Author Topic: First Ride 1920 Douglas W-20 2-3/4hp Flat Tank (Read 2400 times)

Tim OConnor · « **on:** 25 Sep 2022 at 13:54 »

My first ride! My first ride on the 1920 Douglas (or any flat tank for that matter). Still needs lots of tuning and I need to finish the lighting system. None the less a milestone.

She is only making about 5mph right now. If you have, or know a source of AMAC jets please let me know. I don't want to drill out and solder my only jet. So, please if you have some AMAC jets or jets converted to fit AMAC I would very much like to purchase them from you.

cycarmark · « **Reply #1 on:** 26 Sep 2022 at 00:21 »

Congratulations on getting the bike going, looks like lots of fun to ride. I'm a few weeks away from getting my B29 running and I hope it goes as well as yours! Attached is a page from the Radco book showing the AMAC jet size and the corresponding more modern (and readlily available) AMAL jet. The way I have fitted the more modern jet to an AMAC carb is to turn down the threaded portion of the modern jet to make a stub, make a 1/4" 26 tpi brass adapter that will fit over the stub and solder it in place. You now have a modern jet with the thread size of the original AMAC jet. That way you can put a new jet into your carb with no permanent modifications to the carb. You will also have a good variety of jets to try if you modify more than one size.

Tim OConnor · « **Reply #2 on:** 26 Sep 2022 at 00:35 »

Quote from: cycarmark on 26 Sep 2022 at 00:21

....make a 1/4" 26 tpi brass adapter that will fit over the stub and solder it in place. You now have a modern jet with the thread size of the original AMAC jet.

Thanks!

I am not sure how to create this brass adapter. I am not a machinest. I have ordered a 1/4 26tpi die, hopefully, it will arrive in a few weeks.

cycarmark · « **Reply #3 on:** 26 Sep 2022 at 02:25 »

Just get a piece of 1/4" brass bar and drill a hole in the end of it to fit the stub on the new jet, then thread the bar and cut off however much you need to solder on to the jet. If you need help I would be glad to modify one, just send it to me, I'm located in Florida.

Tim OConnor · « **Reply #4 on:** 26 Sep 2022 at 02:31 »

That would be great! Thank you!

Let me try to work out what the best size is and acquire one. Thanks!

cardan · « **Reply #5 on:** 26 Sep 2022 at 03:07 »

Hi Tim,

Well done - it runs!

Before you go to a lot of trouble, what do you think is wrong with the jet in the bike? Have you measured it? If you don't have number drills, you can insert a tapered darning needle into the jet, then measure the diameter of the spot where it contacts with a micrometer or vernier.

Because the carb is not automatic, it will work for quite a wide range of main jet sizes. Adjusting the main jet is usually an activity of fine tuning for full-throttle running. Adjusting a thou or two either way will make no difference for the low-speed running in the video.

Cheers

Leon

Jonathan Hewitt · « **Reply #6 on:** 26 Sep 2022 at 08:22 »

Well done Tim ,
nice to see it move however slowly, temporarily of course. Can't wait to get to that stage with my W20, just the clutch to sort !
Jonathan

Tim OConnor · « **Reply #7 on:** 26 Sep 2022 at 11:32 »

thanks!

Going by the tuning instructions in the AMAC guide and "Vintage Motorcycle Workshop", I should be able to open the mixture at least 2/3 open and crack the throttle. I can not. Best I can do is open the mixture 1/4-1/3. Opening the throttle kills the engine. The turning recommendation is to increase the size of the jet until the mixture can be opened 2/3-3/4.

Quote from: cardan on 26 Sep 2022 at 03:07

Hi Tim,

Well done - it runs!

Before you go to a lot of trouble, what do you think is wrong with the jet in the bike? Have you measured it? If you don't have number drills, you can insert a tapered darning needle into the jet, then measure the diameter of the spot where it contacts with a micrometer or vernier.

