Hi, I have a Honda vfr 400 nc30 Jap import! Bike has been great, but recently in the past few months the bike has not been running properly at all!

The bike Boggs down really bad, and will cut out if left on tick over for a minute! I had taken the carbs off and have them a good clean, no problems there and when I put them back on the bike was the same! Bogging down really bad and will cut out!

Found that the rectifier had burnt out and some of the wiring, part of the wiring has been replaced and a new Honda rectifier has been placed on the bike! The earth has been checked and no problems! Once the new rectifier had been placed on the bike there was no difference with the performance, the bike still bogged down and struggled to get 40 mph, the Bike would Rev very slowly and take a long time to rev even on full throttle! The rear two pipes coming off the rear cylinders are much colder than the front two! So I swapped the coils around and took the bike for a spin, it was great for 5 mins but them the bogging occurred again all of a sudden!

I bought new coils genuine Honda ones and put them on the bike but no difference! The rectifier is getting stupid hot and the battery reads 14.5 volts on idle! If I remove the front coil off one cylinder when bike is running the bike cuts out but if I do the same for the rear it keeps running!

Please help

Change your plugs......?

Dud rect/reg may have damaged ignition control unit and thus rear cylinders are not firing, hence poor performance. Idle should be an issue also unless you have increased it significantly. Hot rect/reg and 14.5volts is normal. Check the ignition control unit, mounted below tail/stop lamp bulbs, for strong burnt smell or remove cover and visual inspect.

I had a problem with 23, kept cutting out etc and only running on 2 cylinders on tick over... finally diagnosed it, the sliders weren't actually sliding at all or very little on cylinders 2 and 3.checked the diaphragms for tears or splits, nothing, checked the walls of where the sliders sat in the carbs all seemed clean but gave them a wipe down with some petrol and rag, put it all back together - still the same. So stripped then down again, and my neighbor advised to get some very fine wet flat (i used 1200) and petrol and give the sleeve (where the sliders fit) a very soft and fine rub down, so did this, all OK.

It made a huge difference to the bike running... it idles so much and the bike now flies.

Could be worth checking the sliders are moving.

thanks for reply guys will check these on the weekend

My money is on a fouled plug. Have been there - try giving them a clean with a wire brush.

Feel each cylinders exhaust pipe shortly after a ride - the colder one will be the one with the fouled plug.

I am chasing a similar problem on a NC21 bike idles and front right downpipe is stone cold.I have cleaned out carbs and replaced front coils but still giving above symtoms. The 3 yellow wires from the generator show signs of everheating as the connector plug has melted slightly. New regulator on the way. Getting there slowly I hope

I tested the generator output voltage from mine at different revs, hope it will give you something to compare to:
1.5k rpm = 15.8v
5k rpm = 38v-42v

I've got a new regulator coming next week so hopefully will sort out problem - will let you know if so.

Do not see the immediate connection between your engine problem and the alternator connector problem. What battery voltage do you get at 5000 rpm. Why would you not initially replace the damaged connector and then check charging voltage before replacing rect/reg.

Cold pipe suggests non firing cylinder but bike idles, would expect three cylinder engine would stall without throttle. Do you have spark on the cold cylinder.