The Harley Hummer Club

Help please. I have just completed a rebuild of a 1948 125cc Hummer. It was a basket case when I got it. I have just completed the rebuild and assembly of the entire bike. I am so close to being done. However, I need some help with a starting issue. The bike starts well and will idle. It will rev up but will begin to stumble at mid stroke of the throttle. I cannot get it to rev up at all. I can ride the bike at low RPM's but stumbles as I give it more throttle. It is acting like it is looking for advance of the timing. I have done a leak down test and it holds. I have adjusted the timing to factory and then to extremes both retarded and advanced. I have moved the needle in the carb to lean and then to rich. No help. Looking for suggestions and advice please. Thanks all for your expertise.

Mutt will give you the right answer but I see you may having to drill/clean out your carb jet.

Cleaned the entire Carb. What size should I drill the #5 jet? It is currently at 50 thousandths. It will rev till about mid RPM then begin to stumble. I will check the timing once again using my meter and depth gauge. Thanks

you your carb slide on easy?

Make sure the fuel flowing from the tank to the float is flowing at a faster rate than demand.
Clean and check flow at petcock. Sometimes the petcock internals have restrictions.
Clean and check flow at fuel pipe/hose. Make sure what is coming out of petcock is coming out of fuel pipe/hose.

Do you wack the throttle open or do you slowly increase the revolutions?
Slowly increasing revolutions can sometimes indicate where the problem can be.

If all else fails, walk away (hard to do) clear your mind of frustration, and try another time.

Good Luck and let us know.

I just thought of another possibility... you may have a points condenser that's failing.

I will try to take these in order. Thanks to everyone for their suggestions.

1) The Carb is a little tight when installing on the barrel. the shim is in place and makes a good seal I believe.
2) I will check the flow. I have placed clear lines to see the flow of fuel. When I press the vent on top of the carb the fuel runs fast and clean.
3) I slowly increase the throttle. If I do it fast the bike stalls.
4) I am going to replace the condenser today. All I can find local is 12 volt condensers. I have read the postings and it looks like it is OK to use a 12 volt condenser. Am I wrong?

Going to try timing again today. Thanks to all for the guidance and support

Also is there a way to post pictures of the project. This bike is amazing.

One more item. It looks as though the jet at one time was soldered shut and then redrilled to 30 thousandths. I resized to 50 Thousandths. Is this OK?

Thanks again

To me, it sounds like either ignition or fuel starvation.
If the engine will start easy and idle all day I think it’s the fuel in the bowl is being used faster than it can be replenished.
It is not just, is fuel flowing, the bowl must have fuel readily available.
Is the float valve seat clean and clear?
Is the metering jet completely clean and clear?
Are all of the holes in the nozzle and holder clean and clear?
Is the passage from the float bowl to the nozzle and holder clean and clear?
If you suspect a part, try replacing it with known good part.

Maybe the tank passed some obstruction into the flow of things.

I never ass-u-me I did it right the first time if it is not working as it should.
It never hurts to go back over everything again to make sure it is all functioning as it should.

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.