cold start is fine, hot start, not so much.

[hotshot123]

Ok, i just wanted to get others thought on where i should begin with this one. My neighbor asked me to see if i could help him with his motor (1973 70hp johnson). He has seen me out there working on my stuff and i usually have had good luck doing my own work but i have never ran into this problem and would rather ask here first so im not chasing my tail so much.

Here is what it does: First start of the morning, lift warm up lever, hit choke, it fires right up. Let it warm up a bit then take off and it runs fine. Problem starts like when you run it down the river a ways and stop. it it hard to get running unless you let it sit for a while. if he fishes for a couple of hours, it starts fine but if he decides to leave pretty quick while the motor is still warmed up, it doesnt want to start. Im thinking that after running a bit and shutting down, maybe there is fuel still flowing and flooding it. I suppose it could be elecrtical though so thats why i wanted opinions. ive not had this happen so i dont know where to begin looking. Im guessing that the carbs havent been rebuilt in a long time.

 

[geoffwga1]

Re: cold start is fine, hot start, not so much.

I'm no expert but that sounds to me as if it could be choke related.Could it be that when the motor is still hot,or at least warm,and does not need choke but it's getting it anyway when you switch on (assuming it's automatic).After it has cooled off it needs choke so it starts OK. I had this problem with a 76 Stinger a while back,solved it by choking manually.
Geoffwga1

 

[hotshot123]

Re: cold start is fine, hot start, not so much.

maybe so, i willl look into any suggestions. it has a toggle switch choke but that doesnt mean that it is returning to open on its own. i know sometimes those butterflies get kinda gummy and the soleniod yanks them shut but then they slowly return to open. his may not be going back to open as they should

 

[the machinist]

Re: cold start is fine, hot start, not so much.

Here is another suggestion. That old a motor should have a magneto ignition (points & condensers). Sounds to me like a weak condenser or coil. These are made using a stip of foil separated by a waxed paper insulator & wrapped up. If there is a breakdown in the waxed paper separator, many times it will start on a cold motor. But once electticity runs thru either, the foil expands & shorts out internally. The motor will not start until things cool down & shrink back to normal. As it gets used longer it may even get to where it will may start but only run for a few minutes.

 

[Lone Duck]

Re: cold start is fine, hot start, not so much.

Some times that happens when there is a slightly lean condition. Before you get to tearing into it,open air fuel mixtures 1/8 of a turn and try it.