Have just bought a 93 R1 with a problem.
As soon as it boosts it starts to break down.
if i switch the ignition off /on it will boost to .5 bar and starts breaking down again.
Have replaced all the vacum hoses but problem still there.
Any ideas ? ? ? ?

Q. where is the check engine light located .

 

What do you mean it starts to break down? Does the car shut off, or bog severely? Have you checked your MAP sensor hose?

 

The car bogs badly just as it starts to boost.
I can drive of boost with no problem ,but as soon as it gets to 0 on the boost gauge it starts spluttering and backfiring.

 

First thing's first, change your plugs and wires.

 

I agree. Check this first!

 

If you don't know when the fuel filter was last changed, think about doing that, same with the air filter. Do you have a DP or the stock precat? If it's the latter, might be clogged and the backpressure is significant enough to cause bogging.

 

you might be in "limp home" mode

reset the ecu: pull the neg batt cable, step on brake for like 30 seconds, reattach batt cable, start car, drive, hopefully it works