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post #1 of 12 (permalink) Old 06-23-2019, 06:53 PM Thread Starter
Grand Prix 500
Main Motorcycle: 65 t120r 650 Bonneville
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carb problem

After five years of searching parts and rebuilding I finally filled the gas tank with about a gallon of gas. Discovered that the tank leaked. Got it sealed, hooked up the fuel lines and opened the petcocks only to find that brand new fuel line leaked because of failure (?) to put ferrule on the line at the tank connection. Removed the one ferrule and installed fuel injection hose clamps in their place. All leaks fixed. Started kicking but getting no spark. After figuring that problem out, ready to start kicking again. Opened petcocks and gas started gushing out of the tickler, which didn't happen on first attempt to start. Pulled carb and checked to see what was going on, but didn't see anything obvious. Float works freely, and the little valve (not new) was free. The carb has some new parts and gaskets and was cleaned thoroughly. Anybody know what I'm missing or overlooking, or cause of this problem? At my wits end, and not much hair left to tear out. Carb is 1965 Amal 389 monobloc.
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post #2 of 12 (permalink) Old 06-24-2019, 02:35 AM
SuperBike
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Is it a period carb, have you fitted a sealing washer under the float jet holder?

Rod
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post #3 of 12 (permalink) Old 06-24-2019, 06:45 PM Thread Starter
Grand Prix 500
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I'm not sure what you mean by period carb. It is original 389 carb on a '65 T120R. I used the rebuild kit with gaskets and new needle valve. This didn't happen the first time I tried to start the bike, only after I fixed said leaks in the tank and fuel line. According to Amal parts diagram, nothing is missing and doesn't show a washer, if I understand what you are referring to as a float jet. I'm guessing you mean the little plastic pointy valve that the float pushes up?
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post #4 of 12 (permalink) Old 06-25-2019, 03:50 AM
SuperBike
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Yes thats what I mean. What I wanted to confirm was that there was no washer under the holder for the float needle (sorry I did not mean to write jet). On the original carb it is not required but is on the newer versions. Using the washer on the original carb will cause the problem you have.

Next thing I would check is wether or not the float is hanging up in the bowl, I have in the past had to clean up execs plastic (flashing) from the float. And that the brass sleeve is the right side of the float.

Rod
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post #5 of 12 (permalink) Old 06-25-2019, 08:17 PM Thread Starter
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I'll remove it again and check the float. When I first checked it, the float was moving freely, but I'll check again and the sleeve. I don't understand how the tickler acts as a primer. It doesn't seem to be connected to anything, looks like it's only just a plunger on top of the carb. I normally expect a "primer" to be connected to some sort of diaphram and create a vacuum. Amal diagram shows nothing missing. The plunger does seem to be sloppy in the bushing, not tight tolerances. Could that possibly be a problem? Also would the float needle sticking open cause the bowl to overfill and come out the top via the tickler?
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post #6 of 12 (permalink) Old 06-25-2019, 11:23 PM
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Hi Bonniedude, Might be a bit of debris in needle/seat now if copper seal is good.

Amal now sells a stay up float & viton tip needle for mono block carbs. I've not installed one in mono block yet, but have done several in concentric. Pretty much 100% cures the needle/seat sealing problems. So far I've seen them last very good for 6 years so far. I expect they will last much, much longer. I've tested several & they do not leak a trace even after several days with fuel tap on.

I would recommend considering installing them. You can buy direct from Amal using paypal. They do currency conversion etc. I find parts come in less than 2 weeks to San Francisco area. Or parts sellers/ebay. Make sure it includes the viton tip needle.

http://amalcarb.co.uk/monobloc-stayup-float-kit.html

On an aside if you are using clear fuel hose, keep a close eye on it for leaks & brittleness. They do not last with 10% ethanol fuel. Gates brand black rubber fuel line either carb/evap or fuel injection will last very good. Fuel injection hose has higher thread count making it stiffer & stronger. I like the more flexible carb hose. Rubber & liner are same material in both. Is sold by the foot at many auto parts stores if you ask.
Don
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post #7 of 12 (permalink) Old 06-26-2019, 03:30 AM
SuperBike
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You are overthinking the Tickler. It simply pushes the float down and holds it down so the bowl can flood. It is not a precision machined parts and generally fits like a sausage in a hall way. If the needle sticks or something holds it off it's seat it will flood fuel out of the tickler.

I've not had a great deal to do with concentrics but I have three Monoblok carbs on two bikes. I've not found the standard float to be an issue so long as it does not leak, is fitted and assembled correctly and moves freely. From memory the plastic float fits with the writing to the outside, they all say Amal 276 followed by the little brass sleeve.

Rod
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post #8 of 12 (permalink) Old 06-26-2019, 10:40 AM Thread Starter
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Yeah, overthought it. So, I guess the only logical conclusion is that the float needle is sticking. I checked the play in the float already. It had plenty good free play. The writing is on the outside. I think to determine for sure I'll make a clear plexiglass cover and hook up to the fuel line to see visually what the float needle is doing. Carb is type 389/203
Bore 1 1/8" Appreciate the help.
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post #9 of 12 (permalink) Old 06-27-2019, 03:41 AM
SuperBike
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And you have the little brass sleeve in place on the pivot pin?

Rod
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post #10 of 12 (permalink) Old 06-27-2019, 08:04 PM Thread Starter
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Pulled the carb and took off the cover. Missing the brass sleeve. I don't see one anywhere on the WWW except as part of a kit. I don't really need the whole kit for close to $50.00. I'm thinking my local hardware store, or Mcmaster-Carr catalogue might have something I can use to fabricate one. If all else fails, I'll bite the bullet and buy the kit. I suppose I should inspect the other carb also. The float valve needle was sticking in the closed position, but I suspect because it was dry. These I can buy individually, so I'll change them as a precaution.
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