Engine Backfire Diagnosis Led to Wiped cam Lobes

[Skweegle89]

85swb "Fancy"

Yea it's wired through the oil pressure switch


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[350runner]

There ya go

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[Skweegle89]

85swb "Fancy"

Now,
If I'm not running vac advance do I need to bump my timing up above 12*? Trying to figure out this backfire under load.


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[350runner]

Things it could be.1) flat cam load or valve adjustment needed.
2) lean condition cause by the accelerator pump shot( it's adjustable) linkage in front of carb. 3) rod and jets need to provide more fuel. Just off to of my head. I'd give the valve adjustment a shot first then go from there.

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[Skweegle89]

85swb "Fancy"

The idle surges up and down after its started. Does that narrow it down any or a completely unrelated problem?


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[HotRodPC]

I have a feeling, when it's all sorted out, we find a burnt valve or something in the valve train not quite right. A compression test has been done right?

Probably not a bad idea to adjust the valves IF you can get it to run long enough to do that. The problem just might show it's face during valve adjustment.

The fluctuating idle can be an intermittent vacuum leak. Like when they cylinder that has a burnt valve fires, and it's normal for that instant, then back to leaking again when it's not supposed to be. Or am I getting confused with another thread?

 

[350runner]

Your in the right thread to accurately achieve the proper valve lash the adjustment must be done with the engine off. In this instance one cylinders intake and exhaust valves at a time, starting in the proper firing order. Idle surging can very well be as HR says.

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[Skweegle89]

85swb "Fancy"

I have a feeling, when it's all sorted out, we find a burnt valve or something in the valve train not quite right. A compression test has been done right?

Probably not a bad idea to adjust the valves IF you can get it to run long enough to do that. The problem just might show it's face during valve adjustment.

The fluctuating idle can be an intermittent vacuum leak. Like when they cylinder that has a burnt valve fires, and it's normal for that instant, then back to leaking again when it's not supposed to be. Or am I getting confused with another thread?

I did a compression test. Came back fine. I can't for the life of me find a vac leak. I'm only pulling 2.5" of vacuum at manifold, but also have a fairly hefty cam. I'm not saying it couldn't be a burnt valve, but none of this started until I swapped carbs. Did find a small vac leak at the carb adapter, but got that fixed yesterday. Did have a screw up when I hooked the PCV valve up to the top port on the carb and the carb flooded and filled the crank case full of gas, but I changed the oil and pulled the valve covers and cleaned it all out. Even with this cam I feel like I should be pulling more vacuum.


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[350runner]

Man I'm kinda lost here. At one point you say the eddy gave you problems and was running rich. Then the qjet issue, and swapping it for the Holley didn't show any different. This leads to your valve train

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[Skweegle89]

85swb "Fancy"

The richness of the Eddy was the only problem I had with it. I chalked it up to needing rebuilt. Several days before I swapped carbs it idled up a bit on its own, which it had never done before, but it always started and ran. Didn't have as much power as I did when I first put the qjet on but it still never acted like this. The holly didn't work any better because there was so much gas in the top end. When I cleaned it out I put the qjet back on and it quit all its backfiring unless it's under a load. It smokes now when it's started up. Not a lot, but it's noticeable, but I'm sure the oil needs changed again, as there is still probably gas left in it from what was in the oil pump, etc. I'm not saying it's the carb, I'm just not sure why these symptoms would show up the same day I swapped them out. I will do whatever it is I need to do, wether it's to pull the intake to make sure it's not leaking, or pull the dizzy back out to make sure I'm not a tooth off, or pull the whole damn motor and have it rebuilt, I'm just tired of chasing this problem in circles. It's been 3 months since I started what seemed like would be an easy fix and I'm right back where I started. Just talked to the best mechanic in town and he seems to think the cam is off a tooth or something. That's not the problem, as I drove this thing for months without any of these issues. Was going to drop it off at his shop but I'm not going to pay him to do **** that I can do myself with your guys' help.


