My latest obsession is fuel delivery and I'm wondering if anyone knows the best pressure range for FCR carbs? And would it be different for CV carbs and why?
Anybody? Chris?
If you want to know what an old painter thinks...
pressure is very secondary to volume in this instance.
I've got volume covered, but, as I said, it's my lastest OBBSESION, so I have to know more, and more, and more, and..............
I cannot imagine the optimal pressure being any higher than 3-5 lbs. They are still carbs and thus require very little pressure. Gravity is really more than enough given a large enough supply line.
But in reality you already know this Norm so.........? why the question?
3-5 is what I've been assuming, but I don't have a lot of experience with the numbers and was hoping someone had done more work in this area. I've run a number of bikes with only a gravity feed and never had a problem, but, of course, the fuel pressure will go down as the tank empties and I've never used a gauge.
I'm going to set a bike up with an electric fuel pump, a pressure regulater, and a gauge so I can do some experimenting. I'll probable limit the testing to FCR carbs though.
FCR's -- 3.5psi is what I'm using for years.
Pumps -- three options:
1) self-regulated electric. Thus only one fuel line required. (I've done this for 14 Ducati's)
2) non-regulated electric with return line to tank. Best for volume demand while racing.
3) High volume vacuum. (just did for my DesmoDevil to try something different)
note: Never was impressed by the factory vacuum pump -- I've had fuel volume delivery problems with it and it sucks having to back off the throttle when the carbs are starving.
note: Gravity feed isn't an option as my fuel pickup is lower than the carb's -- fuel doesn't flow up hill very well.
Quote from: ducpainter on August 06, 2009, 04:13:47 PM
If you want to know what an old painter thinks...
pressure is very secondary to volume in this instance.
As long as you stay under 7psi. Any more and you chance overpowering the needles and floats. No FHP with FCR's just general to carbs.
I'm sticking with Mark's #1 for starters. I've never had a fuel starvation problem but I want to see what minor pressure changes do for throttle response and sustained high rpm. I hope to be able to test at some speed tracks like Daytona but I don't know yet.
As some of you know, I'm developing a new motor and while I don't mind buying down a couple of stockish Duc motors, the new ones are going to be waay too expensive for me to use as "throwaways".