Author Topic: Carb Sync  (Read 1528 times)

Andy M

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Carb Sync
« on: March 02, 2011, 07:59:27 AM »
OK, I know, singles forum....... ;D

The Bonneville is popping in the exhaust and generally not feeling it's usual go anywhere self. This has happened before, but usually close enough to MOT day fro me to let someone else do it. Two mechanics said the carbs needed balancing. So, I've ordered a pair of vacuum gauges. I've balanced carbs before, but only on a Ural where the adjustment was simply twin throttle cables.

The plan is:

1. Construct vacuum dampers as per instructions in gauges
2. Warm engine
3. Connect gauges to take off points on top of the carb stubs.
4. Set engine to run at just above idle via a large O-ring between the throttle and the housing.
5. Turn the screw awkwardly mounted between the carbs until both gauges read as close to each other as they'll go.
6. Swap the gauges left to right and check any difference between the two follows the gauge.


Is there anything else I should know about this? Any tips anyone would care to impart?

Cheers

Andy

guest7

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Re: Carb Sync
« Reply #1 on: March 02, 2011, 09:06:47 AM »
Have a cup of coffee at hand.

But then that would be my advice for any job from fitting guttering to rubbing sun cream into Claudia Schiffer's.........
ahem, where was I? oh yes. 002 will be along in a minute I'm sure to give you an exact description of the process.

GC

SteveC#222

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Re: Carb Sync
« Reply #2 on: March 02, 2011, 11:25:00 AM »
OK, I know, singles forum....... ;D

 I've balanced carbs before, but only on a Ural where the adjustment was simply twin throttle cables.


I watched someone one balance a pair of Ural carbs with his toes!  sit on the bike, take your socks off, take the air inlet pipes of the back of the carbs and stick your big toe in each so the slides are resting on your toe nails. As you open the throttle you can feel simultaneously the moment when the slides start to lift!...it actually works!...I bet the Bonnie isn't that simple! ( mind you it probably runs better than the Ural....)
Growing old is inevitable, growing up is optional!

Andy M

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Re: Carb Sync
« Reply #3 on: March 02, 2011, 12:40:51 PM »
My Ural didn't actually use both cylinders at the same time that often, it was actually a single, just with a spare cylinder permanantly installed.  >:( ;D

Andy

johnr

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Re: Carb Sync
« Reply #4 on: March 03, 2011, 08:20:51 PM »
carb balance however is the last thing you need to do. set your tappets, set your points and ignition timing, change your oil, fresh plugs and oil and filter. THEN balance the carbs!

Andy M

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Re: Carb Sync
« Reply #5 on: March 03, 2011, 09:22:25 PM »
carb balance however is the last thing you need to do. set your tappets, set your points and ignition timing, change your oil, fresh plugs and oil and filter. THEN balance the carbs!

Points? Tappets? Ignition Timing? This is a Hinckley, they don't change, shims done less than 2000 miles ago, electronic ignition that'll need a atom bomb to put off. Doesn't leak oil either.  ;D

Andy
« Last Edit: March 03, 2011, 09:29:39 PM by Andy M »

johnr

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Re: Carb Sync
« Reply #6 on: March 03, 2011, 11:49:57 PM »
of course, i should have known that cos im a psychic, and when someone comes on and says their boneville carbs need balancing, my superpowers should have told me it wasnt a meriden, how foolish of me.

but a duff plug will affect carb balance as will a slack or over tight valve, clogged air filter or any of the other things you do on a service.

guest7

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Re: Carb Sync
« Reply #7 on: March 04, 2011, 08:18:00 AM »
It could have been worse John, he could have been whittering on about a 'Thruxton' (Bonneville) and we'd all have been even further off the mark.  :D

A bit like someone with a B25SS telling us he's having trouble with his Gold Star. Technically correct, but oh so off the mark.

What this (and all forums) needs is a mind-reading button sometimes  ;)

GC

Andy M

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Re: Carb Sync
« Reply #8 on: March 04, 2011, 06:19:34 PM »
See the rants section  ;D

Andy

Andy M

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Re: Carb Sync
« Reply #9 on: March 07, 2011, 04:41:58 PM »
The plot, or possibly just the main participant thickens. Having got home with a warm engine and had no bad behaviour for a couple of days I:

1. Construct vacuum dampers as per instructions in gauges
2. Warm engine
3. Connect gauges to take off points on top of the carb stubs.
4. Set engine to run at just above idle via a large O-ring between the throttle and the housing.
4a.Turn the damper screws so flutter on the needles is just gone
5. Do not adjust the screw as both read the same.
6. Swap the gauges left to right and check any difference between the two follows the gauge. It does.

The carbs then are currently balanced  ;D


Why then the popping etc.  ??? Yesterday when doing my annual wash and brush up I WD40'd and crimped up the carb heater connections  :-\ Does carb icing in one pot make it act like it's out of balance? I think it would. Have I cured it? Given today and yesterday have been warm and sunny, I'll let you know next time it sleets  :(

Still, good result today  ;D

Andy

johnr

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Re: Carb Sync
« Reply #10 on: March 08, 2011, 10:10:54 AM »
carb imbalance wont make it pop. carb inbalance will make it run unevenly, and tickover poorly. if its popping its because its pulling in air from somewhere, this is making it run too lean, the popping is unburnt fuel igniting inside the exhaust or whilst the exhaust valve is still open. carb icing might cause it because when its severe enough it can prevent the aomisation of the fuel in the carb and thus the cylinder doesnt run properly if at all. but if its run better since you re crimped the carb icing plumbing, youve answered your own question!!

guest146

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Re: Carb Sync
« Reply #11 on: March 12, 2011, 05:37:48 PM »
A method i have used on cars and bikes is it pull one plug cap of and sent the carb un on the other cylinder to be smooth and ticking over at a certian speed. Then do the same on the other one and have the speed exactly the same. Do the joining clamp back up and slow the pair down together and your not far out. Failing that used gauges.

Ken

chippit

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Re: Carb Sync
« Reply #12 on: March 13, 2011, 08:37:06 PM »
I bought a Morini Dart (spell check came up with moron as an option) as a project in October, it is now on the road!
I would like to buy a carb balancer, what type has anyone tried? The gauges I had did not work as I don't think they were damped.

In the end I used a long length of clear pipe part filled  with 2 stroke oil, fixed it to a board in a 'U' shape with a steel rule to give a refference point  and connected it to each carb (heath robinson, but it worked) I had to be careful when the carbs were way out of balance that the oil didn't get sucked into one of the carbs.

Never had this problem with the SRX!


Ian

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Re: Carb Sync
« Reply #13 on: March 13, 2011, 10:23:45 PM »
Just to go back to the "popping" with the Bonneville. My local dealers mechanic told me that even Triumph couldnt get rid of the dreaded popping altogether with the carb set up. Apparently the fuel injected versions dont seem to suffer with it. Mine is a 2009 basic Bonnie with fuel injection and I cant say Ive ever heard it popping at all.

Ian
1 SRX 1 C400X

Andy M

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Re: Carb Sync
« Reply #14 on: March 14, 2011, 06:29:58 PM »
To meet the Euro regs with carbs they leaned off the mixture. Even with the exhaust gas watering down thingys removed the slightest thing makes them lean. Keep that air filter clean and the exhaust leak free. FI is superior in every way, but I can't afford to swap the bike yet.

My gauges came with a pair of cheap plastic needdle valves. Wind these in and they damp to within the expected width of the needle.

Andy