resistor cause miss??

[swedishsteel]

I have a '36 coupe with 221LB with Eddie Meyer heads and dual carb high rise manifold with two 97's, four speed S10 tranny, 2.75 nine inch rear end. Runs super, except when it gets to operating temp and pulling hard around1000-1500 rpm (just guessing, no tach) it bucks and misses, until it gets wound out a little and then runs strong 'til I shift, then bucks and misses some in the next gear. I turned down the distributor brake one turn and it helped some, but it didn't ping to start with that I could hear. Being it doesn't do it when the engine is still relatively cool, (short run time) I'm wondering/asking if the resistor under the dash could cause weak spark after it gets hot?? Basically stock 6 volt system. I have rebuilt coil by Max and rebuilt distributor by Bubba, so pretty confident the problem isn't there. Accelerator pumps are new and working good. Pulling the choke out doesn't help, so I'm pretty sure it's spark related. Thanks for any ideas. Rod

[fourfords]

I had the identical problem in my 6V positive ground '37. The wiring to the resistor under the dash against the firewall was wired incorrectly which sent too much electricity to the coil and points slowly burning them, which created the"Bucking" and general rough and inconsistent driving until failure. Locate the correct wiring diagram, verify correct wiring, test the resister block making sure it is resisting to the correct voltage (1.5V If I recall), and find a local V8 guy who's willing to help. (This will be more fun, and keep the profanity within reason and will help the learning curve) Then have the points and distributor tested.

[Ggmac]

If it misses at low speed ,I'd guess it's not spark ( resistor ) but maybe your 275 rear is a bit to much and your not in your power band for the motor you built .

[JSeery]

A 2.75 rear end gear sounds like a lot of load on the engine, what is the idea behind using that high of gearing?

[swedishsteel]

The rear end coupled with the 4 speed works very well--60 mph is 2000 rpm. It is not an overdrive tranny. It was behind a 4 cylinder chevy s10. With "normal" start it works fine. When trying to get to 60 quickly from dead stop is when it bucks. If I want to go from 50 to 60 and put the pedal down it pulls smooth and will just keep pulling as long as I keep my foot in it. It isn't a single cylinder miss, like a plug, but more like a momentary loss of spark--best way to describe it. The wiring harness is new and installed correctly. When testing the resistor is that with engine running?? I checked the voltage across the resistor, through the switch and at the coil with engine not running and all voltages were 6+. I have another resistor and checked the resistance across that and the one in the car and they are both .6 ohms. Since the first post I've searched and read on other posts and it is confusing when reading about the resistor. Makes a difference whether engine is running or not????? My electrical acumen is not very high. thanks for the help. rod

[JSeery]

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OK, I was assuming it was an OD like a T5. Reread the OP, it does say 4-speed!

[Brian]

The idea of the resistor is that as it heats up, the resistance increases, which drops the primary voltage down to about 4 1/2 volts. This prolongs the life of the points.
But...cold engine, cold resistor, the primary gets full 6 volts as you've recorded. I think your troubleshooting is following the correct procedure. Check voltage after the resistor once engine has run for a while. What gap are your sparkplugs?

[37 Cab]

What kind of spark plug wires are you running? It sounds like a wire breaking down.

[George/Maine]

I think your dist bushing are worn and shaft is moving egg shaped, and under power chances under different rpms.

[swedishsteel]

Discovered the two nuts on the resistor were only finger tight. Tightened 'em and took it for a stop and hard go 6 mile ride. Ran/pulled good. Voltage across resistor upon return 4.6. Must have been getting the volts but not amps under certain conditions. Taking it to Back to the Fifties this weekend, so it will get a good workout. Thanks for all the help. Rod

[George/Maine]

Most 6 volt systems run about 3 amps when running.
Measuring across resister meaning one end or other each end.
4.6 is way to high.
My guess you have a 1.5 ohm resister wrong for 6 volts.
When charging 6.8 volts minus 4.6 leaves 2.2 volts to coil look to low.
Measure the ohms on resister. should be .5 ohms. .5 x 3 amps= 1.5 volts will increase coil voltage 5 volts.

[swedishsteel]

Originally Posted by George/Maine

Most 6 volt systems run about 3 amps when running.
Measuring across resister meaning one end or other each end.
4.6 is way to high.
My guess you have a 1.5 ohm resister wrong for 6 volts.
When charging 6.8 volts minus 4.6 leaves 2.2 volts to coil look to low.
Measure the ohms on resister. should be .5 ohms. .5 x 3 amps= 1.5 volts will increase coil voltage 5 volts.

Voltage not amps on the coil side when running hot was 4.6, which is about what the same as your figures. I didn't measure amps. It is a stock resistor on the junction block, so should be the right one. When cold, it measured .6 ohms as did an old spare I have in my parts stash. Thanks. Rod

[Tinker]

Sure it's not valves. Have/had this issue, valves sticking and low carb heat. Just a thought.

How often do resistors go bad? and when they do It's real apparent.


Maybe condenser.
2cents

[BUBBAS IGNITION]

Interesting thread regarding the Early Ford Flathead helmet unit. George hit it on the head with the loss of voltage (electrical pressure) caused by loose connections.
Just for a little circuit review heres a drawing i did this morning.......
Low voltage on the coil will idle great and then fall off at rpm increase......