Johnson 20hp Please help I've tried everything!

[jetski39590]

I have a 73 20hp johnson . I have a problem with the motor not running without full or partial choke. Can't idle so to engage drive. I have renewed plugs points condensors full carb service kit, soaked and blown out etc the carb is clean for sure.New fuel pump service kit.I have also bypassed the pump with a bucket of fuel on a step ladder to rule out the pump and tank non returns. I can start the motor no problem and let it warm up for a few minutes but as soon as I try to take off the choke it will die. As per instruction from other post If I spray fuel oil mix down the carb throat it picks and revs great for a few seconds and dies again, another squirt off it goes again. Its sounds like a blocked high speed jet but this is fine could it be reed valves? I have done all I can any suggestions. Oh I've checked the carb bowl after it dies and it has plenty of fuel in there. One last word I should run fine without a carb silencer shouldnt it as I dont have one fitted
Simon UK

 

[DJ]

Re: Johnson 20hp Please help I've tried everything!

Float level correct?

 

[jetski39590]

Re: Johnson 20hp Please help I've tried everything!

There's plenty of fuel in there when I checked after it died. Is the float adjustable? I've checked its in the right way round with the concave part matching the hump in the bowl. I have blown through the fuel intake the right way up and it lets air in and then inverted and it doesn't so looks like the inlet is working correctly. I've heard about getting the float valve adjusted but is this the case with mine as there doesn't seem to have any adjustment other than bending it. Am I right in thinking it has to be a fuel issue not something to do with the advance mechanism. I had a problem last time it was out when the throttle linkage came adrift and bent the brass connector but that all seems fine now. I'm scratching my head

 

[jetski39590]

Re: Johnson 20hp Please help I've tried everything!

Just found this on another post:"Or improper float adjustment, seing that you replaced it and don't say anything about adjusting it. It should be bent so that when the carb is turned upside-down, the float is even and level with the carb bowl's gasket surface on the main casting of the carb.A service manual sure does help a lot."
I'll check this out today would make sense as it would be opening fully and allowing petrol through (as long as it doesn't rain but this is NE England and it rains as much as Scotland)

 

[jetski39590]

Re: Johnson 20hp Please help I've tried everything!

Adjusted float today but still the same. its starting no bother but still won't run without choke

 

[tx1961whaler]

Re: Johnson 20hp Please help I've tried everything!

I believe that the carb is still not 100% clean. The low speed jet needs to be removed from the bottom of the bowl and cleaned with a soft wire. The Welch plug on the top should have been removed and the idle passages cleaned out.
The fact that it runs on choke but not without points the problem straight at the carb. And don't feel the least bit bad; there isn't a single one among us that hasn't had to do the carb two or three times in a row...

 

[kbait]

Re: Johnson 20hp Please help I've tried everything!

Again, use canned air w/straw or compressed air to confirm unobstructed fuel passages in your carb, and confirm all hose connections are leak-free. If all the carb gaskets/packing washers are good, and in place, it should run w/o choke.

 

[JB]

Re: Johnson 20hp Please help I've tried everything!

Gummed up carburetor is so often the cause of your symptoms that folks often forget that there are other things that can cause them.

Assuming for the moment that the carb is as clean as you believe it to be the most likely fault is a leaky gasket on the reed block or a bypass cover. Or somewhere else that extra air is getting sucked in to the crankcase without going through the carb.

Other spots not so easy to spot are badly worn carb throttle shaft or crank seals.

Try spraying some soapy water on all of those gaskets while she is running. Bubbles will signal a leak.

 

[jetski39590]

Re: Johnson 20hp Please help I've tried everything!

I think I've found the problem I had forgotten to replace the rubber washer in the carb bowl so the fuel wasnt being sucked up properly.I noticed a bit of damage on the face that meets the rubber washer that might not seal perfectly. I suspect I have a dodgy coupling on my fuel tank also as is seems to wash back and forth into the tank when I pump the bulb. I disconnected the pipe and stuck the hose directly in the tank and it fired up, took the choke off and it runs and revs ok. It is spitting a bit and a bit smoky but will a good blast on the water sort that? it feels a bit choked up, It hasnt run properly for over a year. I think I'll replace the tank and coupling as the gauge doesnt work and it looks a bit raggy anyway. I sort of misfires every so often not a pop more of a kickback and motor jumps to the side what could cause this? Anyway thanks for the help, we'll see how it goes.