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Amal Type 76 carburettor leaking

Submitted by richard_senior on Mon, 28/10/2013
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Hi Guys,

From what I read, this is not a too uncommon problem, but I cannot seem to find a cause or solution to my specific problem, so here I am.

My 1936 Norton Model 50 is fitted with (so I am lead to believe) the original Amal type 76 carburettor. She has been ridden a few times over the summer following a 13 year lay-up and all seemed to go well. She bogged down a few times and stopped, but upon giving her a âtickleâ again, she fired up and I continued on. A carburettor strip-down followed, to see if there were any obvious issues, but none were found. Since then, every time the fuel is turned on, petrol pours out of the joint of the âMixing Chamber Union Nutâ from what looks like the thread. At first I thought the fuel was leaking from the two holes on the main body, but I am pretty sure it is the nut just underneath. I have replaced all of the fibre washers with new ones direct from Amal, still leaks. I have replaced the float valve and float body, checked the height etc. and lapped it in using Brasso. To my inexperienced eye, it would appear that once âtickledâ, the fuel level rises in the float bowl and when this level reaches the same height within the mixing body (similar to a manometer) it leaks through the washer ? Attached photograph shows were I thinkthe leak starts.I have ordered a small sample of Vitron rubber to see if I can make a new washer to replace the fibre one.

If anyone has any ideas or suggestions, I would be very pleased to hear them.

Thanks,

Richard.

Attachments amal-76-leak-jpg

Submitted by dave_graham1 on Mon, 28/10/2013

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It will do that when tickled too much and that's how it was designed. I think you'll find it is coming from the holes, I've done exactly the same things as you. If it does it when you've been riding for a while your float level needs looking at. Check the clip on the float has locked into the groove on the stem. I found mine had slipped up making the fuel level to high and the bike run very rich. I slid the float back down until it clicked and all was well again. I hope it's as simple as this for you :)

Submitted by terence_terrell on Mon, 28/10/2013

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You've probably done this but make sure the carb is perfectly upright on it's clamp,even a few degrees from vertical can put the chamber too high or low.

Submitted by gordon_johnston on Mon, 28/10/2013

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Agree with Dave for first thing to check. The float clip can become weak with age - check it carefully to make sure it is holding the float chamber needle. This can cause all sorts of difficult to trace symptoms. I fitted a replacement float (autojumble, £2) which cured my problems. Well, the bike's problems to be strictly accurate.

Submitted by paul_knapp on Mon, 28/10/2013

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As above, the carb is flooding! Before you start fiddling with washers, remove the float bowl top and turn on the fuel. You will see the float rise with the level of fuel, and if it doesn't stop when the fuel level isat the required level (immediately below the mixture screw) try grasping the float needle and give it a little twist while lifting. If the float needle is seating correctly, the level will stop rising, if it continues to rise, there is something wrong with the seat.

Also, another thing to check is to make sure the tickler plunger fully retracts andisn't resting on top of float, holding it off it's seat, after you 'tickle' it.

Paul

Submitted by susan_harris on Sat, 09/07/2016

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I know this is an old-ish post, but thanks guys....had exactly the same problem today. Have stripped & rebuilt the carb with all new washers etc. Having never "tickled" before, I thought I had to depress the tickler 'til ISAW fuel.....then found fuel dripping from exactly the same place as in Richard's pic.

Think I'll try just the one small tickle! Roll on tomorrow

Sue

 


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