OK, now i'm baffled - high RPM miss???

[BarryK]

this is the senario:

car ran pretty good including high rpm's except I knew distributor needed to get rebuilt as the timing curve was WAY off.
Over the winter as I was re-doing the engine and engine bay I had the carb sent out for rebuild.
I also replaced the distributor rotor and cap than ended up sending the distributor out for rebuild and re-curve. The distributor had hi-tension points and as they were only a few months old the guy working on the distributor kept them in. The guy working on my distributor (someone very, very well respected on the NCRS board and who has a Sun Distributor machine for proper re-curving) mentioned he wasn't too sure about the replacement cap and rotor I had just gotten from Paragon and put on and mentioned that if I noticed any high-speed break-up to replace them with different units that he recommended.
When reassembling parts back on the motor I replaced the spark plug wires with new Delco 508N wires as per recommendation from JohnZ and Duke.

Since getting the car running again I haven't driven it too much this season but when I have I've noticed it was breaking up at 4,500 - 5,000 rpms and higher.
I was told it may have been the float levels in the carb being too low and of course I remembers what the distributor guy said about the cap and rotor so today I went to fix the problem.

I re-set the float levels on the carb, and replaced the "new" distributor cap and rotor with the older units that I still had knowing I never had any problem with them and no high rpm break-up.
After setting the carb floats and replacing the rotor and cap I checked the timing and it's dead on at 12* initial, 36* total all in by 3,000 rpm and 52* total w/ vacuum advance.
I also re-checked my fuel mixture settings using a vacuum gauge and it's set based on the highest vacuum readings. I'm getting about 12 in/HG vacuum steady on my L76.

Took the car for a test drive and while it improved somewhat the problem is still there over 5,500 or 6,000 and higher rpm.
I don't like having my motor run that hard so I didn't stay up at that rpm range too long but now I'm wondering if instead of a "break-up" like points floating if instead it's maybe a high-rpm miss.

What is my best course of action to help diagnose and fix this issue.

To summarize:
1. the points are hi-tension and less than 1,000 miles on them
2. dwell is rock steady and timing is dead-on where it should be
3. distrib. cap and rotor are back to the "old" set I was running last year with NO problems like this
4. carb was rebuild and floats are set to the correct level and mixture is set right via a vacuum gauge
5. new spark plug wires (and new spark plugs)
6. new fuel filter

I'm getting a miss or a break-up of some type at high rpms.

Any help is greatly appreciated.
Thanks!

 

[firstgear]

it wasn't broke and you had to fix it........that is the problem....

 

[BarryK]

well, in a way it WAS broke - the timing curve was WAY off. Just to keep the total timing to 36* I had to lower retard it so much the initial timing was down to 4*. Mechanical advance was throwing in 32* rather than the correct 24*.
To me that is broke!

 

[jims427400]

Barry,
I did my carbs,pertronics elec. points,rotor,cap,plugs,and still ran bad.Turned out to be plug wires.But then I had to tweek my linkage,too get things truely dialed in.
my car runs really well BUT I too still get a little breakup at 5-6000 too but I'll live w/running it under that..Good luck,I'm interested in finding out your problem..

 

[jims427400]

Barry,
One more thought,instead of setting my timing at 4*,I;m at around 10*.
(Our carb. rebuilder told me to do that)seems to be a little better..

 

[LT4man]

What type of spark plugs are you using?

What type of ignition coil do you have? What is the age?

When you say "hi-tension points" what exactly do you mean? Is there any identification as to the manufacturer of the points? Is this a single or dual point set-up?

Report back to me. Take two aspirin. Check this thread in the morning!

SAVE THE WAVE!

 

[BarryK]

lt

the current plugs that I just installed a couple hundred miles ago are the R45's.

coil is the correct stock type (I don't remember the number and would need to pull the shielding off to check it)

the hi-tension points are the heavy duty points. I don't know what brand they are. They were just installed last July and have very limited use on them - less than 1,000 miles. Standrd points will start floating over about 5,000 rpm's so I made sure that these were the hi-tension points that are good for much higher rpm speeds. They weren't giving me problems last fall so I don't really think they are the issue now although I could be wrong.

