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LM MK2 Carb synchronization

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Lemon 2 Junior View Drop Down
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    Posted: 09 Feb 2016 at 17:17
So valves sorted, now onto the carbs..they need setting from scratch, wife helped with throttle and slide sync and slides seem to be in order, I've read the dellorto manual and to be honest, was a little beyond me...Any advice on where to start with concerning idle and mixture...Bike will start on choke, but right carb is blowing fuel vape and popping from pipe...Any help.much appreciated.
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Doug View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Doug Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 2016 at 17:31
Make sure valves are adjusted correctly and timing is spot on before anything else. Give the carbs a good clean and ensure there are no manifold air leaks. If the exhaust is stock I'd begin with factory settings.
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Mike H View Drop Down
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Post Options Post Options   Thanks (1) Thanks(1)   Quote Mike H Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 2016 at 19:49
Yes really start by stripping cleaning and checking the carbs, can eliminate 'unsolvable' problems when it comes to setting up. Any hard green or brown deposits needs removing and check all jets and airways are clear. This can be difficult as the deposits can reduce the diameter of jets so they still look OK. Guess how I know! If in doubt, get a whole new set of jets.

Check float heights are correct and equal (metal arms parallel to float bowl flange when in the closed [up] position), also that both floats are the same weight (should be embossed on).

Ideally need vacuum gauges and 6mm adaptors for the intake 'manifolds' to balance the slide heights.

Start by getting both slides at the same height, and with a small gap (for idle). With carbs off can use e.g. a 1mm drill bit to set the gap. Thereafter when changing the throttle stop screws always turn BOTH BY THE SAME AMOUNT.

Except: where fine balance of the throttle stop screws is done with help of the vacuum gauges. Exact reading doesn't matter so long as both are equal, as near as is practicable. After that, can set the throttle cable adjusters in the samec way, when slides are hanging on the cables (just off idle).

Mixture screws start at 1.5 turns out. That is to say, screw all the way in, then anti-clockwise 1.5 turns. This is a beginning position only as it may not be enough, 2 - 2.5 turns out tends to be more common. You adjust these until engine idles without you having to use the twistgrip then you can revise the throttle stop screws BUT note that engine needs to be properly warmed up to get absolutely right, which is rarely possible on the stand in your garden, so expect idle to be  bit high after a few miles of actual riding. If so throttle screws can simply be screwed in a bit to compensate (both by the same amount).

After a while with age air leaks may occur down the idle screw threads and interfere with the mixture but you can get small O-rings to put in. In fact carb overhaul kit should include them.

On the LM's the accelerator pump diaphrams could be failing so need checking and replacing if necessary.

HTH




"Chicken nuggets don't dance on a Tuesday."
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Pharisee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pharisee Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 2016 at 20:23
I had a couple of problems balancing the carbs on my LM2 recently. The first problem was actually getting the blanking screws out of the inlet manifolds. They would only unscrew two or three turns before the head of the screw hit the underside of the cylinder head cooling fin. In the end, I had to remove a tiny bit of the fin with a Dremel to allow the blanking screw to pass by. Anyone else had that problem?
The second was that my vacuum gauges didn't come with any M6 adaptors. I had to turn a pair up out of some 6mm brass rod.  All very inconvenient Smile
Light travels faster than sound which is why some people appear bright until they open their mouth.
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Lemon 2 Junior View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lemon 2 Junior Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 2016 at 22:22
Using a drill bit for slide height adjustment is a good idea, will give that a go... been well over twenty years since the bike was last ridden, perhaps a carb overhaul kit may be in order...distributor was replaced as it was found, and all connectors have been checked and clean on rebuild, valves were done yesterday, so perhaps some TLC on the carbs is needed....she does fire up and revs out well, just struggling on transfer from pilot to main by the sounds of it... Dad gave me a 1963 Triumph Thunderbird as when i first past my test nearly twenty years ago, didn't really grasp the whole concept of pre ECU bikes, so many thanks for your help...between you lot and Dad, should hopefully get a basic grasp of old school bikes...i did get some slight trouser movement from side movement as i was warming her up in the shed earlier today, which was nice.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lemon 2 Junior Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 2016 at 22:24
Originally posted by Pharisee Pharisee wrote:

