Starting the Race bike! BSA B50

Here you can talk about all kind of TECH for the B50 B44 B25 And Other BSA unit Singles

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Starting the Race bike! BSA B50

Post by Allflatblack » Mon Sep 10, 2018 1:59 am

Well the day came, I was invited to race the B50 at the Moto America event in NJ this last weekend, so I took a week of non stop fabricating and design to get the bike rolling. I just could not get her to start!

The details:

This is a 500CC B50 with long Carillo rod, NEB Nikasil cylinder and JE piston with a real measured 12.5:1 Compression ration.
Heavily ported dual plug head from the previous owner with 42mm intake port 1.75" ID exhaust port. 44mm Mukuni carb. Titanium valves and RD Beehive springs.
Megacycle X4 cam with big radius tappets, modified high lift intake rocker. Squish set to about 0.050". NEB Clutch and primary gear. Electrex world dual plug ignition.

I have borrowed a very high quality roller starter from a buddy to start the bike as I have no kick start gear. I have melted it down twice.

I have attached a strap to the bike and had my wife tow me down the road. It simply locks the rear wheel on compression stroke. Th ebike weigs 225 lBS.

With a plug out, it spins over happily. I have checked the timing with a timing light and see that at about 250 RPM it appears to be firing at around 10 degrees before dead center, so my advance is not screwed up.

With the wheel up off the ground it is just all that I can do to turn the wheel past compression, bump starting it is pretty much impossible since rolling it backwards onto compression just unwinds since the clutch plates drag at that slow speed. On the roller starter I can roll it backward to compression then spin it up but that only gets me a bump or two until it starts to slip on the tire, not enough to get it going.

I then lifted my wifes front wheel drive explorer into the air and turned the wheel enough to directly contact the lifted tire on the bike. Than ran it in reverse. This worked. It did start the bike but it only ran at around 5000 rpm and died either side of 1/3 throttle. I felt that it is too lean so i re-jetted the carbs to a leaner setup but now it is a rainy day and the front wheel method is sketchy. Killed the battery on the roller again.

I have plenty of friends including Ed V who say that they can push start their B50, but I do not think that they had the head or compression as dialed in as I do. There is no valve or plug interference, it is clearly compression. Unless I made some error and mis marked my carefully dialed in cam i can think of nothing else to look at besides borrowing a car wheel roller to start the bike. Maybe with better carb setup it will be a one bump bike because that is all you can get from it.

Any suggestions and I am all ears. No I do not have the compression release set up. Thank you all once again for your help over the years.
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Re: Starting the Race bike! BSA B50

Post by scootin newton » Mon Sep 10, 2018 8:22 am

Last edited by scootin newton on Wed Sep 26, 2018 11:05 pm, edited 2 times in total.

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Re: Starting the Race bike! BSA B50

Post by bbenxe » Mon Sep 10, 2018 12:35 pm

It sounds like you know the answer already, and it's not 'compression'.
It did start the bike but it only ran at around 5000 rpm and died either side of 1/3 throttle. I felt that it is too lean so i re-jetted the carbs to a leaner setup
B50 is fussy to start unless you've got the fuelling right. Seems you already know that it's not fuelling correctly at low engine speeds and have guessed how to change it. What did you change in the fuelling? For starting you need the right pilot jet and air screw combination, which can pretty much only be set with the bike running. Once you can get it to idle and rev better then starting should become much easier.
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Re: Starting the Race bike! BSA B50

Post by bbenxe » Mon Sep 10, 2018 12:57 pm

And that's a very smart looking fork brace! Is it a universal fit job or BSA/Triumph fork specific?
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Re: Starting the Race bike! BSA B50

Post by stew79 » Mon Sep 10, 2018 1:33 pm

36mm vm mikuni
270 main (1.42 mm dia)
35 pilot (modified mixing chamber size vm22 or vm13/352 is same)
159 p8 needle jet (2.7mm dia x 5mm tall spray tube)
6dh3 needle (middle position)
2.5mm air jet (or just a 2.5mm hole)
no 3 slide (4mm cut away)
will work with a 38 but 36 is easier to ride and live with (thats amusing the timing is in the right place after 3000 ish rpm and the correct plugs/ heat range etc)

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Re: Starting the Race bike! BSA B50

Post by Allflatblack » Mon Sep 10, 2018 9:53 pm

Thanks guys, I am all about the jetting being right, and can only know that once its running. catch 22.

