Johnson 5.5 CD-20C carb and running issues

[RenegadeBird01]

I’m working at rebuilding a Johnson 5.5 just for something to do and as a bit quieter replacement over my el cheapo hangkai. Compression is a bit low on both cylinders at around 70-75 psi, both cylinders have good spark, cylinders are clean with no scoring, has a vacuum pulse fuel pump which works well, and I replaced the oil line to the top of the crank case. I have had it running off of both fuel in the cylinders and a couple sputters hooked up to the carb. The carb is where my issue is happening as far as I can tell. I have ran it through my ultrasonic cleaner 3 times now, removed and replaced the Welch plug, replaced the float, polished the brass seat, and pressure checked the carb, holding 5 psi. However when I hook it all up, prime the system, it will fire initially, run for about 30 seconds and then just absolutely flood everywhere. Gas will pour out both the carb and exhaust and it will not fire again unless you completely drain the carb. My high and low speed needles are both set correctly, and I have even just for troubleshooting ran them both ways to see if it would mitigate the issue. My only conclusion at this point is that something in the fuel system is creating way more pressure than it needs and pushing fuel past the seat although I was always taught that 5psi was plenty in a carb to keep from flooding. I did order a carb kit for it however the seat that was sent is metric threads and will not fit, and I’m a little unsure of the quality of the bowl gasket as it seems to be a rubber material instead of the thick paper of the original. My original carb gaskets were not torn in any way so I am currently reusing them, and I don’t know if that could potentially be part of the issue or not.

 

[jimmbo]

Welcome to iboats

That would be a 1963 Motor, and will require a 24:1 Gas:Oil Mix.
You say unburnt Fuel is coming out the Exhaust? If you have a ruptured Fuel Pump Diaphragm, Fuel can build up in the Crankcase, and be expelled by the Crankcase Vent/Drain into the Exhaust Housing.
Does the Primer Bulb get hard, when you prime the Motor?


"polished the Brass Seat" ????

How did you set the Float Level?


Carb Kits: https://www.marineengine.com/newparts/part_search.php?part_num=18-7043

 

[RenegadeBird01]

Welcome to iboats

That would be a 1963 Motor, and will require a 24:1 Gas:Oil Mix.
You say unburnt Fuel is coming out the Exhaust? If you have a ruptured Fuel Pump Diaphragm, Fuel can build up in the Crankcase, and be expelled by the Crankcase Vent/Drain into the Exhaust Housing.
Does the Primer Bulb get hard, when you prime the Motor?


"polished the Brass Seat" ????

How did you set the Float Level?


Carb Kits: https://www.marineengine.com/newparts/part_search.php?part_num=18-7043

Yes the primer bulb gets hard, I double checked that the pump does pick up and pump fuel. As for polishing the seat, it’s a pretty standard procedure we do on all our carbs at our shop, basically I pull the seat out and use a non abrasive polishing compound on the end of a skewer down where the needle rests to restore a seal at the needle when the bowl is full. The testing procedure to verify if it’s sealing is to assemble the carb, attach a hand vacuum/pressure pump, hold the carb upside down, and gently pressurize the carb to see what psi it holds. As to the float height, the front of the float is just slightly tipped down. I did attempt to disassemble the fuel pump to check all the diaphragms, however it wouldn’t readily separate and as it is pumping and I can’t get replacement parts for that I did not pursue that. The majority of the unburned fuel is definitely coming out of the carb after I replaced the oil line on the left side of the engine.

 

[jimmbo]

To set the carburetor float level, remove the shroud; then unbolt and remove the carburetor. Remove the float chamber (23- Fig. J2, J3 or J4) and invert the carburetor body (5). The upper surface of float (lower, when assembly is inverted) should be level and flush with gasket surface of body. If it is not, carefully bend float lever: then, check after assembly to make sure float does not bind or rub.

 

[RenegadeBird01]

To set the carburetor float level, remove the shroud; then unbolt and remove the carburetor. Remove the float chamber (23- Fig. J2, J3 or J4) and invert the carburetor body (5). The upper surface of float (lower, when assembly is inverted) should be level and flush with gasket surface of body. If it is not, carefully bend float lever: then, check after assembly to make sure float does not bind or rub.

Yeah that sounds about how I have it currently

 

[racerone]

Fact----The fuel pump is driven by PRESSURE and not so much vacuum.-----Did you order factory parts or something cheaper.-----Does spark jump a gap of 5/16" on both leads?----Are coils inspected and newer replacements?----Have you replaced the water pump impeller?----Have you inspected the slip clutch in the lower unit ( below the pump )---That item can bind up and prevent full power to the prop.-----I own more than 1 of these wonderful motors.

 

[Crosbyman]

if you plan to service oldies download the free bible on J&E of those years ... ALL the info you need is in there stoore/print locally

https://www.socalaomci.com/library/johnson_service_manual_10th_edition.pdf

 

[RenegadeBird01]

The

if you plan to service oldies download the free bible on J&E of those years ... ALL the info you need is in there stoore/print locally

https://www.socalaomci.com/library/johnson_service_manual_10th_edition.pdf

That’s super helpful, thanks, I was looking for a more complete service manual

 

[RenegadeBird01]

Fact----The fuel pump is driven by PRESSURE and not so much vacuum.-----Did you order factory parts or something cheaper.-----Does spark jump a gap of 5/16" on both leads?----Are coils inspected and newer replacements?----Have you replaced the water pump impeller?----Have you inspected the slip clutch in the lower unit ( below the pump )---That item can bind up and prevent full power to the prop.-----I own more than 1 of these wonderful motors.

Yeah spark and coils are fine as well as the plugs. I haven’t gotten to the drive section of the motor yet as I’m still working on getting it running. The carb kit I ordered was supposedly a sierra kit, but I suspect it’s not, however I wasn’t really using anything out of it other than the float which did appear to be the same as when I cleaned and rebuilt the carb I was able to reuse all the original parts.