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Thread: Off idle hesitation, fluctuating idle, poor Gas milage

  1. #21

    Default Off idle hesitation, fluctuating idle, poor Gas milage

    I am thinking that if you have timing at 16 degrees initial you might want to drop it to 12 or 14 degrees and see how it runs. After you set the new timing what's the idle rpm and if you have any hesitation from idle to 2500. You are setting timing with a light and not on the handheld correct? Just want to make sure. Also vac advance is disconnected when setting timing



    EDIT: I read your post more carefully, if you have no hesitation now and 50 degrees at cruise that would be acceptable. Maybe lower to 16 degrees and see if its any better. You are matching your target idle now.

  2. #22

    Default Off idle hesitation, fluctuating idle, poor Gas milage

    bojo wrote:

    I am thinking that if you have timing at 16 degrees initial you might want to drop it to 12 or 14 degrees and see how it runs. After you set the new timing what's the idle rpm and if you have any hesitation from idle to 2500. You are setting timing with a light and not on the handheld correct? Just want to make sure. Also vac advance is disconnected when setting timing



    EDIT: I read your post more carefully, if you have no hesitation now and 50 degrees at cruise that would be acceptable. Maybe lower to 16 degrees and see if its any better.

    Will do bojo. Thanks and I will try this for a while and see what happens. Larry

  3. #23

    Default Off idle hesitation, fluctuating idle, poor Gas milage

    Glad to hear that the hesitation is gone. It sounds like it was a combination of different things with your timing. If that's the case, you may want to try switching back to the MILD cam setting to see if it brings back the performance you lost backing it down to Street/Stock. I'm with bojo on backing the initial down to 16. It may even like a little more total advance, say up around 34-36*. Keep us updated!

  4. #24

    Default Off idle hesitation, fluctuating idle, poor Gas milage

    JWZ28 wrote:
    Glad to hear that the hesitation is gone. It sounds like it was a combination of different things with your timing. If that's the case, you may want to try switching back to the MILD cam setting to see if it brings back the performance you lost backing it down to Street/Stock. I'm with bojo on backing the initial down to 16. It may even like a little more total advance, say up around 34-36*. Keep us updated!

    Thanks JWZ28. Its kind of like starting all over, but in a better place . I am going to drive it a bit and see how things work out. Could possibly switch back to mild cam, but want to get some time on the new setting a tinker a bit with that first. I read a pretty lengthy article on ported vs un-ported or straight vacuum and straight vacuum rules according to the 30 plus year vet of building distributors. Getting excited about the TBI again . I will post back after putting some miles on it. Larry

  5. #25

    Default Off idle hesitation, fluctuating idle, poor Gas milage

    See, now that's the ticket. Get out and enjoy it now that it's tolerable. Tinker a bit here and there, one thing at a time and make sure you write down your settings somewhere so you can go back to where you had it if it doesn't like a change you make.



    As far as ported vs unported goes, you probably read the same article I did when I was still fighting mine. My engine HATED unported (full manifold) vacuum when it was carbed due to the lumpy cam I have, but it's the exact opposite with the EFI. Unported definitely seems to be better for performance with this system.

  6. #26

    Default Off idle hesitation, fluctuating idle, poor Gas milage

    Well I guess it was just wishful thinking. The hesitation seemed to have been gone after switching over to full vacuum in the garage, but after driving, it was still there and it actually seemed to continue the hesitation over a longer period of time. It was better with ported vacuum. As I had mentioned before, it seemed the worst was between 1100 and 1400 rpm and as soon as the mechanical advance started moving the timing around 1500 is when it cleared up and ran smooth. So I purchased a distributor advance spring kit and used one light and one heavy and that seemed to help tremendously. The advance starts moving on very light throttle and even though there is some stumble or hesitation, it is so little that I can live with it. The only real issue I have is how can I bring my idle down in neutral? It wants to idle around 1100 rpms, and so I get some run on problems when I shut it down. All of my settings are still what is posted above.

