Forum

[Dennis C]

Somehow this next bit got lost in posting

Mazak

In the early 1930s Morris Ashby in Britain had licensed the New Jersey zamak alloy. The high-purity refluxer zinc was not available in Britain and so they acquired the right to manufacture the alloy using a locally available electrolytically refined zinc of 99.95% purity. This was given the name Mazak, partly to distinguish it from zamak and partly from the initials of Morris Ashby. In 1933, National Smelting licensed the refluxer patent with the intent of using it to produce 99.99% zinc in their plant at Avonmouth.

[JTL]

Hi all ... Grunda, I know your advice was serious. Also the later comments indicate, that a new carb body is the way to go compared to repairing the old one. I have talked to a friend of mine who says soldering is no good for this alloy. I'm not qiute sure what alloy it is; it's an Amal made in Spain. Weliding is definite for specialists. So in the end replacing just the body might be a solution. But, bacause there is a but. In line of my long term tuning mods for the Bullet I want to end up with a 32 mm carb and not a 30 mm, as the one I have now. This is why I mentioned the Mikuni TM32. all the best. Jacob ... by the way I have been on the first real test drive with the new piston. Had to use my old Mikcarb VM28. Still ok for a ride around the block.

[JTL]

Pete F ... by the way what is JB weld? Jacob

[ed.lazda]

I had a big hole in the float bowl of my Mikcarb (after I tried to put in a drain screw but the metal wouldn't hold the threads). I then sealed it up with the Araldite metal epoxy, which is probably very similar to JB weld. It's firmly stuck to the metal and petrol proof. Worth a try?

[Alan R]

Hi guys---------- JTL, take a look at this }--------- http://www.jbweld.com/ ----------- Basically it's a two-pack, Epoxy resin glue.....

[JTL]

Hi ... just found some Plastic Padding Chemical Metal in the shed. It states that it is petrol proof. JB weld seems to be not available here in Denmark, so I might as well try the Plasic Padding stuff. If I go for a repair as the next thing. Right now the bike has the old Mikcarb back on. This means the new piston will be run in with the VM28. Today I did some small rides and a longer one after the air cooled down. So many little, new sounds to notice and think about. But thimngs seems to be fine. Jacob

[John Turner]

I have seen this before on the MK2 bodies. It is caused by either the jet holder not being threaded far enough or the thread in the body not having enough of a chamfer. When the jet holder is then tightened it, the last 1mm will be very tight and cracks the end of the thread where the jet holder fits. The ones I have seen are only a small crack a couple of mm long and do not cause any problems. I ran with one of these for several years and the bike ran and ticked over perfectly.
John

[PeteF]

Dennis,
Yes, seems we are both right.

JTL'
JB Weld is an apoxy and the Plastic Padding stuff is probably similar.
If you do try it, I would open the crack a bit into a "v" and really clean and roughen the area round it so the stuff can get a grip.

[JTL]

John Turner, your description is more or less spot on. It is good news that it does mot effect the fuel mixture. That just leaves me with another problem: my bike running too rich with the MK2. I have tried all sorts of jet combinations, and still too rich. I have developed a fairly good sense of mixture symptoms (too lean; too rich). Black exhaust and very soothy combustion chamber is still the result even though the bike runs very good... So, Pete F, I will remember your advise for preparing the crack if it comes to a repair. Right now I will focus on running in the new piston to get a good ring bedding, burning off grease from reassembling and everything else not suppoesed to be there. Then it is carb time again. The old VM28 does well, but lack the power of the 30 mm MK2... all the best Jacob

[simon]

I'd be very surprised if a hissing internally was caused by poorly fitting piston rings. That would suggest considerable blow by which if it was there would most likely cook the rings and piston with escaping combustion gas. My guess will be poor valve seating or the decomp valve as has been suggested. A stethoscope type pipe in the carb throat will let you know if its inlet side and the same in the exhaust pipe for compression (and or the decomp valve). You might have simply set the tappets too tight so if it is valves try slackening the tappets before you pull the head. If it is rings your oil will be prematurely black and you'll be making oil smoke. The decopression valve can be pulled out and valve ground quite easily and will work much better afterwards. You can stick a spark plug in the hole temporarily to isolate it and test the exhaust valve. Whatever it turns out to be I would suggest you don't ignore it as down that path only expense and disappointment lies!