Carb leak - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 8 (permalink) Old 08-24-2019, 01:31 PM Thread Starter
Grand Prix 125
Join Date: Jun 2018
Posts: 37
Unhappy Carb leak

Triumph 1972 650 Bonneville T120R 4-speed.

OK. I finally got it back together. Electrical, pistons, valves are working. Opened the fuel valve and found a large leak through the small vent hole on the fuel primer push button.

Connections right tank to right carb
left tank to left carb
left carb to right carb

Opened right tank fuel valve and pressed primer on right carb and pretty fast leak appeared through the small vent hole.

Any thoughts, tips, help would be appreciated.
Thanks for all of the help so far. If I ever get this thing started and timed, maybe I'll be able to help, possibly as a bad example.
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post #2 of 8 (permalink) Old 08-24-2019, 06:34 PM
SOTP Vintage Series
Main Motorcycle: 1971 t120r
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i expect it is the float needle sticking or just not sealing. If it is just a sealing problem,smear a tiny bit of grease over the viton tip. Works for ages.

Now,where did that bit fall off ?
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post #3 of 8 (permalink) Old 08-24-2019, 08:34 PM
Production 125
Main Motorcycle: 350 EXC-F KTM 2018
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Location: Sussex County, NJ
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Other Motorcycle: 1971 TR6C Trophy
I had the same issue, the float bowl is either stuck or the float needle isnt closing off the hole. Fuel pisses out that hole, right?
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post #4 of 8 (permalink) Old 08-25-2019, 03:15 AM
Moto Grand Prix
Main Motorcycle: 1973 Triumph TR7RV
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Location: Pleasant Hill, CA USA
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Other Motorcycle: 1964 Triumph Mountain Cub
Hi Vinny, Are you still using plastic floats & needles? You MUST use only genuine Amal stayup floats & viton tip alloy needles.

Use only genuine Amal gaskets for bowl. Verify the float is not hanging up on gaskets. New gaskets should clear stayup floats fine.

Visually inspect there is no dirt etc. in brass needle seat pressed into carb & banjo screen is clean.

Sometimes if you get dirt in needle/seat you can remove bowl drain & let fuel flow, sticking a thin wire or even a twig if along side of road up drain hole & work float up/down to flush out needle/seat.

In any case if you have old plastic float & needle don't use them. You'll have a bike fire. Don't ask me how I know.

If you have rust in tank it will be so fine as to end up going through tank & banjo screens. You'll need to install real fuel filters in fuel lines. Rust will end up in carb.

Please fill in you location as it helps with localized advise. I've even made some good local friends from their location posted.
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post #5 of 8 (permalink) Old 08-25-2019, 04:34 AM
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Fuel is supposed to come out when you press the tickler. It’s a flooding device for cold starting.
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post #6 of 8 (permalink) Old 08-25-2019, 05:36 AM
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Location: Great Southern Land
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Sometimes [and this happened to me] the viton alloy needles are slightly to big for the seat. When I tickled mine the float would stay down [and the needle would stay up] until I gave it a sharp tap. I cured this by using some fine 400 grade emery and then polish on the three corners of the needles. This and a small amount of polishing on the top section of the seat fixed it. Note that I didn't touch the viton section at all, nor did I touch the actual seat hole or the area around it.

The viton alloy needles also have a slightly serrated finish on the corners, have a look at them under say 40X magnification and you will see what I mean. The sanding and polishing corrects this.

Great Southern Land.
(Where women blow and men chunder).
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post #7 of 8 (permalink) Old 08-25-2019, 10:39 AM Thread Starter
Grand Prix 125
Join Date: Jun 2018
Posts: 37

I pulled the float chamber. The float had separated from the valve. All good now. Except it doesn't start. I'll post a new thread.

Last edited by Vinny Cotroneo; 08-25-2019 at 10:44 AM.
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post #8 of 8 (permalink) Old 08-25-2019, 10:40 AM Thread Starter
Grand Prix 125
Join Date: Jun 2018
Posts: 37
Thank you. All good now.
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