What causes idle surge after rev'g motor [video]
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What causes idle surge after rev'g motor [video]

  1. #1
    Senior Member Franger's Avatar
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    Default What causes idle surge after rev'g motor [video]

    What causes the motor to "surge" like a blown motor when it's first started and then after it's is rev'd??? It surges between 900 and 1200 RPM's then smooths out and ends up at 1200 RPM .... until I rev it again .....

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    Senior Member 67weiman's Avatar
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    I would guess a carb issue, lean condition like a vac leak... ??? I don't know...

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    Senior Member EVILFORCE's Avatar
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    What is your timimg doing?

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    Senior Member dankdave79's Avatar
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    Put a rootz efi kit on it no more surge

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    gn7
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    Trailer tests are terrible "tests" just for the reason I am going to give you.

    The surge is almost certainly a rich condition. When he went to start it, he probably gave it a little squirt. When he revs it, squirts again. Bet your ass that the engine isn't using the entire shot and a little collects in the plenum. It burns out and it returns to a normal idle, until he jazzes it again.

    NO BIG DEAL!!! Don't change a thing until you test run it on the water. If you attempt to fix the trailer surge, it might just show up as a lean bog when you accelerate on the water.

    Also, its nowhere near warmed up in the vid. It will have a total different attitude when it warmed up. You will probably have to raise the idle to get it to idle in the water in gear.

    Thin still bad ass to see running. You guys busted your asses on this thing, but you did it right. Hopefully it gives you many seasons of trouble gree fun!



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    Quote Originally Posted by EVILFORCE View Post
    What is your timimg doing?
    Steady at 37* @ 3000 RPM....

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    Senior Member Franger's Avatar
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    Quote Originally Posted by gn7 View Post
    Trailer tests are terrible "tests" just for the reason I am going to give you.

    The surge is almost certainly a rich condition. When he went to start it, he probably gave it a little squirt. When he revs it, squirts again. Bet your ass that the engine isn't using the entire shot and a little collects in the plenum. It burns out and it returns to a normal idle, until he jazzes it again.

    NO BIG DEAL!!! Don't change a thing until you test run it on the water. If you attempt to fix the trailer surge, it might just show up as a lean bog when you accelerate on the water.

    Also, its nowhere near warmed up in the vid. It will have a total different attitude when it warmed up. You will probably have to raise the idle to get it to idle in the water in gear.

    Thin still bad ass to see running. You guys busted your asses on this thing, but you did it right. Hopefully it gives you many seasons of trouble gree fun!
    Hey Bob, I had already warmed it up, the water temp was 160 when he started it in the vid. What I have him do is run fuel pump for about 3 seconds then turn off, hit starter button and that's it, no throttle when it is starting. I'm sure I'll need to raise the idle once I'm on the water.

    Other than the surge I'm happy. I changed a few things since the one time it ran last summer. Ditched the Weiand and went with a Victor Ram, replaced the PRW ss rockers w/ Crower ss rockers, added the Webster stud girdles. Replaced all fuel lines and fittings from pump to carbs. Grounded the heads to the block on all 4 corners which seems to have gotten rid of the intermittent loss of spark from MSD. Went to a nice shinny Powermaster alt, replaced all the gaskets and O rings in the gear box and the shaft log seal, changed from 15's to 18's, changed the 11-1/8 X 15 Stellings prop to a 11-1/8 X 16 Menkens and cut 1/8" off the propshaft. Had to go with different valve covers as the others w/blue AN fittings hit the girdles, the newer ones are cooler anyway .... I went with the Baldwin B279 filter and Joe Gibbs marine 15-50 syn ...... I think she's ready

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    Quote Originally Posted by dankdave79 View Post
    Put a rootz efi kit on it no more surge
    Great idea, you got one laying around you'd like to donate to the cause

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    gn7
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    It could possibly be reduced with a tweek on the idle mixture screws once you have it on the water.
    You do realize there are guys watching that vid thinking WTF, I'd kill for that idle, and you are trying to eliminate it?? SURGE IS SOOOOOO COOOOOL!



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    Quote Originally Posted by gn7 View Post
    It could possibly be reduced with a tweek on the idle mixture screws once you have it on the water.
    You do realize there are guys watching that vid thinking WTF, I'd kill for that idle, and you are trying to eliminate it?? SURGE IS SOOOOOO COOOOOL!
    It is COOL .... but I always thought low idle bad for roller rockers?

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    gn7
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    Quote Originally Posted by Franger View Post
    It is COOL .... but I always thought low idle bad for roller rockers?
    The rockers could care less. Lifters don't care for it. But you have to idle it for some time. Rollers take it better than alot of people think. There is quite abit of oil pouring down on those things even at an idle. Small blocks don't anywhere near the oil on the lifters at a idle that the BBCs do.



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    Quote Originally Posted by gn7 View Post
    It could possibly be reduced with a tweek on the idle mixture screws once you have it on the water.
    You do realize there are guys watching that vid thinking WTF, I'd kill for that idle, and you are trying to eliminate it?? SURGE IS SOOOOOO COOOOOL!
    Sound familiar David?
    If God is your co-pilot, change seats!
    Acts 2:38, the perfect answer to the perfect question.

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    Senior Member Franger's Avatar
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    Quote Originally Posted by gn7 View Post
    The rockers could care less. Lifters don't care for it. But you have to idle it for some time. Rollers take it better than alot of people think. There is quite abit of oil pouring down on those things even at an idle. Small blocks don't anywhere near the oil on the lifters at a idle that the BBCs do.
    oops ... I meant to say lifters. I picked up a new set of Comp EndurX when I built the motor last year, they aren't Morels etc so I want to make em last till I can change them next winter. Thinking bout Morels or the Isky red zone ezroll ??? Will be looking for advice when I change over to better lifter next winter for sure.

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    Quote Originally Posted by steelcomp View Post
    Sound familiar David?
    Hum .... are you and gn7 the same guy

    Thanks Scott, you and Bob are invaluable sources of info, I seriously would not be where I am at with this motor without both of you guys

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