H1 missfire

[Ogri211]

I know this subject has been covered many times, I have had an ongoing problem with my H1B, it starts and runs fine, it will rev cleanly and pulls like a train, but if I am giving it a handfull after about 10 mins it starts to mis on 1 pot at highj revs and sounds like pre ignition, I tried changing my condensers with spare units from my Gt 750 which caused a misfire at 5000 rpm, I have since read that you must use the correct Mitsubishi condensers with the standard coils. I have read that a problem with leaking check valves can also cause these symptoms, I have noticed a small oil leak under my bike that looks as if it may be coming through the crankcase drain, any help appreciated.

[Kawaclive]

Hi
If the misfire only occurs after 10 mins have you checked that the breather in the fuel filler cap is not blocked causing a vacuum
in the fuel tank and fuel starvation.
If you think the misfire is only on one cylinder then use a strobe timing light on the HT leads when it is misfiring to trace which cylinder it is. The misfiring cylinder may have a darker or sooted up plug. You can then try swopping the coil to see if it moves the problem and if not the swop the condenser to see if that does it.
Also check for air leaks at the inlet, head and base gaskets and ensure the choke cables are free and all 3 chokes are seating properly as you may have 1 cable snagging holding a choke slightly open.

[Ogri211]

Thanks for the reply, ive tried opening the fuel cap when its missfiring no difference I also checked the flow from the taps all ok , a bit difficult to check the missfire with a strobe as it only does it flat out under load IE: about 90 mph so that wont work, Ive stopped immediately after a bad missfire and removed the plugs no difference as it only does it at high revs and I dont want to push it in case it is an oil pump issue and I sieze the engine. I have no air leaks and the choke cables are all purposely left with lots of play to avoid one sticking so Im still thinking check valve, It is quite difficult to tell what cylinder is missfiring, I think it is the right hand one as my friend saw a backfire through it.

[BIG H]

Have you tried a new set of plugs? you have not said you have.
The symptom you have is also typical of not enough fuel in the float bowls,
the floats are set too low.
Check the floats via the fuel level method.

[Ogri211]

Thanks for the reply , I have changed the plugs several times, and I set up the float heights using the 4 stilts in the container, also it will run for about 10 minutes flat out before a problem starts so Im pretty sure its not fuel starvation thats the problem, when it missfires I have tried putting on the fuel enrich lever (choke) and it makes not a bit of difference, I have bought a capacitor checker so I am going to check my condensers when I get home and set the points and timing, I am making up a tester for checking my check valve crack pressure as I suspect that may be the problem.

[BIG H]

If you understand electricity & electronic components you can remove the condensors (which are crap)
on the stator & connect directly to the ignition coils correct value (for your H1B) 0.22uf (220nf) capacitors.
I did this to my KH125, it has made a big difference to engine running, especially at high revs.
This mod can be done to the other triples with points ignition.( or any other point ignition engine ).

[SAM]

If you understand electricity & electronic components you can remove the condensors (which are crap)
on the stator & connect directly to the ignition coils correct value (for your H1B) 0.22uf (220nf) capacitors.
I did this to my KH125, it has made a big difference to engine running, especially at high revs.
This mod can be done to the other triples with points ignition.( or any other point ignition engine ).

Wow! I have learnt something

[Ogri211]

Do you wire the capacitors on the coil + to the points wire and - to earth?

[BIG H]

The capacitors you require need to be made from Polypropylene, 0.22uf (220nf) & have a minimum voltage rating of 850 volts.
These cheap ones on ebay rated at 1000v will do the job, don't waste your money on high spec audio grade capacitors.
https://www.ebay.co.uk/itm/2x-MKP4-220N ... 2477620993
Connect capacitor to the wire that goes to the contact breaker & the other end to earth,see sketch.

[BIG H]

Your problem may also be 1 or more ignition coil breaking down as it gets hot.
Check resistance values of the ig-coil hot & cold.
If using resistor plug caps check them too.

[scouse]

As a footnote note
If you leave the ignition switched on, youlll find the coils get hot
So assuming the battery is good and is charging you could switch the ignition on and make a cuppa, come back and try and start the bike.
This will reveal 2 things, if the battery is flat, it's the battery, if the bike missfires on start up, it's a coil breaking down PS the same coils are used on S Series bikes and the KH 250

Gary T

[Ogri211]

Thanks do you need to get original coils or do the ones off Ebay like



http://www.ebay.co.uk/itm/Ignition-Coil ... SwmOJaBL~u

work OK.

[BIG H]

The capacitors will need to be protected.
I did this by putting the capacitor in a plastic box & sealing it with potting compound.

[scouse]

Thanks do you need to get original coils or do the ones off Ebay like



http://www.ebay.co.uk/itm/Ignition-Coil ... SwmOJaBL~u

work OK.

Personally I would find the fault before buying anything, guessing can lead to you spending money you don't need to

Gary T

[Hucklow Tom]

The capacitors will need to be protected.
I did this by putting the capacitor in a plastic box & sealing it with potting compound.

Hi BIG H

Very interesting stuff. I am going to try this as I have had several dud condensers recently.

But, being a bit wooden with electrics , my question is, do these capacitors have a polarity or can I connect up either way?

Mine have various writing on but no + or -.

Cheers

Tom

[BIG H]

You can connect the capacitors either way round.
Capacitors that are polarized are always clearly marked + & -

[Hucklow Tom]

Thanks for that

[BIG H]

If you are doing this mod on a 250/400 the capacitance value is 0.18uf (180nf)
as stated in the w/shop manual.

[mraxl]

The condensers (capacitors) on points systems are to reduce arcing at the points and preserve point life. They do nothing to make more spark at the plug. However, a shorted condenser can keep a cylinder from firing.
Any value near 0.20 uf is good.... not critical at all.
They will usually either be good or bad and not cause an intermittent misfire.

[Ogri211]

I have changed the coils, set the timing bang on, reset the the check valves on the oil feed pipes to about 5 psi, the bike starts lovely, ticks over nice but it still cuts onto 2 when im driving fast after a short distance I just cant figure it out, I have some oil leaking from my left hand base gasket but it is only a small amount and only after a lot of fast ring. I've changed the plugs, tried putting the lights off, tried opening the fuel cap but nothing seems to get rid of the missfire when I am blasting it.

[SAM]

So does miss fire move with carb change?

[Ogri211]

It would be hard to tell cause it only does it flat out so its hard to tell what cylinder is missing.