A/F meter

Tech tips and how to's

Moderators: notoptoy, garth, S Allen

User avatar
cktrap
Site Supporter
Posts: 598
Joined: Sun Mar 23, 2008 8:56 pm
Location: colleyville,tx

A/F meter

Postby cktrap » Tue Oct 10, 2017 6:58 pm

I installed an A/F meter and have a question. Does the motor need to be under load to get your readings?
Thanks
Keith
'70 SRL311
'70 SPL311
'010 GMC 2500HD
'68 spl311 parts car

User avatar
Nissanman
Roadster Fanatic-Site Supporter
Posts: 2711
Joined: Mon Apr 16, 2007 8:07 pm
Location: Adelaide, South Australia

Re: A/F meter

Postby Nissanman » Tue Oct 10, 2017 8:22 pm

No, it should give the AFR all the time the engine is running.
Under load you should see a rich reading, cruise should be stoich for the fuel being used, coast should see a leaner reading.
Nissanman, just trying to help.
1965 SP310 Engine No. G-93326 Car No. SP310-10817
http://nissanman.shutterfly.com/117
McQueen!
He's on the road again!

User avatar
cktrap
Site Supporter
Posts: 598
Joined: Sun Mar 23, 2008 8:56 pm
Location: colleyville,tx

Re: A/F meter

Postby cktrap » Tue Oct 10, 2017 9:01 pm

It works all the time. The car is on jack stands. At idle I'm reading about 11. I was thinking I couldn't get a accurate reading for the upper rpm' without the engine under load.
Keith
'70 SRL311
'70 SPL311
'010 GMC 2500HD
'68 spl311 parts car

User avatar
redroadster
Roadsteraholic
Posts: 672
Joined: Tue Mar 12, 2013 10:58 am
Location: KCMO

Re: A/F meter

Postby redroadster » Tue Oct 10, 2017 9:33 pm

Any pics ?

User avatar
spyder
Roadster Fanatic-Site Supporter
Posts: 1940
Joined: Tue Apr 12, 2005 1:43 am
Location: Live Oak, TX.

Re: A/F meter

Postby spyder » Wed Oct 11, 2017 2:00 am

cktrap wrote:I installed an A/F meter and have a question. Does the motor need to be under load to get your readings?
Thanks
Keith


Is it a wideband? Mine is a simple rich / lean narrow band unit so I can see if I am running too lean pushing the motor. I have a heated 4 wire O2 sensor which takes about a minute to work.


JT68
Site Supporter
Posts: 1163
Joined: Sun Jan 27, 2013 9:43 am
Location: Cumming, GA

Re: A/F meter

Postby JT68 » Wed Oct 11, 2017 3:50 am

Depending on your bleed screw setting, you probably need to go down one or two sizes on idle jet.

With it just reving in the garage you won't be engaging the mains. The dance is getting the idle somewhat lean with adequate (not too much) enrichment off idle, under load, without introducing bog. You will likely need a co-pilot to monitor AFM as you drive varying rpm and load. Don't worry to much about instantaneous readings (accelerator pump has a huge impact there) focus on how it reads steady state in each gear, rpm, throttle position. Gradually lean things out, going too lean too fast will just make things annoying and confusing. With this, perfect is the enemy of good, the engine will be happier slightly rich, than overly lean. Its a balancing act. Also nothing is partucularly valid until things come up to temp! J
JT
talented enthusiast

User avatar
Gregs672000
Roadster Fanatic-Site Supporter
Posts: 5578
Joined: Fri Aug 07, 2009 11:47 pm
Location: Tacoma, WA

