Runs Rough

jwaldrich

jwaldrich

Senior Member
Had a sweet running bone stock 1915 Model T. I put a high volume intake manifold on there and it was still sweet running.

Then I put a Z head on it and now it runs rough at higher RPM's Idles pretty smooth. I've messed with the fuel air mixture with no success but I think it is in the timer.

Suggestions? What should I be looking for?
 
Runs rough is a pretty subjective description. is it missing or are you feeling the looseness in the rotating assembly?
 
Running Mag, freshly rebuilt coils by a recognized coil man. Holley NH. Running 6 volt.
The timer is at 11 o'clock when fully retarded and about 1 o'clock when fully advanced.
 
If you are running on mag, you are not running on 6 volts when you are at the higher rpm's. The mag can put out as much as 20 volts on mag at the higher rpm's. Pull the mag plug to see if there is lint on it from the band linings, it can block the current flow. Retard the spark to see if the engine smooth's out.
 
Higher compression needs a "hotter" spark, i.e. higher output voltage from the coils. If the magnets are weak, or corroded/loose connections, or frayed wire (only a few strands still intact), coil output will be weak and the higher compression will actually kill the spark.
 
40 Deluxe said:
Higher compression needs a "hotter" spark, i.e. higher output voltage from the coils. If the magnets are weak, or corroded/loose connections, or frayed wire (only a few strands still intact), coil output will be weak and the higher compression will actually kill the spark.
Click to expand...

I'll check the voltage output but previously it was over 20 volts. Wires are good and the coils all read 1.3 - 1.4 amps on a buzz box. All were recently tested and one rebuilt by Ron Patterson on his HCCT with the same amperage readings.

The bands are wood but I'll take a look at the mag post anyway.
 
14mm or 1/2 inch pipe thread plugs? Try setting the gap at .025. Check your fuel flow. You could have blockage in the line that is not allowing enough fuel at higher speeds but is fine at the lower RPM's.
I am sure you have done it but you could also recheck your timing, lever full up firing just after top dead center. If you are running a roller type timer, check the condition to the timer its self and the roller. You could be having roller bounce. Same thing with brush type, like New Day. The surface where the brush rides needs to be flat.
 
Sorry I was so vague. 1/2 pipe thread, running on magneto, coils freshly rebuilt, wooden bands.
Am headed out momentarily to fuss with the mag post and timer.
 
29spcoupe said:
If you are running on mag, you are not running on 6 volts when you are at the higher rpm's. The mag can put out as much as 20 volts on mag at the higher rpm's. Pull the mag plug to see if there is lint on it from the band linings, it can block the current flow. Retard the spark to see if the engine smooth's out.
Click to expand...

Running on MAG and it's putting out over 20 volts.
Just installed a "new from the vendor" commutator control rod and I have to pull the timer control to the max to get it to run smoothly. Not really happy with that.
 
redmodelt said:
14mm or 1/2 inch pipe thread plugs? Try setting the gap at .025. Check your fuel flow. You could have blockage in the line that is not allowing enough fuel at higher speeds but is fine at the lower RPM's.
I am sure you have done it but you could also recheck your timing, lever full up firing just after top dead center. If you are running a roller type timer, check the condition to the timer its self and the roller. You could be having roller bounce. Same thing with brush type, like New Day. The surface where the brush rides needs to be flat.
Click to expand...

Fixed the timer rod story. Plugs were already gapped at .25
It stalled out the other day. No fuel to the carb. Fixed that but I may have a dirty carb now so will try another carb.
 
Still some work to do. Put a Stromberg OF on it and fine tuning is still needed. Seems gas starved and get an occasional back fire.
 
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