Weber questions for basic tuning - Page 2

Mark Henry · 08-07-2019, 02:36 PM

Cool thanks Paul, I can live with the rich idle. what would you aim for for AFR? Or is 12.5:1 good?
I know aircooled like things a bit rich, but my big T4 with nickies and EFI tolerates 13.5 just fine.

1QuickS · 08-07-2019, 03:39 PM

Well, peak HP is 12.5 to 12.7. Jet to be as lean as possible without affecting driveability, cruise can be lean but you want richer mixture under power. Play with jetting, your engine will tell you what it wants.

juanbenae · juanbenae's Garage

Quote:

Originally Posted by Mark Henry

Cool thanks Paul, I can live with the rich idle. what would you aim for for AFR? Or is 12.5:1 good?
I know aircooled like things a bit rich, but my big T4 with nickies and EFI tolerates 13.5 just fine.

if your are getting 12.5 at flat idle with no drivability issues that is spectacular! the best ive been able to do at flat idle is mid 10's to low 11's depending on ambient temps with the 60 idles. I went down to 55's and was able to get mid 11's to low 12 AF numbers at flat idle, but the thing would not hardly run when on the idle circuit with much popping, coughing and bucking.

with the 160 mains im right about where paul suggests the sweet spot to be at low to high 12's under hard acceleration. I did have a momentary lean spike at one time when going from the idle to main during heavy acceleration that was so brief there was not even any noticeable flat spot in the power range. I got that cured none the less with the "hatchet" accelerator pump activation lever that is discussed in a number of carb threads the last couple years. the improvement has to do with the shape of the part and how it effects the activation of the AP and duration. there are a number of good reads on it if you were to search "hatchet". as I reall all the PMO carbs now are equipped with the part it's such an improvement.

the rich condition freaked me out at the onset, but after much research, reading of plugs, monitoring AF in real time ive learned to live with it. in fact ive recently moved from sea level to a 4000' foot elevation and having driven it to 6k feet and points above the changes in AF were not as drastic as id expected. it still needs some attention and the hotter weather is contributing but I am between homes and have no decent work space with all my tools in storage. fortunate to have a small one car garage to even keep the car in at this point.

good luck, and keep us posted. although if you are at 12.5 AF at idle and can drive it with out spitting and coughing you are light years ahead of me,,,

Mark Henry · 06:45 PM

Quote:

Originally Posted by 1QuickS

Well, peak HP is 12.5 to 12.7. Jet to be as lean as possible without affecting driveability, cruise can be lean but you want richer mixture under power. Play with jetting, your engine will tell you what it wants.

Paul I want to thank you, back 3 years ago during the rebuild of my IDA's I read and followed your tech articles religiously.

I'll take your advice, leave it alone for now and maybe play with it once my head temp gauge (Micro 1000) is installed.

Quote:

Originally Posted by juanbenae

if your are getting 12.5 at flat idle with no drivability issues that is spectacular! the best ive been able to do at flat idle is mid 10's to low 11's depending on ambient temps with the 60 idles. I went down to 55's and was able to get mid 11's to low 12 AF numbers at flat idle, but the thing would not hardly run when on the idle circuit with much popping, coughing and bucking.

with the 160 mains im right about where paul suggests the sweet spot to be at low to high 12's under hard acceleration. I did have a momentary lean spike at one time when going from the idle to main during heavy acceleration that was so brief there was not even any noticeable flat spot in the power range. I got that cured none the less with the "hatchet" accelerator pump activation lever that is discussed in a number of carb threads the last couple years. the improvement has to do with the shape of the part and how it effects the activation of the AP and duration. there are a number of good reads on it if you were to search "hatchet". as I reall all the PMO carbs now are equipped with the part it's such an improvement.

the rich condition freaked me out at the onset, but after much research, reading of plugs, monitoring AF in real time ive learned to live with it. in fact ive recently moved from sea level to a 4000' foot elevation and having driven it to 6k feet and points above the changes in AF were not as drastic as id expected. it still needs some attention and the hotter weather is contributing but I am between homes and have no decent work space with all my tools in storage. fortunate to have a small one car garage to even keep the car in at this point.

good luck, and keep us posted. although if you are at 12.5 AF at idle and can drive it with out spitting and coughing you are light years ahead of me,,,

Except for normal warm up time you would think it was FI.
No coughs, transitions, flat spot, nada. Totally smooth torque curve, press it a little and it drives like a grocery getter, press it hard and it roars to life.

Only bad is it's a thirsty bugger compared to the old 1.8 T4 engine (914 conversion), but some of that could be the operators foot.

If you have the carbs sorted and still have coughing and spitting it's often a linkage issue, the stock weber linkage ball joints were sloppy. I made new drop link rods bent (one is straight, 4-6 drop link is S bent) to push at a 90* angle to the throttle shafts and used 1/4" ball rod ends, like the pic below but I cut off the rubber seal. Then I was extra careful making sure both carbs opened perfectly equal from idle to WOT. Since the ends I use are only RH thread you have to tweak the drop links or crossbar arm ends to do the fine adjustments
I have a lot of experience with linkage/sync issues with the aircooled bugs (my background) and have been building custom linkages for over 20 years, because I got tired of the crappy hex bars.

The Money shot

you can see the one drop link.

1QuickS · 08-08-2019, 10:25 AM

I recommend an easy, side-to-side balancing on my site but synopsis is this:

check that throttle cross bar is blueprinted in that the 8mm ball studs are co-planar with axis of the tube (use flat surface and four, same-sized hex nuts as height gauges to level cross bar and then to check for ball studs being at same height from the work surface)
set drop links to same length
use hand throttle or home made, adjustable link between cross bar and bell crank at cylinder #3 to set engine speed to 2000 to 3000 RPM (this replicates linkage action while driving and removes all clearance errors in the linkages)
loosen the two nuts securing the cross bar bracket at cylinder #5 just enough to allow it to move
the clearance in the bracket's mounting holes allows to adjust side-to-side balance without adjusting drop links, tap bracket in forward/rearward direction at its top where the large, threaded ball stud is located and monitor side-to-side air flow readings
if you do not get all the adjustment needed to balance air flows by moving bracket at #5 cylinder then tighten it and repeat adjusting procedure using bracket at #2 cylinder.
once you have tried this you will not do it any other way.