1939bcoupe Posted February 12, 2019 Share Posted February 12, 2019 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 More sharing options...
JFranklin Posted February 12, 2019 Share Posted February 12, 2019 Weak or broken valve springs come to mind. 1 Link to comment Share on other sites More sharing options...
Grimy Posted February 12, 2019 Share Posted February 12, 2019 Especially with the Pertronix, I'd experiment with opening the plug gap to 0.030. If there's an improvement, try .032 or even .035. 2 Link to comment Share on other sites More sharing options...
Ben Bruce aka First Born Posted February 12, 2019 Share Posted February 12, 2019 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 More sharing options...
1939bcoupe Posted February 12, 2019 Author Share Posted February 12, 2019 I opened up the plugs and I think the missing got worse Took it to 40 in second and still misses. Keep the ideas coming. Frank Link to comment Share on other sites More sharing options...
Grimy Posted February 12, 2019 Share Posted February 12, 2019 Did this occur BEFORE the Pertronix install? That is, is the Pertronix recently installed? Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 12, 2019 Author Share Posted February 12, 2019 I acquired the car with the pertronics already installed. I replaced the original pertronics with a new pertronics in hopes that the old one was bad. Link to comment Share on other sites More sharing options...
Grimy Posted February 12, 2019 Share Posted February 12, 2019 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 More sharing options...
1939bcoupe Posted February 12, 2019 Author Share Posted February 12, 2019 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 that Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 12, 2019 Author Share Posted February 12, 2019 I thought is might be the fuel pump. I replaced the manual with an electric. Link to comment Share on other sites More sharing options...
Grimy Posted February 12, 2019 Share Posted February 12, 2019 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? 1 Link to comment Share on other sites More sharing options...
Grimy Posted February 13, 2019 Share Posted February 13, 2019 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 More sharing options...
Hubert_25-25 Posted February 13, 2019 Share Posted February 13, 2019 (edited) 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 February 13, 2019 by Hubert_25-25 (see edit history) Link to comment Share on other sites More sharing options...
Guest Posted February 13, 2019 Share Posted February 13, 2019 (edited) 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 February 13, 2019 by Guest (see edit history) Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 13, 2019 Author Share Posted February 13, 2019 Well, I put a coil from a 36 Cad ( definitely American made)😀 I used to have in it and it started right up and I let it warm up. I revved it up and sounds good but cannot test drive until the weather improves. This would be my third coil test.🤞 Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 13, 2019 Author Share Posted February 13, 2019 ☹️Tried it again, with warm engine and miss came back. When I hold the rpm high with engine cooler-not problem. When warmed up miss comes back at higher rpm. Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 13, 2019 Author Share Posted February 13, 2019 Maybe move the accelerator pump to a longer stroke to put more gas in? Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 14, 2019 Author Share Posted February 14, 2019 Continuing saga, compression is 95 to 100 all 8 cylinders. Link to comment Share on other sites More sharing options...
Grimy Posted February 14, 2019 Share Posted February 14, 2019 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. 2 Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 14, 2019 Author Share Posted February 14, 2019 Thanks, checking the vacuum advance tomorrow. I think I may need more that just a set of points to put it back to original. Condenser etc. Can anyone send a pic of the point set up ? Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 14, 2019 Author Share Posted February 14, 2019 I forgot, yes 6 V. negative ground, generator. Car came with the pertronic so need everything to convert back to point system. Link to comment Share on other sites More sharing options...
Pete Phillips Posted February 14, 2019 Share Posted February 14, 2019 I vote for fuel starvation. Is the fuel filter clean? Is the fuel pump beginning to fail? Pete Phillips, BCA #7338 Link to comment Share on other sites More sharing options...
Grimy Posted February 14, 2019 Share Posted February 14, 2019 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 More sharing options...
1939bcoupe Posted February 14, 2019 Author Share Posted February 14, 2019 Fuel filter at carb is clean and electric pump works well. Disconnected line at carb and fuel flowing well. One other strange thing, it runs really bad when I remove stock air filter and go for ride. Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 14, 2019 Author Share Posted February 14, 2019 I have 39 shop manual and blue MOTOR manual. Car misses in garage when held at higher (rpm) speed no load after warm up. Have to check for light show tomorrow night, plugs still out from compression test.😀 Link to comment Share on other sites More sharing options...
maok Posted February 14, 2019 Share Posted February 14, 2019 Have you checked the timing? Is the distributor advancing as rpm increases? Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 14, 2019 Author Share Posted February 14, 2019 found pic of distributor👍 Link to comment Share on other sites More sharing options...
Grimy Posted February 14, 2019 Share Posted February 14, 2019 13 minutes ago, 1939bcoupe said: found pic of distributor Excellent! You'll find the issue. Link to comment Share on other sites More sharing options...
SteveBigD4 Posted February 14, 2019 Share Posted February 14, 2019 Removing the air filter leans up the mixture a bit so it may indicate that the missing problem is a lean running condition. Perhaps a vacuum leak? Steve D 2 Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 14, 2019 Author Share Posted February 14, 2019 Vacuum advance is working. plate moves. UGH, please keep suggestions coming. The heat control thermostat is working and in the correct position. Frank Link to comment Share on other sites More sharing options...
Grimy Posted February 14, 2019 Share Posted February 14, 2019 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 More sharing options...
1939bcoupe Posted February 15, 2019 Author Share Posted February 15, 2019 Where is a good place to attach the vacuum gauge, on the wiper outlet on the intake manifold? Link to comment Share on other sites More sharing options...
Grimy Posted February 15, 2019 Share Posted February 15, 2019 YES 1 Link to comment Share on other sites More sharing options...
neil morse Posted February 15, 2019 Share Posted February 15, 2019 A lot of good information here, as usual. But every time I read the title of this thread, I keep thinking I'm going to see some racy pictures of "Miss Buick of 1939!" 😁 Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 15, 2019 Author Share Posted February 15, 2019 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 More sharing options...
1939bcoupe Posted February 15, 2019 Author Share Posted February 15, 2019 Oh yea, the misses do not happen evenly. They jump around and are not synchronized.. Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 16, 2019 Author Share Posted February 16, 2019 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 More sharing options...
raydurr Posted February 16, 2019 Share Posted February 16, 2019 Waldrons exhaust supplies some prebent systems. Link to comment Share on other sites More sharing options...
1939bcoupe Posted February 16, 2019 Author Share Posted February 16, 2019 I remembered, Classic exhaust systems was the one I used before. Maybe just replace the muffler. If this solves the problem, I'll give everyone a full report.😀 Link to comment Share on other sites More sharing options...
Grimy Posted February 16, 2019 Share Posted February 16, 2019 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 More sharing options...
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