Carbs

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

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minetymenace
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Carbs

Post by minetymenace »

Who has what carb fitted? I'm building a fast road B50 (MMX cam, 500cc, standard head) and am thinking about a carb. Ed and Stan say go for a Mikuni, but where to start, don't know much about them and am struggling to find out more, think this must be the ideal solution, but I have no experience or spare jets. Tom Beckett suggests starting with 34mm MkII Anal Smooth 170 main, 106 pilot and No3 slide (must dig out my Anal box :shock: ). Ideas and figures please (dont forget to mention cam, displacement vaulve size etc)
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carb

Post by b50root »

Hi minetymenace. Im using a 34 mm Amal mkII carb on my B50. Im using a MX cam and a free ( empty ) goldstar silencer ( Noice expander ) Goes great on high revs. If I want power in the low area I´m using a A65 silencer with smaller outlet. The bike is very sensitive on the exhaust!!!


106 pilot and I think 180 Main ( I have to check, could be 170) I dont know the slide ( I have to check there too ).

Rickard :roll:
Andrew

Post by Andrew »

minety

I run a 580 CCM with a 34mm Dellorto PHBE. I used to run an Amal mk2, but the Dellorto is in a different league. Slightly harder to set up than the Amal, but well worth the effort. And its cheaper....
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Post by minetymenace »

Andrew, thanks for this, just been getting prices for the Amals, yes they are dear, I'll look into the delorto's. PS Mark Cook is on my list of people to visit, he is less than 10 miles away, I did call him at the start of the project, and I will shortly be getting to the stage when I need his services, but a the sun is out :) I have to share my free time between riding my bike :D , doing the "Honey Do's" :? , riding my bike :D , building the project :) , riding my bike :D , playing with the kids :lol: and riding my bike 8) ! I only managed a quick visit to the Bristol Branch BSA camping weekend on Saturday (nice B44) Have fun...
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Post by minetymenace »

Rickard, thanks for this, is it left or right handed?
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Amal MKII

Post by b50root »

The lever is on the left side so I say it´s a left handed carb.
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Post by Canberra »

Just a follow up on the carb line.

I have a MkII 2900 series on a CCM head with large valves and CCM MX cam. The piston bore is presently 88.5 and from day 1 I have always had problems with the low end set up and running rich :( . I had a blocked cold start jet the other day :x and found it was fitted with a 50 size jet. That does seem a bit large and I cannot get the pilot jet out to check that one although I was informed it was a 25 on purchase (many moons ago).

When I did the big bore conversion in 1981and fitted the carb CCM recommended a 300 Main jet, 107 Needle, 25 pilot and No 3 slide. I have reduced the main jet since initial running down a few sizes.

Question one - CCM manual shows the same number for the pilot and cold start jets. Should this be a 25 for both?

Question two - any suggestion for loosening the pilot jet?

Question three - Minetymenace, what did you end up with?

John
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Post by Andrew »

canberra - I had terrible problems setting up an Amal Mk2 on my CCM, including rich running and poor low end performance....but the problems were eventually traced to the ignition, which wasn't advancing properly...

worth a thought..?
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Timing

Post by Canberra »

I am running a Boyer at the moment but originally ran with points set at the 30 deg and had same problems. The Boyer is running with no pre-ignition so is very close but I need to recheck setting to the 34 deg. Will do that ASAP.

John
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Post by Mark Cook »

Hello John,

25 for both pilot and starter sounds about right. I have ended up with this on some motors. I think I have gone down to about 260 - 270 on the main. Caution, watch out for original CCM data -- is can be a bit iffy.

Some of your trouble will be the MX cam. It ruins the idle and does not perform at higher revs. Some of this can be corrected by degreeing in the cam. I have found some to be over 15 deg. out!!!

For best results, as Andrew has said, use a PHBE delorto.Image

Mark
Last edited by Mark Cook on Wed Jan 26, 2005 2:40 pm, edited 2 times in total.
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Post by b50root »

Hi Mark How can you check that your cam is right degreeing?

Is there any easy way?

Rickard
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And the leg bone is connected to the knee bone!

Post by Canberra »

Thanks for that Mark. I will change the cold start jet ASAP and if I can get the pilot out replace that if I need to. I am tempted to replace the bowl and jets. By the way the bowl is a 3.2mm seating version.

I have a timing degree plate which I will put on the rotor when I get a chance and see what the cam is actually doing.

My last notes show I am running a 270 at the moment and will check that as I may have reduced that without amending the notes. The original 300 jet I set up was "smoking" and giving me a shocking performance at sea level. There may also be now an additional altitude effect as I am now living at a between 535 and 600m here.

John
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Post by Mark Cook »

Let me know when you are playing with your cam timing and I will dig out some figures and notes. I'm sure others will be tempted to play afterwards.

Oops sorry Rickard, didn't notice you above :oops:

As with many other things to do I'll Jot down a prceedure for you. I'll do it when I'm doing the next one and take some piccies.

