QuestionQUESTION: Good day-
recently I upgraded to a Weber carb on my Spitfire, and installed pacesetter headers and exhaust. On my first outing to shake it down- a 20 mile trip, due to what seemed like a lack of power, I came back and checked the plugs....very lean condition.
Weber suggests a carter 4070 electric fuel pump to keep up with the carb demand. is this the correct direction to head? Or could it possibly be something simpler.
Webber also suggests that the timing be advanced when installing their carb. I don't want to detonate the engine. any suggestions?
regards,
Brian
ANSWER: Hi Brian,
Don't run it any more while lean as it can burn a hole in a piston while lean.
Any time you make a mod like new type carb and exhaust system you alter the required jetting and ignition curve and timing.
You need to check what number main jet is in the Weber now and get an assortment of several richer jets and maybe even a few air correction jets for the emulsion tube. If you can find a local who races a sports car with Webers, they probably will have an assortment that you might borrow to get in the ball park. If not, you should buy several sizes richer main jets and richer air correction jets.
Any mod to an engine that increases performance will require more fuel to feed the monster. Unless you have access to a dyno and CO equipment, you will have to use "Plug Readings" (harder to do with unleaded gas but can be done)
You don't necessaraly need to go fast, just find a long hill to climb at a high RPM in a lower gear for at least a minute or so and turn the ignition off and push the clutch in at the same time to get the engine to stop turning as quick as possible (don't get into the stearing lock position when doing this or you may not need any jets at all)
Plug reading was an art with leaded gas but can still be used a little with unleaded. You sound like you already know what a lean plug looks like so a rich plug is flat black around the outer edge and some black on the insulator. A good reading would be flat black around the outer edge and a fairly clean insulator. (This is if the correct heat range plug is used) A "hot" or "cold" plug will give a false reading.
A fuel pump that can't supply the carb will give a "ON-Off", "ON-Off" run and show lean on the plug. A proper pump test is a "T" in the fuel line between the pump and the carb and a pressure gauge hung under a wiper blade connected in the "T" and a full throttle run up a hill.
I hope this helps, let me know. I will be glad to help further your project.
Howard
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QUESTION: part of my reason to check the plugs following my run was that I've been keeping an eye on the amount of gas running through the clear fuel filter. Upon arriving home and looking, there was very little gas in the filter housing.
Last night i noticed upon going down to work on the car, that the filter was completely filled to the brim! (haven't touched or ran the car in days)
Why does it seem as if the fuel system is building up pressure?
I've installed a breather (foam air cleaner material with K&N spray on it) on the return line that used to return back to the tank from the charcoal canister.
Any ideas?
I've ordered the jetting, and I'm waiting for it to come
ANSWER: An air pocket in a filter is no indication of anything and if you seen air in a filter when shut off and later air is missing does not mean anything either, The filter should be between the pump and the carb and when you shut down there is still pump pressure in that line and just from heat soak from the engine it will raise the temp of that fuel which raises pressure since the float valve is closed and the pump valves will not allow fuel to return to the tank. The air pocket either raised up the line or the air was absorbed by the fuel.
The line from the charcoal canister to the tank was a vapor line for the tank to vent into the charcoal canister. This line should be connected to the canister to catch the vapors from the tank. The vent for the canister is a large pipe. On different year models it went either to the outside air or to an electric valve first which connected the canister to vacuum just as the engine was shut down so as to place a vacuum to the carb float chamber via the float chamber vent line so as to stop any more fuel from leaving the jet. This was done to stop "Run-On" or "Dieseling" when a hot engine was shut down. Probably most of this system was removed when the Weber was installed.
Howard
---------- FOLLOW-UP ----------
QUESTION: I may have found my problem. I checked the timing,. and found it had jumped to 16 degrees advanced. I backed it down to 10deg and this weekend will do a test run up the hill as suggested. I also noticed that #1 plug was lean before, but trhis time I checked #4 plug and found it to be almost black from warming up the engine to check the timing.
AnswerHi Brian,
That's good you found the timing off. The black on the plug may be from warming up on the choke system. You need to drive the car a little then do the plug check again. The timing off will effect the way it runs but can not change the color of the plug, only fuel mixture can do that. Flat black from starting on the choke is normal and requires a warm up drive to burn it off and get the color set from the mixture.
Sounds like you are getting it right. Still do the plug color test though even if it seems to run right.
