CB250N Cafe Racer The Hornet and the 5K wall

Here is a photo taken by the seller of me riding away from his house..

So now the saga..

Well I have spent the last few days rebuilding the carbs on the bike, had them off about 15 times, checking and rechecking cleaning and checking again.

A photo of my work area, I am in a small unit with no space..

I spent a lot of time reading blogs, forums and tuning guides and kept coming to the 5K wall that honda twins of this vintage had. This was the problem I was having with the CB250N it would not rev past 5k  and I now was pretty sure it was not the carbs.

Okay this led me to electrics, COOL…. I know but in a past life I did this as a job and my hobby is Ham radio and electronics so now I went from an area i was okay in (Mechanics) to an area I actually loved electrics.

I was able to get the bike running so the first thing i did was put a timing light on it to see if the high RPM pulser was triggering the advance, it was advancing but I noticed that as the bike surged and lost power it lost spark, okay so it really is looking like an electronics problem.

Okay next I pulled the wiring to the CDI on the left hand of the air box… WTF I just noticed that the frame has been resprayed with the bloody wiring loom on the bike, there is paint in the connectors, there is paint on the earth points and paint everywhere it should not be….

So out came the dremel (mini grinder) and I started to sand all the paint of the earth points for the coils and CDI. I removed some extra wire that had been spliced between the CDI and the stator and reran the loom to get an extra two inches to rejoin the loom.

A photo of the “new” rewired loom you cant see much but I replaced connectors in the harness and removed a 6 inch splice someone had added to the stator wiring (blue white CDI voltage wires) and reran the loom to allow for the shorter length

Gapped the plugs and cranked it,…. Its alive its alive it is revving to red line and just sounds heaps better.

I hosed the stator with with a dry silicon lube I use that repels water and doesnt harm wiring to protect it and stop corrosion.

So I have been over the bike and so far have a small list of things for RWC (MOT) they are as follows…

Replace Brake Lever (I broke it putting the bike in the car)
Re wire front brake switch
Plastic weld LH side cover crack
Lube Clutch and Throttle cables
Pull apart RH switch block and clean Hi/Lo switch
Replace Fuel line and add inline filter
Sync Carbs
Reweld header it has a small crack near the muffler

On the plus side the previous owner who could not get it to run well had done the following already…

New chain and sprockets
New Rear Indicators
New Brake pads and bleed brakes
Replacement seat from wrecker
New brake light

Anyway that will do for this post… but for those that didnt see the last post in the welcome section here is a rendering of what I want the bike to look like when done

One thought on “CB250N Cafe Racer The Hornet and the 5K wall”

  1. Yes, it should start the same. Most marreactuufns actually install 2 separate looms on their bikes, one for the basic running of the bike, and the other for the extras of lights, electric start, horn, turn signals, etc So long as the stator is putting out power, the pulse generator is telling the spark plug when to fire and the plug is sparking, it should run (assuming it was running before and no changes were made to the air/fuel or mechanical side of the bike).

Leave a Reply

Your email address will not be published. Required fields are marked *