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Mikuni 44 phh - pump stroke really supposed to be 7.5 mm???


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Since I've been having various issues trying to tune my Mikunis for a new engine, I decided to check my pump lever stroke measurement - this is something that I did not check when I put the carbs on the car.

 

The Mikuni manual clearly shows that the pump lever is supposed to move 7.5 mm when a cotter pin is used in the center of the three holes on the rod - for 44 PHH carbs.

 

With the carbs still on the car, I used my borescope and a piece of stiff wire with the 7.5 mm measurement clearly marked on it.  Operating the linkage to full open, I saw the pump lever move about half the 7.5 mm distance.  

 

Now, two of my Mikuni carbs were near new when I bought them, and one is obviously a bit older.  However, all three of them have about 3-4 mm of stroke instead of the factory spec.  The spec being off, especially for the new carbs is really surprising. I can't believe it... and then the older carb was set the same.  I even have another rebuilt one laying around, and I checked that one too.  It had about 4.5 mm of stroke.

 

Is there a chance that factory manual is incorrect?  Anyone else ever gone through the trouble to check their pump lever stroke dimension?  

 

I have now pulled each of the three carbs off the car and am proceeding with setting the rod such that the pump lever travel is 7.5 mm when the linkage is operated (using cotter pin in middle hole).  I hope I am not making a mistake because its a pain to go through all of this for a misprint.

 

 

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Actually, here is a thought...  My Mikunis all have the cooling body on them, that extra layer with the two barbs that attaches between the bottom of the carb and the pump body assembly.  The Mikuni manual diagrams do not feature this part, so presumably the measurement they give is without it.  That would probably make up the extra few millimetres that we are missing.  

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  • 1 month later...

If you look at where the measurement is taken, it measures the full stroke of the lever.  That's not going to change without the cooling block or with.  The pump lever actuating rods just have to be longer on the carbs that have the cooling bodies.

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