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1980 175mx Mikuni vm24 carb brass overflow cracked

  • ajhuxley
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Anybody had the problem of the internal brass overflow pipe in the float bowl cracking. Seems to be a common problem on Jap carbs
Just wondered if anyone had ideas for fixes?
1/ I've tried soldering but it wont take and heat has made the crack worse. pic attached
2/ Easiest would be to get another float bowl but ebay seems to be pretty pricey to buy a second hand carb and not sure if I'd have the same problem
3/ Theres a lot of replica Chinese carbs for $30 but Im suspicious of quality, anyone know if they re any good ?
4/ dont suppose anyones got a float bowl for sale?
01 May 2019 14:27 #1

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Replied by Mothersbaugh on topic 1980 175mx Mikuni vm24 carb brass overflow cracked

It's just an overflow tube. Not like it's the pilot tube or anything. Any chance you could make a new one?
01 May 2019 21:08 #2

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I've seen that happen before.

A hobby shop had some brass tubing that was a little bigger. I cleaned the original tube and with a good soldering iron I was able to solder the new tube over the old tube.

I'll look and see if I have a spare float bowl.. I might.
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
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01 May 2019 21:54 #3

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It's only an overflow tube so just solder it over on the outside. Fit a vacuum fuel tap off something & run a vacuum line from somewhere on the inlet so there's no chance of a random flooding while sitting un-attended. Or just turn fuel off when stopped with ordinary fuel tap -- petcock in the usa sorry. Just be sure there's still a breather of some sort leading into the bowl which i think there is from high up on the side. No air getting in & chances are the floats won't drop on full throttle. Happened with my boys yz80 in 1980 when mud plugged both breathers pipes--well overflow/breather & high up one. Had me head scratching on the day trying to diagnose that between races.

I'll keep out of the chinese carb argument/discussion as have one for a dt175 but never tried it but did bolt on one for my honda 185 & ran perfect out of the box.
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Last edit: 02 May 2019 15:55 by RT325.
02 May 2019 15:51 #4

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thanks to all for replying. I've managed to track down a 2nd hand carb for $40, lets see what turns up!
08 May 2019 03:47 #5

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@markt - Did you use a soldering iron to do this? I just couldn't get the solder to take on the original pipe even with loads of flux but I was using a flame as I figured an iron wouldn't heat it enough
Last edit: 08 May 2019 03:50 by ajhuxley.
08 May 2019 03:49 #6

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Yes. I'm not sure of the wattage but it's pretty powerful. Tube has to be squeaky clean.

I brought a box of carb parts home from storage and then forgot to look for the spare bowl.:Ugh

I'll try to remember to check tonight...
1963 YG1-T, 1965 MG1-T, Allstate 250, 1970 CT1b, 1971 R5, 1973 AT3MX, 1974 TS400L, 1975 RD350, 1976 DT175C, 1976 Husqvarna 250CR, 1981 DT175G, 1988 DT50, 1990 "Super" DT50, 1991 RT180, 2017 XT250
08 May 2019 06:20 #7

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had a result with the 2nd hand carb, perfect float bowl with overflow intact. All fixed now.

But now I am having a problem try to get a decent seal with the float bowl gasket. Seems whenever the bikes on side stand the angle of the carb means the gas is over one corner and seeps through the gasket (used a new gasket but actually went back to the original as it seems to seep less)
Anyone had similar experience and can recommend a better gasket type
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12 May 2019 07:18 #8

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I've had a few overflow tubes crack as well as the tube on the petcock.

The float bowl gasket will be pretty stiff when new. After it gets soaked with gas it will be a little more pliable and you can snug up the bowls screws some more. But the distance between the screws is fairly long and the bowl can be brittle after 45 years so be careful, I cracked one. It may still weep a little when parked. I'm in the habit of turning off the petcock 1/4 mile from home to let the fuel level get below the bowl gasket.
The hours spent riding my Enduros is not deducted from my life span.
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12 May 2019 12:40 #9

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thanks 1971Dt250, it seems to have settled in and sealed itself. I think @markT mentioned he's seen this happen in another post. So Im pretty pleased right now I dont have to take the carb off for about the 4th time!
bad news about these brass tubes :-(
Thanks for the reply
A
13 May 2019 12:48 #10

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