The Honda Owners Club

I have just bought my first bike & have been dogged with a problem I was wondering if you could give me help
I have a 1980 Honda CB250N my problem first started with the RPM staying at 2000 when I came to a stop the RPM slowly dropped to normal after around 30/35 seconds I was told it was a carb problem I had them stripped & cleaned with new plugs & caps fitted by a bike shop When I got the bike back it was only running on one piston Under power wind up it stuttered around 2500/3000 RPM then it would pick up on changing up a gear then everything went to rat again with little revs & one pot working before picking up again on closing the throttle it would also bang & fart from the exhaust I have had the carbs rechecked & they seem fine Have removed the spark plug from the dead pot & it sparks well As nothing was touched apart from the carbs I have been told the problem may be the carbs have not been reset correctly or it could be the coil The leads to each pot were changed over & the bike would not start A compression test using a gauge reported everything fine One more point when I remove the plug from the dead piston it is some times very black & sometimes very wet Anybody able to help?
Alan Bruce, Scotland

Hi Alan and welcome to the forum from me.

I had a similar problem with my 400N. I ended up replacing the air cut off diaphragms on both carbs which sorted it. They are prone to perish on bikes of this age. It may not be the problem but they are worth looking at.

Regards

Chimpy

Good description of problems you get with an air leak.

Not familiar with the Superdreams so would go with what Chimpy suggests.

The carbs on a CB250N don't have the air cut off valves. They were only fitted to the CB400N so it can't be that. Although, if you do have air cut off valves on your carbs perhaps the problem is you've got the wrong carbs fitted!

It does sound like you've got an air leak somewhere. I'd suggest getting new rubber inlet stubs, and fitting them with new "O" rings to the cylinder head. Also make sure that the clips on the inlet stubs are tight, and last but not least make sure the Philips screws that are used to attach the carb balancing tool are nice and tight. Air can leak in from all of these points, and 'cos our bikes are so old, the rubber isn't what it once was

Oh, and good luck.

Al.

hi i had the same prob to the letter i spent a lot of money trying to fix it.its the rubbers in the air box,due to its age they go hard and do not seal so the only fix is to put cones on it,to do this you will have to cut the air box up t get them in or take it out. good luck