I had a couple of problems balancing the carbs on my LM2 recently. The first problem was actually getting the blanking screws out of the inlet manifolds. They would only unscrew two or three turns before the head of the screw hit the underside of the cylinder head cooling fin. In the end, I had to remove a tiny bit of the fin with a Dremel to allow the blanking screw to pass by. Anyone else had that problem?
The second was that my vacuum gauges didn't come with any M6 adaptors. I had to turn a pair up out of some 6mm brass rod.  All very inconvenient Smile


how did you get on? was looking at a carbtune, but for £70 i would hope I wouldn't have to bugger about with adapters.
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Pharisee View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pharisee Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 2016 at 22:54
Originally posted by Lemon 2 Junior Lemon 2 Junior wrote:


how did you get on? was looking at a carbtune, but for £70 i would hope I wouldn't have to bugger about with adapters.


Once I'd got the M6 adaptors, it was fairly easy. I only have a cheap carb balancing kit that I bought off eBay but it did a reasonable job. Adjusted the slide stops to give the same reading on both gauges (at a tick-over of about 1100 rpm). It was a bit subjective as the gauge needles were bouncing about a bit. Once I was happy with that, I adjusted the cables so that both slides lifted at the same time when the throttle was opened slightly. Made sure that both gauge needles moved at the same time. I've not had the Lemon very long so I'm no expert but it ticks over nicely when it's warmed up.
Light travels faster than sound which is why some people appear bright until they open their mouth.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lemon 2 Junior Quote  Post ReplyReply Direct Link To This Post Posted: 09 Feb 2016 at 23:15
ah good, yep slightly different to modern bikes, I can tune my Triumph Sprint ECU with my mobile phone, but can't tune a set of carbs manually...sums it all up.
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Phil View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Phil Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 2016 at 08:45
Just to add, when you balance the carbs using vacuum gauges once you have got them balanced on tick over, try swapping the gauges from side to side to make sure both gauges read the same as each other. When you do the revving up test make sure the bars are straight ahead, depending how the cables are routed you will find that putting the bars on full lock will alter the carb balance on an open throttle

Good luck
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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 2016 at 08:53
Best and cheapest setup for balancing two carbs (or FI) is a manometer. Never goes wrong and far more accurate than vacuum gauges. See how to do it in the FAQ section.
Brian.

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dukedesmo Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 2016 at 10:01
Originally posted by Lemon 2 Junior Lemon 2 Junior wrote:



how did you get on? was looking at a carbtune, but for £70 i would hope I wouldn't have to bugger about with adapters.
 
I have a (Morgan) Carbtune, bought it for my Ducatis. Works fine on the LM and was supplied with both M5 and M6 adapters.
 
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red leader one View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote red leader one Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 2016 at 10:05
Pretty heavy then.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dukedesmo Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 2016 at 10:46
Indeed, chain required to restrain the beast.
 
Funny thing is that I made a short video of the bike running that day to try and capture the noise through the 'solo per competizione' Lafranconis.
 
I set up the camera (my phone) on the bench to the rear and right side of the bike and revved it a bit but the pressure waves from the exhausts blasted the phone onto the floor. Luckily the phone didn't break so the whole episode is captured on video...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Pharisee Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 2016 at 11:32
Originally posted by Dukedesmo Dukedesmo wrote:

I have a (Morgan) Carbtune, bought it for my Ducatis. Works fine on the LM and was supplied with both M5 and M6 adapters.


Your threaded holes appear to be in a different place to mine Shocked

Mine are on the edge that face directly towards the rocker box. Is it possible that my inlet tracts have been swapped  over (left cylinder to right cylinder) at some time in the past?


Light travels faster than sound which is why some people appear bright until they open their mouth.
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Dukedesmo View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dukedesmo Quote  Post ReplyReply Direct Link To This Post Posted: 10 Feb 2016 at 11:46
Originally posted by Pharisee Pharisee wrote:


Your threaded holes appear to be in a different place to mine Shocked

Mine are on the edge that face directly towards the rocker box. Is it possible that my inlet tracts have been swapped  over (left cylinder to right cylinder) at some time in the past?

 
Certainly looks odd, I've not tried swapping them but assuming the holes are equally spaced it might be a possibility?
 
Here's a close-up of mine;
 
 
Really easy to get at.
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