Results 1 to 10 of 10

Thread: RPM is dropping from 1,100 to 600-500

  1. #1
    Registered User
    Member ID
    CZCC-29967
    Join Date
    Dec 2013
    Location
    Panama
    Age
    43
    Posts
    157

    Default RPM is dropping from 1,100 to 600-500

    Took my 240z for a spin yesterday and got into heavy traffic. RPM mantained at 1,100 in light traffic but once i started going bumper to bumper, the rpm started to lower to 800 rpm and the raised back to 1100. The car carries Datsun L24 motor with crank and rods from a L26, special oversized 84mm flat top black coated pistons from D.L. Potter Engineering with E88 Head and Far 311 New Race Cam and 2 original SU Hitachi round top carburetors rebuilt reason why it has a rough idle.

    Anyway,i would like to mention that i did cancel the EGR system and that the fast idle Actuator was removed as the diaphgram is broken:

    Click image for larger version. 

Name:	servo 3.jpg 
Views:	16 
Size:	150.9 KB 
ID:	74309

    Could there be some air escape somewhere on the engine which is causing this RPM lowering. FInally when i reached to my destination point, i parked the car for some minutes at idle. The Rpm lowered to 500 and the car engine shut down. I would also like to mention that i can feel some failure of the engine when speeding up at 2000 RPM.

  2. #2
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    68 threads started in less than one year
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  3. #3
    Registered User
    Member ID
    CZCC-29967
    Join Date
    Dec 2013
    Location
    Panama
    Age
    43
    Posts
    157

    Default

    Quote Originally Posted by madkaw View Post
    68 threads started in less than one year
    Madkaw,

    Im trying to get a solution without changing the Far 311 Race Cam back to the stock cam. Its gonna get really expensive if i need to revert to the original cam. Unfortunately in Panama there is a lot of traffic Jam and heat, you always get stucked in 20 to 30 minutes traffic and with this kind of cam i wont be able to install an AC System to the car.

  4. #4
    Registered User Stanley's Avatar
    Member ID
    CZCC-24191
    Join Date
    Apr 2011
    Location
    Redondo beach
    Posts
    641

    Default

    Check carefully for vacuum leaks and plug anything threaded that's removed from balance tube with correct BSPT thread plugs?

    I would change to 65 series tires rather than the usual 70 series, only my opinion. That will put your rpm at any speed a little higher which might be better around town with the cam. It will also make your speedometer optimistic, but there's a calculator on this site.
    I expect it would also drop your top speed by about 10 or 15 mph, and reduce gas mileage at cruising speed (unless you reduce your speed).
    Also the smaller tire might not look right unless the car is slightly lowered.

  5. #5
    Low Budget/High Value
    Member ID
    CZCC-20342
    Join Date
    Oct 2009
    Location
    Washington County, OR
    Posts
    3,629

    Default

    Quote Originally Posted by jalexquijano View Post
    heavy traffic. RPM mantained at 1,100 in light traffic but once i started going bumper to bumper, the rpm started to lower to 800 rpm and the raised back to 1100.

    2 original SU Hitachi round top carburetors rebuilt reason why it has a rough idle.

    when i reached to my destination point, i parked the car for some minutes at idle. The Rpm lowered to 500 and the car engine shut down. I would also like to mention that i can feel some failure of the engine when speeding up at 2000 RPM.
    Doesn't this seem more like the classic vapor lock from the fuel supply lines? Hot weather, original carbs, probably mechanical fuel pump.
    1976 280Z, with some minor modifications

  6. #6
    Registered User
    Member ID
    CZCC-29967
    Join Date
    Dec 2013
    Location
    Panama
    Age
    43
    Posts
    157

    Default

    Click image for larger version. 

Name:	IMG_00001119.jpg 
Views:	13 
Size:	167.5 KB 
ID:	74356Click image for larger version. 

Name:	IMG_00001103.jpg 
Views:	21 
Size:	187.6 KB 
ID:	74357

    My car has a recently installed Electric Fuel Pump! So this should not be the issue! I believe it must have a vacumm leak somewhere which is causing this rough idling.

    Any clues? How do i check for vacuum leaks? I did indeed removed the EGR system as the Servo Diaphgram was broken and thus avoid any leak. I attaching a picture of the system as it is.
    Last edited by jalexquijano; 09-29-2014 at 12:16 PM.

  7. #7
    Registered User
    Member ID
    CZCC-30294
    Join Date
    Mar 2014
    Location
    Vancouver
    Age
    34
    Posts
    125

    Default

    Sounds like a vacuum leak. But I am no expert. I've heard of people using propane to detect leaks, if you spray it near a leak, the isle should technically smooth out. Once the propane is removed, your idle issue will return. Any connection in which you recently disconnected, make sure the connection is tight, and the hose is in good condition.

    I know nothing about deleting the EGR, but some of that vacuum tube routing looks sketchy. Including the bolt at the end of one of those tubes.
    Last edited by HuD 91gt; 09-30-2014 at 10:16 PM.

  8. #8
    Registered User siteunseen's Avatar
    Member ID
    CZCC-24724
    Join Date
    Jul 2011
    Location
    Alabama
    Posts
    1,967

    Default

    I don't see a fuel filter. There's 3 on my 240. Clogged carburetors cause a rough idle.
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

  9. #9
    Registered User siteunseen's Avatar
    Member ID
    CZCC-24724
    Join Date
    Jul 2011
    Location
    Alabama
    Posts
    1,967

    Default

    What PSI is the "recently installed Electric Fuel Pump! So this should not be the issue!" set at? You know, the fuel pressure regulators that come with " I want perfect and powerfull flow for my car."
    1972 240Z #918 New Sight Orange
    1977 280Z #305 Light Blue Metallic
    1972 240Z #110 Persimmons Red

  10. #10
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Really no reason for your car to idle that fast in the first place, the cam is not that big. You probably have a vacuum leak as suggested. Search you tube for troubleshooting vacuum leaks
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Dropping 83 ZX Motor Into My 77 Z
    By Captain Obvious in forum Engine and Drivetrain (280ZX)
    Replies: 16
    Last Post: 09-02-2013, 11:35 AM
  2. Dropping 83 ZX Motor Into My 77 Z
    By Captain Obvious in forum Engine and Drivetrain (S30)
    Replies: 1
    Last Post: 08-31-2013, 08:40 PM
  3. wtb/need help findind dropping resistor 77 280
    By blue77z in forum Electrical (S30)
    Replies: 9
    Last Post: 01-12-2012, 06:56 PM
  4. 240Z prices are dropping.
    By ozlime240z in forum Australia and New Zealand
    Replies: 15
    Last Post: 09-08-2006, 06:23 PM
  5. Dropping fuel tank
    By m240 in forum Misc (S30)
    Replies: 14
    Last Post: 09-16-2003, 03:59 PM

Bookmarks

Bookmarks

Posting Permissions

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