no power

[Mutt]

Ok, to start off with, prior to 1958, NO 125,165 or HUMMER came from the factory with a brake light switch; unless it was specifically ordered with one, one installed by the dealer or bought as an Accessory and installed by the owner. Look at any Factory Pohlman Studio photo. BUT, 1955-57 B models never came with a brake light switch regardless. They were never offered for 55-57 B, because of the problem you have. The magneto didn't put out sufficient current to run the motor and the high draw of the 21c.p. tail light bulb. In 1958, the Department of Transportation mandated that ALL vehicles sold in the USA MUST come with brake lights. Harley then resigned the ignition system, removing the ignition coil of the 55-57 B model and installing a lighting coil in place of the former and a standard external coil under the tank. Problem was solved. A 125 should have at least 90 psi, but will run will far less, say maybe 55 or 60 psi. Is the motor rebuilt? Did ya install new cranks seals? Were the crank shafts pitted or grooved in the area on the shafts exactly where the seals ride? Did ya start with the lower (high speed) needle out 1 full turn from lightly seated? Do you have the correct main nozzle and tube in the carb? Is the carb the correct model or equvilent (MT43A)? What happens when you open the lower needle up 1/4 turn more or 1/4 turn less?

[250_Sprint]

Mutt will know.

[hennesse]

The Hummer wiring diagram on the website is NOT correct for the 1955 to 1957 "B" Hummers. It is correct for the 1958-1959.

Let's verify that you have the correct 1955-1957 Hummer magneto-generator, as sometimes parts get swapped over the years. These have a lower coil from which the spark plug wire directly emerges, and an upper coil that runs the head/tail lamps. You do NOT have a frame-mounted external coil.

I am wondering where the wire for the brake light switch is connected. On the 1955-1957, there shouldn't be any place to connect it! This makes me wonder if you have the correct magneto-generator.

[Mutt]

1955-57 B wiring diagram (post it into the wiring page Dave)

55 wiring dia.JPG (62.65 KiB) Viewed 26641 times

[56b1093]

Mutt, engine is not rebuilt. Compression is 80psi. Carb is Mt31b. I set both screws as described in manual. When running at 1/2 throttle, I can turn high speed jet all the way in until seated and it keeps getting faster. Book says to turn in until it slows and then back out 1/8to 1/4 turn, but I can't make it do that. Is my carb not correct or acceptable for the bike?
As far as the wiring, it has 2 coils in it, one of which I bought from you about a year ago. I think it is wired so that 1 coil runs the lights and the other the ignition, but the way it acts, I wonder if 1 is running the taillight and ignition while the other is the headlight. Wiring is not my thing, my brother did the wiring.

[Mutt]

Look inside the bottom of the float bowl. You will see a number like 3/8 or 9/16 or similar. I believe the MT-31B is only 1/2" venturi. You need a carb with a 5/8" venturi

[Mutt]

does your spark plug wire come off the rear side of the lower coil or do you have a coil right under the gas tank?

[56b1093]

Mutt, I just checked the bike out this morning. It says 7/16 in the bottom of the bowl. Do you have the correct carb that I could buy, or know where I can get one? Also, the spark plug wire comes out of the back of the lower coil. I am also in need of a new gas cap and fuel petcock.
Thanks for all of your help.

[Mutt]

56B, that carb is too small. (3/16" smaller) I dont have any Tillotson carbs in stock right now. Here is MT48A carb. It is for a Cushman, but it has the 5/8" venturi size. You could swap all the parts off your carb onto this one and everything should be fine

https://www.ebay.com/itm/394590471415