hi all i need some advise again

took the car out for a test 5-6 miles.
after about 30 mins,the engine revs dropped by about 3-4 hundred.

on inspection taking each plug lead off in turn,number 2 made no difference

i have tried a new plug no difference
i tried changing ove a plug lead no difference.

has anyone else got any ideas?
i am thinking of swapping over the coils to see if that works?

only other faults i think it could be maybe number 2 carb playing up or something wrong in the cylinder head?

thanks for any advise
simon

Pull the plugs out and check fuel is getting to all cylinders by turning the motor over you should be able to se a spray of fuel come out of all the plug holes if not could be a blocked jet etc .

Also lay the plugs on the head turn engine over as see if u get a spark on all 4 plugs

CDI Unit may be on it's way out - try an alternative from someone else's. Position of CDI on 'blade is very important. Isn't your's located above the exhaust headers - if so, first place I would look! This seems to be a weak point of the older 'blade engined BEC's. New unit's are approx £40 but salvage from a 250 Superdream I think is the option and it had a much better heat sink...

hi hellfire
i have the uprated rectifer with a small fan (computer) on it ,is this the same as a c.d.i unit ?

many thanks

Its not the same as the CDi but I think the rectifier is what Hellfire meant. The CDi is the ECU or brain for controlling sparks, which obviously wouldnt be interchangeable with a CB250

Not totally familiar with the blade, does it use 4 coils or 2? If it's 2 coils then you wouldnt lose just one cylinder from an electrical problem, you would lose 2...

Try checking the carb, as the floats could be stuck, could have a blocked jet...

If its electrical, you will have a wet plug, if its carb then the plug will be dry

when i took the plugs out they did seem dry.

Two coil packs on the blade, so most likely look at the carbs.

One thing to check that Ive just though of, there's a vacuum pipe that attaches to one of the centre inlet tracts which attaches to the vacuum shut-off for the fuel feed on the bike. You dont generally use this on the car and its easily forgotten, and if left open it bleeds air in on that cylinder and makes it run lean, so could give similar symptoms to what you describe.

Correction the CDI Unit was meant to read Rectifier...

Chris,

Should the vacum pipe be blocked off then Chris?? What's the best way to do it? I think I have just left my pip hanging down the side of the engine.

Rich.

Yes it should be blocked off, I just put a suitably sized bolt up the end, anything really so it doesnt draw in air

quote:

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Originally posted by ChrisGamlin
Yes it should be blocked off, I just put a suitably sized bolt up the end, anything really so it doesnt draw in air

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Nope, but if you can take a pic of your carbs (especially focussing on the underside) I'll see if I can point it out. Its just a little pipe maybe 4-5m bore that attaches directly to the head under the carbs, which feeds into one of the inlet tracts for the vacuum. If looking at the engine from the inlet side, I think it's on the second from left inlet tract.

Thinking about it, there was a thread about it several months ago and there was a pic there, so I'll see if I can find it.

Hi Chris:

I'm interested to see whgat you come back with. I've taken my carbs off many times and have not found a vacuum hose connetced to the head

--Chris

OK, found the pipe to 3, but also found one blocked off to 1, whats this about?

ta
Chris




Blocked off pipe to cylinder 1, dead centre of the pic.

then i think its the coil,

coils are sensitive strange things,

have seen problem with coils wich measured like they should (ohms) but still didn't respond like they should...

and because of everything being a matter of miliseconds...

put my money on the coil..

Tks

p.s. offcourse only if the coil is of the dual coil type i mean that in one coil housing there are 2 coils integrated!! else offcourse its stupid because the problem is only on 1 cilinder.

The vacumm hose could be the problem easyl becomeing loose..

Tks

Chris, thats the hose in the first two pics above, if you take the carbs off the head you'll see that pipe ends up tapping into the inlet tract of that cylinder, so by leaving it open you've effectively got an air leak on that cylinder so it will run leaner than the rest. just put a bolt up inside it to block it up and you should find it runs better.

Its likely not present on earlier carbed blade engines as they used a fuel pump rather than gravity fed fuel, so didnt need a seperate shut off valve (as the electric pump would perform this function)

Chris

That'll explain why mine hasn't got one then Chris as it's 1994 engine! Didn't think I recognized it!

Thanks anyway,
Rich.