'll have a think what else..

Ha.. Yes mate, that's exactly it. Good to hear. And aircraft eh ? Were you an engine guy, or airframe ? Those old piston engines are something aren't they.. Beautiful..

Now, my son is a qualified mechanic, and he started doing bikes up, against my advice, and after having the dilemma explained to him, and he found out real quick, despite his resolve to do it honestly and fairly, that it was really hard to make money without cutting corners. Now he just fixes them for fun and to get bikes back on the road or track.. That works. He does a good job then, and breaks even, and everyone is happy.

Also, over here, the tax rules say that anything you do, even a hobby, is taxable if it's "ongoing", or "regular". I value my reputation for honesty, given I operate in a small community, and my integrity, too much to be seen as dishonest in any way... even to the IRD. Even though people would consider it ok to deceivethe IRD, it would still reflect on the worth of my word.. The crux of professional behavior is giving people confidence and trust in your methods and procedures. Anything that detracts from your trustworthiness undermines that.

I'm a mechanic and I always find there's a bit of a moral dilemma too in fixing thing up to sell for a profit.. Just how gooder job do you do, and how honest are you going to be when you sell it. I decided early in my career not to ever do that, buy and sell, after seeing mates do it.. to their discredit.

Right.. I'm in NZ.. Plenty of rain over there lately alright.

Where are you Tin ? Southern hemisphere ? Yeah trying to fix things without manuals is why people throw expensive parts at bikes I suspect.. And I can't help much without the manuals to see what they have either.. Manuals are good !

Yeah I suppose they are only glued to start with.. so if we get the good glue it should be ok. I'd probably consider it if it was my own bike.. Professionalism would dictate I suggest not to if asked though.. haha.

"And so little time"... (Oh I don't know.. I heard it somewhere..).

That sounds like badly made really.. Can you see how they were held in ? Some bikes the magnets are glued in and some have some sort of clip or blocks of hard rubbery stuff between the magnets holding them in.. I've seen cases where on magnet was loose.. but never the whole lot. I don't think I'd try repairing it though.. to much potential for real damage if they came off again, smashed the stator, broke, and went through the engine. Perhaps there is a problem with them.. and perhaps there is a superseded part.. I'd check the genuine parts supply, and check for warranty or recall info....

And I had an afterthought... but it's a bit obvious.. you don't think it could be the brakes grinding.. worn out brake pads or shoes make a grinding noise.. especially with prolong application when the metal gets warmed up.. even though they are almost silent during intermittent and light use.

It could be caused(whatever it was), by the fact the bike was facing downhill/on an angle(causing something to swing against an axle say), or it might be caused by the de-acceleration causing noise in the gears or diff on over-run. I presume you did have the throttle closed ? You could try revving it out in a low gear and then throttling off suddenly. If it's in the gears it might show up then, whereas if it's something swinging it is less likely to.

Thanks guys.. When we are trying to diagnose things it's always a good idea to eliminate any of the complicating factors we can.

Oh Ok. The barrel type adjusters are easy to adjust, you just tighten them till the wheel won't turn, then back them off till it does turn without drag. A light scuffing of the shoes is ok.. It's important you do them till it won't turn first though. If you just wind them out till the shoes touch, the shoes can be touching at only one point and will get more clearance once they centralise. Locking them right up ensures they are centralised so they don't reposition themselves when you use the brakes. I'd try locking all four shoes right up and then bleeding the brakes. That way you know there's no lost travel in the hydraulic fluid having to push the shoes out as you are bleeding. You should be able to get a good hard pedal with very little travel doing that.. If you can't, then you might need to try bleeding a different way. I generally pump the lever fast till it won't pump up any more, then still holding it down, release the bleeder as far as possible as fast as possible. If you pump the fluid through slowly, or release the bleeder too slowly, bubbles of air can rise up the pipe and not get flushed through. If there's no travel in the shoes, you know whatever free play or pumping up there is happening is in the hydraulics. The other test of the bleeding is, lock the shoes with the adjusters, pump the lever till it's hard, take note of how far it is from the handlebar, then let the lever off, wait about five seconds, then pull the lever in once and see how far it is from the handlebar.. It should be the same distance as when it had been pumped up.. If you can pump it up it still has air in it.

They can get worn seals/cylinder gouges and the test of that is to pump the pressure up and then hold it on and see if the lever creeps, and another test for worn seals only is, let the lever right off, then very gently start pulling it in being very careful not to develop any pressure. If the lever moves in when you are moving it very slowly and gently, but pumps up with quick grabs of the lever, it means the seals are worn and just brushing past the cylinder wall but/and depending on pressure to flare them out and seal properly. If the seals are worn like that they will have a flat edge where they touch the cylinder wall. Originally the seals have a thin sharp edge where they touch the cylinder wall. If the lever pumps up pressure though, and has a firm feel with minimum travel, but doesn't stop the bike well then it will be something in the drum, seized cylinders or dirty/glazed, or contaminated shoes. I think from memory there are two types of adjuster on the old suzukis, a rotated barrel that screws out, and a ratcheting lever type. The ratchet lever type aren't too reliable when they get old and rusty and sometimes need a clean up with a fine file on the teeth to make them work properly.