Running and rectifier problem

[JamHonda]

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! 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 in the bike! The earth has been checked and no problems! Once the new rectifier had been placed in 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 14.6 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

[sinedtomuch]

Have you tested all the plugs for a spark?

With regards to the 14.6V at idle, this is rather high 1V+ too high. Sure your multimeter is accurate?

[JamHonda]

Yeah tested all plugs, they all seem to spark okay. not sure about the multimeter, but it does seem high

[smallfrowne]

Oh eck. I had similar issues. All started with the rectifier going bad. 14.6V doesn't sound too bad though, maybe a smidge high but not excessive. What reading do you get at 5k rpm? Rectifiers do get stupid hot, it's how they work and why they normally have cooling fins. On the NC30 the RR lives in a place perfect for cooking them - no airflow so they do die quite easily. The original didn't even have cooling fins.


Do all pipes heat up ok now you've changed the coils? I had this issue too, it wasn't majorly obvious because the spark plugs still sparked when you took them out to check - but the rear pipes didnt get hot. I got a 2nd hand coil off a kawasaki and still wasn't quite right so I checked the plug caps and leads with the multimeter and the resistance seemed higher on a couple compared with the others.

On the bad ones the connection of cap to lead was crudded up on some of the leads so I took them apart and re-soldered the joint. Probably could've just got new caps and leads, but it ran fine after that.

TL;DR: Check the resistance of the leads and caps with a multimeter for badness.
____________________
'90 VFR750; '89 NC30; '95 DR650; '89 CD250U; ~'82 CG125; ~C90

[JamHonda]

thanks for reply, no the rear pipes are still much colder than the front after changing the coils. The rear pipes are cold enough to put your hand around even after the bike has been running for 2 minutes.

[JamHonda]

Forgot the mention that there is a large pop of air, sounds like its coming form under the tank. This only happens very occasionally though