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Just go down one size on air correctors
 

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Richard doesn't believe in safety margin;)
 

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Discussion Starter #24
😄 yes, i prefer losing 4hp than melting 4 pistons... actually since we’re on the topic: on idle, I’m at 12.6 AFR. but when driving downhill with throttle closed at about 3000rpm, it goes at 14.6 to 14.8... Do you think this can harm my engine, or is it normal? I tried open richness screws, but no effect
 

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Discussion Starter #25
OK, update on today's test: As you suggested I went down 0.1 (200 instead of 210) with air correctors with decent results: between 12.4 to 13.3 WOT. I have no noticeable enrichment at 1900-2500 rpm half throttle (still 11.7-12.2 though), and drivability is quite good now. Able to cruise at 35mph on 5th gear, 30 on 4th with smooth engine response. than it pulls strongly from 2500.

I'll keep on fine tuning, especially trying to drill this 3rd hole at the top of my E. tubes. I'm curious to see if it will be leaning the mix only at the bottom of main circuit range, or on the whole range. I'll let you know.
 

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but when driving downhill with throttle closed at about 3000rpm, it goes at 14.6 to 14.8... Do you think this can harm my engine, or is it normal? I tried open richness screws, but no effect
Those numbers are fine at anything other than high power. In fact they are good at low throttle openings if you want to improve fuel consumption.
 

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Discussion Starter #28
very interesting... So it seems that the main effect is a lower RPMs (at least on F16, which have holes only at the bottom - Actually stock F9 already have 2X1mm holes at about 3mm, so maybe the effect of 2 new ones is not as dramatic). I would have bet it would affect the whole RPM range. I drilled mine 2X1mm holes at the very top, right under the collar under the jet holder as I really wanted to lean and/or delay main circuit. I think now it's probably a bit too high... I'll do a few test (if the snow is not coming before the end of the month) with stock F9, then with modified ones
 

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I looked at a David Vizard tutorial about drilling holes and what he said corresponds with what is in John Passini's books. Holes at the top weaken the low end and holes further down weaken at higher rpm. What you don't know without experimenting is what distances correspond to what rpm.. I guessed at 3.4 mm and then moved to 3.9 mm to weaken at 4700 rpm.
F9's may look similar to F11 but they are different internally. Look at the Weber engineering drawings for them. I tried F9's and they did not work well in my motor. They ran too lean at the top and I had to fit bigger main jets which resulted in being too rich lower down. I am able to run smaller main jets with F16's. Plus one of my friends flew F16's :)
 

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Discussion Starter #30
I looked at a David Vizard tutorial about drilling holes and what he said corresponds with what is in John Passini's books. Holes at the top weaken the low end and holes further down weaken at higher rpm. What you don't know without experimenting is what distances correspond to what rpm.. I guessed at 3.4 mm and then moved to 3.9 mm to weaken at 4700 rpm.
F9's may look similar to F11 but they are different internally. Look at the Weber engineering drawings for them. I tried F9's and they did not work well in my motor. They ran too lean at the top and I had to fit bigger main jets which resulted in being too rich lower down. I am able to run smaller main jets with F16's. Plus one of my friends flew F16's :)
It's funny as F9 seemed to work much better on my engine... It may be because I had 1600 cc carbs on a 2000. That said I didn't have AFG gauge at the time. I may try those one again
 
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