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Mikuni question

Submitted by david_henshaw on Fri, 25/03/2011
Forums
Commando

Hi

I have recently fitted a single Mikuni VM36 to my 1974 850 MkII. Starting is much improved and it nowhas a very reliable tickover. I note that the right hand pipe has gone very blue in justa few miles. This seems odd to me, with a single carb set up. I can't find any obvious leaks, and there's no misfiring at all. The plugs both look fine. Any ideas, please?

Also, the engine runs really well and pulls strongly and smoothly through the whole rev range, but tends to snatch a bit when it's not under load. I haven't quite got to grips with fine-tuning the Mikuni yet, so again, I'd appreciate any pointers.

Many thanks

Trevor

Attachments P1030939.JPG

Submitted by dominic_gomes on Fri, 25/03/2011

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You might want to compare rocker clearances on both cylinders and your timing for each cylinder. Either could cause lean running on the one cylinder. I would suspect the timing.

Submitted by david_henshaw on Mon, 28/03/2011

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If it's of any interest, the solution was actually quite simple. The two hidden manifold bolts and the outer one on the right had worked loose, allowing air in. I had bought the carb as a kit, and there were no spring washerswith the manifold screws, nor any mention of them. They were tightened really hard,but it took them less than twenty miles to slacken off! A relatively easy fix with the old washers off the Amals, even if you have to take off theMikuni to get to the middle two manifold-to-head screws.

Trevor

Submitted by Xanna_jeannett… on Mon, 28/03/2011

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Previously wrote:

Hi

I have recently fitted a single Mikuni VM36 to my 1974 850 MkII. Starting is much improved and it nowhas a very reliable tickover. I note that the right hand pipe has gone very blue in justa few miles. This seems odd to me, with a single carb set up. I can't find any obvious leaks, and there's no misfiring at all. The plugs both look fine. Any ideas, please?

Also, the engine runs really well and pulls strongly and smoothly through the whole rev range, but tends to snatch a bit when it's not under load. I haven't quite got to grips with fine-tuning the Mikuni yet, so again, I'd appreciate any pointers.

Many thanks

Trevor

hello too find lean runing put some petrol in a small pump action bottel and when the engine is running give it a squirt of petrol round the inlet manifold and see if the engine picks up revs then you will know you have a air leak in there? yours anna J ..ps SU carbs are better than a Mikuni ? 70 MpH On a Commando

Submitted by david_henshaw on Sun, 05/06/2011

Permalink

Previously wrote:

Hi

I have recently fitted a single Mikuni VM36 to my 1974 850 MkII. Starting is much improved and it nowhas a very reliable tickover. I note that the right hand pipe has gone very blue in justa few miles. This seems odd to me, with a single carb set up. I can't find any obvious leaks, and there's no misfiring at all. The plugs both look fine. Any ideas, please?

Also, the engine runs really well and pulls strongly and smoothly through the whole rev range, but tends to snatch a bit when it's not under load. I haven't quite got to grips with fine-tuning the Mikuni yet, so again, I'd appreciate any pointers.

Many thanks

Trevor

 


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