Re: A/F meter

Postby Gregs672000 » Wed Oct 11, 2017 8:52 pm

As noted, 11 is way to rich at idle. Not sure what carbs you're running, but it looks like it is not SU carbureted. For Mikini style carbs, the idle mix screw should be somewhat independent of the slow speed jet, but not completely. What does it read at say 1500-2000rpm? This is a progressive system where, as you open the throttle plates you expose more and more fuel feed holes to the vacuum side of the intake and draw more fuel. The idle screws are always on the vac side, but I do believe it draws fuel from the same circuit as the slow speed system. There is an inspection hole on each barrel right in front of the throttle plate (slotted screw) that will expose the holes and allow you to see the top of the throttle plate and its position. With the plates shut, none of the holes should be on the engine side of the plate. If they are, you're drawing fuel through the slow speed system as well as the idle.
This is what I would do...
Make sure your valve lash is correct for all cylinders. Warm it up and make sure airflow is balanced and equal for all cylinders. Carefully screw in all idle screws until they GENTLY seat (these are brass screws and distort easily, so be nice to them), counting the number of turns until they seat. Then turn each one out the same number of turns, purposely going a turn or so less that they were turned out before, then start the car. Read your meter and if way lean or too rich, adjust each one the same until your getting close to 14 on the meter (try a quarter turn each one, read the meter, etc). This can be a process, especially if the engine is rocking a bunch or way off... just keep playing. If you are not able to get it lean enough at idle, swap out the slow speed jet for one a step down and try again. Once you're fairly close at idle, increase the engine up to 1500-2000rpm and read your meter... 13.5 or so to 14.5 is probably good, other wise you probably need a different jet size in the correct direction lean or rich. Once your slow speed jet is selected, go back to your idle and do some fine adjustments a 1/4 turn at a time, one at a time, noting rpm and smoothness changes with each one. Focus on one barrel or cylinder at a time during this fine tuning. An external rpm meter is nice to have here in order to watch for minor rpm changes that can be hard to see otherwise. Turn the idle screw 1/4 turn at a time one way or the other, count to 5 to give it time to settle and note changes, adjusting until it starts dropping rpms on either end (richer or leaner) to find the middle, then move to the next barrel. Each barrel can be slightly different due to differences in each cylinder's demand, but they should be very close to each other. Once you find the best adjustment for EACH cylinder, read your meter at idle and you may find it is not where you want it, so then adjust all 4 the same amount until you're happy with your reading on the meter (can be small adjustments, but do the same for all).
In general, you want to read in the 14s at idle and cruise, 12.5 or so on acceleration with the accelerator pumps squirting and the engine under load. These values can vary depending on your cam, with likely richer mixes at idle and slower rpms with a more radical cam due to the overlap. And of course, the main system has to be jetted as well! Depending on the carbs and venturi size, they don't typically kick in until at about 3000 rpm when the engine vacuum pulls the mixture through that system. I think mine are on at about 3500rpm or so (?). I've also noted my engine tends to idle smoother in the mid 13s. It will die in the 11s!
Others may have different opinions or methods, but I hope this helps, and that you're not adjusting SUs!
Greg Burrows
'67 2000 #588
Tacoma, WA

User avatar
cktrap
Site Supporter
Posts: 598
Joined: Sun Mar 23, 2008 8:56 pm
Location: colleyville,tx

Re: A/F meter

Postby cktrap » Wed Oct 11, 2017 9:57 pm

They are solexes. The manual said 12-13 was ideal. I'm at 11.8-12.1. The car is about 2 weekends away from putting on the road so I can't check the readings under load. I'll work on it to get it leaner. I probably need to go back and set up the carbs again and be a little more patient.Here's a picture of my cam card. I did notice that my exhaust valves need to be set at 10.
Thanks for the advice. I was hoping you would chime in.
Keith
You do not have the required permissions to view the files attached to this post.
'70 SRL311
'70 SPL311
'010 GMC 2500HD
'68 spl311 parts car

User avatar
msampsel
Roadster Nut-Site Supporter
Posts: 1789
Joined: Mon Jul 14, 2014 5:31 pm
Location: SoAZ

Re: A/F meter

Postby msampsel » Thu Oct 12, 2017 6:24 pm

Hi Keith,

I noticed your cam settings are similar though slightly more aggressive than mine.

4.75” lift
260 duration

I set my wideband (lambda ha ha) at ~ 13.2.

Acceleration is as good as its ever been (after I (just recently) put Marvel mystery oil in the dashpots, SU’s). I set my lambda at 13.2 or so reading at 3000-4000 rpm. Did all this with car on jackstands and no load. Then when driven with load I noticed no difference.

