ET: Engine (Twin) Mikuni carbs

Monkeypants

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Two front head & 34 mm Mikuni VMs. There are two tees, one just barely visible in the photo
IMG_20200527_144140.jpg
 
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brian gains

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vibrac: it would be interesting to know if you find any appreciable muck in the carb'. In conversation this week I was told that the floats 'stick' on their vertical guide pins after being left dry due to vibration causing notches on the pins which stop the float rising with the level of the fuel.
Anything is worth considering but have yet to pull mine apart to inspect. At the moment I'm always at the ready to give the float chamber a tap with the handle of a screwdriver.
 

Robert Watson

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John McDougall took every 34 mm Mikuni he put on a bike, which was more than a few, and took a drill to the guide holes as he experienced several that would have a float stick on the guide pins.
 

Michael Vane-Hunt

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I did the same using numbered drills. Then I carried the next size of drill with me. One carb float had to be resized 3 times.
 
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vibrac

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vibrac: it would be interesting to know if you find any appreciable muck in the carb'. In conversation this week I was told that the floats 'stick' on their vertical guide pins after being left dry due to vibration causing notches on the pins which stop the float rising with the level of the fuel.
Anything is worth considering but have yet to pull mine apart to inspect. At the moment I'm always at the ready to give the float chamber a tap with the handle of a screwdriver.
Thanks Brian I will look today the carb (not old) has been empty all winter had one run before a strip for primary leak and then on next start up the float or needle stuck. Tank has always been clean and I empty it in the autumn and squirt some WD 40 in over winter. Stand by for photos I have a new float needle somewhere.
As an aside I have a pre monoblock carb on my KSS velo on its third float chamber and miriad float needles and reseating attempts it still floods at random times on tickeling I blame the so called petrol.
 
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erik

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Hello Vincent ! On your bike the two carbs are connected with a bypass! Is there any advantage to do this? Regards Erik
 

vibrac

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Thanks Brian I will look today the cartb (not old) has been empty all winter had one run before a strip for primary leak and then on next start up the float or needle stuck. Tank has always been clean and I empty it in the autumn and squirt some WD 40 in over winter. Stand by for photos I have a new float needle somewhere.
As an aside I have a pre monoblock carb on my KSS velo on its third float chamber and miriad float needles and reseating attempts it still floods at random times on tickeling I blame the so called petrol.
Ok after breakfast I whipped off the Mikuni and opened up the float bowl, first problem is that you have to upend the carb to easily undo the 4 cross heads so there is no way you can leave the float & needle undisturbed
the carb was the cleanest thing in my workshop not a spot of any dirt. I removed the float tab and inspected the needle under a glass no ridges or blemishes so the reason for flooding remains a mystery.
I will add a filter however, who knows I may be forced to go into a supermarket filling station one day...
 

vibrac

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Back together with filter added.
Now its sat for 10 mins taps on, no leaks , I give up!
NB see Where the starter sits next to the Alton and F106?
1590661333111.jpeg
 
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