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Amal Mk.1 carb. synchronisation

Submitted by mark_ross on Sat, 26/09/2015
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Commando

I am trying to sync my Mk1 amals on my 72 750 combat, with a syncpro carby sync, When I calibrate the unit, alls well but whenI hook up the two separate hoses to the manifolds and the gauge on one carby is way off the chart I have changed the hoses over and the offending cylinder/ carby has the same unreadable vacuum.Any ideas what may be causing so much vacuum on one pot/carby?I donât think it is the carby sync as it seems ok when changing the hoses over.

Thanks in advance

Mark RossGold CoastQLD Oz

Submitted by simon_ratcliff on Sat, 26/09/2015

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The Syncpro looks similar to the Morgan carb tune which uses rods instead of liquid mercury.

With the Morgan a high reading indicates a high vacuum which indicates that the slide is nearer to closed than open. As the slide is opened the vacuum between the slide and cylinder decreases.

Have you checked the inlet stub tube you're attaching the syncpro hose to is not blocked?

Submitted by simon_ratcliff on Sat, 26/09/2015

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Actually, forget the previous suggestion - with a blocked tube you'd get zero reading - still a bit early. I can only assume the slide is completely shut if the reading is going off the scale.

Submitted by mark_ross on Sat, 26/09/2015

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Previously simon_ratcliff wrote:

Actually, forget the previous suggestion - with a blocked tube you'd get zero reading - still a bit early. I can only assume the slide is completely shut if the reading is going off the scale.

Swapped the tubes on the sync pro the carby was the constant, will recheck slide and see what happens then, Thanks will advise of what I can find out.

Submitted by mark_ross on Sat, 26/09/2015

Permalink

Previously simon_ratcliff wrote:

The Syncpro looks similar to the Morgan carb tune which uses rods instead of liquid mercury.

With the Morgan a high reading indicates a high vacuum which indicates that the slide is nearer to closed than open. As the slide is opened the vacuum between the slide and cylinder decreases.

Have you checked the inlet stub tube you're attaching the syncpro hose to is not blocked?

I swapped over and tried all 4 hoses that come with the sync pro same will check slides and go from there.

Thanks

Submitted by mark_ross on Sat, 26/09/2015

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Previously mark_ross wrote:

Previously simon_ratcliff wrote:

The Syncpro looks similar to the Morgan carb tune which uses rods instead of liquid mercury.

With the Morgan a high reading indicates a high vacuum which indicates that the slide is nearer to closed than open. As the slide is opened the vacuum between the slide and cylinder decreases.

Have you checked the inlet stub tube you're attaching the syncpro hose to is not blocked?

I swapped over and tried all 4 hoses that come with the sync pro same will check slides and go from there.

Thanks

Yes had the carbs and manifolds off for a clean, checked the stubs both clear

Submitted by simon_ratcliff on Sat, 26/09/2015

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Does the slide of the carburettor giving the high reading move up and down when the throttle is operated? When you say the reading goes off the scale does it literally go to the very top of the column and out of interest, what is the reading on the other carb?

Submitted by mark_ross on Sat, 26/09/2015

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Previously simon_ratcliff wrote:

Does the slide of the carburettor giving the high reading move up and down when the throttle is operated? When you say the reading goes off the scale does it literally go to the very top of the column and out of interest, what is the reading on the other carb?

Hi Simon

Never got a chance to check with throttle opening, as it is a fluid in the gauge type tool, as soon as I connected the rubber hose it shot straight to the top and being in danger of sucking the fluid into the motor, I had to pull the hose off of that carby,and quickly, The other carby was only 1/4 of the way on the gauge, If it was a digital reading not a fluid one there wouldn't have been any worries. I have synced the carbs by ear (like I have always done) slides leave bottom togeather and are even through the whole pull, on test ride the bike pulls well and plenty of power all the way through the range with no backfire or flatspot plug colour is good, it idles as good as I can get an pair of Amal mk1's to idle.

Submitted by simon_ratcliff on Sat, 26/09/2015

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If the exhaust pipes are the same colour and you can feel with your hand equal exhaust gas temp and pressure out of each silencer when the engine is revved then I wouldn't worry about the gauge readings.

If there's a difference between the two then It's possible you've got one good and one bad cylinder and the gauge readings are correct.

Submitted by simon_ratcliff on Sun, 27/09/2015

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I should have stated prior to checking exhaust temp. and pressure to visibly synchronise the slides. This can be done very accurately by inserting the round end of a 1/4" drill bit between the slide and body of each carb.

By opening the throttle carefully by a fraction and watching the drill bits you'll be able to see if the slides are synchronised. Adjust cables as required.

If there's a difference in exhaust temp and pressure or the Syncpro gauge indicates an imbalance then a possibility is the slide to carb body fits are significantly different or there's a significant difference between piston ring and cylinder sealing on each bore. A leak down test is very useful in determining condition of piston rings/cylinder bores, valve seats/faces and head gasket.

 


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