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 Posted: Sep 7, 2017 04:05AM
Total posts: 6561
Last post: Sep 21, 2017
Member since:May 23, 2002
3 in 1 works good for thin oil, but what I've found that works best for me is Automatic Transmission Fluid.

"Retired:  No Job, No Money, Wife and I!  Will travel anywhere for Minis"

hockey91dad@hotmail.com

 Posted: Sep 6, 2017 09:09PM
Total posts: 842
Last post: Sep 20, 2017
Member since:Jul 15, 2008
US
Quote:
Originally Posted by helpmymini
the oil is so easy to change, why don't you just experiment with everything from brake fluid to gear lube?
Yeah, that's the plan. I currently have 20w50 motor oil in the dashpots. I have an unopened quart of Marvel Mystery Oil—thought I'd try that. It looks to be pretty thin. 

 

Michael, Santa Barbara, CA

. . . the sled, not the flower

      Poser MotorSports

 Posted: Sep 6, 2017 06:01PM
Total posts: 3795
Last post: Sep 18, 2017
Member since:Apr 26, 2005
the oil is so easy to change, why don't you just experiment with everything from brake fluid to gear lube?

Mark Looman, Ada Michigan 1967 Austin Cooper S
 Posted: Sep 5, 2017 03:29PM
 Edited:  Sep 6, 2017 09:00PM
Total posts: 842
Last post: Sep 20, 2017
Member since:Jul 15, 2008
US
 
 
Originally Posted by croc7
If your hesitation is from what you have diagnosed as an overly rich condition, wouldn't a thicker oil aggravate the flat spot?
Oops. Right you are.
I am in fact dyslexic—I read at about the 4th grade level, but I can't blame this one on dyslexia. More like just plan lameness.

Years ago when I bought my first GPS unit I changed the default voice from "American Guy" to "British Gal." Although some of her terms were a little hard to interpret; parkway for highway, throughway for boulevard, etc., I found her voice charming... until I rented a car in Washington DC and she said "You are about to enter a roundabout. Please enter in a counter-cyclonic direction." Wait, what?! That was the end of British Gal.

 

Michael, Santa Barbara, CA

. . . the sled, not the flower

      Poser MotorSports

 Posted: Sep 5, 2017 03:10PM
Total posts: 842
Last post: Sep 20, 2017
Member since:Jul 15, 2008
US
Quote:
Originally Posted by croc7
If your hesitation is from what you have diagnosed as an overly rich condition, wouldn't a thicker oil aggravate the flat spot?
Oops. Right you are.

 

Michael, Santa Barbara, CA

. . . the sled, not the flower

      Poser MotorSports

 Posted: Sep 5, 2017 11:31AM
Total posts: 7253
Last post: Sep 22, 2017
Member since:Aug 14, 2002
CA
Quote:
Originally Posted by croc7
If your hesitation is from what you have diagnosed as an overly rich condition, wouldn't a thicker oil aggravate the flat spot?
Yes. Heavier oil slows the rise of the dashpot and the vacuum draws more fuel.

.

"Hang on a minute lads....I've got a great idea."

 Posted: Sep 5, 2017 10:46AM
Total posts: 616
Last post: Sep 20, 2017
Member since:Aug 15, 2002
US
If your hesitation is from what you have diagnosed as an overly rich condition, wouldn't a thicker oil aggravate the flat spot?

 

"To catch one, you need one"....John Cooper

 Posted: Sep 2, 2017 02:41PM
Total posts: 842
Last post: Sep 20, 2017
Member since:Jul 15, 2008
US
Quote:
Originally Posted by Alex

"Truly in tune" - checked on a rolling road or with a wideband lamba sensor in the exhaust system ?
Nope, no dyno. Just following Haynes' instructions. 

Quote:
Originally Posted by nkerr

...but you can narrow it down by being systematic, keeping notes, and seeing which helps, and gradually fine tune it, it just takes a lot more steps when you don't have much data to work with (other than feel, or by reading the spark plug colors).

I was pretty systematic. Not my usual MO. As a result I think I have it narrowed down—at least as best I can w/o a dyno. 

 
Originally Posted by nkerr

Dashpot oil:  thinner viscosity allows it to rise faster, allowing more air and less fuel during acceleration (leans it out).  Thicker does the opposite.

