Page 1 of 2 12 LastLast
Results 1 to 10 of 18

Thread: Recommended CO level/range for 2.7 RS Engine?

  1. #1

    Recommended CO level/range for 2.7 RS Engine?

    What is the recommended CO setting for a 2.7 RS spec engine with MFI? Mine is measuring 3.5% @ approximately 2500 rpm and 2.25% at idle. At these settings I'm getting some slight surging between 2000 rpm and 3200 rpm. I'm thinking I should adjust the part throttle fuel mixture setting on the MFI pump to richen the mixture more, but I have a CO meter, so thought I'd ask the experts what level I should set it at? Otherwise I guess I'll just keep adjusting it richer one click at a time until the surging goes away.
    Last edited by 73ess; 02-06-2018 at 11:41 PM.

  2. #2
    # 2991
    Join Date
    Feb 2012
    Location
    Edmonton
    Posts
    289
    Here's the specs from the Porsche MFI check measure adjust manual
    Looks like you might need to lean the part load and richen the idle

    Name:  image.jpg
Views: 315
Size:  24.0 KB

  3. #3
    My experience has been that although we used to use the factory C/O numbers, that they only worked because we had real gas at that time. We have found that with today's corn syrup idle C/O settings have to be in the 6% range.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  4. #4
    Title corrected...interesting topic!
    Peter Kane

    '72 911S Targa
    Message Board Co-Moderator - Early 911S Registry #100

  5. #5
    Thanks Ed. Good to know! So I will adjust the part throttle mixture screw setting to the 6% range. What should the CO setting be at idle speed? I'm assuming that the spring loaded idle mixture screw adjusts the CO setting at idle speed, but my experienced Porsche mechanic tells me that he usually doesn't touch the idle mixture screw on MFI pumps. In his experience it doesn't have much affect on CO values. He says the part throttle mixture screw will adjust/affect the CO setting both at idle AND part throttle.

    On a somewhat related note. What is the proper CO setting(s) for a 73.5 911T with CIS injection? Do I measure at idle speed AND part throttle as well?

    Quote Originally Posted by edmayo View Post
    My experience has been that although we used to use the factory C/O numbers, that they only worked because we had real gas at that time. We have found that with today's corn syrup idle C/O settings have to be in the 6% range.

  6. #6
    The 6% number is the idle setting, adjusted with the spring loaded idle mixture screw. The load setting is another matter, a no-load setting for that range was usually in the 9% range, which would equate to around 3-4% under load (full throttle 3rd gear). While it's correct that adjusting the load screw (rack adjustment) will affect BOTH idle and load, and the idle screw will ONLY affect idle, as to which you adjust depends on which range you're trying to correct. Normally the procedure is drive and adjust the load setting, then finish up with the idle setting, since that won't affect the load setting.
    73 CIS will need about the same idle percentage, but there is only ONE adjustment, which affects all ranges.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  7. #7
    Banned
    Join Date
    Nov 2004
    Location
    Scottsdale, AZ
    Posts
    9,752
    6% idle CO for CIS?
    Say what?!

    Think you'll find HC off the chart with a number like that.
    With all due respect to Ed, try half that.

  8. #8
    I might have been a little "heavy"on that, but point is today's fuels don't necessarily work with previous settings. You have to set the numbers for what "works" and not be tied to what previously worked.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  9. #9
    Senior Member 210bhp's Avatar
    Join Date
    Feb 2004
    Location
    Scotland
    Posts
    2,037
    My RS runs at about 7% at idle without any mid range surge or flat spots and returns close to 25mpg on a very long (Contenental) trip so I’m sure combustion must be close to optimum at the current mileage (180000 kilometres) with a top end rebuild 40000km ago.

    Regards
    Mike
    Last edited by 210bhp; 02-06-2018 at 06:32 AM.
    RS#1551(sold)
    67S
    73E (home after 25 years) and sold again
    Early S reg. #681

  10. #10
    Banned
    Join Date
    Nov 2004
    Location
    Scottsdale, AZ
    Posts
    9,752
    Quote Originally Posted by edmayo View Post
    You have to set the numbers for what "works" and not be tied to what previously worked.
    Dat's a fact.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Message Board Disclaimer and Terms of Use
This is a public forum. Messages posted here can be viewed by the public. The Early 911S Registry is not responsible for messages posted in its online forums, and any message will express the views of the author and not the Early 911S Registry. Use of online forums shall constitute the agreement of the user not to post anything of religious or political content, false and defamatory, inaccurate, abusive, vulgar, hateful, harassing, obscene, profane, sexually oriented, threatening, invasive of a person's privacy, or otherwise to violate the law and the further agreement of the user to be solely responsible for and hold the Early 911S Registry harmless in the event of any claim based on their message. Any viewer who finds a message objectionable should contact us immediately by email. The Early 911S Registry has the ability to remove objectionable messages and we will make every effort to do so, within a reasonable time frame, if we determine that removal is necessary.