Engine Backfire Diagnosis Led to Wiped cam Lobes

[Skweegle89]

85swb "Fancy"

Well it wasn't the filter. Once I kicked it off fast idle it wouldn't stay idling. Even if I feathered the throttle it would idle extremely rough. To restart it I have to pump the gas forever to get it to fire. It reaks of gas but there wasn't any in the carb when I looked down the throat.


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[Skweegle89]

85swb "Fancy"

Alright iv got the symptoms narrowed down pretty well now. After I feather the throttle and get it idling, I let it run for a bit. Runs fine. Kill it, immediately start it back up. It will idle rough for 20 secs and then die. If I feather the throttle and keep it from dying, I can romp on it a couple times and it will idle just fine. Wtf is going on? This never happened with the eddy, so it's got to be carb specific. The seconday butterflies are completely closed as far as I can tell.


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[Skweegle89]

85swb "Fancy"

And there a whistling noise coming from the inside of the carb when the idle dips real low. It stops when the idle surges back up. If I hold my hand over the choke plate lightly it almost stops whistling.


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[350runner]

32° outside really isn't carb tuning weather. Plug the ports I mentioned b4 and let's start from there.

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Edit...

 

[Skweegle89]

85swb "Fancy"

I plugged all the ports. Started it up. It spit and sputtered for about a minute and then fast idle kicked in. I let it run for a minute, the hit the gas to kick the fast idle off and it died.


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[350runner]

Let me talk to mark.

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[Quadrajet Power]

I'm back. In sales meetings all week. Tell you what, let me build another carb for you and will send it out to swap out with you. May be something in the circuits that didn't clean out through the cleaning process. It's rare, but can happen.

 

[HotRodPC]

And there a whistling noise coming from the inside of the carb when the idle dips real low. It stops when the idle surges back up. If I hold my hand over the choke plate lightly it almost stops whistling.


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Hey Zach, I've not read the whole thread there here to see what problem you're having, but I see new carb mentioned, new fuel filter, not idleing, ideling for about 20 seconds blah blah, and the whistling....

2 things, are you the guy has the quadrajet rebuilt? Make sure you using the correct carb base gasket. I've seen this several times where a guy used the wrong gasket. Though there was no leak around the base, there was a vac leak under carb to another port under the carb. In short, an internal vac leak.

#2, do you still have an EGR valve on this engine? This really sounds like a stuck open EGR valve. It's got all the classic symptoms.

 

[Skweegle89]

85swb "Fancy"

I'm back. In sales meetings all week. Tell you what, let me build another carb for you and will send it out to swap out with you. May be something in the circuits that didn't clean out through the cleaning process. It's rare, but can happen.

Let me swap out these base gaskets first. I had the thick one you gave me on it before, but maybe it didn't take. I will try another gasket before you go through all that trouble. Should I run a thick gasket between the intake and the adapter as well?


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[HotRodPC]

Oh you're using an adapter/spacer too? Are you using an OEM intake manifold? If so, that adapter sure might be the problem and causing an internal vac leak. Some of the OEM intakes have hot choke stove ports and such that the base gasket blocks off under the carb. Can you get a pic of your intake? If by chance you get the carb off, get a pic of the intake too without the carb.

 

[Skweegle89]

85swb "Fancy"

Hey Zach, I've not read the whole thread there here to see what problem you're having, but I see new carb mentioned, new fuel filter, not idleing, ideling for about 20 seconds blah blah, and the whistling....



2 things, are you the guy has the quadrajet rebuilt? Make sure you using the correct carb base gasket. I've seen this several times where a guy used the wrong gasket. Though there was no leak around the base, there was a vac leak under carb to another port under the carb. In short, an internal vac leak.



#2, do you still have an EGR valve on this engine? This really sounds like a stuck open EGR valve. It's got all the classic symptoms.

No EGR valve. I tried the thick base gasket that came with the carb and it was doing this, so I thought I had a vac leak. I swappedit out for the thin gasket that came with my adapter (swapping from eddy so I have to run an adapter) and it continued to do the same thing. The only thing I haven't done is changed gaskets between intake and adapter, but iv used about a half a can of carb cleaner looking for leaks everywhere and can't find one.


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[Skweegle89]

85swb "Fancy"

Oh you're using an adapter/spacer too? Are you using an OEM intake manifold? If so, that adapter sure might be the problem and causing an internal vac leak. Some of the OEM intakes have hot choke stove ports and such that the base gasket blocks off under the carb. Can you get a pic of your intake? If by chance you get the carb off, get a pic of the intake too without the carb.

It's a summit stage 2 intake. I will try to get the gaskets today and will take pics before I swap them out.


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[350runner]

But remember you didn't find that blind bolt hole till after you switched back to the thin gasket. I believe you should be ok using the thin gasket between the adaptor and intake.

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[Skweegle89]

85swb "Fancy"

But remember you didn't find that blind bolt hole till after you switched back to the thin gasket. I believe you should be ok using the thin gasket between the adaptor and intake.

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True. I will swap gaskets before I try anything else. I ran it out of gas in my driveway messing with it lastnight so now I have to deal with that.


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[HotRodPC]

It's a summit stage 2 intake. I will try to get the gaskets today and will take pics before I swap them out.


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OK, then lemme ask this. Has this truck EVER run good with this intake on it? Here's why I ask. Some of the Summit brand intakes are made by Wiend and I've heard some were made by ProComp which is cheap China ****. Now they all aren't bad and if you got a good one, then you got a good one and it can work well. Some of the ProComp intakes have been known to have runners have been off. Meaning they don't match the head ports. The way to know is to lay an intake gasket on the intake runners and compare to make sure all your intake runners will match up with the gasket and heads.

I'll assume you've already done a vac leak search using some carb cleaner or starting fluid? You can use WD-40 too but it doesn't discipate like the other 2 and leaves a mess on your motor. Spray the intake runners down both sides, across the front where it meets the block, and also along the back. The back is hard to do, but it still works. Just spray it back there while motor is running and if it idles up or smoothes out, then you know it sucked it in and there's your problem or 1 of them. Then spray around the base of the carb. Just sounds to me like all the classic signs of bad vac leak somewhere. And the whistling kinda makes me think it can be internal.