Mid Range RPM Hesitation

[beermanpete]

It sounds like you have weak spark. Check the condition of the plug wires and the connectors where they go into the distributor. Be sure to check the coil wire as well.

What coil are you using? Are you using the ballast resistor?

[madkaw]

Sorry Bruce, his symptoms sound like bad float adjustment. Seems like we have had quite a few of these threads lately.

Check visually like Bruce stated. Could be a weak charge at the plug. Make sure your getting close to 14 volts while running at the battery.

Also check anything related to fuel supply- filters, lines

[boro92]

FWIW, I just put in a Pertronix and experienced the same issue upon install.

Note: Prior to the Pertronix install, I had the car tuned on a wide band and carbs synced as appropriate. Timing was re-adjusted and put back to factory spec post install.

Hesitation occured at around 4.5k RPM as you noted.

On my car in particular, the vacuum advance was disabled. For fun, I just hooked it back up and the hesitation went away. It now revs hard (though power band sucks post 5k rpm) to 7k. Unfortunately, my tach wont read past 4.5k under hard accelleration now...but that's another problem all together.

Are all vacuum lines hooked up on the car? What's the timing your'e getting under full advance?

[landmizzle]

Hi all,

So I removed the Pertronixs and put points back on. As I expected no change in performance; 4K + RPM hesitation still exists.

One thing I did notice is that with the points and using my trusty Sears Engine Analyzer, the points were reading "bad" as shown here. [ATTACH=CONFIG]49205[/ATTACH] If you look closely at the second scale from the bottom, you see that the needle is towards the left and is pointing to the "bad" portion of the scale. The "OK" portion of the scale is a little more to the left and is highlighted in red.

However, the points are good, but just to play it safe, I put on another set and got the same results.

The manual for the engine analyzer suggest that;

"A reading in the BAD zone of the points scale may

indicate defective points or any of the following

faults may exist:

• Poor distributor ground

• Poor connection on the primary lead from the

distributor to the ignition coil

= Defective distributor pigtail lead

= Misaligned points

• Poor points/plate ground inside distributor

Correct the defect and repeat the test, "

I don't think it's the points or misaligned points. I suppose it could be a bad ground somewhere, but I don't think so. The primary connection from the coil to the dizzy seems fine too. I'm assuming the pigtail lead is the spade connector that connects to the outside of the dizzy and connects at the same point as the capacitor. That looks fine also.

The whole "bad" points thing may be a wild goose chase, but I'm pretty sure the point always read "OK" in the past. It has been along time since I've used points though.

I've dropped timing down to 5 BTDC which is as retarded as the engine will go without really starting to idle poorly. Before it was set at about 8 BTDC. I don't know what my total advance timing is nor how to measure it. Any suggestions how to measure total advance?

I'm using the original coil (or very vintage..) with the ballast resister. The vacuum line to the dizzy is hooked up and seems to be working since the timing does advance when I blip the throttle as measured with a timing light.

Doesn't seem I'm getting anywhere particularly fast.

[madkaw]

To check your mechanical advance just aim your timing light to your marks on the pulley and hold throttle to atleast 2800 rpm. You might need to make additional marks on the pulley( 6mm is about 5 degrees) . Your mechanical should kick in atleast another 15 degrees from static- maybe 20+ with that dizzy.

If the timing doesn't increase this much, then your advance maybe jammed up.

I would also invest In a new coil just to eliminate this from the equation. And the correct ohm coil so you can eliminate more stuff like that ballast resistor

[240260280z]

Do you have a bent needle in a carb that sticks as it rises?

If idle is ok and WOT is OK then the only transitional factors are:

1. rate at which carb piston rises

- too fast and you go lean for a bit

- sticking and you go lean for a bit

2. fuel delivery

- weak pump or low default level ... but this seems unlikely if you have power back at WOT

3. Funky timing

- but you checked it ok

[landmizzle]

Hi Blue,

The hesitation occurs at 4k RPM and above to red-line. Power does not return at some point above 4.5 K RPM. So if by transitional, you mean the that power comes back at say, 6 K RPM, that's not the case here. Sorry if I wasn't clear.

It's not likely a bent needle as the pistons move up and smoothly when pushed up with my finger. They come down smoothly also. I believe I'm running 20 wt oil in the domes right now. Early on (back in February) when I first started experiencing the problem, I experimented with different weight oils (viz. ATF, 20 wt, etc.). I don't remember the exact results, but I'm thinking it didn't help in the since that it cured the problem, else I would have stopped there and not have had the dizzy rebuilt nor mess with the floats on the carb.

So, I suppose it still could be the float level is off (too low). IF so, I'm not looking forward to attempting to adjust those again.....Fuel pump is a possibility as you suggested.

The car will rev quite nicely to red-line in neutral under no load. I'm still a little bothered by the "bad points" status indicated by my cheap Sears engine analyzer. I may put the old dizzy on to see if that makes it go away.

I don't want to blindly replace parts as that can get expensive real quick and still not solve anything. I've done that already to some degree with having the dizzy rebuilt.

[240260280z]

Could be fuel delivery problem. What is fuel pressure?

You can try pinching off the return fuel line for a quick and dirty test to see if it makes a difference.

I also had a points car that went weaker at high RPM's and this seemed like a fuel issue. After checking everything it turned out to be the distributor, however your checks above seem to have ruled that out.

[madkaw]

I doubt the points has anything to do with this problem or the engine wouldn't rev up freely with no load-forget that stupid tester. Just make sure your connections are tight on all your wiring. You seem to have the problem under heavy load which requires a strong spark and more fuel. You need to stop whining and pull the float covers off and adjust them floats. It's not that hard once you get the hang of getting the covers off-are we talking 45 minutes? Make sure you are tweaking them the correct way.

Did you check the advance yet?????

Does the car hesitate or bog UNDER LOAD at any other rpm less than 4500--i.e. pulling up a hill hard in the gas???? =coil

[landmizzle]

Hi Steve,

Well, I didn't realize I was whining. Sorry if my lack of confidence with the floats annoys you.

I did check the total advance and it goes well beyond the degree markers; so I'm guessing 30+ BTDC. If I get time, I'll attempt to make some more degree markers.

Replacing the dizzy with the old one that has the Pertronix installed resulted in no change. So it's safe to rule out distributors, mechanical weights, points, Pertronix, capacitors, etc.

Takes us back to the carbs again or possibly the fuel pump, doesn't it...

I'll try the floats again. 45 minutes? Think not at least for me. Yes, removing the covers is a bear....

[madkaw]

Sorry,

I guess that sounded bad-- didn't it. Okay, well you need to start over and make sure you have covered the basics(loose electrical connections,good battery, charging alternator, good fuel flow). I am usually the first to say -look at the carbs last-but the symptoms warrant another look. Yes the lids are a pain in the a$$, but once you remember how to twist and tilt and turn the bowl lids, it gets much easier. Regardless of the setting you have right now on the floats-adjust them richer. If you go too rich you will know right away when you get it running again-it will be obvious!!

Hope this helps

Edited November 7, 2011 by madkaw

[landmizzle]

Hi Steve,

I appreciate that.

I'll probably attack the floats this weekend. Life's too hectic for me to do much on this issue until the weekend.

Thank you for all your suggestions.