1959 Johnston 5.5 Stumbles

Hi Have a 1959 5.5 hp seahorse. Changed out coils, points and condenser. At low rpm about the speed you would troll at the engine stumbles . It almost cuts out then resumes operating normally. Have tried adjusting low speed mixture it makes no difference. Any advice would be very helpful. Its an old girl but still very reliable Also changed hose and gasket on tank and always make sure the tank cap is tight.
Thanks in advance,
Brian

Re: 1959 Johnston 5.5 Stumbles

when you adjust the lo speed needle it does nothing at all? If so you may need to re-rebuild the carb and make sure the packing is in there correctly and that the brass nut/bushing that the lo speed needle passes through is snugged down. The rpms should go up when you twist the needle in (i.e. make mix leaner) and they should drop when you twist the needle out (i.e. make mix richer). Only slight adjustments are needed. a 1/4 - 1/8 turn can make a big difference. you should wait 5-10 sec between each adjustment to allow the change to take effect. You may need to adjust the idle set screw too. The trick is to get the hi/lo/idle screws all adjusted and balanced with each other. It can be a little tedious at first, but once they're set they should be good for a long while. This link may help.

http://forums.iboats.com/showthread.php?t=167352

Re: 1959 Johnston 5.5 Stumbles

Hi kfa4303,
Bu no difference I mean It doesnt change the stumbling issue. adjusting the low speed needle the engine does increase and decrease in rpm . Thank you for the advice and tips going to look closer at it tonight and try more adjustments
Brian

Re: 1959 Johnston 5.5 Stumbles

If the carb is ok and you've changed the points and condensers, you may want to replace the spark plug wires and boots. I just put fresh ones on my motor and it made a HUGE difference. Starts with half a pull every time and just fires more smoothly in general. If you do change them, make sure you get 7mm copper core wires NOT graphite car wires, and be sure you twist them on to the coils, rather than just poking them on there. I got mine at NAPA for about $3 a foot x 6 feet + a couple boots = $20 well spent. What plugs are you running? Most folks here use Champion J4C or J6C gaped at .30.

Re: 1959 Johnston 5.5 Stumbles

my cd 14 did the same thing, would idle ok, then sputter, then be ok. i added some seafoam to the gas , and after a couple of half hour runs in a barrel it cleared up. then was the test on the water, ..it idled perfectly, but midrange it sputtered, half an hour on the water (same seafoam in the tank) that cleared up, now the motor starts first pull cold, every time. i do fully agree with kfa on the wires. even if you do a carb rebuild. the metallic core wires will corrode at the coil and at the boot, causing your motor to act a bit funky.