Simon Slocombe Posted February 2, 2020 Share Posted February 2, 2020 Engine very reluctant to start when warm. Starts no problem from cold, and runs very well otherwise. Any ideas? Quote Link to comment Share on other sites More sharing options...
RobPearce Posted February 2, 2020 Share Posted February 2, 2020 Can you clarify what you mean by "reluctant"? Does it crank very slowly when hot? Churns over really fast but no sign of firing? The former is probably a weak starter or a bad connection between it and the battery, or the engine earth strap. Heat makes things expand and a slightly-loose-but-not-a-problem connection could become a very poor contact on a hot engine. The latter could be an over-rich mixture or a problem with fuel evaporation. You have a non-standard carb setup so excessive heat soak is plausible. Couple that with a worn fuel pump and you'll have lots of trouble with hot starts. Quote Link to comment Share on other sites More sharing options...
Simon Slocombe Posted February 3, 2020 Author Share Posted February 3, 2020 Hi Rob, Thanks for your input. The engine turns over at good speed, hi-torque starter and new battery see to that. I too suspected fuel evaporation and re-routed fuel line etc. At the mot, two weeks ago, the tester.commented that emissions were at the lean end of the range and could possibly be richened up a little, hence the confusion. It also has had new plugs and leads and uses electronic ignition. Quote Link to comment Share on other sites More sharing options...
Flying Farmer Posted February 10, 2020 Share Posted February 10, 2020 Possibly the same problem as I had with the Holley I had fitted years ago. The fuel boils in the carb after switching off the engine. The fuel vapour is heavier than air and fills the inlet manifold driving out all the air. This makes a super rich mixture that will never fire when hot. Best cure I found was a readily accessible switch to the fuel pump. Switch the pump off about 15 seconds before switching off the engine so the level of the fuel in the float chambers is much lower and therefore there is less to boil away. You can test this by pulling up the top on the inertia switch when the engine is hot and see if it helps. My switch used to be on the dash where the choke knob used to be and was marked as a cooling fan to confuse potential thieves. I have long since converted to efi so don't need the switch any more. Neil Quote Link to comment Share on other sites More sharing options...
Andymoltu Posted February 19, 2020 Share Posted February 19, 2020 I found half throttle does the trick when warm. Andy Quote Link to comment Share on other sites More sharing options...
V Mad Posted April 26, 2020 Share Posted April 26, 2020 Quoted from Andymoltu- I found half throttle does the trick when warm. Andy This is a good tip. Quote Link to comment Share on other sites More sharing options...
V Mad Posted April 26, 2020 Share Posted April 26, 2020 First eliminate ignition problems as the cause. Second, if you have a non-standard type fuel pump, then check the fuel pressure. Normal is 2.7 psi. If it is much more than that it could be the cuase of hot starting problems. Quote Link to comment Share on other sites More sharing options...
Simon Slocombe Posted January 10, 2021 Author Share Posted January 10, 2021 Problem solved, fitted Filter King and hey presto, now starts easily hot or cold. Thanks for advice. 1 Quote Link to comment Share on other sites More sharing options...
Ian Buck Posted June 10 Share Posted June 10 Have the same issue, not sure what a filter king is ? Help please Quote Link to comment Share on other sites More sharing options...
Dannyb Posted June 10 Share Posted June 10 It's a fuel regulator and filter. Just Google it. Danny Quote Link to comment Share on other sites More sharing options...
glang Posted June 10 Share Posted June 10 Ian first of all try just an inline fuel filter because dirt getting to the carbs can cause them to malfunction and give hot starting problems. I am very sceptical that the pressure regulators available work to zero flow (this is difficult to acheive without recirculating fuel back to the tank) so that they wont help with any carb problem before the engine has actually started.... Quote Link to comment Share on other sites More sharing options...
65redspit Posted June 10 Share Posted June 10 This is a "FilterKing" installation... works a treat, carbs need low pressure 3.4psi is approx optimal for Weber DCOE's Quote Link to comment Share on other sites More sharing options...
glang Posted June 10 Share Posted June 10 Yes a Filter King is a great bit of kit for controlling the pressure from an electric pump to ensure there is sufficient fuel flow whatever the demand. However people think they are the solution for cases where the carb float valves leak when fully closed and as I say this is almost impossible to do without a recirc line back to the tank. This could be confirmed using a pressure gauge in the supply line while running the pump with engine stopped... Quote Link to comment Share on other sites More sharing options...
65redspit Posted June 10 Share Posted June 10 38 minutes ago, glang said: Yes a Filter King is a great bit of kit for controlling the pressure from an electric pump to ensure there is sufficient fuel flow whatever the demand. However people think they are the solution for cases where the carb float valves leak when fully closed and as I say this is almost impossible to do without a recirc line back to the tank. This could be confirmed using a pressure gauge in the supply line while running the pump with engine stopped... If a carburettor is set up properly and in good order it shouldn't leak. Too much fuel pressure will overcome the floats resistance and cause it to leak, hence a fuel reg being an essential part in the fuel delivery system. If the pressure is right and it still leaks you need to look at the set up and condition of the carb's internals. I think the myth around the fuel reg stems because to many installing a pressure reg seems easier and less risky than fiddling with the dark arts of a carbertooter... Quote Link to comment Share on other sites More sharing options...
glang Posted June 10 Share Posted June 10 I just dont think a simple regulator can limit pressure when theres no flow. Its very difficult to do and thats confirmed online, in fact even Malpassi only talk about pressure regulation when theres fuel demand... Quote Link to comment Share on other sites More sharing options...
65redspit Posted June 10 Share Posted June 10 Of course you need the flow but that's totally different to pressure. Flow rate won't cause a float chamber to leak but pressure will.... Quote Link to comment Share on other sites More sharing options...
glang Posted June 10 Share Posted June 10 No what I mean is its very difficult for a regulator valve like a Filter King to close fully and keep the pressure on the outlet at say 2.5psi with a pump pressure of for example 7.5psi when the carb float valve is closed. Its only when fuel is flowing into the carb that the Filter King can regulate its opening to allow a pressure drop from inlet to outlet... Quote Link to comment Share on other sites More sharing options...
65redspit Posted June 11 Share Posted June 11 7 hours ago, glang said: No what I mean is its very difficult for a regulator valve like a Filter King to close fully and keep the pressure on the outlet at say 2.5psi with a pump pressure of for example 7.5psi when the carb float valve is closed. Its only when fuel is flowing into the carb that the Filter King can regulate its opening to allow a pressure drop from inlet to outlet... Ah gotcha 👍🏻 Quote Link to comment Share on other sites More sharing options...
glang Posted June 11 Share Posted June 11 Yes fuel injection systems have a similar problem (although running at much higher pressures) where the pressure at the injectors must be kept stable even with the engine stopped and its achieved by returning the excess to the tank so there always a flow. I would be interested to know if anyone has seen a Filter King or similar do the equivalent for carburettors but suspect not... Quote Link to comment Share on other sites More sharing options...
65redspit Posted June 11 Share Posted June 11 2 hours ago, glang said: Yes fuel injection systems have a similar problem (although running at much higher pressures) where the pressure at the injectors must be kept stable even with the engine stopped and its achieved by returning the excess to the tank so there always a flow. I would be interested to know if anyone has seen a Filter King or similar do the equivalent for carburettors but suspect not... no it doesn't but I run a Mocal non return valve in the fuel lines just before the carbs which works a treat... Quote Link to comment Share on other sites More sharing options...
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