July 14, 2019 at 9:05 pm #178872
Hi Guys, I’ve been restoring a 1957 Johnson 18hp for the better part of the year and have only been able to get it to run intermittently despite new coils, ignition system, spark plugs and wires, water pump impeller, and many carburetor rebuilds. Is there anyone around the Philadelphia area that I could possibly meet in person to try and figure out the last few gremlins that are plaguing me? Thanks!
Current issue is that it starts and runs for about 1.5 seconds then shuts off. Timing is correct, both plugs have spark at the cylinders, and the carburetor has a new float and various gaskets along with compression washers. This motor has run on the water within the last two weeks up to full throttle and back to idle a couple times but then had issues idling and starting.
July 14, 2019 at 11:57 pm #178885
- This topic was modified 1 month ago by Mumbles.
well if electricals are ok it seems to be starving for fuel with a full carb of fuel it should run more than 1.5 seconds for certain
you did install the fat gasket at the bottom of the carb….under the HS nozzle going up the carb
try spaying gas in the carb face see it runs longer to confirm fuel starvation from the carb body itself
if it runs recheck fuel delivery … clean all passages with a fine wire in case something is crudded solid air blow everything
make certain the choke plate opens up!
since it did run good a short while ago I would overall anything where fuel flows from the tank to the carb including the top chamber doesn’t take much to plug up all these small orifices …try bypassing the side filter for a test
July 15, 2019 at 8:43 am #178901
- This reply was modified 1 month, 1 week ago by crosbyman.
Thanks for the quick reply! I did install the fat gasket at the bottom of the high speed jet and the choke is working correctly. Additionally to further troubleshoot this I bypassed the fuel filter and had gas going straight into the bottom of the carb. I removed the air silencer and sprayed carb cleaner down the throat but it still wouldn’t run longer than 1.5 seconds.
I have a spare carburetor for this motor that I rebuilt as well that I also tried on the motor yesterday and the motor runs exactly the same. 1.5 seconds then shuts off. The top air passageways of both seem to be debris free. When off of the motor to test this I’ve removed the low speed needle and using my mouth blown air into the throat while blocking off the opposite side of the throat with my hand (as well as the other orifices). Air comes out the front of the low speed passageway pretty well and without any particulate. It’s really got me stumped
July 15, 2019 at 9:11 am #178904
- This reply was modified 1 month, 1 week ago by ErikL.
hum….. ? tried rechecking under the flywheel for pinched wires…. bad condensers plug wires crossed over
can you feel air sucked in good the carb face if you try starting it ?
without suction it can’t feed itself with gas
any chance the small check valves behind the carb plate are defective causing vacum loss ??
I am at a loss to…:-(
US Member - 2 Years
Topics: 32July 15, 2019 at 10:57 am #178910
Sorry buddy, I am in Providence RI….Let me know if you are planning any trips in this area, would be glad to help…July 15, 2019 at 11:32 am #178916
Unfortunately I don’t think I’ll be around providence any time soon but thanks for the offer 🙂 so far I haven’t seen any pinched wires, everything looks to be in good condition. I haven’t tried putting my hand over the throat but that’s not a bad idea. I have compression but maybe the reed valve is bad or something. Thanks for the thoughts!July 15, 2019 at 4:29 pm #178940
compression won’t help engine needs crankcase suction to pull the fuel fumes inwards before…. compressing them before ignition
check the air nipple behind the carb to ensure it is only pushing air to the tank or…..
sucking air which interfere with crankcase suction on the carb (venturi effect)
btw fuel tank cap screwed down and tank pump working to fill the carb…?July 15, 2019 at 5:35 pm #178942
So this engine has a single fuel line conversion however most of that has been removed for this troubleshooting. The intake manifold plate I drilled for a vacuum line I have replaced with a plate that was not drilled and the positive pressure nipple was replaced with a tefloned 1/8”NPT plug to prevent air leaks. Currently the bowl in the carb is filled directly from a fuel bulb which I’ve checked works properly. Gas tank to fuel bulb to carb. No filter or fuel pump currently to eliminate variables.
US Member - 1 Year
Topics: 20July 16, 2019 at 10:17 am #178974
I had a motor with a bad piston skirt. but the rings were undamaged. it was scored right in line with the exhaust port. That in turn caused it to not to develop enough suction through the carb. It would run for a few seconds until whatever fuel mix that had coated the cylinder walls was gone . Just a thought something to look intoJuly 16, 2019 at 10:55 am #178976
btw sorry to ask but what are the compression #s
did you feel much air being sucked in the carb ?
it never happened to me but bad crank seals could apparently let the air get sucked in the crankcase ..lowering air/fuel suction from the carb jetsJuly 16, 2019 at 2:14 pm #178983
do the top one and retry.. maybe the bottom one is ok ??
looks like it is a simple O ring on the bottom but the head must come off .
US Member - 2 Years
Topics: 32July 17, 2019 at 1:37 pm #179038
Do I see metal shavings/chips in your picture?? If so, you better figure out what made that mess before doing anything else…July 17, 2019 at 2:27 pm #179040
If you’re referring to the yellow flecks by where the mag plate bolts down it’s just random debris from the dirty rag I was using to clean out the grease in there. Not from the motor 👍🏻
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