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1987 48 hp Johnson Carbs Seats different sizes

T

tfish60

Member
Two cylinder Johnson, I am trying to figure out why my carb seats have different size orfice, and the needles one red tip one black. Rebuilt both carbs with correct kit, now the upper carb running lean. ( the kits I bought #0396701 of course had similar seat ofrice size).
 
How did you determine that the upper carburetor is running ---" lean "-----Mixing gas and oil sat 50:1 on this motor ?
 
Yes 50:1, I took a friend to run the motor, with silencer off, I could visually, see less gas going into the throat as the throttle plates began to open. This is the point she bogs. Also, at the same point I sprayed a small amount of carb cleaner into the throat, instantly stopped bogging rpm increased. Bottom carb the amount of gas being sprayed into the throat is considerably more.
 
"I am trying to figure out why my carb seats have different size orfice, and the needles one red tip one black", by carb seats do you mean float valve seat? is this motor new to you? that carb kit covers over 10 years of motors and different HP's. trying to under stand different needle tips and orifice size.
 
Yes float valve seats are correct, and it is new to me. I am befuddled by the same thing. I have rebuilt many carbs in the past never had an issue like this. I am going to pull the upper carb, and compare the kit seats with the ones I have. I didn't notice this problem until I had the lean issue. Pulled the carbs went through them checking and re cleaning, not finding anything outside of these two orfice problems. I saved my old carb internals, went back and started inspecting and there it was, easy to see, size difference is obvious. The motors runs great until the throttle valves begin to open, then she bogs.
 
Some years the rubber tip was red and other times they were black.-----No difference in the way they perform.----What other trouble shooting has been done on this motor ?----Compression test values should be posted.
 
Carb seats are the inlet fuel supply to bowl. The fuel you see from emulsion tube is controlled by main jet and gasket between carb body and bowl base. If it boggs when carbs open need to check the sync and link. Only way seats would cause this is float level is way off or floats installed incorrectly/
 
compression 151 149,new plugs champion gapped 30 thousandths. New fuel lines, from tank to engine, new bulb, clear fuel lines under the cowling, now air detected while running. It needed a new clear sleeve on the throttle cam roller, ten thousandths gap between cam roller and throttle cam. throttle plates close completely, checked both move at same time together, I checked spark, 7\16 blue streak, plugs, new water pump, new forward reverse pinion gears, new seals in the lower unit, idle timing 4 degrees. I was just running it on the muffs, and noticed at idle fuel spraying out of the air bleed top carb only.
 
racerone said:
Some years the rubber tip was red and other times they were black.-----No difference in the way they perform.----What other trouble shooting has been done on this motor ?----Compression test values should be posted.
Click to expand...


compression 151 149,new plugs champion gapped 30 thousandths. New fuel lines, from tank to engine, new bulb, clear fuel lines under the cowling, now air detected while running. It needed a new clear sleeve on the throttle cam roller, ten thousandths gap between cam roller and throttle cam. throttle plates close completely, checked both move at same time together, I checked spark, 7\16 blue streak, plugs, new water pump, new forward reverse pinion gears, new seals in the lower unit, idle timing 4 degrees. I was just running it on the muffs, and noticed at idle fuel spraying out of the air bleed top carb only.
 
racerone said:
Something wrong in the top carburetor.
Click to expand...

I pulled the top carb tore it down recleaned everything, reset float, pressure tested float valve. Installed fired her up still gas spitting out of air bleed. The only thing I haven't done is removed the bb on top and cleaned the tiny tube from top down. I have cleaned it from the other direction carb cleaner and compressed air.. it seems there has to be something in the top of that carb disrupting fuel air mix.
 
Possible cause of fuel blowing thru idle jet is chipped/broken reed,reed gasket blown or reed block loose or top piston scuffed ..
 
The reason I pulled the carbs in the first place was poor idle. When docking for example going from forward to neutral reverse it would die. I had no problem with getting on plane or wot running. So I just don't see it been piston or reeds, the compression is just too good to be scuffed piston. Somehow I have caused this problem, I just cant find the reason.
 
faztbullet said:
Possible cause of fuel blowing thru idle jet is chipped/broken reed,reed gasket blown or reed block loose or top piston scuffed ..
Click to expand...


Also remember when I spray fuel into the carb throats she picks up, this problem begins as soon as the throttle plates begin to open.
 
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