Re: 9.9 Johnson Carb Question

[joesnuffy]

Out of the 3 I worked on the 1991 carb was the easiest for me to dial in. It has the adjustment screw to allow it the butterly to be tweaked while running at idle speed and dialing it in. It has like a SS hex head screw on it to make adjustments even while running tells me that was done for a reason. I will post the diagram of 1991 carb. It also had a totally different look and build to it. You can look for yourself but out of 3 I own I got the best results with this particular carb. I was working on like a 75,85,91 . The 75,85 had a carb like yours not much difference in them. The 91 best I could tell did not have the bearing needle valve it was eliminated (?). If at all possible try a 1991 style carb. I did notice that the low speed needle had to be turned out more on the older style carbs like 2 1/2 + turns to get a good idle. I did swap carbs while working on engines a 15hp carb compared to a 9.9hp carb in my humble opinion are almost identical except high speed jet size and yours is running well at high speed that would be the size you need if you tried a 15hp and it wouldn’t run high speed well. I measured carb throat sizes on 9.9 and 15s and they were very close.

Like Fleetwin said you can tweak when the butterfly opens or not to see if that helps and make sure throttle butterly is closing all the way not a weak spring. Check your reed valves also to see if their closing properly no light coming thru when they are closed.

Hope that helps,
Joe

http://www.marineengine.com/parts/johns … Carburetor

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