#121  
Old 10-03-2021, 07:42 AM
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I would first do a dry test to save some time and then if anything checks way out of normal do a wet test.

So you dropped a Carb on from another motor without adjusting the idle mixture again?!!

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  #122  
Old 10-03-2021, 07:43 AM
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Originally Posted by NeighborsComplaint View Post
Your vid sounds like wrong firing order.

I will check this again just to confirm.


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  #123  
Old 10-03-2021, 07:44 AM
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Originally Posted by steve25 View Post
I would first do a dry test to save some time and then if anything checks way out of normal do a wet test.

So you dropped a Carb on from another motor without adjusting the idle mixture again?!!

Ok. Iíll grab a tester from HF this morning.


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  #124  
Old 10-03-2021, 07:49 AM
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Originally Posted by 1969400HO View Post
A backfire is a symptom a vlv that is opened when ignition is applied to the cylinder.
I would at this point remove all 8 plugs.
Put the (I Think is) 15/16's socket on the crank bolt, manual trans in Neutral if have that, and rotate the engine one way then the other a little bit maybe 1/8th turn back and forth,
looking at the Dist and see if there is a lag - slop . like a worn out Timing chain exhibits.
1. Drifting timing
2. Backfire thru open valves.
3. Symptoms of a fuel delivery somewhat.

I am very suspicious there on those parts to verify Timing chain & Gears mounted properly.
New from a previous buil, long ago doesn't mean "good" or proper!!

And considering it was mounted like new, Yet NOW has worked its way loose with such few miles possibly? ?
This is a easy Quick fairly simple thing to do.

Usually electronic will NOT exhibit drifting, they usually fail 100%.
Or maybe try another Distributor all together also..
Again, If you had a BORO-Scope could probe into the TC area and look at things.
One last thing, What does the gear on the camshaft look like?? Is it intact of possibly being Ate up for some reason.? ?

A failing TC setup would definitely affect the fuel delivery centric roller and cause weak fuel delivery so poor operation at higher RPM's. yada yada
So if you verified fuel pressure then that Might point to what I focus on here some.

Since I am going to pull all the plugs to check compression, I could also look for slop in the distributor.

I do have a BORO-scope that the wife bought me for Christmas. Iíve never used it (not even sure I know how) but Iím assuming that to check the TC, I would pull the fuel pump and snake the scope into the timing cover?


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  #125  
Old 10-03-2021, 08:04 AM
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Don’t waste time with the scope unless !something with the compression test goes off the rails!

The correct firing order is on the intake manifold for reference.

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And he was not talking about 1/8 or 1/4 mile ETs!
  #126  
Old 10-03-2021, 11:41 AM
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Default Rebuilt 400 HO suddenly runs rough

Quote:
Originally Posted by steve25 View Post
Donít waste time with the scope unless !something with the compression test goes off the rails!

The correct firing order is on the intake manifold for reference.

The 4 and 6 plug wires were mixed up!. It definitely made a difference in the starting/idle. The timing also didnít jump around. Total timing is at 35. Is that correct?

Here it is with correct firing order:

https://youtu.be/Hv_kIQ7ZHI4
https://youtu.be/Hv_kIQ7ZHI4

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  #127  
Old 10-03-2021, 11:52 AM
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Guess I missed the part you said all was well running till you filled up at a gas station, "then" things went bad gradually.
How does to run "ok" then after fueling went "bad" when you were driving?
And now find plug wires mixed up?

That I don't understand at all.

Was running good, then fueled up, then degraded fairly rapidly, worsening seemingly, barely running.

Put about a 1/2 gallon from the fuel pump supply side into a clean container and let settle and see what it looks like.


Last edited by 1969400HO; 10-03-2021 at 12:13 PM.
  #128  
Old 10-03-2021, 12:08 PM
wbnapier wbnapier is offline
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That sounds fine... Maybe you've solved your problem?

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  #129  
Old 10-03-2021, 12:35 PM
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Originally Posted by 1969400HO View Post
Guess I missed the part you said all was well running till you filled up at a gas station, "then" things went bad gradually.
How does to run "ok" then after fueling went "bad" when you were driving?
And now find plug wires mixed up?

That I don't understand at all.

Was running good, then fueled up, then degraded fairly rapidly, worsening seemingly, barely running.

Put about a 1/2 gallon from the fuel pump supply side into a clean container and let settle and see what it looks like.
No, the sequence went like this:
It was running fine, and then it felt like it started to stumble. I thought maybe the gas gauge was incorrect, so I stopped to get gas. But it only took about 5-6 gallons, so the gas gauge was fine. However, the stumbling got markedly worse as I limped home (about 5 miles). No power, backfiring, sputtering, etc.

The mixed up wires had to have happened when I pulled the cap to do the points. That one is completely on me.

I'm going to take it out for a spin now. If it runs ok, then the issue I was having was either the points, which definitely looked a bit tired for only 300 miles or so, or all the grit in the carb. I will report back shortly!

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  #130  
Old 10-03-2021, 12:48 PM
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Yes, 35 degrees is safe with those 670 closed chambered heads, but for the best around town drivability they may like 38 degrees total with the vacuum advance disconnected and then 8 degrees of vacuum advance coming in at 1800.

Ruining 38 degrees will Hinge on how the motor cranks when hot, if the motor pings at part throttle it knocks at full throttle which in terms of full throttle is to be avoided 100%!

