Decided to keep my '56 Mk2....

[berniejones]

Seems I can't move the 'for sale' thread so I've started a new one - it's about getting the bike to start nicely.

I've just ordered the Thorspark EI, I've also ordered a service kit for the SU carb.

These will be fitted over the next few days and I'll see if it sorts my starting problem.

However when removing the carb and inlet tract I had another opportunity to wonder at why the ally casting was designed the way it is.

The hollow inlet pipe continues past the junction into the cylinder head for about 40mm and so the front mounting bolt passing down through it requires an airtight seal under the head to prevent an air leak there. It seems plain daft to me why it would be designed like this - why not terminate the inlet with a smooth 90 degree turn down into the head and use a solid casting for the front fixing bolt? It would improve gas flow and remove the need to seal the front bolt.

Cheers,
Bernie

[Roger Gwynn]

It's called a log manifold and aids gas flow somehow, I have never looked into it but that's what Bruce says and he is right 99% of the time.

[berniejones]

Thanks Roger - I did wonder if the 'extension' bit might be intentional and designed as a sort of damper to smooth pressure fluctuations in the gas flow - but then decided I was likely overthinking it! Would be interesting to find out more....

I may need 'The Bruce' to come back and cast another spell over this bike - he's seen it once as part of the verification for registration process but I may need wizardry if my fettlin' doesn't sort it!

Cheers,
Bernie

[berniejones]

Latest update - still not good.

Stripped the MC2 and rebuilt using a full service kit from Burlen.
Reset the float level
Ensured all joints airtight
Enptied the tank and refilled with fresh fuel

No difference, one small sign of ignition after about 20 kicks. New pertonix coil, healthy spark.

Pulled #1 plug and completely dry.

Spoke to Burlen and very tempted to grab a 900 series Mk1 concentric and fit that - will have to make an adapter plate but that should be easy.

I'm still waiting for the Thorspark EI to arrive but t the moment I don't think that will help.

Any other checks I could make please? Almost at the point of checking valve timing although I know it's fine!

Cheers,
Bernie

[Paul_Linden]

The plugs should be wet with petrol after repeated action of the kick start.
To rule out a stuck float valve, undo the top of the float chamber so you can see the float (hopefully floating on petrol). Hold the top of the float chamber over the float chamber and turn the petrol on. It should flow freely. In doing this you have also filled the float chamber some more. Replace the top of the float chamber, turn the ignition on, hold the throttle fully open and kick the kick start. Good luck!

[simon.holyfield]

Is your battery really healthy?

[paul.jameson]

Put your finger up the air intake of the carb and lift the slide. It should lift very easily and return smoothly with a slight clunk as it hits the "bridge". Even the slightest stiffness with this test needs investigating. If all is well here, check that the cap on top of the carb does not have a vent hole - or other leak. The carb will not operate with air leaking in here, in contrast to BMC Minis and such like which did have a hole. Some carbs are marked to show which way the top of the piston chamber should go on. From experience, if your carb is so marked - with an X or similar - you need the top the right way round.

[berniejones]

Thanks all,

I'm pretty sure the carb is fine. Float level set correctly, new needle and body fitted from the Burlen service kit.
Top lifted until overflowing and then kicked over.

Slide is free, jet block adjusted so that there's no binding. No hole in cap.

However that doesn't fit with dry plugs so maybe something still to be discovered there - maybe I'm just not getting a fast enough kick over?

I fitted a heavy duty battery last summer and it's been fully charged - but I can reconnect the charger and try again while it's charging.

Will be back on it again later this week.

Cheers,
Bernie

[simon.holyfield]

I only mentioned the battery Bernie, because I believe our bikes were rebuilt around the same time - and I have just replaced mine. It was causing misfires.

[berniejones]

It's always difficult when you can't isolate a single cause of a problem isn't it.

My recently completed B40 SS90 drove me mad as it would start and idle fine but stutter on pickup and cut out at higher revs.
I bought a new carb from Burlen, fitted EI, new coil, new plugs, checed timings a zillion times.

Turned out to be dirty contacts on the original ignition switch that I'd decided to keep for originality!

Maybe I ned to rule that out on the Ariel too!

Cheers,
Bernie