Engine loses power around 5000RPM

[Jacksboys]

 

[Swedefish]

Time for Swedefish to chim in with a stupid question 
What kind of air cleaner do you run?
You say that the O2 read rich , too rich or?
Bear with me, just a thought.

[Jacksboys]

Time for Swedefish to chim in with a stupid question 
What kind of air cleaner do you run?
You say that the O2 read rich , too rich or?
Bear with me, just a thought.

I run a 2 inch tall by about 14 inch diameter paper filter.
I have the basic narrow band O2 sensor, so I do not know for sure how rich it is, but the gauge is not maxed out.

[dodge freak 2]

Just a 2" high air filter? Well whats the distance from the carb vents, to the top of the air cleaner lid? It needs 3/4" or more. If not, the fuel in the bowl may stop flowing, do to vacuum. Thus, the motor will stop revving.

BTW. I just looked at this thread, can't believe its 6 pages, if this has already been checked, sorry.

[Jacksboys]

Just a 2" high air filter? Well whats the distance from the carb vents, to the top of the air cleaner lid? It needs 3/4" or more. If not, the fuel in the bowl may stop flowing, do to vacuum. Thus, the motor will stop revving.

BTW. I just looked at this thread, can't believe its 6 pages, if this has already been checked, sorry.

I had this setup on the last engine build and did not have any problems, so I doubt that its the problem.   

[Swedefish]

Last summer I did run a 600 edelbrock on my 383, and it behaved exactly like you`re describing.
At about 4500-4800 rpm it just flatend out and didn`t rev any higher. I bought a carb jet and needles set from Mancini and started to tune the carb. I had to step up from .95 to .104 jets then it really woke up. Also changed the step up needles.

[Jacksboys]

Last summer I did run a 600 edelbrock on my 383, and it behaved exactly like you`re describing.
At about 4500-4800 rpm it just flatend out and didn`t rev any higher. I bought a carb jet and needles set from Mancini and started to tune the carb. I had to step up from .95 to .104 jets then it really woke up. Also changed the step up needles.

Ok, I just want to make sure everyone is still understanding what is going on.  Not only does it feel like I am losing power, but the tachometer gets erratic at around 4500-5000 rpm.  I mean, you can seriously see the tachometer needle jumping back and forth.  I know that I should run a little larger carb, but I would rather spend money on the electrical issue first and then worry about the carb.   

[matt63]

I wouldn't rule out anything at this point.  There are some basic rules to troubleshooting that can help.  I wish I used them more often.

1) don't rule something out assuming it is okay without verifying it first.  This can lead to lots of time and $$$ chasing your tail.
2) check both the obvious and the easy things first.  Swapping a carb or ECU or distributor for a known good unit is relatively easy (assuming you can borrow one).
3) make sure the basics are right ie timing, float levels, grounds, connections.  I've pissed away $$$ and time on the float level issue.
4) use diagnostic tools where possible to gather  real info ie timing lights, pressure gages

I'm sure there are more!  As an example, my friend bought a pickup truck for cheap because it ran horribly.  The air cleaner was badly plugged.

[Chryco Psycho]

I cannot send you a PM  you Matt as your box is full

[ntstlgl1970]

Also I would not trust just an oxygen sensor to determine the problem. An ignition misfire will show as a rich mixture on an oxygen sensor, remember - it only sees oxygen - because there is a bunch of unburned air/fuel mixture in the exhaust.
If it shows on the tach, something is probably going on with the ignition.

What is the fuel pressure at when the problem occurs?
What is the voltage at the coil "+" when the problem occurs?
What does the engine vacuum do when the problem occurs, and what does it measure?
What is the reluctor gap set at in the distributor?

[Jacksboys]

What is the fuel pressure at when the problem occurs?

I am not sure.  It is a mechanical pump and I do not have a guage.  

What is the voltage at the coil "+" when the problem occurs?

Not sure, I will have to test it at some point. 

What does the engine vacuum do when the problem occurs, and what does it measure?

Not sure, I do not have anything hooked up to a vacuum.

What is the reluctor gap set at in the distributor?

Not sure,  I will have to check this also. 



Also, if an O2 sensor sees a bunch of oxygen, then it would read Lean. 

[Chryco Psycho]

while it doesn`t explain the tach having a 600 cfm carb on a 383 will cause the powerband to literally stop under 5000 RPM , that would be the first change I would make get at least a 750 on it , beg borrow or buy to do it

[dodge freak 2]

If you are running a dual plane intake, the carb needs to be bigger than if it was on a single plane.

Something about the carb only seeing 1/2 the motor, thus the 180 name.

[Jacksboys]

I tried a couple more things today.  First I put on some new plug wires and nothing changed.  I then tried a new cap and nothing changed.  I also checked the voltage on the positive side of the coil and it never dropped when the rpm went up. 

I will not have enough time to take the distributor apart this weekend, so I will have to do it next weekend.

I still need to purchase another balast resistor.  What is it suppose to be rated at for the orange box?

I will get a 750 carb in the future.

[dodge freak 2]

You know 5000 rpms is low, I would think power might be down but it still should rev past 5000 rpms, even with a 600 carb.

How old are the valve springs?

What again is the motor doing @ 5000 and higher. Breaking up or just stops pulling.