Hi,

I recently bought a 1988 3EN1 and it ran great but the idle became uneven and I suspected that it was not firing on all cylinders. I decided to check the electrics and stripped down the carbs.

I found that three of the carb diagphrams had tiny holes in them (there was an identical circular imprint on all of them that seemed to be the weak point.



One of the slides also had an over stretched spring so I decided to swap the diagphrams and springs with good parts from a 3HE FZR 600.

Problem is that the slides have larger holes on the 3EN and longer springs:





The 3EN has stock needles and jets, stock exhaust and K&N air filter. Will fitting the 600 diagphrams and shorter springs mess up the running of the 400 engine?

Cheers

Nigel

Why not just run the 600 carbs complete and change them to 400 settings.

Hi EC,

Thanks for the quick reply.

I'm assuming from what you said that others have done a straight swap with 600 carbs and just changed the jets?

The 600 carbs I have aren't complete, they're a donor set, so either way I'm stripping both sets of carbs down to make one good one. Didn't know if the 3EN slide and spring differences had much effect on the running and if I should try to keep them as is.

I have just had another look at the diagphrams and realised its possible to swap the diagphrams over between the slides (Dohh!) So now I'm just wondering about the difference in spring lengths but not quite as concerned about this. They're 112mm vs 94mm.

If you can swap the diaphrams then that's probably easiest - the bike runs with the carbs, it just needs the diaphrams and it should be ok

Just a quick update. I got everything back together after resetting the float heights, bench synched and used new carb repair kits.

Played with the idle mixture screws and the bike is about as good as I can get it right now. It definately runs smoother and the throttle response is good across the range.

Float heights are 22.5mm, mixture screws 2.5 turns out.

I'll be doing the valves next followed by a carb synch using a Carbtune kit. Hopefully this will set everything up nicely for the summer.