Suzuki RF 400R 93, not running right?

Question

I have serviced my bike. new plugs , leads, filters, carbs seals. The compression is excellent. even had it dyno tuned. But yet after a while it starts to run on 3 and some times two cylinders. it not coils cause it never the same cylinders that go.unless i have two faulty coils. rest of the wiring is all fine, no shorts.

only things i have not replaced or tried are the valves and cdi unit.

any ideas what could be causing my troubles.

Answer 1

If its random across both sets of coils sounds like its something common to to both such as ignition pick ups breaking down ( had this on a gsx550 of a similar era). Could be some thing on the charging system, if your not charging properly, or battery if failing, may not have enough go in it to run cdi fully. Again gsx wouldn't fire at all if battery was a bit low on charge.

Answer 2

Hi there,
dunno if this will help, recently serviced a 600 bandit for a mate who bought all the parts, plugs,oil and filter and air and fuel filters also changing the fork springs and oil, anyway after servicing bike and adjusting tappets, I went to warm up bike and the bike started1st time and was ok when it was warming up on choke, once warm, I took it for a short blast before balancing the carbs and on lightthrottle it would misfire and was low on power, so straight back to garage and stripped out the plugs to see which plugs were misfiring, 2 outer plugs were fine but inner plugs had been burning weak, could tell by colour, so I set about rechecking all my work and whilst doing so cam to the conclusion that it had to be connected with air flow, The filter my mate had bought was a cheap copy air filter and he was told it would fit his bike without any mods, I took out the airfilter and cleaned his old filter refitted the old filter and bingo fault cured. The cheap copy airfilter was allowing the 2 middle cylinders to be fed to much air for the fuel being supplied and it was misfiring.
New standard airfilter bought and fitted and carbs balanced and no further problems

Answer 3

An rf400 only runs one pickup to fire both coils the same as water cooled gsxr's of the same era, so it is either your pick up or black box (cdi unit). A duff coil would only affect two cylinders, the air filter would affect all cylinders.

Answer 4

Most likely cause is air filter or petrol is contaminated. Try old air filter, drain carbs in to a clear glass and see if their is water.

Answer 5

air filter