Because the carb is not automatic, it will work for quite a wide range of main jet sizes. Adjusting the main jet is usually an activity of fine tuning for full-throttle running. Adjusting a thou or two either way will make no difference for the low-speed running in the video.

Cheers

Leon

Tim OConnor · « **Reply #8 on:** 26 Sep 2022 at 11:32 »

Thanks!

Quote from: Jonathan Hewitt on 26 Sep 2022 at 08:22

Well done Tim ,
nice to see it move however slowly, temporarily of course. Can't wait to get to that stage with my W20, just the clutch to sort !
Jonathan

cycarmark · « **Reply #9 on:** 26 Sep 2022 at 13:30 »

Another thing to consider is float height. With the AMAC carb on my 1920 Clyno two stroke, the float needle was very adjustable since it had no grooves or a clip in it and instead had a spring wound around the needle that allowed the float to be raised or lowered. If yours is the same, I would recommend raising the fuel level and seeing if that made it more rich. On the Clyno I had to lean it out with the float until the air and throttle lever worked properly and I could get it to two stroke most all the time. It runs great now and I really like the fact that I can adjust the mixture "on the go".

Tim OConnor · « **Reply #10 on:** 26 Sep 2022 at 13:42 »

Nice feature! Sadly, not on mine. I have the float at the highest point and it just reaches the overflow hole on the carb under the slider.

Quote from: cycarmark on 26 Sep 2022 at 13:30

Another thing to consider is float height. With the AMAC carb on my 1920 Clyno two stroke, the float needle was very adjustable since it had no grooves or a clip in it and instead had a spring wound around the needle that allowed the float to be raised or lowered. If yours is the same, I would recommend raising the fuel level and seeing if that made it more rich. On the Clyno I had to lean it out with the float until the air and throttle lever worked properly and I could get it to two stroke most all the time. It runs great now and I really like the fact that I can adjust the mixture "on the go".

cycarmark · « **Reply #11 on:** 26 Sep 2022 at 22:10 »

Another thing to check is if the throttle slide is very loose in the carburetor bore. This will cause it to run lean also.

graeme · « **Reply #12 on:** 29 Sep 2022 at 06:40 »

I concur with the last comment. If the slide is at all sloppy in the bore of the carburettor you will never get any sense out of it

Tim OConnor · « **Reply #13 on:** 30 Sep 2022 at 16:10 »

Quote from: graeme on 29 Sep 2022 at 06:40

I concur with the last comment. If the slide is at all sloppy in the bore of the carburettor you will never get any sense out of it

Quote from: graeme on 29 Sep 2022 at 06:40

I concur with the last comment. If the slide is at all sloppy in the bore of the carburettor you will never get any sense out of it

I took a look and it appears loose to ME. However, I have no experience with these. Does this look too sloppy to you guys?

https://youtube.com/shorts/pT6LAv71oNs

cycarmark · « **Reply #14 on:** 01 Oct 2022 at 16:16 »

Yes, that looks loose, not so much as to not be operable, but you are going to have to compensate for it with the air slide. It will also cause erratic operation as was mentioned by Graeme.

graeme · « **Reply #15 on:** 20 Oct 2022 at 08:16 »

Agreed, that does look a bit too sloppy. To get much sense out of it you will need to get that tidied up

Black Sheep · « **Reply #16 on:** 02 Nov 2022 at 10:58 »

Your bike should be fast once it's sorted. My 1913 2 3/4 has been clocked at 50 mph. Quite scary at times!

Tim OConnor · « **Reply #17 on:** 02 Nov 2022 at 15:32 »

Good to know! thank you!

cardan · « **Reply #18 on:** 02 Nov 2022 at 23:55 »

You should also know that 50mph (give or take) is the speed at which TS con rods exit the crank case. In my (boring) opinion, 35mph would be a reasonable maximum.

Leon

Tim OConnor · « **Reply #19 on:** 03 Nov 2022 at 00:05 »

really good to know!