Engine loses power around 5000RPM

[Jacksboys]

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.

The valve springs came on the Edelbrock heads, suppose to be good to .575 lift (I have .477/.480).

You can seriously see the tachometer needle jumping back and forth (while driving or just reving it).  The engine is pulling strong and it feels like it just lost some power.  The engine still has enough power that the transmission does not wnat to shift yet even though it has weakened.  I have to get off of the gas pedal to let the tranny shift, and then the engine goes back to normal operation.

I have also noticed that it is happening more at 4000-4500 rpm here lately.

[dodge freak 2]

Well I decided to read the whole thread 

How old are those Eddy heads? Where they checked out before bolting them on?

I head Edelbrock heads can be way off. Some shops swear to take apart even a brand new head and check everything. They claim every head has a few things wrong, guilds too tight, valve seats not round, springs weak.

I would pull the heads-if they were not check out ever-and have them look over.

It sounds like valve springs, lifters pumping up. The fact it does it at 4500 when good and hot, could very well be weak valve springs. Maybe the hight was wrong, even a new spring will be weak if the install hight is wrong.

Now yeah, swapping carbs be much quicker and easier, I have a bunch over here in cold snowy Michigan--this stinks, its snowing every day-but I take it you live some where nice 

I can't see how a too small of carb could be heat related, thou.

[ChallengerHK]

When you say jumping, do you mean like 1-200 rpm or more like 1-2000 rpm?

[dodge freak 2]

If its doing it at 4000 rpms now, its not the 600 carb.--Unless the carb is bad, too low of float level--clog fuel filter--you have try it with out the fuel filter, right?

Even if the filter is new, chances are by removing it, the motor would pick up a few hundred rpms-if is fuel related.

The head might be bad. The valve guilds are sticking--I see on speedtalk that many Edelbrock heads have too tight of valve guilds..

I know, taking the heads off a big job, best to check the easy stuff out first but if all else fails, have both heads look at by a good machine shop.

Sorry, but thats my guess. 

[dodge freak 2]

I am pretty sure it has nothing to due with the fuel because I have an O2 sensor and I did not see a lean spot.
I have the Edelbrock heads, so airflow is not a problem, and 5500RPM should be a breeze.

This was only the second time I have spun it up that high while I was watching the tach.  The first time (about a month ago) I thought it was just my imagination, so I did not worry about it. 

The tach does not fluctuate up and down, it  shakes erratically until I shift into 2nd, then it is fine again until it gets near 5000RPM again.  I can still feel the engine trying to increase in RPM past the 5000 mark but it is very weak.

I forgot to mention that this happened once before with a different distributor that I tried to refurbish, but the problems started at 3000RPM.  Then I got the Mopar Performance dist. and I thought that solved the problem...I guess not. 

I am 99% sure it has to due with the electronic ignition.  I might borrow my father's coil and see if it makes a difference, since that would be the cheapest route first.

Hmmm, maybe its with the dist....funny it did it at 3000 rpms, by changing the dist...thats not the heads then.

[Jacksboys]

When you say jumping, do you mean like 1-200 rpm or more like 1-2000 rpm?

I would say in the 200-300 rpm range.  My father revved it once slowly up to 4500 and he said the tach quickly dropped to 4000, and he let off.  

[dodge freak 2]

If its spark related, a scope would show it.

You have any good repair shops around there-that work on old cars?

Since its doing it with no load, it be easy to see-with a scope, if the spark plugs are misfiring. Should cost $50 or so and 10 mins to find out if its in the ignition

[Jacksboys]

Hmmm, maybe its with the dist....funny it did it at 3000 rpms, by changing the dist...thats not the heads then.

I agree that it must be something electrical, so I do not want to take anything apart until I check everything else.  

[Jacksboys]

If its spark related, a scope would show it.

You have any good repair shops around there-that work on old cars?

Since its doing it with no load, it be easy to see-with a scope, if the spark plugs are misfiring. Should cost $50 or so and 10 mins to find out if its in the ignition

I hate to sound dumb, but I do not know what you mean by testing with a scope.

[dodge freak 2]

You been screwing with this for 6 months 


A good shop with the right equipment can pin point where the problem is. With a vacuum gauge it show if the valve guilds are sticking. A electrical scope would show if the spark plugs are misfiring.

You need to find a shop and stop guessing.

Some old guy in a good auto repair shop could find where abouts the problem is in under 1 hour. 

[dodge freak 2]

Not sure how to describe a "scope" They stop using them in the 80's when I was getting in to cars.

With it, all the plugs you can "see" firing--it show a straight line--if the plugs misfire, the line breaks up. Does not tell you why but then you know its spark related.

In the 70's all auto shops had them. Saves lots of time.

If the plugs are firing fine and the motor breaks up, you know for sure its not with the spark plugs.

[dodge freak 2]

"scope" is the nickname, I don't know whats its really called. Always  hear the guys call it a "scope"

Its big and cost $$$. When cars started to lose the points, dist. they got other stuff.

Maybe the new equipment would work too.

Make some phone calls Monday. Somebody should be able to tell you where the problem is after spending an hour with your car.

[Jacksboys]

You been screwing with this for 6 months 


A good shop with the right equipment can pin point where the problem is. With a vacuum gauge it show if the valve guilds are sticking. A electrical scope would show if the spark plugs are misfiring.

You need to find a shop and stop guessing.

Some old guy in a good auto repair shop could find where abouts the problem is in under 1 hour. 

In my defense about the 6 months:  I go to school and work a bunch, so I do not have much time to mess with it on a regular basis.   I also do not trust most of the mechanics out here because they do not know anything about mopars. Plus I would rather do the job myself so I know what the problem is and know how to fix future problems.

The car drives great otherwise, so it is not like I am stuck with it in my garage.

[Jacksboys]

Not sure how to describe a "scope" They stop using them in the 80's when I was getting in to cars.

With it, all the plugs you can "see" firing--it show a straight line--if the plugs misfire, the line breaks up. Does not tell you why but then you know its spark related.

In the 70's all auto shops had them. Saves lots of time.

If the plugs are firing fine and the motor breaks up, you know for sure its not with the spark plugs.

"scope" is the nickname, I don't know whats its really called. Always  hear the guys call it a "scope"

Its big and cost $$$. When cars started to lose the points, dist. they got other stuff.

Maybe the new equipment would work too.

Make some phone calls Monday. Somebody should be able to tell you where the problem is after spending an hour with your car.

Thanks for the info.  Since they are not commonly used anymore, do you think it is possibe to pick up a used one cheap?

[dodge freak 2]

Awe, a good mechanic should be able to see where the problem is.

These old cars are so easy compare to these new cars.

What you have to lose, they won't hurt your car. Sure beats changing stuff thats not needed.

It runs but not as good as a new car. Thats no good--should run "better"