mailman wrote:
I'm having a bit of an odd-ish (to me) fuelling issue.
I have changed to a BBB needle, which is now providing quite a nice AFR ratio in the mid range and at cruise, and at wot it is also pretty good... that is, until about 4500-5000rpm, at this point it starts to lean out quite a bit. The weird thing about it is that it leans out up there regardless of whether I'm using what or 3/4 throttle.
Can anyone provide any insight into the possible cause of this?
the engine's demand for air is what sucks the piston open, the butterfly is there to limit how much air it's actually getting. With a big carb, there's not really a lot of difference between how much the engine can get through the carb between WOT and 3/4 throttle
mailman wrote:
And a possible solution? I am looking at either a BAZ or BAL needle, but they both then lean out that mid range again. I could possibly get another BBB needle and alter the final stages to provide more fuel. I'm just a little confused that it's a engine revs thing not a throttle position thing.
you could also look at a BDG, it looks leaner than BBB at low & cruise openings, but wind the jet down a bit to put it in the same low & cruise range as your BBB, and you'll get richer at the bigger openings
http://www.morrismini.com/SUNeedlesV2.a ... &size=.100mailman wrote:
I've also changed to NGK BP6ES's, and they are definitely less sooty than my 7's, they are still a little black after. I get the feeling that my idle mixture needs leaned out a touch, but that's hard to get right in conjunction with the rest of the range.
7's shouldn't have been in there in the first place - 6's are the starting point, I use 5's
mailman wrote:
Needles I'm also considering are:
BBZ and BCJ, with the BCJ actually being the fore-runner at this point. I am nervous about what the effect of adding all of that extra richness in at the 3/4 ish range will be.
BCJ looks the opposite of what you want....
I'd sand a little off the tip of your BBB if I was you.
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