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Fluctuating Tickover


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I've recently changed the carbs on my 6 and have noticed a curious increase in tickover speed when stationary and I apply the brakes. Normal tickover is 800rpm rising to 1200rpm, I suspect the servo but not sure what I'm looking for.

 

Otherwise, it goes like I stole it and stops o'k. You're thoughts most appreciated.

 

Cheers, H.

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Cheers Pete, I see where you'er going. If the rev's drop I've got some sort of air leak on the servo which increases when the diaphragm moves.

 

Will give it a go in the morning.

 

Again cheers, H.

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Peter -

 

I blanked off the servo vacuum feed to no avail - no drop in rpm. I sat and tried it through the rev range2/3000rpm (neighbours gone to work) still the same.

After some research (Buckeye Triumph) I'm beginning to suspect master cylinder to servo front seal.

 

I thought an air leak might effect the ignition timing so blanked that off as well - still the same.

 

I've just found an old Redex vacuum gauge so I'll try and hook it up for weekend and give it blast down some good bike roads I know.

 

Poolboy -

 

The SU's were US so to speak, so I never really noticed it before.

Being a biker I liked the look of the Mikuni set up from Vintage Performance Developments ( 6 months from order to delivery and customs were a pain also) and I'm blown away with the performance improvements (now it can fill it's lungs). I followed their installation instructions implicitly and can't think of anything that may point to the carbs being the problem unless someone wiser than I can tell me what to look for.

 

Cheers, H.

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I don't think there's much experience of Mikunis on the forum yet. I'm not sure I follow what you've said above. You blanked off the servo vacuum pipe and it made no difference but you suspect the master cylinder to servo seal?

 

Where are you picking the vacuum up from? Maybe a photo would help.

Edited by peejay4A
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Since the brake servo is out of the equation, we need some other reason why pressing the brake speeds up tickover.

Maybe pressing the brake pedal is moving the accelerator pedal. Or the clutch pedal.

Time to ferret around in the footwell.

Peter

Edited by Peter Cobbold
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I know of one , maybe 2 persons who have Mikuni, but only one of those have any sort of technical ability.

His name is Al and he goes by TRick6;

I bet he'll share what he knows if you send him a PM thru the 6-pack forum

Here's a sample:

http://www.6-pack.org/j15/index.php/forum/search?q=mikuni&searchuser=TRick6&searchdate=all&childforums=1&limit=5

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poolboy/Peter/peej4a,

Sorry I didn't word the reply to Peter that well, it was in response to blanking off the vacuum pipe to the servo and seeing the effect. The actual fault disappeared by doing this and if there was a significant air leak on the servo I would have expected a possible drop in rpm on tickover if I'm thinking correctly. This not being the case I assumed the seal between the servo/master cylinder was faulty which after removing the servo I found to be so. In fact the M/cylinder had started leaking and the operating shaft from the servo was badly corroded on the inside of the servo behind the seal. Looks like I've caught it just in time. I've ordered a new Servo and M/cylinder from TR Shop (on offer and free postage) will be here Monday. In the meantime I'll repair the brake fluid damage to the paint work below the servo now I can see it and get at it!.

Hopefully this will cure the problem and improve the braking, although I didn't think there was anything wrong with the brakes (mind you size 11's and 16 stone tend to mask things a bit).

By the way, 6-pack is a great site along with Buckeye Triumph, lots useful info. I will try and post some pic's of the Mikuni's when she's back together.

 

Cheers all, H.

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Update-

I fitted the new servo/master-cylinder and problem cured.

Will give it a good run at the weekend on the Lakes Tour.

Ive included a pic of the mikunis. Will post some more when I get the hang of it.

 

Cheers H.

.post-12401-0-77193000-1409867640_thumb.jpg

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Poolboy,

 

One of the points I checked out when I first discovered the fault. It's been crimped and soldered, not pretty but functional. Getting the hang of attaching photos I think, at least from the iPad. Hopefully some more below.

 

Cheers, H.

 

.post-12401-0-91179900-1409893521_thumb.jpgpost-12401-0-11824000-1409893585_thumb.jpgpost-12401-0-51118000-1409893650_thumb.jpg

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