How dead is my engine....?

Motorcycling
1

Hi Guys,My 1990 Honda CB1 (NC27) is poorly and I’m going to try to locate the cause but would be grateful if anyone can give any suggestions…

Tuesday morning my bike started ok - as usual.

I rode it out of the garage to the end of the drive and put it on the stand to go and close the garage door - as usual.

I noticed it wasn’t sounding right, instead of the usual sportsbike rumble it sounded more like two mopeds idling. As I increased the throttle it sounded lumpy so I turned it off.

I tried starting it when I got back from work but it wouldn’t fire - got some noise which sounded like misfiring but nothing else.

Apparently it is the same engine as a CBR400 but not tuned. My bike has 30,000km on the clock and is used for commuting and does around 3,000km a year (only done 11,000km since 2000 on it). Is serviced.

I’m going to have a look tonight but if anyone can give any pointers that would be great.

Thanks,

Mark.

(I suspect head gasket :frowning: :crying: )

2

Sounds like a possible spark plug or fuelling issue, perhaps some of the cylinders refusing to spark up then all of them refusing. Have you taken the plugs out, and if so how do they look?

3

Why do you suspect the head gasket ? it would most likely still start ok if that was gone, but would just boil up fairly quickly.
Best to start with checking spark / whether you’re getting fuel first and go from there.

4

start with the basics spark plugs clean and adjust.then fuel is the plugs wet if so u have fuel.is the fuel contaminated with water,drain a little from the float chamber on one of the carbs and let it settle to see if it seperates (heavy water on the bottom fuel on top)are the spark plug caps screwed on tight.have u a spark (put spark plug on side of engine and turn engine over if u c a spark its not coils.other than that u have to start looking at the engine

5

I’d go with this…Also check the vacuum pipes and see that none are split or have fallen off :slight_smile:

6

Thanks for the responses guys.

Yes, you’re absolutely right I’m jumping to silly conclusions without checking the basics.

Tonight I started taking it apart;

  1. On opening the airbox and removing the air filter there was a small quantity of watery mayo in one of the recesses of the plastic near what looked like a breather pipe going to the crankcase (there are 2 small ones either end which then union to one larger pipe). With airbox cover off I hit the starter got a couple of blue flames out of no 2 but no more.

  2. With coolant cap removed (no mayo on the cap) I turned the engine over, no bubbling or movement in the coolant.

  3. I removed the spark plugs (from left to right sitting on bike)
    plug 1 - normal, plug 2 - oil around base of thread core normal, plug 3 - slight traces of oil on metal rim around core, plug 4 - sooty/normal (normal = brownish/light black deposits, tip of core clean). They all had that lovely petrol aroma… :smiley:

  4. Looking down the spark plug recesses into the cylinder with a powerful torch - the top of each of the pistons looks sooty black but dry. On turning the engine over no abnormal noise.

  5. I connected up plug 1 and turned the engine over, didn’t see a spark - but then the battery died.

Am charging up the battery and will get my compression tester out - I’m hoping the small adapter is the right size, so I can confirm compression.

The current plugs are denso - is there a better brand to use on this engine?

I’ll report back once battery is charged and I can check more.

Thanks,

Mark.

7

Older bikes like that it would be better if you had NGK Iridiums on it. They produce a powerful spark with less power than standards.
Also if your battery gave up so quickly I would replace that now rather than later.

8

OK, get the battery charged and change the plugs.Denso plugs are pretty damned good, and IME you get fewer duds with Denso than with NGK (I’ve had a lot of NGK plugs over the past 25 years that have been totally dud when brand new)
I still usually buy NGK though, simply because they are easily available.
As for the Iridium plugs… age of bike makes no difference to what you use, although the Denso Iridium ones actually need less volts than the NGK ones as they have a smaller diameter electrode.Best thing about iridium plugs is that they last a lot longer than std .

9

With no odd mechanical noise from the engine, the plugs sounding like they are ok and then the battery dying so quickly, could this be a case of the classic Honda faulty regulator/rectifior?

Misfire followed by dead battery??

10

Its good - but its not right :stuck_out_tongue: Rectifier failed 8 months ago, fried the battery a bit and both were replaced promptly.Ok - update.I only managed to test the compression in cylinder 1 & 4 (didn’t have adapter on tester so had to use solid press tube which couldn’t get access into 2 & 3) and got readings of 8.5-8.75 - seems a bit low…Then I tested all the ignition leads and plugs - now the plugs despite looking ‘normal’ seemed to only produce a spark which didn’t go from centre electrode to the side electrode, but went from the centre electrode down towards the insulator - the result being a barely visible flash. I got my dremel out and mini wire brush and gave them a ell’ of a polish up and reduced the gap slightly.Result, a proper spark - tested it…and… SHE LIVES!!!Ok, some more questions for you lovely people;1. Has my bike been combusting something (other than petrol :D) which ‘coated’ the spark plug surfaces? Fuel additives?2. Is compression of 8.5 - 8.75 seriously low?3. I’ve searched google and spark plug websites and got gaps of 0.6 - 0.9 (0.4 on iridium) for my CB-1 - what is the correct gap?Thanks, Mark.