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Design For Machining Vacuum Take Off Point For Old Style Carbs

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malmac

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#1
Anybody made up some custom vacuum take off points so they can more easily balance their carbs?

Just trying to avoid reinventing the wheel.


Thanks in advance.


Mal
1967 BMW R60
 

Groundhog

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#2
Not sure what you are balancing but this trick might work.

I've had a couple XKE Jags with triple SU carbs. Years and years ago an old master Jag mechanic showed me an easy way to balance the carbs. Take a piece of plastic tubing. A a 2 foot section of garden hose will work. Any old hose or tube will work. With the motor at an idle hold the tube at the mouth of one of the carbs and hold the other end to your ear. Listen to the sound. Move the tubing to another carb and hold the hose in the same relative spot as the first. Adjust the carb until it sounds like the first carb. Repeat for the third carb. It works!!

I know this method sounds inaccurate but it is not. Later in life, working as a motorcycle mechanic I would use the hose method to sync all 4 carbs on Gold Wings. Then I would check the balance with a manometer. The hose method was always spot on. It is amazing how much difference in sound a 1/16 of a turn on the screw will make.
 

malmac

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#3
Groundhog


Thank you for your input - I will try that option - it may be the ticket to getting the old girl singing in tune.

Regards


Mal
 

malmac

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#4
27221485594_34c1d88220.jpg

This is the design that I propose to machine up. Quite a small piece and this will be the challenge.

Mal
 

malmac

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#5
Not sure why the photo did not work.

27221485594_34c1d88220.jpg
 

rgray

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#6
I to have learned to use a hose as groundhog says. Back in the 90's Arctic cat had the special carb sinc tool from suzuki. All dealers got one as part of the required special tool package.
I remember the service guys at arctic cat telling of a suzuki factory tech from japan using a hose to balance the carbs instead of the expensive "special tool" they were selling us.
He just used a length of 5/16 fuel line. One end in carb mouth and one end in ear. Works great just like groundhog says.
 

rgray

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#7
If you feel you do need a port I always liked the ones with a screw in the top of the nipple rather than a rubber cap.
 

malmac

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#8
Russ

I could easily put a small screw in the end - the gauges I have come with some extension pipes (for the inner cylinders on 4 cylinder engines I am guessing). These pipes have one end blocked off and a very small hole drilled in the centre. Do you know why the hole has to be so small? If I put a screw in the end the hole is going to be quite a lot larger - depending on why the hole is so small, I could move the narrow section down further into the body of the fitting.

Mal
 

rgray

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#9
You sent me looking for my suzuki carb balancer. Didn't find it guess I sold it on ebay years ago.
Remembering a few things though. The suzuki one had brass end pieces that were threaded and the mikuni carb on the snowmobile had a philips screw in the throat of the carb on the engine side of the slide. There was no nipple protuding from the carb just a threaded hole with a screw.
If working on a motorcycle with protuding nipples the brass end pieces were removed and the hose pushed on the nipple.
If I remember right (questionable) I think some of the hondas had a protuding nipple with a very small screw plugging the end of them instead of a rubber cap.

The hole size I don't believe makes any difference. It just needs to be consistant for all lines/carbs. Different engines and different line/fitting sizes are going to effect the setting, but the balancer needs reset every time used anyway. Tipicaly one would get the engine running consitantly and then adjust the ballancer by hooking one hose up at a time and adjusting the ball leavel this way all 4 are adjusted the same since they all show the same leavel when hooked up to the same carb one after the other. Then they can all be hooked to a cylinder and the difference in carb balance viewed and adjusted.

I hope we are talking about the floating ball type balancer. that's what I had.
 

malmac

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#10
Hi Russ
I actually have a set of gauges (two) and with the 1200 I connect a line to each throttle body and adjust the opening of the butterflies so they open as near as possible to the same time - it certainly makes the bike run smoother - so something is working. Want to be able to do the same thing on the old bikes, but need to fit these vacuum spigots first.

I think you are right about the hole size - as long as both holes are the same it will be fine. Thanks for taking the time to write a reply.


Mal
 

pdentrem

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#11
The restriction in the fitting is to reduce the size and speed of the pulsation in the tubes. If you look at some YouTube videos on carb sync, you will see that when using colored fluid in the tubes the fluid bounces around quite a bit. Thus the restriction.
Pierre
 

malmac

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#12
Pierre

The rubber tubes have small screws on my unit which dampen down the flutter. Just trying to sort out the actual size for the inside of the spigots. At present looking at a 1mm hole.


Mal
 

pdentrem

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#13
You may be right. When I made mine, I used a 1/16th drill and I believe it was still too big. I may fill the hole with solder and re size smaller for the next time.
 

malmac

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#14
well looks like off to the machine shop for some number drills.

Dropped into my metal supplier today but he is closed for end of year stocktake - well that will have to wait till next week.

Mal
 

cascao

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#15
Standard M5 thread is M5 x 0,8mm.
 

malmac

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#16
Cascao

You are 100% right - I found this out once I pulled out my metric taps and Dies. I originally did a poor job measuring the a 5mm thread with my thread pitch tool.

Thank you for pointing this out.


Mal
 

uncle harry

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#17
well looks like off to the machine shop for some number drills.

Dropped into my metal supplier today but he is closed for end of year stocktake - well that will have to wait till next week.

Mal
You might want to check out a welder's supply store for torch tip cleaning drills. Quite tiny they are.
 

hermetic

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#18
carbalancer.jpeg I used one of these to great effect on twin and triple SU's and also on .Honda4's very cheap, and no machining necessary. Also seen a 3/8" thick aluminium gasket with a vacuum take off point tapped into it fitted between carb and engine. Good luck with it!
 

malmac

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#19
27380587493_a3f9a579db_c.jpg

I had an old carby body, so knocked up a screw in spigot - just to test the concept machining wise. In this case I used a 1mm drill - maybe OK - maybe still too big. Thank you to all who made suggestions - no hard decision has been made at this stage. The bike is up and running, however tuning was just by ear and feel - it's OK but I am sure it could be a bit better.


Mal
 
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