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[bucket]

There's no such thing as a dizzy that's a tooth off. Even if it ends up installed several teeth from where it was before, you just rotate the housing to compensate. If it's in time, you're fine.

Now about this vacuum. Are you sure the gauge is not faulty? Are you sure it wasn't hooked to the timed vacuum port? Did you try the unused vacuum port? Was the vacuum steady? What did the vacuum read when you open and close the throttle? Was the vacuum higher at a steady raised RPM?

 

[Skweegle89]

85swb "Fancy"

There's no such thing as a dizzy that's a tooth off. Even if it ends up installed several teeth from where it was before, you just rotate the housing to compensate. If it's in time, you're fine.



Now about this vacuum. Are you sure the gauge is not faulty? Are you sure it wasn't hooked to the timed vacuum port? Did you try the unused vacuum port? Was the vacuum steady? What did the vacuum read when you open and close the throttle? Was the vacuum higher at a steady raised RPM?

I put it on the bottom left port on the carb. It's the lowest port on the carb, I assume it's manifold. The needle held steady at 2.5" at idle and rose steadily with increased throttle. The more throttle I gave it, the more vacuum I got. It never jumped around unless I snapped the throttle. I don't recall what the reading was with higher throttle, but I don't have a tach to know what RPM I was turning anyway.


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[350runner]

Here's one note to self. Engines don't idle up and down on their own. Root cause needs to be found vacuum leak, burnt valve, bad break booster, trans modulator and such are some causes.The qjet issue... well we found out why that caused the flooding issue. Holley didn't work because of gas in the oil or it was jetted too rich? Now that ask is said and done and all has been gone through fingers point to the valve train. cam lobe or valve lash being out of adjustment because no-one ever does a valve adjustment...

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[HotRodPC]

Your in the right thread to accurately achieve the proper valve lash the adjustment must be done with the engine off. In this instance one cylinders intake and exhaust valves at a time, starting in the proper firing order. Idle surging can very well be as HR says.

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FOR THIS MOTOR, I'd have to disagree whichoo on "to accurately achieve the proper valve lash the adjustment MUST be done with the engine off" For a solid or roller cam I'd agree all day long and that in fact is accurate and you don't adjust valves on a solid or roller cam motor with the engine running at all. For a hydraulic cam and lifter motor, NOPE, I personally feel the ONLY way to get an accurate valve lash is to do it with the motor running. Of course you do it the way you're suggesting for an initial valve adjustment to get the hydraulic cam motor to run which I never did on any of the hydro motors I've built. I just set them all at zero lash and a 1/4 turn. Once it's running, then I do a valve adjustment with it running.

Reason being, on a hydraulic cam/lifter motor, especially a used one, you have no clue of the tension on the plunger in the lifter until the lifter is pumped up with oil which requires oil pressure. Engine not running means zero oil pressure and lifter has bled down.

 

[Skweegle89]

85swb "Fancy"

FOR THIS MOTOR, I'd have to disagree whichoo on "to accurately achieve the proper valve lash the adjustment MUST be done with the engine off" For a solid or roller cam I'd agree all day long and that in fact is accurate and you don't adjust valves on a solid or roller cam motor with the engine running at all. For a hydraulic cam and lifter motor, NOPE, I personally feel the ONLY way to get an accurate valve lash is to do it with the motor running. Of course you do it the way you're suggesting for an initial valve adjustment to get the hydraulic cam motor to run which I never did on any of the hydro motors I've built. I just set them all at zero lash and a 1/4 turn. Once it's running, then I do a valve adjustment with it running.



Reason being, on a hydraulic cam/lifter motor, especially a used one, you have no clue of the tension on the plunger in the lifter until the lifter is pumped up with oil which requires oil pressure. Engine not running means zero oil pressure and lifter has bled down.

I don't have a roller setup.


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