  7. #27

    Default Off idle hesitation, fluctuating idle, poor Gas milage

    In your first post you say timing is at 18 degrees.



    Try this as you have nothing to lose.

    Set timing to 14 degrees

    Use ported vacuum.



    Using ported vacuum you will not have any vacuum advance at idle.



    Let me know how it runs with those settings, hopefully you see rpm drop some at idle.

  8. #28

    Default Off idle hesitation, fluctuating idle, poor Gas milage

    bojo wrote:

    In your first post you say timing is at 18 degrees.



    Try this as you have nothing to lose.

    Set timing to 14 degrees

    Use ported vacuum.



    Using ported vacuum you will not have any vacuum advance at idle.



    Let me know how it runs with those settings, hopefully you see rpm drop some at idle.

    Thanks bojo, I just tried that and initially the idle went down, but after re-adjusting the IAC count and letting it run a bit, it was right back up there. I took it out and drove it a bit and I figured performance would suffer slightly, but I couldn't tell any difference, heck it might have been a tad bit better. All in all, things are better. I also swapped out the 180 thermostat for a 195. Not sure that really did anything except my exhaust system seems quieter


    EDIT:

    I also tried going back to the mild cam settings and the idle went down, and I thought all was good, but then the hesitation came back and eventually so did the fast idle issue.

    Also, not sure if this is any useful information, but at idle in neutral I am pulling 14" of vacuum and in gear 11-12" Would you recommend anything different then the 19 setting for the PV? I have played with different settings but could not tell any difference.

  9. #29

    Default Off idle hesitation, fluctuating idle, poor Gas milage

    I was looking at the tune up specs for a 350 (motors produced between 1970-75)with auto and it lists initial timing at 8 degrees. Maybe your engine does not like too much timing. You could try lowering the timing by 2 degree increments until you reach 8 degrees and see if things improve.



    On a side note I have been studying a/f ratios and timing relationships and the richer the fuel mixture at idle the less timing is required, richer ratios burn much faster. The optimum pressures developed in motors should occur around 10 -14 degrees ATDC so igniting a richer mixture earlier could be causing the issues. An alternative is to change your idle A/F to like 14.5 and see if that helps too. These are just some thoughts that I have but it could be the problems.



    When the Atomic is installed without it controlling timing its just like putting on a carb but you have much better control of the A/F ratio through the motors rpm range. When the Atomic is controlling timing you now have the A/F management in addition to specifying when and how much timing to bring in and when. Again just my thoughts here.

  10. #30

    Default Off idle hesitation, fluctuating idle, poor Gas milage

    bojo wrote:

    I was looking at the tune up specs for a 350 (motors produced between 1970-75)with auto and it lists initial timing at 8 degrees. Maybe your engine does not like too much timing. You could try lowering the timing by 2 degree increments until you reach 8 degrees and see if things improve.



    On a side note I have been studying a/f ratios and timing relationships and the richer the fuel mixture at idle the less timing is required, richer ratios burn much faster. The optimum pressures developed in motors should occur around 10 -14 degrees ATDC so igniting a richer mixture earlier could be causing the issues. An alternative is to change your idle A/F to like 14.5 and see if that helps too. These are just some thoughts that I have but it could be the problems.



    When the Atomic is installed without it controlling timing its just like putting on a carb but you have much better control of the A/F ratio through the motors rpm range. When the Atomic is controlling timing you now have the A/F management in addition to specifying when and how much timing to bring in and when. Again just my thoughts here.

    Thanks again for the advice bojo. There really isn't much about this engine that is 70's other then the block, ex268h cam, flat top trw pistons, procomp aluminum heads, edlebrock intake, but I am willing to try anything at least once. I had just read a lot of feedback on the cam before I bought it and most folks were running between 16 and 20 degrees advanced. I originally started around 12 and when the car was carburated, it didn't like it there. But I will give it a shot. So are you suggestion that I back the timing down and richen the mixture or leave it where it is and lean the mixture?

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