The fork brace is tarrozzi from "fast from the past", two different ones mixed to get the right size. They will do that for you. i can forward the part numbers if anyone likes.
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Re: Starting the Race bike! BSA B50

Post by minetymenace » Mon Sep 10, 2018 10:13 pm

Allflatblack wrote: i can forward the part numbers if anyone likes.
Oh yes please :grin:
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Re: Starting the Race bike! BSA B50

Post by skippy » Mon Sep 10, 2018 11:35 pm

With duel plugs do you need 10degs advance at startup. But then I don't understand that type of ignition system.
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Re: Starting the Race bike! BSA B50

Post by mlb50 » Tue Sep 11, 2018 12:44 am

Looks fantastic, bound to have heaps of power. Your next problem is going to be how to stop it! The TLS front end is a wee bit feeble...
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Re: Starting the Race bike! BSA B50

Post by BSA_WM20 » Tue Sep 11, 2018 9:01 am

mlb50 wrote:Looks fantastic, bound to have heaps of power. Your next problem is going to be how to stop it! The TLS front end is a wee bit feeble...
When set up properly the said same brake used to pull up A75's from well over 100 mph.
The real problem will be stopping the front wheel locking up.

Same brake on my 71 A65L would happily lock up the front wheel at speeds just under the ton.

All that is required is the actually read the instructions BSA printed for adjusting the brake.
BMW used an almost identical brake for near 20 years and it was praised as being a great stopper.
Perhaps Germans are better at reading manuals than the British bike riders.
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Re: Starting the Race bike! BSA B50

Post by minetymenace » Tue Sep 11, 2018 9:56 am

RTFM? Only girls do that, real men absorb instructions by osmosis. :cool:
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Re: Starting the Race bike! BSA B50

Post by beat » Tue Sep 11, 2018 9:25 pm

Allflatblack wrote: I felt that it is too lean so i re-jetted the carbs to a leaner setup
:?: :?: :shock:

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Re: Starting the Race bike! BSA B50

Post by stew79 » Wed Sep 12, 2018 10:13 am

the compression may be a bit high, the 44mm carb may be way too big, but even with a more suitable sized one with the right jets, the timing is not going to help at all. looking at the info on the electrex web site, with 10 deg at 250 ish rpm as a start point, (which is a quite normal universally used figure) it goes down hill from there on. at 1000 rpm 25 deg, 2000 rpm 35 deg, 3000 rpm 38 deg, 4000 rpm 38 deg, 5000 rpm 26 deg and so on. tick over and initial pick up will be terrible with too much advance, although 38 deg at 4000 rpm is a good initial figure, it then starts to retard back just as things get going ? thats a typical 2 stroke curve.

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Re: Starting the Race bike! BSA B50

Post by minetymenace » Wed Sep 12, 2018 10:21 am

Mark Cook uses a chainsaw de-compressor on his engines, press the titty button and it snaps shut when the engine fires, seems to work well.
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Re: Starting the Race bike! BSA B50

Post by Grouty » Wed Sep 12, 2018 3:11 pm

I'll second the blue titty button .......
I think mine is around 11:1 Very hard to push the piston past tdc with the kick lever. Almost impossible to bump start.
But the magic button ..... every time :ok

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Re: Starting the Race bike! BSA B50

Post by Jeff K » Wed Sep 12, 2018 3:37 pm

Long, long time ago I had a 501cc Maico flat tracker set up for ice racing. It came with two compression releases. One at the top of the head and one in the back of the cylinder above the carburetor. It was a very high compression motor and it took both compression releases to kick it over. I think if it is not just fuel problems , then you may need a compression release that is up to the job.
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Re: Starting the Race bike! BSA B50

Post by Allflatblack » Thu Sep 13, 2018 4:59 pm

Well the other day I ordered a decompressor that is used in Hot Harley engines. I will report my findings.
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Re: Starting the Race bike! BSA B50

Post by stew79 » Thu Sep 13, 2018 5:30 pm

fit the std decompressor back ? in april was watching a man try to start a 500 single H*nda race bike on car driven rollers. he had removed the std decomp parts altogether ? they only weigh a few grams ? the thing was set up very badly so took dozens of attempts to finally run. must have taken half an hour and chewed up his tire trying to get over tdc 20 times !

