cm250t custom

[lingeringstin...]

If you've been inside your carb then you've probably already seen everything but one time I had a bike that would start and idle fine but the moment you opened the throttle it would die. Turns out the fecking needle had actually come loose from the slide (little clip thingy failed) and it was just sitting loose down in the main jet regardless of what I did with the throttle.

I don't know which carb you've got but on a lot of them the idle jet and the main jet are at two different levels in the fuel bowl, so the idle may be getting fuel but if the floats are out of order there may not be enough fuel in the bowl to come up to the main jet.

Also some carbs (old Honda designs as I recall) incorporate a little pump mechanism that was supposed to give a wee squirt as you opened the throttle but they were shit and if the pump wasn't working right all you'd get at initial throttle blip was a suction of mostly air and the bike would die.

[vorlon]

so update.
took the carbs off and cleaned them, put back and found the choke cable was no good. ordered a new one. carbs off again and another clean. put back on. took all the fuel out of the tank and replaced with new E5.
engine started but seemd to be on choke all the time. so off again and given a good look. it seems that i bent a tab which is part of the return spring. bent it back and back on again. success and its seems to be running ok.

[vorlon]

so bike runs now but a new issue. the trip meter is not working, this appears to be digital. any clues please?

[lingeringstin...]

I'm running near as dammit that same engine and they're basically quite reliable with not much complication. However, I have found mine to be the pickiest engine I've ever had regarding carb issues. It throws a wobbly at the slightest malfunction when most of the bikes I've ever had would tolerate with all sorts of carb shananigans.

I don't know why those particular Honda engines are like that but bear in mind that it's basically a 125 twin (exact same valves and cam) that was poked out to a 250 before they stopped making them altogether.

I don't remember if your model had one or two cv carbs setup but mine is really happy now with a single 27mm slide carb and a Quadzilla quadbike single carb intake. Never had any issue with the ignition system. It's the easiest bike to bump start I've ever had, so I wouldn't think spark was the issue.

[stinkwheel]

[vorlon]

is there a twin disc option for this bike?

[stinkwheel]

[Easy-X]

The old fella's Harley has a wet weight of 330kg... single disk up front
____________________
Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[vorlon]

so something new just happened. i went out to get the bike turned ready for tomorrows ride to work and i noticed a wet patch. thurns out the tank has a leak. looks like and old crappy repair job by the last owner. i will need to get this proffesionally done i feel. any recommendations please? possibly will need some paint also.
i sent a mail to a company called dream machine(got fromclassic motorcycle mechanics)

[Robby]

Find a tank on ebay. Repairs are tricky, and if it's rusted through in one place then the rest of it won't be far behind.

Dream machine are very good, but expensive.

[vorlon]

wow no joke they are expensive 400 for the tank, 590 for tank+paint plus vat!
may try to do this myself as the tanks i have seen for sale were worse than mine. any idea what the paint is anyone? ral no or best match.

[Robby]

If you're buying a tank, I would try to just buy one the same colour as what you have now.

[vorlon]

i would but they were all in horrible condition. when i took off all the putty it is just a coupleof small pinhole, so i think i can repair this myself

[lingeringstin...]

Oh dear, the dreaded vintage Jap tank rot. Behind the tank badges I presume?

Yeah you probably CAN repair the pinholes with something but my experience with that sort of thing is that the rest of the tank is also probably rotten in a few other hidden places and it becomes a never ending job.

Unfortunately it usually seems like replacing a tank with the correct one is stupid expensive on "vintage" Jap bikes, which always led me down the path of cobbling whatever I could find that would hold petrol. Random tanks are two a penny on Ebay but the correct one for whatever you need is always rare and expensive.

A lot of "vintage" Jap tanks will be a bit iffy by now. Old Bantam tanks are pretty good because the metal had a higher lead content so they don't tend to rust as bad. but then you have to get a bloody Ewarts fuel tap for them because nothing else fits, but they're still pretty good tanks if you can live with only a couple of gallons at a time.

[Robby]

Cobbling something else on sounds like a good shout. I hadn't thought about old British fuel tanks before, but they are thicker. Also worth thinking about tanks from newer bikes, that have had less time to rust.