A good friend of mine emailed me - I trust his advice like I would JohnZ's - he's that good on these older cars. He's had this problem himself and after trying lots of things he found the newer plugs that are resistor plugs sometimes don't match up well with the radio suppresion wires. The cars originally came with non-resistor plugs but the modern plugs of the R45's are now resistor plugs. His theory is that the added resistor in the plugs caused enough of a voltage drop to create a mis-fire at higher rpm's.
After he switched to a non-resistor plug his problem went away.

I'm going to pick up a set of non-resistor plugs and see if it helps.

 

[Old Bull]

Check your dwell. High point spring pressures also tends to wear the rubbing block quicker especially if it is running dry. The result is diminished point gap, less dwell and high speed miss.

 

[BarryK]

old.
Dwell is 30 and real steady

 

[I'mAVettehead]

Barry, Be sure to replace the condensor when changing the points. Good Luck. Brian

 

[JimVette]

I had a '66 327/350 a few years ago that had a simular problem. Every 2/3 weeks I would take it out and it would run like c**p. I was always taking out the points cleaning and regapping them. I finally Installed a Mallory Unilite and never had a problem with it after that. Unless you take off the dist. cap you could not tell it from stock. Good luck.

 

[Kid_Again]

I wouldn't spend a dime on this until I looked at the plugs. I didn't see reference to that in the thread.

What does each and every plug tip look like?

 

[Ken Anderson]

Hi speed miss = AC spark plugs, especially R's (plug reading means nothing with these plugs). Also run 44's in the summer & 45's in the winter!
+ add in carbon thread wires and a 40 year old coil, or one of the new GM "replacements" and you're lucky to hit 5 grand. Good luck!

 

[74bigblock]

This may be something you've already done... but make sure those new plug wires are routed correctly. If they are touching anything like a ground source, you will arc and break up at higher RPM.

 

[Craig -1965]

High RPM miss...

Barry,
Have you considered dumping the points and conderser for the Printox conversion. I have a 65 327/350 and did the origional distributor rebuild and re curve, but added the electronic kit. Runs great and tune ups are plugs, timing and carb if necessary...... food for thought.

 

[BarryK]

Craig, yes I considered it about two years ago but I'm not convinced of any advantage of the conversion kits other than saving me 2 minutes a year during tune-ups not having to check and set dwell.
I believe that a properly set-up and operating points distributor will operate just as well as an electronic conversion kit. I also think that overall points are still more reliable. I've seen many threads with the conversion kits failing.
I'm not disrespecting your choice and if you are happy with your conversion kit than I'm happy for you - I just don't see the advantage for me to spend $160 to save 2 minutes of labor a year plus IF my points actually did fail I could change them on the side of the road........
:

 

[JL66REDCPE]

I wouldn't spend a dime on this until I looked at the plugs. I didn't see reference to that in the thread.

What does each and every plug tip look like?

EXACTLY !!!

 

[BarryK]

I wouldn't spend a dime on this until I looked at the plugs. I didn't see reference to that in the thread.

What does each and every plug tip look like?

Well, I just started a new thread with this very issue and asking for help in analyzing my plugs with a link to the pictures.

 

[LT4man]

Barry,

I know this is coming a little late. I have been tied up with my elderly mom and one of my brothers being in the hospital. They both seem to be pretty stable.

As far as your high RPM miss.

All of your points (no pun intended) are valid. A point system is easy to maintain and you can perform open distributor surgery on the side of the road if necessary.

With that being said, I will advise you with over 34 years of experience.

Buy the following items:

1. New ignition coil (brand is not important - just make sure it's new)

2. Replace the point & condensor setup with an electronic version
(brand is not important - buy whichever one floats your boat!)

These two items will completely cure your high RPM miss. You will miss being able to work on your Vette on the side of the road. A small sacrifice one has to make.

SAVE THE WAVE!

 

[BarryK]

lt

hope your mom and brother get better soon!

I'm going down a checklist one item at a time and only changing out one item at a time until I find the cause of the missing.

1. swapping out my resistor plugs to non-resistor plugs.
2. swap in new coil
3. swap in new points and condensor

IF the problem is somewhere in the ignotion system and is a spark related problem one of these three items should cure it. if not, than it's on to #4

4. check thru valve train for broken valvesprings, bent pushrods, etc

sorry, I just can't be convinced at this point in time that an $160 electronic conversion kit for my distributor gains me anything that a $10 set of points won't do IF it turns out that it's the points (which I still suspect it's not).

: