Jump to content

high speed miss 39 Buick


1939bcoupe
 Share

Recommended Posts

Hello, I have a high speed miss I need help solving.    At low speeds, no problem, but at 45 and above engine starts missing.  I use a pertronic ignition and Autolite 306 plugs set at 025.  I have the yellow with black and red stripe wires. Any suggestions would be appreciated.

Frank

Link to comment
Share on other sites

3 hours ago, 1939bcoupe said:

Hello, I have a high speed miss I need help solving.    At low speeds, no problem, but at 45 and above engine starts missing.  I use a pertronic ignition and Autolite 306 plugs set at 025.  I have the yellow with black and red stripe wires. Any suggestions would be appreciated.

Frank

 

 If it is left in 2nd and run up to  40 or so, does it miss?

 

  Ben

 

Link to comment
Share on other sites

You might try substituting a coil known to be good.  Trying the easiest stuff first....  High speed miss is often plugs, low speed miss often points (if equipped).  One coil symptom is OK starting and running at first, performance fading or sputtering as the coil gets hot.

Link to comment
Share on other sites

You might want to verify that the vacuum advance is working--apply vacuum with dist cap off and verify that the plate rotates and that there's no chafing of wires during its movement.

 

If that checks out, I'd pull the distributor, put it in a vise, check continuity of power and grounds, and then (if OK) pull the plate and look for dried grease in the cup that would keep the advance weights from moving freely and fully--and oil their pivots while you're in there.

 

Have you done a compression test?

  • Like 1
Link to comment
Share on other sites

And after all of that, put a set of ignition points in it and give that a try.  Some swear BY Pertronix, some swear AT Pertronix, especially if one is still on 6V and running a generator.   For myself, I stay with points and carry a spare set--I can be back on the road in 15 minutes.

Link to comment
Share on other sites

I would suggest the coil as well.  Go buy a good US brand.  My Pertronix coil gave me hell since I figured I had a new coil (about a year old at the time) and I did not think it could be bad.   Now I keep a spare coil in the trunk just in case the running one goes out.  

Edited by Hubert_25-25 (see edit history)
Link to comment
Share on other sites

14 hours ago, 1939bcoupe said:

The car does run better when cool.  When it heats up it get worst.  I did replace the pretronics coil with a replacement I got at O'Reillys.  Didn't seem to help.  I have another extra, I'll try 

Edited by Guest (see edit history)
Link to comment
Share on other sites

5 minutes ago, 1939bcoupe said:

Continuing saga, compression is 95 to 100 all 8 cylinders.

That's excellent news!  So it's either ignition or carburetion and most of us here believe that 90% of carb problems are in the ignition system.  You haven't told us a lot about the car--is it still 6V and does it still have a generator?  If yes to both, I recommend putting points back in it as a cheap test (even if you go back to Pertronix, you'd be well advised to carry points with you in case the Pertronix fails on the road).  The reason for this recommendation is that electronic ignition seems to often demand "clean" "steady" power as delivered by an alternator.  I don't want to argue the point with happy Pertronix-in-6v-generator-equipped-cars folks--I just to rule out the possibility cheaply and easily.

  • Like 2
Link to comment
Share on other sites

Afterthought:  As I understand it, you experience the problem in a LOAD situation (i.e., engine driving the car) at speed.  Next time you get the miss at speed, stop immediately and run engine in neutral under NO-LOAD conditions and see if the miss is still there.  If it's OK at NO-LOAD, I'd suspect the secondary system (plug wires).  Speaking of plug wires, have you revved the engine up (HOT) in the dark to see if there's a light show among the plug wires?

 

Re layout:  Do you have (1) (best) a factory shop manual or (2) a MoToR or Chilton manual covering the car?  1939 might be a little late for a photo of the dist guts to be in the Owners Manual, but check anyway.  If you have none of the above, Google is your friend.

Link to comment
Share on other sites

Try a vacuum gauge on a warm engine and tell us what you see, both the number and the movement of the needle.  Google will give you charts on reading vacuum gauges, but one may be in your MoToR manual.

 

Also, you can use a vacuum gauge to check for plugged muffler or exhaust system as follows:  With vac gauge hooked up and car at rest and warmed up, have an assistant run engine at about 1800-2000 rpm for two minutes, AFTER the vac gauge takes about 20-30 seconds to stabilize.  Note the reading on the gauge once it stabilizes, then again at the end of two minutes.  A significant drop in the second reading from the first indicates possible clogged exhaust--which COULD put a strain on other not-quite-perfect components at speed.

Link to comment
Share on other sites

At idle, it stays around 20.  When I run at higher rpm, it jumps from around  20 to 15.  When I hold at higher rpm it jumps from 20 to 15.  With each miss it drops to 15.  The car has been nicely restored but they forgot about the muffler, it looks rusty and bad on the outside.

Link to comment
Share on other sites

According to the manual that came with the vacuum gauge, it means a restricted exhaust.  Time for a new muffler anyway.  How do I describe to the shop what kind of muffler I need.  There was a place that sold pre bent exhaust systems but I for got the name.  I've bought a few in the past. Getting old is not good for the memory.☹️

Link to comment
Share on other sites

Suggest you check the pipes for critter nests when the muffler is off.

 

Can you please describe your readings more fully? 20 at idle is great, but I'd expect it to stabilize lower, maybe 17-18, initially at rpm when the gauge stabilizes--and then drop lower over the 2-minute period.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...