Hi all, well not 2 weeks into ownership of my 95 CB400 S4 type R and it's appearing to be mutton dressed as lamb

It's been a while since I've had a 400- last bike was DL1000- and when I first set out on it, mistook the slow speed and weak power (top speed was 90 at a push, 2-up 70mph) for it being restricted as the build up was so smooth.

Well had a local engineer/mechanic look into this as the dealer I purchased the bike from is away at the TT (I had called to confirm he was ok with this as it's my only transport so urgency is an issue) Carbs were removed....no washers...OK. So it was suggested we clean them as could be a blocked jet. Upon stripping them down it became clear someone had serviced them recently as they were utterly spotless. Never the less, mechanic cleaned them and re-assembled them and reconnected them.

It was then decided to check the spark plugs. #'s 1&2 removed with little effort, as did 4, however the #3 plug was proving stubborn. It finally came out and we were greeted by this:




The plug was melted and what appeared to be an insert had come out with it leaving the plug hole completely smooth.

So a couple of days passed as I waited to get hold of a time sert insert or a helicoil thread repair. So yesterday my mechanic obtained a helicoil kit and began to insert the new thread. This was successful and a new set of plugs were inserted, all HT leads connected and ignition was turned thumbed to check the piston was clearing the new plugs. All good so we fired it up. It fired on all 4, and was revving smoothly :) Mechanic took it for a spin, and then I went to test it. Not 2 miles into the ride and the revs became frenzied between 8-12k, and shortly after I lost power and proceeded to push the bike back. I left it with the mechanic and he checked all the pipes from the tank/fuel tap and fired it up and took it out- confirmed it was running on 3 again.

Once back we decided to try and pull the #3 plug again. And we were greeted by a familiar sight:



Melted again and thread destroyed with it!!

I'm hoping someone on here may be able to shed some light on this. As it stands I'm going to be taking the bike back to the dealers and discussing this further with them, showing them the evidence. My mechanic seems to think it may be something electrical.

Is that the recommended plug type for that model.? Some engines do not take to plug upgrades well.
The heat range (9 ?) seems OK.I would be tempted to use a grade higher on that cylinder until this has been resolved, as a safety measure.The worst is; it will burn out the same as a 9 or foul ( unlikely)
The cylinder must be running exceedingly hot to achieve that damage.
Mixture on that pot must be way off.....lean. Is it possible the inner cylinders should have larger jets for cooling
(pretty normal procedure on a small ILF ) and an incorrect jet fitted ?
I cannot see how electrics would be the cause..... it is a wasted spark set up.... another cylinder would be effected.
The problem should not be caused by an insert on a four stroke..... I have had problems on 2 strokes with
them causing pre ignition/detonation on highly tuned engines.

You must replace the h/coil with a proper insert.... even if a one off is to be machined. The heat is causing the h/coil to fuse to the plug and unwind at removal. Too much metal removed and you will soon need a head.
The exhaust valves will also be getting cooked.

I would be inclined to return it if feasible.....this could very soon warrant a head replaced.....a money pit.
It would be worth contacting the PO ; pretty easy from the log book info nowadays, and ask him a few questions; it may be why he got shot of it.
Good luck; keep updated.

Someone more specialised in the model may help out; this is just a generalisation.

Hey Willandrip, thanks for the reply- what you are saying pretty much coincided with what the mechanic looking at it speculated, he feels it's running very lean. The carbs were all sporting 98 main jets, which I did think seemed small.

I think I will be seeking to return it, i've spoken to the dealer and explained the situation, and he should be due to collect it this Monday. Pretty gutted as I really wanted to keep this bike and made the error of getting some shocks for it when I thought it was just restricted. As you mentioned, I feel there may be further damage to the internal components and I'm not sure how much I would trust just a new brass insert and gasket set over the long term.

Will keep informed on how I get on.

Oh should have mentioned the original plugs were CR8EH, and from what I could locate (Wemoto) the 95 S4 takes CR9EK's, and it's melted both.

You would not make the insert brass; it would corrode to the plug threads in that application and unscrew from the head.
Mild steel/alloy far better.

You have already gone up a heat range then.!

What size jets should it have had ?

I would count your blessings if the dealer will accept it returned; many would not consider it ,knowing the problem.

Pity about the shocks; someone here may use them if you are lucky.

Personally I would move that one on ( and I like challenges and things like this)

Believe me I hope to get it back to them and either take my DL1000 back I swapped, or a different bike, I've had challenging bikes before but this ones proving terminal I fear.

Just a quick update, the bikes gone back to the dealer and I've got my money back- if you see a black Type R super four for sale, with stainless headers and standard end can, P reg, treat it with caution.

I've managed to get a 2006 Hornet 6 instead :) Will miss the 400, but can't be doing with the stress for daily transport.

Hi newbie owner of second hand cb400 here,need help about my bike,i just bought it last 2 weeks ago,after a week ive noticed that the accelerator cable is only one but i checked the manual using internet suposed to be its a two cable,question-in this case can this 1 cable use affect the performance of the bike?

Thanks in advance!!

rehpotsirhc wrote:Hi newbie owner of second hand cb400 here,need help about my bike,i just bought it last 2 weeks ago,after a week ive noticed that the accelerator cable is only one but i checked the manual using internet suposed to be its a two cable,question-in this case can this 1 cable use affect the performance of the bike?

Thanks in advance!!

CB400 Superfour has 2 cables one pulls the throttle open the other pulls to close the throttle, although the springs should be enough to close the throttle on their own.
The pull off cable is original equipment put there by the manufacturer it would be better if you replaced it.