Fixing an old fuel tank is difficult. I've tried brazing one up before. Things I discovered:

1. Getting every last bit of fuel vapour out is difficult. I drained the tank, left it open in the garage for a week, flushed it through a lot with water, left it open some more. Still made little fireballs when I started brazing.

2. For the braze to stick, you need to have clean metal. This means sanding back the area in question. You will find more pinholes doing this. I thought I had 2 or 3 holes, I had more than 20.

3. For the braze to stick you need to get enough heat into the metal. This is tricky, because the tank is a big heat sink. So it doesn't stick that well, and you end up with small leaks.

4. The right way to do it is to weld in fresh metal. This means cutting back to where the existing metal is thick enough to weld, cutting and shaping the repair patches, and welding them in. I don't have the skills for that.

5. Even if this works, the whole thing needs to be repainted afterwards.

[A100man]

[Easy-X]

The alternative to brazing would be soldering. Silver solder you can do with MAPP gas, Lead with any old gas. Only good for small holes though.
____________________
Royal Enfield Continental GT 535, Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[lingeringstin...]

[quote="A100man"][quote="lingeringstink"]Old Bantam tanks are pretty good because the metal had a higher lead content so they don't tend to rust as bad. [/quote]

Lead? As part of the steel alloy? Really?

Edit.. I have though seen article of folk using plumbing solder and a spade-sized iron to flow lead into tank pin-holes[/quote]


Yeah, that's a weird one but some old bloke told me that decades ago. The story was (according to him) that the fuel tanks on old Brit bikes had a higher lead content in the metal to prevent sparking on the pavement if the bike was in a crash. I have no idea if that is true but that's what the old guy said. One thing I do know is that the old Bantam tank I use has not had any paint on it for at least 30 years and it's not rusted through. It's got a weird patina but it doesn't rot. There's a small flake of red paint on it somewhere so it was either a tank off a GPO Bantam or an Ariel tank. All I know is it has never rusted like old Jap tanks do.

[vorlon]

update, so repaired the tank with solder, they were just pinholes. also covered with filler, sanded down and painted. then used wagner rust treatment and then tank sealer. that should do it.

[stinkwheel]

[vorlon]

ok, so new problem. this thing hates me.
so it was running but not well. read somewhere that this could be the coil not the carbs. checked and the right side spark was pretty weak. so got a coil (https://www.squaremotorcycleparts.co.uk/products/ignition-coil-honda-cm250-cm-250-custom-1982-1983)

and fitted it, tried the spark test and nothing on either side. re did all the connections and still nothing. put the old coil back on and the same, no spark at all. what next?

[vorlon]

so, update. tried new coil, working cdi from ebay, still the same. is not kil switch. local bike shop took a look and said stator/grenerator. where do i get one of these? cant see on ebay. is the same engine as a superdream, right. i would have thought there would be loads of options!

[Nobby the Bastard]

Ah, the old 'throw parts at it until it starts working' trick.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[lingeringstin...]

[quote="vorlon"]so, update. tried new coil, working cdi from ebay, still the same. is not kil switch. local bike shop took a look and said stator/grenerator. where do i get one of these? cant see on ebay. is the same engine as a superdream, right. i would have thought there would be loads of options![/quote]

I'm running a copy of a Honda twin (CMX250 or early Rebel 250 engines) and the whole ignition system is the same as a Jinlun or Zongshen 125/250 and several other Chonda twin engines roughly referred to as 253FMI, and it's the same as the 125 versions whatever they're called.

My engine is actually an abomination made out of Honda parts and Chinky stuff but it all bolts together just fine. I've had no problems with the Chinky ignition system I use

But here's something weird: I once bought an actual Honda rotor for a 250 Rebel off Ebay to use on my Chinese copy electrical system and it would not make electricity. No idea why. The rotor was identical looking and fit right on but there was nothing happening. I eventually got another Chinese rotor off something else (Quadzilla 250e is the same engine) and that worked.

Someplace like CMPO might be a source for new stuff if you're not keen on Ebay unknowns.