Oscillating Idle
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Joined: Dec 2007
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From: Boise, Idaho
Oscillating Idle
Hi all,
My '84's developed a symptom that I'm not quite sure what the cause is.
It's been increasingly difficult to keep it at idle. It likes to stall and die, and when it is idling, the RPMs continually go up and down. Not up and down in the sense that it's starting to die, and then catches itself, but like someone's massaging the gas pedal with their foot.
I've adjust both timing and idle mixture with a vacuum gauge (done that plenty of times before, so I'm pretty familiar with that procedure), and the vacuum at idle is about 18 - 19 hg or so.
Fresh rebuild on the carb about 3 months ago. Holley 600cfm 4bbl. Duraspark II conversion. It's ran great for months until about a week or two ago.
Any ideas?
My '84's developed a symptom that I'm not quite sure what the cause is.
It's been increasingly difficult to keep it at idle. It likes to stall and die, and when it is idling, the RPMs continually go up and down. Not up and down in the sense that it's starting to die, and then catches itself, but like someone's massaging the gas pedal with their foot.
I've adjust both timing and idle mixture with a vacuum gauge (done that plenty of times before, so I'm pretty familiar with that procedure), and the vacuum at idle is about 18 - 19 hg or so.
Fresh rebuild on the carb about 3 months ago. Holley 600cfm 4bbl. Duraspark II conversion. It's ran great for months until about a week or two ago.
Any ideas?
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Moderator
Joined: Dec 2007
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From: Boise, Idaho
Possibly. I hadn't thought of that. For $5, it's worth a shot changing it out.
I don't think it this would be it since it does it when it first fires up in the morning too. I also had a horrible venting problem on my other Bronco, and it didn't suffer these particular symptoms.
I'll have to recheck them, but it only has 3 vacuum lines. Distributor, PVC, and brake booster. All of them are fresh, new lines.
This is one that I was curious about. I rebuilt the carb but have no idea how old the floats are. Possibly a float that's going out?
2. gas tank vent not open?
3. vacuum line cracked and possibly sealing itself?
4. float level fluctuating?
Lead Driver
Joined: Mar 2008
Posts: 7,192
Likes: 384
From: Near Los Angeles
Possibly. I hadn't thought of that. For $5, it's worth a shot changing it out.
I don't think it this would be it since it does it when it first fires up in the morning too. I also had a horrible venting problem on my other Bronco, and it didn't suffer these particular symptoms.
I'll have to recheck them, but it only has 3 vacuum lines. Distributor, PVC, and brake booster. All of them are fresh, new lines.
This is one that I was curious about. I rebuilt the carb but have no idea how old the floats are. Possibly a float that's going out?
I don't think it this would be it since it does it when it first fires up in the morning too. I also had a horrible venting problem on my other Bronco, and it didn't suffer these particular symptoms.
I'll have to recheck them, but it only has 3 vacuum lines. Distributor, PVC, and brake booster. All of them are fresh, new lines.
This is one that I was curious about. I rebuilt the carb but have no idea how old the floats are. Possibly a float that's going out?
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Moderator
Joined: Dec 2007
Posts: 7,987
Likes: 104
From: Boise, Idaho
I'll be checking into it this weekend. I picked up a fuel filter and will also blow some carb cleaner through the needle/seats, as well as the idle circuits. Shouldn't be too difficult.
I'll also check out the distributor for play. I forgot about that. I've had that happen before.
As for timing, I've tuned the idle mixture and the timing with a vacuum gauge and it's pretty top notch. I don't believe the running issue is directly related to just being out of tune.
I'll also comb over the vacuum lines.
I'll also check out the distributor for play. I forgot about that. I've had that happen before.
As for timing, I've tuned the idle mixture and the timing with a vacuum gauge and it's pretty top notch. I don't believe the running issue is directly related to just being out of tune.
I'll also comb over the vacuum lines.
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Moderator
Joined: Dec 2007
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From: Boise, Idaho
Alright, I think I found it.
Turned out to be pretty simple. I pulled off the old fuel filter and tried to blow through it. It was about 10x harder than the new one.
Put the new one on and then went to adjust the idle mixture. Realized that it was turned way in to accommodate for the less fuel it was getting. Both mixture screws were only about 3/4 turns out.
New fuel filter, reset the idle mixture (now about 1 1/2 turns out), and it's much better than it was.
I like $5 fixes.
Turned out to be pretty simple. I pulled off the old fuel filter and tried to blow through it. It was about 10x harder than the new one.
Put the new one on and then went to adjust the idle mixture. Realized that it was turned way in to accommodate for the less fuel it was getting. Both mixture screws were only about 3/4 turns out.
New fuel filter, reset the idle mixture (now about 1 1/2 turns out), and it's much better than it was.
I like $5 fixes.
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Postmaster
Joined: Dec 2006
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From: Spokane, WA
Kevin could probably use some of that $5 fixing right now. Oh, BTW, is it true that women throw themselves at you and him?
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Lead Driver
Joined: Mar 2008
Posts: 7,192
Likes: 384
From: Near Los Angeles
Good fun to all.
In all honesty, before I dialed in this carb, I had no idea the 300 was capable of such power. I mean I was only taching 4--5k rpm, and loving the HECK out of it when it let go. It was wonderful fun. And if the block is shot, or a piston, then I have engine #1 in the garage. And I have a chance to install a bigger cam. Untill the next bank job, I prob. won't get on it like that. Oh heck, I know that is bs. It was fantastic fun. I got to have it again...and with an automatic!! I haven't felt an engine come on like that since I was in high school and diving a friend's Z28.
If you would of told me that a 300 could get it on like that, I never would have believed it. But now I got to have it again. It was everything a sbc can be, and pushing an F350!! It has taken this long to be majorly impressed.
I guess all this time I have been driving around with the carb only coming into power mode at high rpms, and never shifting to secondaries. Now with the power mode on the primaries kicking in, that activates the secondaries, and it is like shifting into warp drive. I know I am exagerating a bit, but please understand that I have been driving this truck like this for two years, never knowing what was there with a simple dialing in of the carb. I read about others doing it, but just figured mine was already there. I feel like a kid waiting to ride his christmas 'stingray' bide. Hole in piston or no.
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Joined: Dec 2007
Posts: 7,987
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From: Boise, Idaho
Besides the tow bill, about $10 for a full new set of keepers and good to go. I'm jealous.
And yes, all the stories are true...
On this topic though, it's been fun driving the '84 around the last week or so. Power's about doubled. Kinda makes sense when enough fuel can't get to the carb.
Lead Driver
Joined: Mar 2008
Posts: 7,192
Likes: 384
From: Near Los Angeles
Looks like he ended up getting it!
Besides the tow bill, about $10 for a full new set of keepers and good to go. I'm jealous.
And yes, all the stories are true...
On this topic though, it's been fun driving the '84 around the last week or so. Power's about doubled. Kinda makes sense when enough fuel can't get to the carb.
Besides the tow bill, about $10 for a full new set of keepers and good to go. I'm jealous.
And yes, all the stories are true...
On this topic though, it's been fun driving the '84 around the last week or so. Power's about doubled. Kinda makes sense when enough fuel can't get to the carb.
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