cm250t custom

[vorlon]

i just bought this bike yesterday, wanted to get bsomething for the daily commute and this appeared on autotrader. i had one when they were new back in 1982. this is the same year and hasnt done 10k miles yet.
i drove it back the 70 miles and all was fine. stopped off to top the tank and then parked on the drive. the idea is to keep it parked at the side of the house behind a locked gate, so needed to move a few things. went back to the bike and it would not start and run. the throttle would not rev properly. tried it a couple of times. pushed it and parked it overnight. tried it again today and it does not want to catch at all.
now its been a while so i need pointers on where to start please.
i had thought that mabye i had accidently topped up with diesel(but i dont think so)
also should i be adding any kind of additive as the new fuel is so much different now

[stinkwheel]

Back to basics. It's probably sat for a long time so there are a few things that could be going on. Contaminated fuel, blocked passageways, corroded connectors etc.

Check it has a spark. I'd give it new plugs unless you know they were done recently. Make sure the air filter is clean and useable, check in the tank with a torch for water/dirt/rust, check there's fuel flow out of the tap. Crack the float bown drains and see if fuel runs out, catch some and see if it's dirty/contaminated.

Remember the basics are fuel, air, spark and compression. If it's not running, one or more of those is missing.

It's a basic engine, shouldn't need additives. You might want to run it on E5 fuel though. Fuel hoses and internal seals in the carbs and fuel tap probably aren't ethanol safe. It wouldn't have cause any issues in this short a time though.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[vorlon]

thanks. well the guys who sold it to me said he'd serviced it, it also had a new battery and back tyre.
i'll check what i can . very odd that it should just stop like that though.

[stinkwheel]

Don't believe anything a previous owner says with regard to servicing. That goes for both private sellers and dealers.

I'd say going for one long run then conking out and refusing to start is fairly usual for a bike that has been parked up for a protracted period of time. You give it just long enough to drag all the dirty, crappy fuel that was left in it through the tap and carbs. Any dried out seals and gaskets either plump up or fail and leak and the sparkplug bakes on any historic fouling.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[Nobby the Bastard]

I would also be suspicious of the need to replace the battery. Does the charging system work?
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[WD Forte]

I'd agree on taking any previous 'servicing' with a pinch of salt and its always best to assume it hasn't been serviced and do it yourself.

Check you didn't accidentally leave the kill switch on STOP
Been there done that.

As its an AC CDI bike I'd do a stator test to check the
charge coils, source coils and pulser all check out AOK
____________________
bikers smell of wee

[jeffyjeff]

[Robby]

My first reaction would be water and/or rust in the carbs. Easy enough to check, drain the carbs into a cup using the drain screw, and look for anything in the cup that isn't petrol.

To do 10k miles in 42 years, it's spent a lot of that time not moving and quietly rusting.

[stinkwheel]

[WD Forte]

No idea what the actual problem is, it could well be age related crap build up and residue for all we know.
Having had similar aged Hondas with AC CDI I'm assuming it's using the
same system
the source coils can break down when the charge coils are OK
and work/run but behave erratically as they warm up
I've known AC-CDI boxes to work well one minute than suddenly shit the bed with no warning.
This system shorts the source coil output to ground to stop the sparks
on both the ignition switch and kill switch
the kill switches especially could have build up of crud bridging the contacts

Hopefully it's just time and weather got in and it just needs
some detailed TLC
____________________
bikers smell of wee

[vorlon]

wow, thanks guys. so i drained the bowls on each carb, r/h one had a tiny amount of bits in but otherwise clean. tank is also clean. checked the plugs, both were a little black. after a quick clean the both produced a spark, new plugs on order. still will not turn over, choke or not.

[stinkwheel]

So it turns over and doesn't start or it doesn't turn over?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[vorlon]

turns over, sometimes sounds like it wants to, but does not catch.
oh and kill switch was the first thing i checked too, got burned before

[A100man]

[Easy-X]

Are the plugs damp with petrol after trying to start the engine?
____________________
Husqvarna Vitpilen 401, Yamaha XSR700, Honda Rebel, Yamaha DT175, Suzuki SV650 (loan) Fazer 600, Keeway Superlight 125, 50cc turd scooter

[vorlon]

so i put brand new plugs in and with the choke fully pulled out it finally came to life. however if i gave some throttle it would die. it got a little bettter after a while but not right. also gave all the electrics a squirt with wd40. then it started to rain so i came in.

[jeffyjeff]

I think you are probably going to have to disassemble those carburetors a little further than the float bowls. Remove the carburetors and clean thoroughly. Make sure the jets are clear, adjust the float height, and check needle valve operation. Check the condition of the rubber donuts between the carburetor and cylinder head. Air leaks here lean out your fuel mixture. The fuel petcock might have a filter in it or next to it; if so, make sure that it is not restricted.
____________________
History shows again and again how nature points out the folly of men - BOC

[WD Forte]

It may well need a carb strip/clean but at that age I'd also check
the tank strainer amongst other stuff.
Does it have a manual or vac fuel tap?

BTW WD40 is ok as a water repellent but it's better to use switch cleaner in anything that has electrical contacts
____________________
bikers smell of wee

[vorlon]

fuel tap is manual, where is the best place to get a carb kit from?

[blurredman]

[vorlon]

thought i'd post a pic. going to try to clean the carbs at the weekend

od pic wont attach

[lingeringstin...]

Sounds like a jet is blocked. It's fairly common on those carbs, especially after the bike had stood around for a while unused. I think the petrol evaporates out of the fuel bowl and the gunk residue then blocks the jets. I'm running near as dammit the same engine as that and spark is never an issue. If it doesn't want to start it's because a carb jet is gunked up. Luckily it's a quick and easy thing to put right with a can of tiger piss.

[Robby]

[stinkwheel]

[vorlon]

so took the carbs off, cleaned all inside and checked all the jets were clear. put back on bike and it kinda started. needed choke for a while (although i may not have that right) but will not tick over properly and just stalls if i add throttle. the book said to alter the screw but that didnt really help much. what next?
oh, and i drained some of the fuel and looked in the tank. all clear.