Bloop - what do you think about this problem?
 

The pilot jet adjusting screw on my 1976 B100P was sheared off when I acquired the bike. I have a spare screw, but the bike runs fine as it is, so I’m wondering whether it is worth trying to fix. I was just wondering whether anyone here has had a similar issue and if so how they dealt with it (I asked the question on a CCM forum a while ago and the consensus was: leave it alone).
I think the only way would be to drill out the brass screw, but the slightest slip might ruin the aluminium carburettor body (it could be replaced with a similar new Mikuni VM20, but the 43 year old patina could not be).
What brought this to mind was the exhaust manifold issue I had recently with my K6, and the set of left handed twist drills I bought (but didn’t need) to fix that.
So, if anyone out there has experience of removing soft brass screws from ancient aluminium throttle bodies with left handed drills perhaps you would drop me a line with your advice. If the answer (as with the CCM crew) is to leave it well alone then that is fine.
Alan
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Re: Bloop - what do you think about this problem?
 

1) buy spare carb
2) think about fixing old carb
3) talk yourself out of it
4) "I'm bored - might as well have a go"
5) oh bugger!
6) fit spare carb

Re: Bloop - what do you think about this problem?
 

Excellent!

Re: Bloop - what do you think about this problem?
 

If it's running fine, leave it. Concentrate on easier matters, like trying to set the points gap and timing through the slots in the flywheel :-D

Re: Bloop - what do you think about this problem?
 

I certainly wouldn't try to drill it out freehand. I'd strip the carb and file off (or use a milling machine if you have one around) the remnants of the screw until you can define the centre. Then set it up on a pillar drill or mill (angle plate etc) and use a spotting or centre drill to start the hole at the centre of the brass and go bigger a bit at a time, effectively shelling out the screw. Not a 5min job.

Unfortunately the thermal expansion of brass and alum alloys are very similar, so heat of itself will be of little use. Soaking in a proper penetrating oil might help but I wouldn't hold my breath.

Alternatively leave it alone ………………….

Re: Bloop - what do you think about this problem?
 

... I know exactly what you mean, it is frustrating having the screwdriver and feeler gauge stick to the magnets just as you get everything in place!


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Re: Bloop - what do you think about this problem?
 

Thank you for that. I think the consensus is the same as the CCM guys - if it ain’t very broke, don’t try to fix it.

By chance I was changing the piston rings on that little bike this morn and had a look at the carburettor. I agree it could not really be done freehand, and I don’t think it is worth the effort and risk to mill it out.

The piston rings are changed (it still has a standard size piston so I suspect this was its first new set of rings in 43 years and 17,000 miles). Compression is back up to 100 PSI (from 75 PSI previously) - which is I suppose about 6.5:1 - I think that is fine for a 43 year old 2 stroke. The bike started 3rd kick after I’d put it back together, it certainly felt like it had a bit more power on a short run around the block. It is howling a gale this morn so I’ll leave a proper test for another day.

So - the carburettor is working fine, the bike starts easily and ticks over. It is missing a little at the top end but that is nothing to do with the pilot jet (I think the ignition needs advancing a little bit more). All that being said - the decision is to leave the pilot jet adjuster alone.

Alan


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Re: Bloop - what do you think about this problem?
 

It's worth removing the silencer and giving it a really good hammering with a rubber mallet on the seams to loosen all the baked-on crap that it will be full of. Don't bother with the old caustic soda trick, it doesn't really get the old carbon out, percussive maintenance is the only thing that really works. I got lumps of coal out of the exhausts on my old 380 triple :)

Re: Bloop - what do you think about this problem?
 

You are probably right, there is probably a bucketful of carbon in the Bloop’s muffler. I’d be loath to try bashing it out though, the exhaust is 43 years old, a bit fragile and would be very difficult to replace.

It would be nice to get the speed up to 60 MPH (plenty with drum brakes and 6v lights), and I think having changed the piston rings it will probably do that now. I don’t think it would be worth squeezing anything more out of a cooking bike.

Alan


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Re: Bloop - what do you think about this problem?
 

You could try the other approach of scarifying the inside. I got an old clutch cable and spread the strands in one end so they made like a chimney sweep's brush. Then fix the other end of the cable in the jaws of an electric drill, poke the brush end up the silencer from the header pipe end and then switch the drill on. Gets loads of carbon out that way, too.