Backfires when it starts but runs fine

[steveclv]

OK, time for me to ask a question that has me stumped

125 Chrysler 1984
New sparkplugs, WOT timing @ 30 degrees, Carb mixture 'ideal to a touch rich', link & sync completed, choke works

Every time I start the engine whether it's hot or cold it backfires once through the exhaust. Regular as clockwork. Second turn of the key and she fires right up and runs really well, slightly smokey at idle but they all are.

Any ideas as this one has me totally out of ideas.

 

[~Nickolas~]

Re: Backfires when it starts but runs fine

I have a 77 Chrysler 135 and my motor does the same thing. This is the first Chrysler I have ever had and I just rebuilt the carbs & fuel pump, adjusted idle screws 2 turns out each. Fires right up and idles beautifully but..... first crank and POW. This is the only outboard I have ever had that does this. Maybe it''s a Chrysler thing? I would think that the engine would be running lean with backfiring but I dunno for sure. Now does your do this with it choked or not choked or both ways? I think mine only does it when it is not choked. And if I advance the throttle a bit before I start it then it will not back fire. By the way this only happens when it is cold so maybe it just needs to be choked when started cold. I am going to experiment with my motor tomorrow or the next day and see what happens.

Nick

 

[my1stboat1]

Re: Backfires when it starts but runs fine

my 85 force does the same thing... But only on 1st initial startup... after that fine all day

 

[jason32038]

Re: Backfires when it starts but runs fine

I wouldnt call it a backfire..it's more like an attempt to start. Most likely only 1 cylinder fired at that point which makes a pop.

 

[Pacoson71]

Re: Backfires when it starts but runs fine

My friends 85Hp would sneeze on cold start up. great motor after that! .... just a tissue

 

[jerryjerry05]

Re: Backfires when it starts but runs fine

The air screw setting at 2 turns worries me.MOst need to be set at 1 to 1 and 1/8 turn.
Maybe too much fuel being drawn in while choking?
Mine do that once in a while.After letting set for a while.
A real bad backfire can do damage to the pump diaphram.J

 

[~Nickolas~]

Re: Backfires when it starts but runs fine

I initially set both screws to 1 1/2 turns out but then adjusted out another half turn to see if a little richer would take the POW away but it didn't. I just put these back on the motor and haven't messed with it much yet. I'll screw them back in a half turn and see how the motor runs after it warms up. Better rich than lean so just sitting there running a few times won't hurt it. I tell ya I thought this engine ran good as it set but after going through the carbs and pump it's like a whole new motor. Tachs up nice and quick and has a nice tone to it. Can't wait to get it out in the water to see what she will do. Problem is I am working on 3 boats at the same time and want to get them all out in the water!!!

Nick