Mark
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Post by Ed V »

Mark, I am going to save you a lot of writing as I just sent this information to a customer of mine. The intake centerline of the MX cam is 94.5º not the 104º on the article as he was using a different cam. This should get the dial indicators and degree wheels buzzing.
Degreeing in the cam requires that you have a degree wheel for installing in the crankshaft opposite of the cam end of the crank and a dial indicator preferably on a magnetic base for measuring the cam follower lift.

I start by installing the piston and cylinder on the cases without the rings in place, this is just for finding true top dead center, now install the degree wheel on the crank and mount a pointer off on one of the primary mounting screws, I have a small strip of sheet metal shaped into an arrow with a hole in one end so I can bend it around where I need it so I can read the wheel. Now mount the dial indicator so that it is reading the top of the piston and with the piston where you think is tdc zero the indicator, at this point also your degree wheel should be pointing at tdc, now rotate the crank forward so the indicator reads .020" less than it did at tdc and note the degrees on the degree wheel, now rotate the crank rearward past tdc until the indicator reads .020" again and note the reading on the degree wheel, if the degree wheel is mounted correctly at tdc both readings will be the same if not subtract one reading from the other and that is the amount you will need to move the degree wheel on the crank to be at true tdc. Double check this a couple times to be sure it is mounted correctly otherwise you will not be able to degree the cam correctly.
Once you are sure the degree wheel is zeroed you can get on with degreeing the cam, I usually just put a pushrod on the intake cam follower and put the tip of the dial indicator in the cup of the pushrod and with the cam follower at its lowest lift zero the dial indicator allowing for abour.400" of travel of the cam follower. Now rotate the engine around until the cam follower is at full lift and note the reading on the degree wheel, now rotate the engine back until the indicator reads .005" less than full lift and note the reading on the degree wheel, now rotate the engine forward past full lift to where is shows .005" again and note the reading of the degree wheel if your cam is installed correctly both readings will be the same if not you will need to advance or retard the cam to get the correct readings which in your case is 104º.

I don`t worry about the opening and closing degrees as much as I do the lobe centers as they are a better indicator of where the power band of the engine is going to be. Do this a couple of times to be sure of your readings. If you need to move the cam just 1 or 2 degrees you will need to make an offset key for the crank gear so that you can get the setting you are looking for as moving a whole tooth on the gear is too much.

This will make more sense if you read it while you are degreeing the cam in.

Ed
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Post by Ed V »

In the above post I mention using an offset key to degree the cam but a better idea is to purchase one of Mark Cooks Pinion gears with the 5 keyways. I need to purchase some myself to have on the shelf.

Ed
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Post by HPbyStan »

Another advantage of using cam lobe centerline as a reference instead of opening and closing numbers is, when you use opening and closing numbers it's of utmost importance to have the dial indicater exactually on line with the valve stem. If you use lobe centerline, you just go to what looks like max lift and read the crankshaft degrees at, say, .050" either side of max lift. Half way between those numbers will be the lobe centerline and almost any misalignment of the dial indicater will give the same reading. A fast way to get a cams lobe centerline from a timing card is to add the valve opening number, 180, and the valve closing number, divide by 2 and subtract the smaller number.
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Post by HPbyStan »

My last post is for degreeing in the cam with the engine together obviously.
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Post by minetymenace »

Knew it was somthing like that, nice to have it all laid out so neatly. Thanks Yanks :D

Canberra, this answer is nearlyfive months late, sorry: "Don't know yet, feeling rather skint, I'll post when poverty is past."
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Setting up the timing disc

Post by Canberra »

Thanks for all the information.

Easy enough to set up the timing disc to TDC as I have a special homemade tool that screws into the spark plug hole. What will slow me doing the work is I will have to see if I can find someone to lend me a dial gauge. I will have a go at doing the cam timing check with the motor in the frame and set up to reference full valve open off the exhaust valve collar. To do this I am a bit worried about what effect if any the tappet clearance has on the measuring, any thoughts?

At the same time I can do a propor job in remarking the rotor for the 34deg ignition timing.

I am guessing if the cam is within a degree or so I will let it go as the effect of the type of muffler on the bike dramatically changes the ability to rev out or move the power band down the rev range even with the same cam setting.

I have for years used two mufflers which is same as Rickard found (we did not copy each other either). One a long reverse cone one (Dunstal type) pushes the ability to rev the engine up the rev range and a shorter older style BSA twin muffler that lowers the power band and less of the revs.

I have the latter one on now as the former has gone to the graveyard but as I have been using the bike for commuting in city and open parkway travel it is what I prefer to use at present. The baffles have been recently "modified" to ensure I can get the gas out better as I found it was too restrictive on the open road. I just have to close the throttle when I pass the men in blue.

When I set up and do the work I will post few pics for reference.

John
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