Alfa Romeo Forums banner

1 - 20 of 30 Posts

·
Registered
Joined
·
28 Posts
Discussion Starter #1
Hi,

After camshaft changed and many hours trying to set the weber DCOE right, I finally decided to stop the guess work and purchase a Wide-Band AFR meter. The good news: I was correct when i sensed that I was running too rich when Main Circuit come into action (AFR of 10.9 to 11.1). Idle circuit seems reasonably rich (13.2 to 13.8), and WOT seems also quite nice and pulls strongly with 13.3 to 12.6. So it seems the solution is to delay the moment the main circuit come into action. To do so, I installed a smaller pump jet (30 instead of 35), and it make it a bit better, but I'm still at about 11.2 at transition phase. I have heard that a smaller Air Correction jet would delay main circuit action (which seems weird as I expected the opposite...).

Does anybody have a magic trick to delay Main Circuit action (other than closing progression holes as I'm quite reluctant messing with this). E.Tubes maybe... (BTW I drilled 2 2mm holes at the top of my F9 and it seems also a bit better)

thank you
 

·
Push hard and live
Joined
·
8,982 Posts
Try Keith Franck’s VF tubes, or whatever he’s calling them now.
 

·
Super Moderator
Joined
·
11,246 Posts
Try F-16 E-tubes with correctly set float level. Don't mess with pump circuit. #35 jets, normal (short) pump rods and 45 to 55 pump exhaust jets or bleed back. You did not mention Weber type or size, but 3 prog hole bodies with transition a bit leaner than 2 prog hole bodies. DON'T mess with the prog holes! Easy way to ruin a body.
If you are running 45DCOE's you likely may have the notched plates installed to access progression holes early. Not necessary on 40mm. If you have old large top 45's, they may have non-notched plates, but will have larger 2 prog hole bodies to compensate. Mis-match here of plate and body type prog holes will cause everlasting headaches.
The F-16 E-tubes are NOT always "best" but do allow greater flexibility in fuel level mixture changes and slosh in corners. Once CLOSE with F-16, you can try others, but most stay with them and call it good enough. This IS NOT electronic FI and mixtures WILL and always have varied with Webers.
This is only my opinion from my own experience.
 

·
Premium Member
Joined
·
13,160 Posts
Were the tests done at part throttle or WOT?
Idle jets have very little effect at WOT, even at low rpm.
Main jets and emulsion tubes have significant effect at part throttle. Air correctors have little effect at part throttle but they influence the full range at WOT
 

·
Registered
Joined
·
28 Posts
Discussion Starter #5
Try F-16 E-tubes with correctly set float level. Don't mess with pump circuit. #35 jets, normal (short) pump rods and 45 to 55 pump exhaust jets or bleed back. You did not mention Weber type or size, but 3 prog hole bodies with transition a bit leaner than 2 prog hole bodies. DON'T mess with the prog holes! Easy way to ruin a body.
If you are running 45DCOE's you likely may have the notched plates installed to access progression holes early. Not necessary on 40mm. If you have old large top 45's, they may have non-notched plates, but will have larger 2 prog hole bodies to compensate. Mis-match here of plate and body type prog holes will cause everlasting headaches.
The F-16 E-tubes are NOT always "best" but do allow greater flexibility in fuel level mixture changes and slosh in corners. Once CLOSE with F-16, you can try others, but most stay with them and call it good enough. This IS NOT electronic FI and mixtures WILL and always have varied with Webers.
This is only my opinion from my own experience.
Thanks Gordon,

F16 were original on my carb. Actually my 2000 is ruining with 40 DCOE form a 1600 engine (43/44, 3 progression holes), and that’s why I suspect a progression or early main circuit start. Earlier today, I tried smaller main jets (125) with a big air corrector (210) as a benchmark. It does help a bit with an AFR of 11.5 around 2000 rpm, but I still need much less fuel. Maybe the solution is new carbs...
 

·
Registered
Joined
·
28 Posts
Discussion Starter #6
Were the tests done at part throttle or WOT?
Idle jets have very little effect at WOT, even at low rpm.
Main jets and emulsion tubes have significant effect at part throttle. Air correctors have little effect at part throttle but they influence the full range at WOT
Part throttle is a bit rich, but not too bad. I have the issue at WOT. If air correction has a little effect, I’ll try to drill a couple of 1mm holes at the top end of the E.Tube and see if it leans the mixture...
 

·
Super Moderator
Joined
·
11,246 Posts
Lets go back. Which DCOE's? 40 or 45? Which engine? Which cams?
 

·
Premium Member
Joined
·
13,160 Posts
There is no transition on WOT except when you first step on the peddle. In my experience is that when you step on the gas at a bit less than 3000 rpm the AFR is very briefly all over the place and that is influenced by the accelerator pump set up. Then it is pretty lean and it gradually gets richer until about 4600 rpm and then it leans out to the AFR that you have set with the MJ/AC combination that you have selected for max power. The rich dip is influenced by both the MJ and the emulsion tube but you cannot get rid of it by tuning the carbs. Search on my 78 spider on the dyno revisited thread and you will see what I did to minimize the rich dip. Progression holes and idle jets have little or no effect when the throttle is wide open.
 