That's what I was looking for. I'll start with slightly thicker oil as the initial hesitation seems to me to be a slightly over-rich condition. Not going to mess with a different needle. The needles were selected by my engine builder as were the settings on my 123 dizzy. Gonna leave well enough alone. This flat spot I'm experiencing is really rather minor. Thanks for everyone's help. Will advise.

 

Michael, Santa Barbara, CA

. . . the sled, not the flower

      Poser MotorSports

 Posted: Sep 2, 2017 01:15PM
Total posts: 3628
Last post: Sep 12, 2017
Member since:Jun 23, 2000
US
My question was just for general knowledge. I am curious what AFR they targeted at idle for a "bog standard car with the correct needle fitted."

I admit it is a lot easier looking at a lambda reading when adjusting the idle setting. My current issue is that with distributor less ignition, my idle is hunting slightly which makes the lift pin check method non-functional.

Although today in the 105 F heat, there was little hunting at the stop signs.
Terry

 Posted: Aug 29, 2017 01:54PM
Total posts: 9445
Last post: Sep 22, 2017
Member since:Mar 24, 1999
GB
Using the lifting pin only works with a completely bog standard car with the correct needle fitted - away from that state of tune, the mixture will only be correct at idle.

Metric is for people who can't do fractions...

 Posted: Aug 29, 2017 10:29AM
Total posts: 3628
Last post: Sep 12, 2017
Member since:Jun 23, 2000
US
Not exactly on topic, but when an SU is properly tuned by the lifting pin method what should the lambda reading be?
What change would be expected in lambda when lifting?

Terry

 Posted: Aug 29, 2017 06:08AM
Total posts: 7174
Last post: Sep 21, 2017
Member since:Feb 7, 2006
If you have fixed needles in your carbs make sure the jets are centered correctly as one or both of them could be sticking slightly. To check just loosen up the dashpot damper so there is no resistance and lift the pistons they should move easily, when they drop there should be a clunk then you know they are centered.
If you think your needle may be on the weak side to test it loosen up the needle and move it up into the piston slightly so the needle will be running slightly richer then take a look at needle charts mintylamb.co.uk is a decent one to use.
You could also test it with the choke slightly out to see if that improves things.
If you have the newer swinging needles they self center.
As pointed out by Alex and Norm you may need to get a wide band sensor or a session on a rolling road.

If in doubt, flat out . Colin Mc Rae MBE 1968-2007.

 Posted: Aug 29, 2017 02:52AM
Total posts: 615
Last post: Sep 21, 2017
Member since:Sep 24, 2011
as Alex pointed out, without measuring the mixture at each throttle position it is just guesswork, but you can narrow it down by being systematic, keeping notes, and seeing which helps, and gradually fine tune it, it just takes a lot more steps when you don't have much data to work with (other than feel, or by reading the spark plug colors).


Dashpot oil:  thinner viscosity allows it to rise faster, allowing more air and less fuel during acceleration (leans it out).  Thicker does the opposite.

Needle tuning:  the needle has 1/8" increments of diameter change, allowing you to fine tune WHERE in the throttle stroke you richen or lean the mixture.

Ignition timing:  adjusting the mechanical advance by spring strength or by weight shape moves the spark advance up or down the rpm range, helping the engine use the fuel it gets most efficiently.


N

 Posted: Aug 28, 2017 10:29PM
Total posts: 9445
Last post: Sep 22, 2017
Member since:Mar 24, 1999
GB
"Truly in tune" - checked on a rolling road or with a wideband lamba sensor in the exhaust system ?

Metric is for people who can't do fractions...

 Posted: Aug 28, 2017 06:58PM
Total posts: 842
Last post: Sep 20, 2017
Member since:Jul 15, 2008
US

I’ve synced and adjusted my twin SUs and I think I’ve finally got them dialed in. The motor idles well, pulls strong and the plugs look great. There’s just… one… little… thing. I’m getting a slight hesitation—a flat spot, so to speak, right at the bottom of each shift under light throttle pressure. Most people unfamiliar with my car probably wouldn’t even notice. The hesitation lasts only a split second and doesn’t occur at all under hard acceleration. Perhaps I’m noticing now only because the carbs are truly in tune, mixture-wise.

 

Seems to me I read somewhere that this kind of flat spot is most likely related to the dashpot oil. I can’t recall if I should try increasing or decreasing the viscosity. Which is it? Thanks!

 

Michael, Santa Barbara, CA

. . . the sled, not the flower

      Poser MotorSports