Tillotson hw-27a pop-off

Hello! I have my race engine ready for next weekend but when i check the popoff its wayy to high at 0.90 bar… i have the same spring in my other carb and its perfectly at 0.68 what can be the problem? I race carb is mounted on engine and other karb is hand held…

Are the valve and seat wet? If not that can make the reading high.

Its freshly rebuilt and it has a ouled seat and needle…

Isn’t around 1bar normal ? Mine is about the same, when soaked in gasolin.

That is higher than standard as standard is 0.7 bar and then holding pressure around 0.5-0.55bar

Disassemble everything again and make sure lever is totally flat with the body. Do you have an adapter so you could check the pop off without the diaphragms?


Should checking the pop of shown on you picture , measure the same, as fully assembled through the fuel inlet ?

Pop off will be the same wether you measure directly on the valve or fully assembled through the fuel inlet IF everything is sealed properly :grin:

But this way will eliminate any defects on the membranes that will affect pop off when you are measuring. And you could verify if it it the valve that is leaking or something else



Nice advice thanks …

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