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Re: Starting the Race bike! BSA B50

Post by Allflatblack » Thu Sep 13, 2018 9:06 pm

I have a dual plug head. I have the second plug right where the std decomp is located so it would not work both ways. Plus the rockers have been smoothed so the place the lifter was located is gone. I am going single plug with the centrally located plug as the primary and the std sparkplug hole will be the decomp for now.
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Re: Starting the Race bike! BSA B50

Post by stew79 » Fri Sep 14, 2018 9:24 am

it all becomes clear, i didnt realize the std leaver is in an awkward place for the extra plug. but as the ex valve only has to be lifted 10 thou or so of its seat to release the compression, could a special tappet cover be made with a clever lever or arm to do that ? could be less work than loosing the extra plug ?

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Re: Starting the Race bike! BSA B50

Post by Allflatblack » Fri Sep 14, 2018 1:26 pm

Stew,

if this becomes necessary to have installed, there may be meat in the head to drill and tap for a release. thats what the harleys do. Will see this weekend!
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Re: Starting the Race bike! BSA B50

Post by Grouty » Fri Sep 14, 2018 2:30 pm

My blue button is located just under the spark plug. So would not get in the way if I also had a central plug.

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Re: Starting the Race bike! BSA B50

Post by stew79 » Fri Sep 14, 2018 4:52 pm

a question about the little button, i can see how it works on a small 2 stroke, but that cant generate much vacuum on the over run to open the valve at the wrong time. on a 4 stroke at say 5000 rpm, shut the throttle and it makes a lot of vacuum. wount that open the valve against the little spring ? sucking in air, mud etc?

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Re: Starting the Race bike! BSA B50

Post by minetymenace » Fri Sep 14, 2018 10:22 pm

Nope
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Re: Starting the Race bike! BSA B50

Post by Allflatblack » Mon Sep 17, 2018 5:35 pm

Well she runs! I reverted back to the single plug ignition and in that process saw that I had bumped y ignition timing off a bunch. Far too advanced. I still had to use the compression release. I started it twice on a set of car roller with some real effort. Drove it around then adjusted the carb a bunch: it was set way too high of an Idle. I finally got it to run on the electric roller starter by refining my method: third gear, roll it back against compression on the rollers, click down the compression release. No clutch choke on and stomp it.
Started it and took it for a mile or two ride. Very Very fast bike. Clutch felt great, it grabs a bit high, i will adjust that out hopefully. Shifted smoothly, Brakes are great. Ill tune it in and set the fairing on it for GP 500 next month at the Barber Vintage Festival in Birmingham Alabama. #647

I will keep you all posted on how it all turns out. Thanks again for your help, its been great.
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Re: Starting the Race bike! BSA B50

Post by beat » Mon Sep 17, 2018 7:53 pm

Allflatblack wrote:I will keep you all posted on how it all turns out.
can't await <212
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Re: Starting the Race bike! BSA B50

Post by bbenxe » Mon Sep 17, 2018 10:43 pm

Allflatblack wrote: Started it and took it for a mile or two ride. Very Very fast bike.
Hurrah!
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Re: Starting the Race bike! BSA B50

Post by Jeff K » Tue Sep 18, 2018 1:53 pm

:ok :ok :ok :ok :ok

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Re: Starting the Race bike! BSA B50

Post by koncretekid » Sat Sep 22, 2018 3:17 pm

Sorry I missed this whole thread as I was without a computer for a couple of weeks.

I use homemade rollers with a Dodge starter motor. I have to start the bike in second gear on the road racer, and yes rolling it backwards in 2nd gear just before backing it up on the starters helps (required). You might have to repeat the rolling it backwards thing if the starter won't turn the motor. I don't open the throttle, but I turn the slide stop screw in one full turn and flood the carb or squirt some raw gas onto the filter. Of course with a Mikuni, you can't flood the carb to start, so I suppose you would engage the enrichment lever and definitely squirt the raw gas on the filter when cold. I do have a twin plug head and about the same set-up as yours. And make sure your battery is at 12 + volts with the ignition on, as the Boyer won't work with less than 11 volts.

The biggest thing is don't open the throttle! You can bump start these things if you're heavy enough but you definitely have to have it in second gear and have backed it up against compression before you get two big gorillas to give you a push.

I also have a B50 road bike with dual plugs along with the compression release. I just had to slim down a 5/8" deep socket to get it to pass by the compression release to change the center plug. With only 10 to 1 compression and by flooding the carb, it starts easily with the kick start.

Can't wait to hear results of your run a Barber. Wish I could be there.

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Re: Starting the Race bike! BSA B50

Post by Allflatblack » Tue Sep 25, 2018 9:15 pm

Will report!
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