Enjoy
67 1600 (Mods only a mother could love)
78 911 SC Targa (Severe Oversteer but still loved)

User avatar
cktrap
Site Supporter
Posts: 598
Joined: Sun Mar 23, 2008 8:56 pm
Location: colleyville,tx

Re: A/F meter

Postby cktrap » Thu Oct 12, 2017 6:59 pm

May have to try that. Interesting that there is not a difference.
'70 SRL311
'70 SPL311
'010 GMC 2500HD
'68 spl311 parts car

2mAn
Roadster Fanatic
Posts: 415
Joined: Mon Jan 09, 2017 5:02 pm

Re: A/F meter

Postby 2mAn » Thu Oct 12, 2017 8:36 pm

Where are you guys mounting them? I think right after the collector would be the most ideal but I guess the space is non-existent
Simon
Current Cars:
-1988 BMW 325i. The daily driver
-1968 Datsun Roadster SRL311 with Nissan Competition Package. The "someday" vintage racer

User avatar
Gregs672000
Roadster Fanatic-Site Supporter
Posts: 5578
Joined: Fri Aug 07, 2009 11:47 pm
Location: Tacoma, WA

Re: A/F meter

Postby Gregs672000 » Thu Oct 12, 2017 8:57 pm

cktrap wrote:They are solexes. The manual said 12-13 was ideal. I'm at 11.8-12.1. The car is about 2 weekends away from putting on the road so I can't check the readings under load. I'll work on it to get it leaner. I probably need to go back and set up the carbs again and be a little more patient.Here's a picture of my cam card. I did notice that my exhaust valves need to be set at 10.
Thanks for the advice. I was hoping you would chime in.
Keith

It's been my understanding that 14.7 is most efficient, I usually idle in the 13.5-14 range at home elevation, richer in the mountains. Jetting will vary a lot based in sea level, humidity and typical air temps. Regarding your cam, if the cam duration you list is at 50thousands, that's a lot of duration that will likely put the power band way up in the rpm range. May make for a rich idle too i would think. In comparison, the Racer Brown cam I'm running at the moment is 469 lift, 248 duration at 50thou (336 cam lift X 1.396 rocker ratio = 469). My preferred (I think) Isky cam is 536 lift and 246 duration at 50 thou (384 cam lift X 1.396 rocker =536). Both come on at about 3200-3500 rpms with that duration. Cam timing will make a big difference there too! :wink:
Happy to try to help!
Greg Burrows
'67 2000 #588
Tacoma, WA

JT68
Site Supporter
Posts: 1163
Joined: Sun Jan 27, 2013 9:43 am
Location: Cumming, GA

Re: A/F meter

Postby JT68 » Thu Oct 12, 2017 9:18 pm

It's a fundamentally different situation w/SU & solexes

SU's only have one metering circuit, and other than idle speed, idle mixture is the only adjustment so if the needle is right, and the idle mixture is right, everything works out.

With solexes, there are 3 circuits. Without any load the engine won't even get off the idle circuit. The pump circuit will certainly be rich at idle but may be appropriate under load

Driving under load at various rpm's speeds and gears will be needed to get it right - but that is half the fun! The AFM is much more fun than " plug cuts".
JT
talented enthusiast

User avatar
Nissanman
Roadster Fanatic-Site Supporter
Posts: 2711
Joined: Mon Apr 16, 2007 8:07 pm
Location: Adelaide, South Australia

Re: A/F meter

Postby Nissanman » Thu Oct 12, 2017 11:06 pm

2mAn, I mounted the sensor @12:00 about 60mm forward of the collector flange. The Innovate instructions say to avoid anywhere between 12:15 and 12:45 due to the likelihood of the sensor being exposed to condensation. Plenty of room in that location, right under the starter motor :)
Nissanman, just trying to help.
1965 SP310 Engine No. G-93326 Car No. SP310-10817
http://nissanman.shutterfly.com/117
McQueen!
He's on the road again!

2mAn
Roadster Fanatic
Posts: 415
Joined: Mon Jan 09, 2017 5:02 pm

Re: A/F meter

Postby 2mAn » Thu Oct 12, 2017 11:27 pm

Nissanman wrote:2mAn, I mounted the sensor @12:00 about 60mm forward of the collector flange. The Innovate instructions say to avoid anywhere between 12:15 and 12:45 due to the likelihood of the sensor being exposed to condensation. Plenty of room in that location, right under the starter motor :)



Hmm I never thought about mounting it further upstream of the collector. Does it end up in a single cylinders runner?

Sorry, I dont mean to derail the thread. I do think this is fairly relevant, but I can stop if the OP wants me to
Simon
Current Cars:
-1988 BMW 325i. The daily driver
-1968 Datsun Roadster SRL311 with Nissan Competition Package. The "someday" vintage racer


Return to “Tech Discussions”

Who is online

Users browsing this forum: No registered users and 0 guests

Datsun Roadster Forum-311s.org : Disclaimer