·
Registered
Joined
·
28 Posts
Discussion Starter #9
Lets go back. Which DCOE's? 40 or 45? Which engine? Which cams?
Engine is the 2000, but carbs are the Weber 43/44 from the 1600. I got the cams from Alfaholics in uk, but these are actually catcams:
exhaust: http://www.catcams.com/products/camshafts/datasheet.aspx?ENGINE_id=4&CAMSETUP_id=39&Language=english
intake:http://www.catcams.com/products/camshafts/datasheet.aspx?ENGINE_id=4&CAMSETUP_id=40&Language=english
jetting, I have 50F4 for idle, 125 main jets, F9 e.tubes, 210 air correctors, and 30 pump jets.
besides this rich spot at WOT at 1900-2500 rpm, it works quite well
 

·
Premium Member
Joined
·
13,160 Posts
You are expecting a lot to have well controlled AFR at WOT below 2500 rpm. Flatten it in a lower gear then upshift.
 

·
Super Moderator
Joined
·
11,246 Posts
Always remember Webers were REPLACED by FI. EFI can actually do a better job than Webers. That says a whole lot of really good things about the Weber 40/45DCOE design.
 

·
Registered
Joined
·
28 Posts
Discussion Starter #12
Always remember Webers were REPLACED by FI. EFI can actually do a better job than Webers. That says a whole lot of really good things about the Weber 40/45DCOE design.
Yep, I might have been spoiled by modern engines with EFI :) ... I did try the car again with 125 MJ and 210 AC, and it's not so bad now. I navigate around Lambda .0.94 (3000 rpm) to 0.92 (4000 to 6000rpm).1900 to 2400 still around 0.81 but at least the engine is not drowning as it used to. I'll still try to drill another 1mm hole at the top of my tube. at least it will give me a reference point...
 

·
Registered
Joined
·
28 Posts
Discussion Starter #13
You are expecting a lot to have well controlled AFR at WOT below 2500 rpm. Flatten it in a lower gear then upshift.
Do I? :)

Yes, it might be me trying to replicate EFI too much. But the engine behavior was quite frustrating as pulling strongly from idle, than suffocating between 1900-2400rpm, and pulling strongly again from 2500. It's a bit better now as I can still cruise below 2500. I'll still try Emulsion tube drilling (1 more 1mm hole) to see the difference
 

·
Super Moderator
Joined
·
11,246 Posts
You and Ed are doing VALUABLE research into changes others may try. Keep it up. When customers ask me which way to go on set up, both of your collected BB input becomes a useful resource!
 

·
Registered
Joined
·
28 Posts
Discussion Starter #15
You and Ed are doing VALUABLE research into changes others may try. Keep it up. When customers ask me which way to go on set up, both of your collected BB input becomes a useful resource!
So you are a professional? Are you selling/rebuilding classic cars? If you have a website, I'd love to have a look at it
 

·
Premium Member
Joined
·
13,160 Posts
I have done around 90 dyno pulls on 2L Nords with Webers. The protocol is to bring it to 3000 rpm in 3rd gear then floor it. There is a little initial hesitation and then it pulls properly and provides good data. That is also the method that I used in more than 100 road tests except that i floored it at about 2700 rpm in 3rd gear on an uphill road. That is how I got to 190 HP from the current motor. Trying this out at 2500 or less would probably stall the motor.

I have modified emulsion tubes and posted the results but that was done after I was certain that everything else was optimum. I would not start modifying E-tubes until I was confident that I had the best combination of main jet and air corrector for the currently installed E-tubes.
 

·
Super Moderator
Joined
·
11,246 Posts
YES!
1604345
 

·
Registered
Joined
·
28 Posts
Discussion Starter #18
First, thanks to the both of you for your very relevant and valuable inputs. As a non professional it's always difficult to understand what's possible to do, and what's the normal behavior for an engine. If I got you correctly, it's quite usual to get a flat spot at before 2500 rpm, and there is not much to do about it. As I mentioned earlier, It's now much better with smaller MJ and bigger AC. I also noticed a better acceleration and top speed on my favorite uphill road. For the moment, I got the best results from 3000 to 6000rpm with a lambda of 0.9 - 0.93 at WOT.

I want to set the car for fast road use, not for track. I'm not really interested in high end power, but good drivability along with decent ability to rev. The cams from Alfaholics in UK were a bit expensive, but give a very good compromise between torque at low rev, and power at mid/high rev. Back to the richness at 1900-2400 rpm, I noticed I'm also a bit rich on small opening to mid throttle (about L 0.85). I'll still need to try drilling a 3rd hole at the very top of E.tube to see if there is an improvement without leaning higher rev too much. Worst case scenario, I can close the new holes with epoxy (BTW, I find this info on a video of David Vizard (
). Anyway I have got a second set of F9 ETubes to make my tests.

Last thing, what lambda would you recommend on small to mid throttle openings? I'm currently around 0.95
 

·
Premium Member
Joined
·
13,160 Posts
I have not seen performance data related to Lambda. Everyone I know uses AFR. Anything between 12 and 13.5 is decent and 12.5 to 13.2 is good. Below 11 and above 14 will noticeably reduce torque. Maybe you can convert the numbers?
 

·
Registered
Joined
·
28 Posts
Discussion Starter #20
I have not seen performance data related to Lambda. Everyone I know uses AFR. Anything between 12 and 13.5 is decent and 12.5 to 13.2 is good. Below 11 and above 14 will noticeably reduce torque. Maybe you can convert the numbers?
Lambda 1 is the stoichiometric point, so if you multiply Lambda by 14.7, you get AFR. I'm running between 13.2 and 13.7 WOT, so I'm probably a bit lean... As I don't want to melt my pistons, I probably should enrich it a bit
 
1 - 20 of 30 Posts
Top