471 Big Block high rpm problems

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OK I checked the distributor cap and it seems to be perfectly aligned with the rotor.
When I turn the engine to 0 it points directly to the #1 cylinder socket on the cap.
 
Need to run it with a vacuum gauge, you may be pulling enough at WOT to close your power valve and the related miss fire can fool the wideband.
 
Or just throw in a 6.5 valve and see if the problem moves up the scale or goes away. If none of that works you may have to get out a degree wheel and spec card and see where that cam is at.....
 
As Columbo would say... One more thing.... Have you tried reversing polarity on the distributor?
 
After reading post #24 again you may be on to it. Cam timing sure could be off if nothing else changed.
 
Will try to run it tomorrow without air filter and also will test with vacuum gauge. Will have someone to help so it will be way easier.
Where should I connect the vacuum gauge to test? I have a spacer with plugged in port under the carb, can I use this port to check it?
 
Miszny said:
Will try to run it tomorrow without air filter and also will test with vacuum gauge. Will have someone to help so it will be way easier.
Where should I connect the vacuum gauge to test? I have a spacer with plugged in port under the carb, can I use this port to check it?
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Yes that is fine or any manifold vacuum source on the carb just not ported vacuum.
 
If your air filter has ever gotten wet and it is a paper filter the fibers will swell and restrict flow.....

prost!
 
I also forgot to mention that magnetic pickup is new in the distributor as well as cap and rotor...
I tried to reverse wires on the distributor and car started running badly, did not test high rpms and switched it back the way it was.

My vacuum value is shown in the photo, it is how much I am pulling in Park position. Wile in gear at 850 rpms its showing between 5 and 6. I also checked my power valve and it is 5,5.
It means that I should have like 2,5 valve right? Would it really be the cause of my problem?
I am not sure if I understand how this valve really works...

I also realized today while testing that I did not press the pedal all the way to the floor, I did it today and it was a bit better but it would still brake up ocassionaly.

IMG_8602.jpg
 
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This is how it runs in Park position. Not sure if you can see in this movie that it starts to be a bit shaky at the top.

Also I know that this cheap tach is not known for accuracy but I checked it with VDO didgital tach and it was almost perfect showing between 100-300 rpm more.

 
When you put it back together from the cam gear coming loose did you have you move the distributor for it to run?
 
mguner said:
When you put it back together from the cam gear coming loose did you have you move the distributor for it to run?
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All was out, so I just put the cam gear and distributor in like with new engine assembly. I put the #1 piston in tdc, and put the distributor in so it points to right terminal in the distributor cap.
Afterwards it started right up for the brake in process.
 
Hi

Turned out that squirter for the secondaries had damaged washers.
As soon as I fix my transmission I will come back to this topic and check if doing a rebuild on my car actually helps to fix this issue. I will do a total rebuild on my carb before next tests. I have plenty of time before my trans parts arrive.

Thanks for trying to help me out.
 
That makes sense... I listened to your video, and when you rev'd it once and then rev'd again immediately, it broke up, which sounded like an accelerator pump issue.

By the way, the engine will not behave the same when running under load on the highway at speed as when you are revving it in neutral. There is no load on the engine when sitting still, and the fuel-air mix in the cylinders will not be the same as at the same RPM's when running under load. As the air-fuel mix changes with load, the spark energy and voltage required to properly fire the cylinders will change with RPM's.

Do you now have an AFR meter, with the oxygen sensor installed in the exhaust pipe behind the engine?

What are your full cam specifications? I ask because that vacuum level that you show on the gauge at 850 RPM in gear could be too low.
 
I dont have fixed in car afr sensor, but I have an external sensor that you put into exhaust, hook it up to a laptop and see your values there.
I will check it again, just need to fix my transmission.

Lobe separation: 110
Intake centerline: 106
Duration Intake: 284
Duration exhaust: 296
Duration intake @.50”: 240
Duration exhaust @.50”: 246
Valve lift intake: .507
Valve lift exghaust: .510

I am using it with 1.6:1 rockers so valve lift is:
intake: .540
exhaust: .544
 
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It is possible that the hyd lifters are pumping up at 5000 rpm. We had a BB Mopar with hyd lifters on the dyno the other day and it wouldn't pull past 5000 rpm. If the springs and rocker arm ratio are over powering the lifters then they will start having issues at higher speed.
 
I fixed the problem. Replaced the power valve to 3,5 and while inspecting the carb I saw that seals in the secondaries squirter were cracked resulting in gasoline dripping down the intake.
In the end I did total rebuild and cleaning of the carb. Runs great now.
Thanks for trying to help me out!
 
That's great to hear! I would add that your idle vacuum could probably be higher, now that the carb is in good shape I would try adding more initial timing (but watch the total timing so it doesn't go too high of course).
 
MOPEkidD-3 said:
That's great to hear! I would add that your idle vacuum could probably be higher, now that the carb is in good shape I would try adding more initial timing (but watch the total timing so it doesn't go too high of course).
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Timing is 20 initial and 36 total. Should I really go much more?
 
Miszny said:
Timing is 20 initial and 36 total. Should I really go much more?
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I wouldn't go higher on the total but you can test what happens if you crank more advance in at idle; if the vacuum increases keep going until the engine kicks back against the starter when you crank it warmed up. Then when you find a good number go in and limit the mechanical/total timing in the distributor.
 
I will probably try some tuning but with current settings it seems to really run well.
When hot the starter sometimes has hard time to turn it on the initial turn. I have mini starter in it.
What about advance curve? At what rpm should I have full advance? As far as I remember it is all in at around 2500rpm.
 
Miszny said:
I will probably try some tuning but with current settings it seems to really run well.
When hot the starter sometimes has hard time to turn it on the initial turn. I have mini starter in it.
What about advance curve? At what rpm should I have full advance? As far as I remember it is all in at around 2500rpm.
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If that's the case it's probably close to ideal then, advance curve should be OK too. Has your idle vacuum increased since you fixed up the carb?
 
I will check if vacuum changed next weekend and post some info.
 
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