Please note that the posts in this blog are in reverse order, so the newest posts are at the top and the oldest posts are at the bottom. You can enlarge most of the photos by clicking on them.

Thursday, May 26, 2011


Yes, it's alive again! Not 100% fit and healthy, but alive nonetheless. When I got home from work tonight, I whipped the overalls on and went straight into the garage, determined to make some progress. First job was to open up the carbs and give them one last check-over before installing them. One of the vacuum pistons wasn't sliding up and down quite as free as the other one, so that was the first thing I sorted. Then I checked the air-screws to make sure they were both 2-turns out. The carbs have been ultrasonically cleaned and completely overhauled with new Keyster kits, so no real point in checking the jets/needles, etc.

Once they were ready to go back on, I dug out the brand new inlet-stubs and fitted new o-rings to them. Then it was simply a case of connecting the cables to the carbs (from the left hand side) and offering them into the gap without the inlet-stubs attached. Once the carbs were in position, I fitted the stubs and tightened the 8mm bolts. With the overflow tubes in place, that was the first job done! Easy!

Next job on tonight's agenda was the clutch. Last time out it was stuck solid - no doubt due to being sat idle in the garage for over two years! I removed the clutch housing and then stripped the clutch down, separating the plates and then rebuilding it. Only took 10 minutes and I managed to reuse the existing (new) gasket. 

With 2.2 litres of 10/40w added to the engine, it was time to fit the petrol tank and see if she would start. I was pleased to see that the Yuasa battery had kept its charge after sitting unused for a couple of months. The starter motor positively whizzed the crank around and the old girl spluttered into life.

She revved and ticked over pretty good, but not perfectly. The exhaust is blowing around the collector box (because I failed to buy new sealing rings) and after a while, petrol started to flow from the overflow pipes (GRRRR).

But overall, I'm happy that at least she's breathing and this is definitely a step forward. From here I can start fine-tuning things. Unfortunately, I couldn't take her out on the road to test the all-important 5000rpm barrier because the new front brake reservoir is dry. That's not a job for tonight!

I'm away for the Bank Holiday weekend, so there'll be no more progress until next week. Feelin good!!!


Klaas De Craemer said...

Nice to hear that! Now for the last stretch :)

Ian said...

Huge grats matey and most welcome news

MadDogMcQ said...

Cheers guys! I think the carbs are gonna have to come off for the HUNDREDTH time.

Thomas said...

A pleasure following your blog! I've bought a 1981 CB250N with only 8500 miles on the clock a month ago, totally original. I've removed a fairing, done a few minor repairs, nothing much, and polished, but had the 5 K RPM limit too - until this weekend, where I checked the ignition and carbs AGAIN, suddenly realizing that somebody in the past had exchanged the main and secondary jets by mistake in both carbs. Secondary jet area is 2,3 times smaller than the main, not leaving much gas for high RPMs. Now it flies from idle to red line. Great little bike! Hope you find your gremlin soon.....Thomas, Copenhagen Denmark
Thomas, Copenhagen Denmark

MadDogMcQ said...

Many thanks Thomas. The jets on mine are correct, so I'm going to try something new this weekend and will post the results.

CbDave250 said...

Hi, just curious as to how you sorted out your sticky piston? i've a CB250N myself in original condition but the piston in one of the carbs is sticky and i've tried cleaning the top pot.. i've cleaned it up with some 1200 paper, i've polished them till they shine... but still they don't slide together.

What did you do?


Anonymous said...

Hi - do you happen to have the torque specs for bolts? (namely the large and small bolts mounting the engine on the frame)

thanks mate

Klaas De Craemer said...

The engine mount bolts do not have torque specs. Just make sure they won't come loose and you'll be fine.

MadDogMcQ said...

Hi CbDave250! Sorry about the delay in responding. I noticed that with the cover retaining screws out, the pistion would slide freely if I "twisted" the cover slightly. With no twisting action, the piston stuck again.

So while applying a slight twisting force on the cover, I tightened the retaining screws and tried the piston again - it was fine!

CbDave250 said...

Thanks for that. no worrys about the delay! i lost this page, i will go have a play later! Cheers for the info!

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.