Hi all, Just taken the head off the M20 as the gasket started to squeak on a long hill. Apart from that running really well. Thought I'd share what I found inside.
The exhaust valve head and stem are rather yellow but the seats are perfect.
How do you think she is running and what has caused the yellowing?
Cheers, Mick.
email (option): mick@motorbikemike.org.uk
Hi Mick,
I've just had a couple of weeks playing with my carbs to get my M20 running sweet and I think I now have it.
from all the literarure I've read and now witnessed in practice, ideally you should see an even black plug, it does look as though your running a bit weak/lean.
If your getting any spitting from the carb at start up when it's hot then it may be running a bit weak on the pilot jet, just rotate the pilot jet screw in 1/4 a turn and re-try, if your unsure on the initial position of the pilot jet screw then wind it in entirely and then back it out by 2 full turns as a good starting point. Run the engine on tick over for a few minutes to get heat into the head and then re-examine the plug.
The only other adjustment is the needle jet, which should be set at the 2nd notch, else as Tim has stated, lift the needle by 1 notch.
I highly recommend you put a solid copper head gasket back on it now you have it apart.
Julian
email (option): 79aust@sky.com
Hi Mick...Your engine shows signs of weakness as noted in previous posts. That would be expected after blowing a head gasket though, when air will be sucked in through the failed gasket on the induction stroke and weaken the mixture. Consequently I wouldn't alter the mixture settings initially.
I also notice you don't appear to have a standard (correct) spark plug.
I would take the following action...
Thoroughly clean off both the head and barrel gasket faces and check them for a reasonable surface finish (not heavily corroded) and also with a straight edge to ensure they are flat...
Clean all the head bolt threads and check the threads in the barrel.
Remove the exhaust valve and lap in the valve/valve seat...This needs to be done occasionally anyway to maintain good compression and now is as good a time as any to 'refresh' the faces...
If you have the wrong plug grade/type replace it with the correct one...A B6HS NGK or an L86C Champion...Gap to .018" before fitting..
Fit an annealed, 1mm thick solid copper head gasket for far greater reliability (and you can use them more than once). The 'replica' composite gaskets currently available are unreliable and if you use one you may well end up doing this job again fairly soon.....You should also have an annealed copper washer fitted under the head of the 1/4" dia. timing access bolt in the head.
Lubricate the head bolts with a light machine oil ONLY on assembly and torque down to 28-30ft. lbs. following the tightening sequence shown in the factory worksheets.
After assembly take the bike out for a short run and THEN check the plug for colour...It should be a 'biscuity' brown in the center and a little darker round the edge. If it is a very pale or white colour make the adjustments required to richen the mixture...in other words reset the carb from scratch.
Check you have the correct slide cutaway, main jet and needle jet, reset to the standard settings for needle and pilot air screw...test...and then make fine adjustments if required...Ian
email (option): ian@wright52.plus.com
Hi Mick...You may well get away with liquid metal...I've found it's pretty durable and heat resistant. Alternatively weld, braze or even silver solder would do it, followed up by a light skim....I'm not familiar with Lodge plug grades and applications but that aspect should be more important than physical fitment details if it comes down to it...
Ensure the head gasket is thoroughly annealed before fitting...Heat to red and quench immediately in clean cold water to achieve maximum softening of the copper....Ian
email (option): ian@wright52.plus.com
Hi Mick...Sounds like you may have it sorted....Ian
email (option): ian@wright52.plus.com
Hi All,
with the plastic metal in place and two hours slaving over the surface plate my head now looks presentable-
The grey areas are where the plastic metal ended up. I must say how impressed I am with the stuff. I honestly didn't think it would stay put. Its also damn hard.I hope it stands up to being where it is, time will tell.
Cheers, Mick.
email (option): mick@motorbikemike.org.uk
Hi Mick...I was putting my M20 together for a trip to Normandy a few years back and suffered a minor disaster...Whilst tightening the head bolts I broke a fin on a brand new head..
...I didn't have time to mess about so for a 'quick fix' I glued the fin on with liquid metal...
As you can imagine it's not a very wide joint for the liquid metal to adhere to.
Anyway, it set OK and I slapped a bit of cylinder paint over it...
About 6 months later I actually got round to doing a welded repair, but first had to knock the fin off as it was still solid....Ian
email (option): ian@wright52.plus.com