1948 125 Hummer will not rev up

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Re: 1948 125 Hummer will not rev up

Postby Phatsalmon » Sat Jan 21, 2023 3:50 pm

Ok thanks for the suggestions. I will take the carb apart one more time just to check. I does not hurt as it is very easy. I will disassemble once again, clear all the ports. I will also check for fuel flow before I put it back on the bike. I will also leave the carb in the ultrasound for an extended length of time. It is a very simple carb, but you are right it never hurts.

Is the #5 jet supposed to be 50 thousands of an orifice? Does it need to be bigger?

Thanks again. Remember that this was in baskets when we started I have nothing to base the condition on before we started the project.
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Re: 1948 125 Hummer will not rev up

Postby Backyard Bob » Sat Jan 21, 2023 4:10 pm

I never got into jet sizes on these bikes but have re-jetted a few other carbs after ethanol came along. The one thing that keeps sticking in my head is 'someone soldered the jet and re-drilled it'. The only possible reason I see for this is someone didn't want their kid to go too fast. Who knows. You have a soldered jet and a carb problem. The parts book shows it to be a 'metering jet' and the part number is 27620-47. I'm almost certain Mutt or Duane Taylor will have a replacement.
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Re: 1948 125 Hummer will not rev up

Postby 250_Sprint » Sat Jan 21, 2023 4:36 pm

I don’t rely on ultrasonic cleaning. I am old school and run a single strand of copper wire from old harnesses through the small holes throughout the carburetor. I know this is not what is recommended but my thinking is the wire will bend before any damage can be done to the soft metal.
I cut a long piece, feed it into the jet then slide the jet up and down the strand while rotating the jet. Then blow it out by blowing into it. Using compressed air may shoot the jet across the room, under the table and into a crack in the concrete floor, never to be seen again…
I use the same technique on the longer jets which have holes down the length of their bodies.
Larger diameter jets can sometimes handle 2-single strands. If I feel a single strand is too small and the jet can’t handle 2 strands, I will put kinks in the single strand, then feed it in running the jet up and down the strand with kinks. The kinks rub against the ID of the jet, cleaning as it goes.
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Re: 1948 125 Hummer will not rev up

Postby Backyard Bob » Sat Jan 21, 2023 4:50 pm

"Using compressed air may shoot the jet across the room, under the table and into a crack in the concrete floor, never to be seen again…"
That would be hilarious if it wasn't so true... but I laughed anyway. Been there, done that.
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Re: 1948 125 Hummer will not rev up

Postby Phatsalmon » Sat Jan 21, 2023 7:23 pm

Ok here is a Mid day update. Reset timing. This took a while as was suggested. Just used my Fluke in alarm mode and my Starett Depth gauge, Cant get better than that I suppose. I also remove the generator and looked to see if the woodruff key was intact. All checked well. I replaced the points once again just because I have a second new set. Probably overkill but what the heck.

Now for the fuel issues. I checked for flow first at the carb. Seemed a bit week. Then went to the petcock, still a bit weak. I then loosened the gas cap and the fuel stream increased noticeably. When I am ready to kick the bike again I will loosen the gas cap a bit.

Now for the Carb, This is a simple L&L carb. Only one jet. The number stamped on the jet is 5. I have enlarged to hole as suggested to 50 thousandths. I will try that. There is no secondary jet with small holes so that is not the issue I believe. I do use Motion Pro jet brushes before and after ultrasound. I have had extreme success using Orange Citrus cleaner on all the other Carbs coming through the shop. It busts the ethanol goo but it will turn the aluminum dark in color. This simple carb does not need any solutions, I believe, plus I do not want to discolor the carb so I am using a simple 409 mixture.

Will continue after lunch. Will keep all informed. Thanks so much to all of you for your suggestions and help.


Still looking to see if I can post pictures on this board. If not I will update our instagram account later today.
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Re: 1948 125 Hummer will not rev up

Postby Backyard Bob » Sat Jan 21, 2023 7:32 pm

Look at your' new posting page (reply)' (under the box you're now looking at). Scroll down (up?) and you'll see an 'upload attachment' tab. This is where you attach your photos. The site is set to accept lower sized photos so if you take them with a modern cell phone or digital camera they will be too large and you need to resize them.
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Re: 1948 125 Hummer will not rev up

Postby 250_Sprint » Sat Jan 21, 2023 8:54 pm

The original gas caps with built in measuring cup, are vented and it sounds like yours is clogged. Mutt once mentioned where the vent is located when looking at the underside of the cap. I don’t remember how to identify it from the underside. I will check my notes or maybe someone who knows will chime in…
At least you found something.
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Re: 1948 125 Hummer will not rev up

Postby Mutt » Sat Jan 21, 2023 9:17 pm

the 2 vents are located at the end of each runner , under the cup. You can see them easily
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Re: 1948 125 Hummer will not rev up

Postby Backyard Bob » Sat Jan 21, 2023 9:20 pm

Good catch.
Yes, I had a '46 Indian Chief I bought replacement caps for and ran into the same problem... I had to run them loose until I found a set of originals. The
replacements caps weren't vented properly. I'm beginning to think the reason we find these bikes is because somebody ran into a problem they couldn't easily fix, not because the motor blew up or something, and they just didn't get around to it.
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Re: 1948 125 Hummer will not rev up

Postby Phatsalmon » Sat Jan 21, 2023 11:08 pm

Last update of the day. Well the bike is running better. everything I did on the bike seems to help however the bike still stalls when opening up the throttle above half way open. Frustrating. Is this normal for this bike? Am I expecting this bike to wind up like any two stroke in error? I don't know where to go from here. Any suggestions? Thanks again to all of you for your help and assistance.
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