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Wernher Von Braun warned before his retirement from NASA back in 1972, said that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!
  #131  
Old 10-03-2021, 01:23 PM
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Default Rebuilt 400 HO suddenly runs rough

Car runs 1000x better! No stuttering or stalling accelerates great! Thanks so much for all the help! You guys rock!

The last annoying things are, when I come to a stop, itís idling at 1200, but if I kick the throttle it goes back down to 800. It did not do this with the previous carb.

To Steveís point: I drive it for about 20 miles (local). When I shut it down, it dieseled a little. And once it was warmed up, it took a bit more cranking to get it started. Should I move the timing to 38 (with vacuum advance disconnected)?

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  #132  
Old 10-03-2021, 01:54 PM
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Have you ever considered getting a 1967 pontiac service manual and following the service instructions in it?
It is difficult to fail if youīd start with this.
If you follow some people's advice regarding the timing settings, it will soon be time to change the engine bearings.
If you want your engine to live a healthy life, use the factory ignition settings.
Especially with the inferior fuel we have today.

FWIW

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  #133  
Old 10-03-2021, 02:12 PM
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Default Rebuilt 400 HO suddenly runs rough

Car also runs a bit hot now.


Kenth
I have the service manual. It says to set initial timing at 6 degrees BTDC. I thought with todayís gas, that this wouldnít necessarily be applicable anymore.

Also, my balancer has two marks on it that are 6 degrees apart. Iím not sure, but Iím assuming that the engine builder added the second mark. I would think that the bottom mark is 0, and that the top one represents an additional 6 degrees BTDC.



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  #134  
Old 10-03-2021, 02:35 PM
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Also, my balancer has two marks on it that are 6 degrees apart. I’m not sure, but I’m assuming that the engine builder added the second mark. I would think that the bottom mark is 0, and that the top one represents an additional 6 degrees BTDC.
I think we have discussed your balancer hub earlier?
The conclusion was that your hub is a factory 1964-65 vintage for 1964-65 timing cover with just a pointer thus the two marks, first mark indicates 6į BTDC and the second mark 0į, instead of one mark on hub (0į? for the scale on 1966-67 vintage timing covers.
Your engine builder simply mounted the wrong hub for your damper.

And, the need for setting the timing out of the scale indicates a too lean F/A mixture. The carb needs to be recalibrated for todays fuel to let the engine give its full potential. This will not happen igniting a too lean mixture with timing set out of the scale.
Also, a too lean F/A mixture will make your engine run hotter than necessary.

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  #135  
Old 10-03-2021, 02:44 PM
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Well yes, your carb needs to be set up right, but your also hitting on all 8 cylinders now which is putting more heat into the coolant!
Is your vacuum advance hooked up and working above 1600 rpm?
No vacuum advance at road cruising speeds and part throttle will make the motor run hotter then it should !

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You can cut out a man's Tongue from his Mouth, but that does not mean heís a liar , it only shows that you fear the truth he might speak about you!

Wernher Von Braun warned before his retirement from NASA back in 1972, said that the next world war would be against the ETs!
And he was not talking about 1/8 or 1/4 mile ETs!
  #136  
Old 10-03-2021, 07:03 PM
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Glad you found the firing order was off. If anything will cause poor running and popping through the carb, that is it. I would get someone who knows Quadrajets go over the carb. You had dirt in the gas and I think you said you ran the car with no filter which is never a good idea. Despite what others have said the stock brass sintered filter are actually very affective at removing debris. They are small and will clog quickly if you have a lot of debris in the tank. You may want to use an inline filter after the pump rather than the stock sintered filter. I wouldnít use both. Properly setting up the carb will be important to getting your car running really well. Also if I were you I would replace the points with a Petronix unit. It will save you a lot of aggravation, for the $80 investment they are a no brainer, especially with a GM motor with the distributor at the back of the motor.

  #137  
Old 10-03-2021, 07:24 PM
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Car runs 1000x better! No stuttering or stalling accelerates great! Thanks so much for all the help! You guys rock!

The last annoying things are, when I come to a stop, itís idling at 1200, but if I kick the throttle it goes back down to 800. It did not do this with the previous carb.

To Steveís point: I drive it for about 20 miles (local). When I shut it down, it dieseled a little. And once it was warmed up, it took a bit more cranking to get it started. Should I move the timing to 38 (with vacuum advance disconnected)?
It's probably dieseling because the idle is sticking at too high an rpm. Fix the hanging throttle and go from there. Auto car should be about 750 in park and 500 in gear, stick car should be about 650-750 at idle with stock components. 800 is too fast.

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  #138  
Old 10-03-2021, 08:13 PM
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Your vid sounds like wrong firing order.
You're welcome.

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  #139  
Old 10-03-2021, 08:21 PM
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My 69 RAIII std bore 400, 50K orig miles.

Was running a bit hot, a water pump rebuild and set the "Plate" to 0.050", gap, helped a little.

Month later rebuilt Rad from a 3 core to 4 core.

Now it Runs almost too cool now.

Always been satisfied with New triple gauges set, they are More concise readout to monitor things.

At the time was new to Rochester carburetors so I followed a Qualdrajet bible- PDF , set up the jets/rods for "total area" to near recommended 0.003xxxxx,.

I never had any carb perform like it dd once I was done tuning setup it as per the manual!!
Very impressive performance.

See the link for resource.

http://corvette-restoration.com/wp-c...arb_Tuning.pdf


Last edited by 1969400HO; 10-03-2021 at 09:18 PM.
  #140  
Old 10-03-2021, 08:43 PM
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You're welcome.

Thank you!


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