Carburettor repair options (non Elan)

[69S4]

I'm hoping for some advice on how to deal with this problem. It's not from my Elan, although under different circumstances it could be I suppose.

One of the carburettors on an old motorcycle (1970 Yamaha) has sprung a float chamber leak. It was weeping to begin with but poking at the area with a scribe has revealed a hole - picture attached. Ideally I'd replace it but they're not available new (not surprising and the UK Mikuni importers actually laughed on the phone when I asked!) or, seemingly, second hand - I've not found anything in months of looking. So I'm looking at repair - it is only a hole after all. I've tried epoxy but it only lasts a month or two before falling out. Any other options I should be considering - does this sort of stuff weld?

[nmauduit]

can't see very well your photo as it is not on the site (only a vignette) : depending on wall thickness and hole size (internal clearance also) you may consider a glued mechanical plug after tapped into the hole (part will need to be very clean), or brazing (proper filler and flux required, depending on the actual alloy which may be tricky to find out - this is where a pro welder is fully justified, lots of experience plus access to alloy composition analysis if need be)...

how did that happen would be a side question, to put in perspective with the strength requirements on the repair...

[Craven]

Take a look at this, it does work.
https://www.youtube.com/watch?v=IPfb5eSY9yo

[69S4]

I'm not sure what happened with the picture - it should have opened to full size. I'll have to see if I can work out why it didn't.

The hole is right through the side wall of the float bowl about 1/3 of the way up from the bottom. It's a little over 1.5mm diameter and it's definitely from storage corrosion - it's not an impact hole. There are some other corrosion pits scattered throughout the bowl, but nothing else goes anywhere near right through the casting. The area round the hole is solid metal - it's not a case that the whole thing is wafer thin and this just happened to be the first perforation. The side wall is probably too thin (from new) to take being tapped but there's space either side so I suppose something could go right through.

With brazing / soldering etc, it would make a neater repair but trying to find someone with the expertise round here is going to be a huge problem. Cost is a factor as well - float bowls go for about £15 new (if could get one).

Try this image - it opens up ok in preview mode for me.

The lumiweld bloke on Youtube looked like he had a bit of a hard time repairing his casting - melting a bit of it on the way. I've got some of those rods and some old parts knocking around - I'll try it and see what happens.

[nmauduit]

I'm not sure what happened with the picture - it should have opened to full size. I'll have to see if I can work out why it didn't.
Try this image - it opens up ok in preview mode for me.

This works for you because you have a "postimg.cc" account installed, when posting photos here I prefer to upload a copy of the photo onto this very site, so that it can remain and does not get lock up or dissapear eventually when hosted somewhere else.

As for the hole (and part value) it's pretty small, maybe you can work out a nut and screw plug (say 2mm? grinding away the protruding bits before assembly) that would reduce the size of the leak, the remaining being plugged with some appropriate epoxy compound ? this fix may get you back on the road for the time you source a replacement part...
If the wall is thin, and the alloy unknown, it is very easy to get the part "collapse" before being wetted by the brazing, that indeed would be the best but there are some risks associated to it (I would not attempt it without being able to practice on an other part of the same alloy, say from a donor carb).

good luck !

[ericbushby]

Hi Stuart,
I would be wary of trying a risky method of repair when you have no spare.
There are Aluminium sealers and fillers on ebay. They are sold for repairing aluminium wheels.
Brands are ISOPON, BIGBOY and others.
The one I have is TechniQ. About £12.00 for small tin. It is a two part mix and I think it may work.
My main point is that no damage will be done if it turns out to be inadequate.
Best of luck,
Eric in Burnley
1967 S3SE DHC

[reb53]

How about a small nut and bolt with some washers, and a fuel resistant O ring each side ?
As long as the float isn't being touched it wouldn't be a problem.
If after a while all seemed well I'd peen over the end of the screw to ensure it didn't vibrate itself loose.

Ralph.

[rgh0]

How about a small nut and bolt with some washers, and a fuel resistant O ring each side ?
As long as the float isn't being touched it wouldn't be a problem.
If after a while all seemed well I'd peen over the end of the screw to ensure it didn't vibrate itself loose.

Ralph.

Maybe just a sealed end pop rivet inserted with a little sealer around it ?

cheers
Rohan

[69S4]

Thanks for all the replies everyone. The 'nut and bolt' option is one that had occurred to me and the position of the hole suggests it might be a viable solution. Not very elegant but needs must as they say. I hadn't thought of a rivet rather than a screw and that might be slightly less visually distracting. I'd think it would have to be applied from the outside as getting the head of a rivet gun inside the bowl might be a challenge. I'll follow that up today and see what's available.

I suppose ideally some 'goop' that could be pushed into the hole and left to set would be the hoped for repair but as was mentioned, 'first do no harm' is top of my priority list. The engine has only just been rebuilt after an engine blow up back in the summer and I don't want it off the road for another six months because I've melted the float bowl.

I'll also have a look at the aluminium wheel fillers and see if anything is suitable. I suspect though that fuel resistance might be their downfall. As mentioned earlier, regular epoxy filled the hole easily enough but then didn't survive subsequent contact with petrol. Are there any fuel resistant (or preferably fuel 'proof' ) epoxies - or any other chemical technologies - that would be worth investigating? Didn't some kind of two part 'putty' used to be available for blocking up holes in fuel tanks years ago. Anyone remember that?

[rgh0]

Yes there is a 2 part epoxy putty for repairing fuel tanks from Permatex, JB weld and others. I successfully used it many years ago as a temporary repair .
It should be OK in filling a small hole but how long it would last would still be a question.

cheers
Rohan

[2cams70]

I'm actually really surprised you can't find a secondhand replacement somewhere in the world no matter how rare you think it is. Dr. Google and Ebay are your best friends. Something small like that won't be that expensive to ship internationally if need be. The world is your oyster.

With rare parts first step is try and find a parts listing and part number. Do a google on the part number and see if anything comes up. With something like a carburettor chances are that the same carburettor family was also used on a different make and model to yours. Once you know these makes and models do a google search again only use search terms such as brand "XYZ carburettor" instead of "Yamaha carburettor" and so on. Also search specifically against the carburettor make and model rather than the bike it is fitted to. It may take a lot of sleuthing but you get the drift.

Something will come up eventually.

[69S4]

Something will come up eventually.

While I was in the course of bodging the existing one for the time being and after 12 months of looking, one did come up on eBay two days ago. It arrived this morning, and after a clean up and unblocking the starter jet, it fits perfectly. I'm currently bench testing the reassembled unit for leaks before putting it back on the bike.

The starter jet is a pressed in brass bush with a 0.5mm hole. I checked and that turns out to be the correct size.
The jet in the old float bowl had a 2.00mm hole. That would explain why the bike would always start but bogged down in seconds. A previous owner must have drilled it out in frustration as it's impossible to get to. A lesson that's equally applicable to Elans

Thanks to everybody for their help and suggestions.