Monobloc float level

[Brian]

I thought I would "tell my story" here to hopefully give a little more info to anyone interested.

Firstly this is a classic "dont fix what isn't broken" tale.

I bought my '61 A10 ten years ago and have done 22,000 miles on it so far. When I bought it the original carby was quite worn so I bought a new 389 to replace the old one. I jetted it as per the book and it has been on the bike all this time and the bike runs very well.

Last week I decided to do some maintenance so put the bike on the bench and did the points, changed oils etc etc. Now for the first time I decide to check the float level and found it was way too high going by the "pip" on the bowl cover. About 3/8" too high. Now my carby has had a alloy washer under the needle seat since it was new and I found by removing this washer the float level came back to the supposedly correct level.

I took the bike down off the bench, gave it a kick and it started and idled perfectly as it has always done. I grabbed my helmet and coat and away I went. I did about 50 k's but had quite a strong tail wind at this stage, then it came time to head home and into the wind. I had gone about 2 k's when I felt the motor starting to loose power and tighten so I immediately slowed down and rode home slowly. when I got home I could see it was pumping oil out the right exhaust so I knew the damage had been done. Pulled the top off the motor and it had nipped up on the right cylinder, fortunately only very slight but enough to trap the rings. The piston only had a few small scores and the bore is untouched so a hone and a new set of rings and I will be going again.

Obviously reducing the float height had leaned it off too much. I had a good look at the carby and with the float height set so it is level with the "pip" on the bowl cover the tickler doesnt touch the float so wont work. This indicates that the float has to be at much higher level for eveything to work as it should. I also put a new 389 on one of my B33's a few years ago and I checked and it also has the alloy washer and the float level going by the "pip" is way too high.

So if anyone has a new monobloc and it has the alloy washer under the seat I would suggest you leave it there regardless of what the float level is in relation to the "pip" on the bowl cover.

The older "original" monoblocs dont have a washer under the needle seat but the new ones do and it seems its there for a reason.

So if I had left the bike as it was and not fiddled I would still be riding it as per normal. Hence the saying "dont fix what isn't broken"

[duTch]

 That's a bitch Brian, is it a plastic or copper/brass float? not that it matters too much now. And what method did you use to do the float level?

 As per a post the other week, I made a dummy cover from 'Clear PVC', and so far so good, it makes checking the level easy, and can see the float/tickler activity in fact I've left it on since with no denigration of the PVC(unlike other materials I've used).

 I think I don't have a washer under mine, but did a while ago experiment with paper washers to no advantage. (so far as I can tell from the stamps, mine is a 389/48- 9/65)

 About all I can say just now

[Brian]

The new ones like mine have a plastic float and the metal part the needle rests on is fixed so you cant alter it to change the float level. The only way to alter the level on these carbies is to lift or lower the seat with washers.

I used a piece of plastic tube from the bottom nut (I made one I could attach a tube to).

[RichardL]

Haven't set a monobloc yet, but this is a usefual cautionary tale for when I get to it on the barn-find A7. Sorry it comes at from your troubles.

Richard L.