Carb problems on 1970 20 hp Johnson.

[heypawpaw]

Bought a Johnson 20rl70, removed carb and cleaned,checked float setting and verified needle and seat closing, changed fuel pump and hoses. Put motor in a drum and it started easily and after adjusting low speed jet idled smoothly. Took boat out for test run and when I open throttle engine accelerates a couple seconds then bogs. If I slow to half throttle it runs fine but as I increase throttle it bogs again. Carb roller touches armature plate at two marks as it should. If I pull choke when engine bogs engine revs but not wide open. On this engine there are two bell cranks on the choke shaft. When the choke is pulled it pushes the inside bell crank closing the butterfly. While increasing throttle if I move the outside bell crank it pushes the inside bell crank to a point where the choke butterfly is closed and rpms increase but not wot if I continue moving outer bell crank rpms increase to wot and engine runs great. I know the choke is only for starting and should be open while running. Am I missing something?

 

[racerone]

Have you removed the high speed jet for cleaning , yes or no ?-----It is screwed horizontally into the carburetor bowl.----Drain plug has to be removed to get it out.

 

[heypawpaw]

Yes I removed the high speed jet, low speed needle and needle and seat and cleaned it and blew carb cleaner through all pasages.

 

[F_R]

Correct HS jet? #67D. Previous owner may have changed it.

 

[heypawpaw]

F_R is there a way to know if jet is right one or do I have to get another jet?

 

[F_R]

Remove it and look at the number stamped on the OD of the inner end. Number is also the diameter in inches (i.e. .067") if you have a way of accurately measuring it.

 

[heypawpaw]

Thanks I'll check it out.

 

[heypawpaw]

F_R I removed high speed jet again today and it has 68 stamped on it so I guess you were right about jet being changed.

 

[F_R]

Well that's close. Only 0.001" off. And off in the direction that should help with your problem, not cause it. Are you sure it is absolutely clean? Even a hint of any gum or varnish in it will cause it to run lean. But don't go jamming drills or wires through it. It is a precision part.

BTW, the "D" means something, I am not sure I remember what. Profile of the orifice, maybe?

 

[AlTn]

with the shift lever in forward, does the carb roller rise to the highest point of the timing cam lobe?

 

[heypawpaw]

Yes it does.

 

[oldboat1]

Would be routine to check spark and compression -- both tested OK? Carb cleaning usually involves complete disassembly and cleaning (I soak, then clean out passages) -- think yours has a nozzle gasket, and would want to be sure that's in place. I know the issue is primarily h.s. operation, but I would open the idle circuits under the domed fittings and clean under there as part of the process. You're right about normal choke operation (choke plate open when warmed up and running).

 

[heypawpaw]

Yes there is a nozzle gasket.I'll have to order a kit to disassemble carb completely, so far I took off bowl removed jets needle and seat and blew out passages with carb cleaner. Did not do compression check and used spark plug grounded against block, very bright spark. I'm thinking that if engine runs wot if I open the outside bell crank on choke shaft spark shouldn't be an issue but I could be wrong. The carb on this engine is slightly different than on my FD20. This one has no packing washer or gland nut on low speed needle and choke shaft is set up different with two bell cranks. I'm wondering why outside bell crank on choke shaft would change engine speed at all?

 

[racerone]

Often times when low speed needle is adjusted for " best idle " it is too lean for proper acceleration.-------Try opening low speed needle 1/4 turn.-------And does spark jump a gap of 1/4" or more, yes or no??

 

[AlTn]

in your carb cleaning, remove the idle speed mixture needle and use carb cleaner and compressed air to clean that passage. When the passage is clean you'll see an equal spray pattern coming from the 4 tiny holes in the carb throat just behind the throttle butterfly.If the carb cleaner ends up going down the passageway to the carb bowl, just use your thumb to block the passageway and force the carb cleaner through the metering well and out those 4 holes. You can also try spraying directly into those holes and out the idle mixture passage, the goal is to get them free flowing.

 

[heypawpaw]

Thanks, I'll check the spark gap and clean out passages to four tiny holes carb throat.

 

[boobie]

F-R the "D" or "C" on a jet tells you which way the fuel goes through it in a carb. Depends on where it's installed.

 

[heypawpaw]

Had to put this project on hold for a while but back on it now. Carb is disassembled bowl removed and passages opened I have a carb kit with new float, needle and seat, and a new high speed jet. Should carb be completely disassembled (butterflies and shafts) or just remove domed fittings and clean passageways? Should bearing be pushed on low speed needle or just put bearing in hole then screw in needle? What is the process to install domed fittings removed to clean passages?

 

[AlTn]

no need to disassemble ( butterflies and shafts ) , domed fitting on top of carb, your choice. You can clean that passageway w/o removing it by using spray carb cleaner and compressed air, you just need to have a spray pattern from each small hole that enter the carb throat behind the throttle butterfly. It's easier to clean with the plug out and you can also get an idea of how that area of the carb works as well as see how far the idle mixture needle extends into the mixing chamber. If you weren't having any problem with the idle mixture as far as the needle leaning or enriching the mixture before, I wouldn't worry about that bearing, just establish that there is one. Only one I've replaced out of 10 or so carbs really didn't need replacing. I just put it on the needle shaft and screwed the needle in. The bearing stayed in place when I screwed the needle back out.

 

[heypawpaw]

Thanks AlTn dome fittings removed and can see the very tip of needle in mixing chamber when lightly seated. Never removed dome fittings before,to replace do I need some type of sealant and do dome fittings just push in or should I tap on dome to make it expand and fit tight?