CB250N SuperDream 1981

[mumbles]

I have striped and rebuild my cb250 cleaning/replacing every part on the bike and have now put it all back together. the problem is the bike has a very rough idle and if I rev from idle (1400RPM) it revs up fine but when I let go of the throttle is revs down to (3500RPM-4000RPM) I have re-cleaned the carbs checked throttle cables clean airbox replaced ignition coil and i have run out of ideas also if it's any help the sparks plugs get carbon black on them everytime
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Warming the world 2 strokes at a time.

2008 rs50 (SOLD) - 2006 gz125 - (Winter Bike) - 1981 CB250N (In Restoration)

[STONEY!]

Check the stator windings mate, also all the fuses and wiring under the left side panel.

[Shaft]

Do the carbs again, it took me four goes to get mine right.

They are susceptible to everything; they have to be operating theatre clean, the float heights have to be perfect and the needle valves are prone to sticking, amongst other things.

Even after getting it running right, mine would occasionally leak out of the left carb, then it just stopped one day and never did it again.

Use genuine rebuild kits if you can, the pattern ones are gash.

If it makes you feel any better, there's some poor bloke running a resto blog that has never been able to get his right, now he's on his third set of carbs.
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Things get better with age; I'm close to being magnificent........
20 RE Interceptor, 83 Z1100A3, 83 GS650 Katana
WooHoo, I'm a Man Point Millionaire! https://www.bikechatforums.com/viewtopic.php?t=234035

[mumbles]

Stoney: I checked all the electrics with an ohm meter like it said to in the Haynes manual does than include the winding's ? and all the fuses ect are perfect I spent 2 weeks reconditioning an already working wiring loom I know for sure their are no problems their

Shaft: I'm going to clean my carbs again, but just one thing I last time I stripped them I tried to set the float height but the float is plastic how do I set it ?
____________________
Warming the world 2 strokes at a time.

2008 rs50 (SOLD) - 2006 gz125 - (Winter Bike) - 1981 CB250N (In Restoration)

[Shaft]

[mumbles]

[Shaft]

Also, check your tank for rust and if in doubt, fit an inline fuel filter.
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Things get better with age; I'm close to being magnificent........
20 RE Interceptor, 83 Z1100A3, 83 GS650 Katana
WooHoo, I'm a Man Point Millionaire! https://www.bikechatforums.com/viewtopic.php?t=234035

[unitynotsocri...]

if it were mine,and I had the money i'd buy a couple of new diaphrams.
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nearly a normal tax paying tosser.......with ferrileness suzi100,cg125,cb125scb100n,cb175,cd100,cj250t,kh250,c15,125 bantam,super 6,rickman gs750,xt500,250rs,dt175,lifan125,dolomite1850,metro,Morris220ld,morrisfg,leyland princess,range rover,corsa,vw camper .now struggling with legs. MORE ORDER = MORE CHAOS

[Shaft]

[bikenut]

wet dream eah!!

anyoww, is ignition advance working properly and re clean the carbs after cleaning out tank, tap and lines, fit fuel filter.

the cables arnt causing the problem are they?? or worn throttle spindles?? cold engine running spray wd or similar around carbs, revs rise??

ps the 250 dont have diaphragms but the 400 does.

[mumbles]

Tank is fresh from the paint shop it's spotless inside and out but i am running an in line filter anyway, Im not sure how to check ingition advanced timing? and i also changed my coil to a cheap Chinese replacement part because i thought my other coil was broken but tuned out it was working fine and i dont know how to check for worn throttle plates, the cables are a little firm even after oiling them and getting new one but i can see the throttle on the carb fully close
____________________
Warming the world 2 strokes at a time.

2008 rs50 (SOLD) - 2006 gz125 - (Winter Bike) - 1981 CB250N (In Restoration)

[bikenut]

timing light for ign advancs, marks on f/wheel to the left of "F", smooth transition from f at idle to full advance marks at 4k revs

on a cool engine running, spray some wd or similar ( remember it willburn ) onto the throttle butterfly shaft area one carb at a time, any rev increase all byits self..........

no is good.

progress onto carb rubbers tween carb and head, any rev increase all by its self.........no is good.

study cmsnl exploded views foryour bike print them off.......over

[bikenut]

the throttle twist grip should return by spring smooothly and fully........as well as on lock to lock.........

bad cables can cause problems returning etc..........

[Pockets]

I have to agree with everything Shaft said earlier, I'm rebuilding a 400 Superdream for no real reason, I've just rebuilt the carbs and still getting niggly little issues like float valves sticking, Shaft is spot-on when he says that you can end up taking the carbs off many times after rebuilding them.

A point worth mentioning is that the Keyster carb rebuild kits don't have the greatest reputation especially the needles, worth bearing in mind.

Finally, have you joined the Superdream forum? there's lots of goo technical assistance available:
https://honda-superdream.proboards.com/index.cgi

[mumbles]

Finally got round to cleaning the carbs up, put em back on the bike and it started first time idled perfectly so I synced the carbs and 2 mins later idled rough and right carb pops in exhaust every now and again and pops though the carb a little more often and it wont rev up but when it does after 5000rpm it revs great no problem
____________________
Warming the world 2 strokes at a time.

2008 rs50 (SOLD) - 2006 gz125 - (Winter Bike) - 1981 CB250N (In Restoration)

[suzukirider19...]

i used a old cb250n engine in a quad project i did some years ago and did away with the std carbs as they were horid to so the least. a good conversion is a set of carb from a suzuki rgv 250 26mm round slide carbs and jetted to suit worked amazing. cost me 50 quid for a set of carb and fit straight into std inlet rubbers.
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husky sm610

[mumbles]

Dont think the carbs are the problem they are very clean like new, I have ordered a new cdi and it already has a new ignition coil so hopefully that cures it

UPDATE: I have been messing about with the mixture screw and it idles a little rough but it's okay and it revs up fine but theirs a little hesitation just before it revs up if you open the throttle fast
____________________
Warming the world 2 strokes at a time.

2008 rs50 (SOLD) - 2006 gz125 - (Winter Bike) - 1981 CB250N (In Restoration)

[prawny1]

check for air leaks aroung the inlet manifold/pipework and check to see if the choke is not coming off properly both can cause revs to hang like that.
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hellkat wrote:

Some people are only alive cos its against the law to kill them.

[mumbles]

[bezzabsa]

[mumbles]

[trevor saxe-coburg-gotha]

[paddlesat16]

Lumpy idle....

could be the carbs need balancing
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I once saw a bloke shagging a donkey.... in Saudi arabia. Theory Test Passed 26/10/09 Mod 1 Passed 26/4/10, Mod 2 Passed 7/6/10 Current Bikes Suzuki GSX1400 K5, Aprillia Pegaso 650, Suzuki DR350T.

[mumbles]

thanks guys engine is running spot on now after adjusting the balance and mixtures screws just the odd pop when revving down now
____________________
Warming the world 2 strokes at a time.

2008 rs50 (SOLD) - 2006 gz125 - (Winter Bike) - 1981 CB250N (In Restoration)

[titan666]

i used to have a twin carb overhead cam cb200

nice bikes and really nice to work on.

good luck mate and look after it
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love my susuki gz 125 maraurder 1998