RonN Posted July 26, 2022 Share Posted July 26, 2022 I am new to Triumph ownership having recently purchased a 1979 Spitfire 1500. I have not used it yet as I have a carburation problem in as much as the front SU HS4 carb seeps petrol into the jet which then runs out the air filter when the engine is not running. I have changed the float, needle valve and jet and set the float height. The breather pipes are clear and the carb is clean. Is there anybody on the forum who has experienced this problem or may have an answer please. Quote Link to comment Share on other sites More sharing options...
65redspit Posted July 26, 2022 Share Posted July 26, 2022 1 hour ago, RonN said: I am new to Triumph ownership having recently purchased a 1979 Spitfire 1500. I have not used it yet as I have a carburation problem in as much as the front SU HS4 carb seeps petrol into the jet which then runs out the air filter when the engine is not running. I have changed the float, needle valve and jet and set the float height. The breather pipes are clear and the carb is clean. Is there anybody on the forum who has experienced this problem or may have an answer please. electric or mechanical fuel pump? Quote Link to comment Share on other sites More sharing options...
RobPearce Posted July 26, 2022 Share Posted July 26, 2022 Common causes are excessive fuel pressure (due to poor quality new pumps), dodgy needle valves, bits of rubber in the fuel line blocking said valves open, or the float jamming down. Quote Link to comment Share on other sites More sharing options...
RonN Posted July 31, 2022 Author Share Posted July 31, 2022 On 26/07/2022 at 17:43, 65redspit said: electric or mechanical fuel pump? mechanical pump Quote Link to comment Share on other sites More sharing options...
RonN Posted July 31, 2022 Author Share Posted July 31, 2022 On 26/07/2022 at 18:23, RobPearce said: Common causes are excessive fuel pressure (due to poor quality new pumps), dodgy needle valves, bits of rubber in the fuel line blocking said valves open, or the float jamming down. Ok thanks, I have had rubber in valve, a dodgy valve and have changed float. Next thing to try would be pump although I think its the original mechanical one. Quote Link to comment Share on other sites More sharing options...
glang Posted July 31, 2022 Share Posted July 31, 2022 If youre sure the float/needle valve is all good the next thing would be to measure the pump pressure. It should be 2.5 to 3.5 psi and if too high can be reduced by putting extra gaskets between the pump and block to move its operating arm away from the cam. Of course you could try this directly without checking the pressure to see if it cures the problem but be aware that when going up a hill at high speed you might find the pump now cant keep up with demand and the engine loses power... Quote Link to comment Share on other sites More sharing options...
RonN Posted August 17, 2022 Author Share Posted August 17, 2022 Thanks for the info, I have ordered a new mechanical pump. I thought I had cured the problem but its started again in the last few days. Quote Link to comment Share on other sites More sharing options...
glang Posted August 17, 2022 Share Posted August 17, 2022 An inline fuel filter is a good idea to rule out the possibility that debris from the tank or fuel lines is affecting the carbs. Have you got one? Quote Link to comment Share on other sites More sharing options...
Wendy Dawes Posted August 17, 2022 Share Posted August 17, 2022 (edited) I have inline filter at the fuel outlet feed pipe at the top of the tank and also in front of the carb on my Herald, Good job as the one at the tank did foul up and block the fuel, simple fix just to change the filter and prime the pump then off you go Edited August 17, 2022 by Wendy Dawes Quote Link to comment Share on other sites More sharing options...
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