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May 11, 2018 20:11:00 GMT
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Very well done on getting it working in time to do some proper reliability testing and trouble shooting.
On the fuel vapourisation front...... modern E5 is very bad for it. Continental E10 is worse.
Main issue seems to be the mechanical fuel pump, which is bolted directly to the block with no heat insulation. The pump gets hot and warms the fuel just where you really don't want it warm - around the pump valves, where it cavitates, stopping the pump from working properly - or even at all sometimes.
To head this problem off on our Spitfire we used an electric Huco pump mounted by the tank (could be under bonnet if preferred but pick the right Huco pump for location), kept the pipes right away from the engine and fitted a carb heat shield. Seems to work.
Nick
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1967 Triumph Vitesse convertible (old friend) 1996 Audi A6 2.5 TDI Avant (still durability testing) 1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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May 18, 2018 10:23:28 GMT
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Very well done on getting it working in time to do some proper reliability testing and trouble shooting. On the fuel vapourisation front...... modern E5 is very bad for it. Continental E10 is worse. Main issue seems to be the mechanical fuel pump, which is bolted directly to the block with no heat insulation. The pump gets hot and warms the fuel just where you really don't want it warm - around the pump valves, where it cavitates, stopping the pump from working properly - or even at all sometimes. To head this problem off on our Spitfire we used an electric Huco pump mounted by the tank (could be under bonnet if preferred but pick the right Huco pump for location), kept the pipes right away from the engine and fitted a carb heat shield. Seems to work. Nick This had me intrigued, so I borrowed a thermal camera from someone at work to see how bad the situation was. After a good blast up a long hill on the dual carriageway at 70mph or so (pretty much flat out). Of course, maybe this isn't the best test as air flow was pretty good - keeping under bonnet temperatures down. Furthermore, fuel flow was probably quite high, which will avoid heat soak of the lines and pump. The fuel pump itself is warm, but I wouldn't say excessively so. It's certainly staying much cooler than the block itself. The carburettor, where I thought the problem was didn't seem too bad. The main body is actually rather cool despite the exhaust just below, presumably due to the air flow. The float bowl was a little hotter, which does show a heat shield is a good idea. By far the biggest concern was the routing of the fuel line. I assumed it would be relatively cool at the front of the engine due to the fan, but this isn't the case. The line runs between the alternator and cylinder head (factory route) which is a hot area. Perhaps the change to copper from steel doesn't help either. Electric pump and revised routing is probably the ultimate solution though as you say...
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May 18, 2018 13:13:09 GMT
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That's a really cool tool (pun sort of intended!) and a very interesting exercise, but now repeat after sitting in traffic for 20 minutes, or driving up an Alp behind a large, slow camper van. I think you'll see some differences. The traffic scenario is the worst as you've low air flows and low fuel flows
The particular problem with the pump is that there is alot of turbulence/velocity in the valves, so if the fuel is already a bit warm at close to boiling point the low local pressures in the valve area cause boiling there and that really spoils the pumping ability.
You are quite right about the standard pipe-run - dunno what they were thinking of! Foolishly I still use this route on my EFI Vitesse for the return line. It doesn't directly affect the running but it is very noticeable that the fuel in the tank heats up (40ÂșC has been measured) which can lead to the fuel pump (Bosch roller cell EFI pump under the boot floor) making nasty noises due to cavitation. Can also be a problem when putting fresh fuel in on top of 1/4 to 1/3 tank of hot fuel as the heat from the old expands the new and causes overflow because the saloon/convertible tank has zero expansion space.
Nick
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Last Edit: May 18, 2018 13:14:07 GMT by vitesseefi
1967 Triumph Vitesse convertible (old friend) 1996 Audi A6 2.5 TDI Avant (still durability testing) 1972 GT6 Mk3 (Restored after loong rest & getting the hang of being a car again)
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