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Wednesday, April 28, 2010

CB250 SUPER NIGHTMARE

I removed the carbs tonight and stripped them down. There was nothing wrong with them - all the jets were fine and clean. The one thing that puzzled me though, was the fact that it had fixed-level floats! I've never seen these before. As you can see from the photo below, the float on the left is the "usual" type with and adjustable metal tang, but mine (on the right) are all plastic and none adjustable. Everything else seemed fine though, so I put it all back together and fired her up. It was immediately apparent that the bike was much better. The engine revved freely and smoothly up to 10krpm. Great, I thought. I pushed the bike outside, put my helmet on and set off onto the main road for a spin.

Sadly, the bike started to splutter and die under load. DAMN this bike!! Damn it to hell! Walk away Tom, walk away.

10 comments:

Paul said...

Tom, don't lose heart, it will be worth it in the end. You have summer just around the corner (well, what you think of as summer anyway). If you sortout all these problems now, they shouldn't happen on the road.

I started my CB400N project a couple of months after you, and it is already on the road, I just have the tank / side panel cosmetics to sort out. On the way to and from the testing centre it would run rough until I opened up the throttle, then it would smooth out and go really well. I have to strip the carbs again as I suspect the needle valves aren't closing properly. I really hate taking them out of this bike as it is such a struggle.

We all know that you can do it !

Paul Hollick
Hartbeespoort, South Africa

Anonymous said...

Keep your chin up Tom :¬)
IT WILL be worth it in the end my friend. She looks a beauty and she shames mine.
MOT'd mine today after 11 years sat in a garage and she passed after spending two months sorting her out. Ive got carbs problems as well so you have my feartfelt sympathy. Mine flies as soon as I hit 5k but before that its as rough as an old dog. Carbs off tomorrow ... again, hehe
Good luck with her and dont get too dowhearted :¬)

IanPike said...

Hi Tom,
Well I hate to say this but... Took mine out for a quick spin today as it is booked in for MOT tomorrow and guess what, lack of power under load!! If it was a four cylinder I would say it is running on three.
Took the plugs out, left one clean and dry but the right one is all sooted up and quite wet.
Looks like my carbs are coming off tomorrow after I have limped down to the MOT centre.
Not to sure what else the problem could be.

IanPike said...

Hi Tom,

Just got back from MOT and it passed!
Also found once over 5000 RPM seemed to have power. Though I did run out of petrol on the way back from the MOT. Seems to drink the fuel so maybe that is my problem. I will take the carbs off this afternoon and have a look.
How are you getting on?

MadDogMcQ said...

Thanks guys! I've not "given up" or anything - I've been a bit pre-occupied with my new bike. Gonna take another look at the carbs tonight and will post a message on the blog.

Good news about the MOT Ian!

IanPike said...

Found my problem, took the carbs off and rolloing around in the bottom of the right float chamber was the main jet!!!!

Have just been out this morning for a ride in the New Forest, first bike ride in over 25 years! it all came flooding back. As has the right hand float chamber all over the garage floor.

Looks like carbs off again! Seems to be a bit of a common thing at the moment.

New bike looks good Tom.

kwacker5 said...

Hi,
I,ve got a cb400nc running fine when i got her in november 09 but needed new throttle cables and choke cable, fitted them , carbs flooding fitted new float needles now their not flooding but starts poor on one cylinder but soon warms up but struggles to gain revs in 5th 6th gear at above 5000 revs , HELP PLEASE

MadDogMcQ said...

Can't help Kwacker - sorry! I'm completely baffled by my own bloody bike. LOL

Anonymous said...

Kwacker5 : does it rev over 5k when stood still and in other gears ? If it revs smoothly over the full rev range in other gears then Im thinking its not your CDI. Possibly the coils breaking down under strain although if it revs freely when stood still or other gears I'd discount this.
Have you reset the float heights since putting in your new needles ? Could it possibly be fuel starvation ? Try new plugs in case you have weak spark or damaged spark plug. Just a few suggestions :¬)

AGinchar said...

I was able to adjust these type of floats on my CB750K. Clean and dry the floats really well and then use the hair dryer to get the plastic warm so height can be changed. If you are careful enough you should get the 15.5mm per specifications in the manual.

Bike Details

Honda CB250N Superdream
Reg No : ORH746W (ORH 746 W)
Reg Date : 1980
Orig Colour : Blue
New Colour : Black
Current Owner : Tom McQuiggan
Current Location : Horwich, Bolton, UK.