Johnson 6hp Seahorse, 6R75R, revs up and dies

[Augoose]

I picked up a used Johnson outboard which seems to have been very well taken care of. I cleaned the carb and put a rebuild kit in it, paying attention to set the float and ensure all passages, to include the ones under the core plug appeared to be clear. I set the slow speed needle jet to 1.5 turns out from lightly seated and put it all back together.
With the choke engaged and primer bulb tight, the engine starts within 1 or 2 pulls, revs up a bit and then dies within 2-3 seconds. I occasionally can feather the choke in and out and keep it running for a bit, the longest is about 30 seconds. I'm assuming I'm just able to keep it running by drawing fuel off the main, but when I go back to the idle circuit it dies.
When the engine runs, it sounds great. I have not run a compression test but I don't think that's the issue.
Opening the bowl drain releases fuel, so I don't think my needle and seat are stuck and I assume my fuel pump is ok as fuel is in the bowl.
I very much suspect the slow speed needle jet or the passageway behind it, as no adjustment to the needle seems to make a difference at all to the symptoms, to include removing it completely. As a test, I plugged my thumb over the passageway where the jet was and the engine wouldn't start at all, leading me to believe that I don't have an air leak somewhere else. I'm wondering if the fuel passage is blocked completely and I'm drawing fuel off the main when I do get it to run or I've got a massive air leak around the slow speed needle jet. I followed a schematic I found online which seems to show two cork washers followed by a nylon washer going in the passageway, followed by the nut. I also tried packing a bit of grease and even teflon tape around the area where the needle body enters the nut but nothing made a different.
The fuel is new as well.
I've got blisters all over my hand from pulling the rope so many times - I would love to get this carb right one of these times!
Thanks

 

[racerone]

Answer a few questions.---Does the idle needle come to a fine point ?-----Often times the end twists off when brute force is used on that needle.-------Does spark jump a gap of 1/4 or more on both leads , yes or no ?------Yes , post your compression test numbers, very important.-----Replacement head gasket is a much better item than original.------is the high speed jet ( orifice plug ) in the very bottom of the float bowl clean , yes or no ?----And I think there is a wee brass orifice at the carburetor / bowl joint that must be clean as well.

 

[Augoose]

Racerone, thanks for the reply.
The idle needle comes to a somewhat blunt point, seems factory with no indication of damage.
I'll check the spark and compression shortly.
I was unaware of the high speed jet at the bottom of the bowl. I just tried to back it out and it is very stuck and it started to strip the screwdriver slot at the top of the jet. I'm going to put a heat gun on it for a bit and see if I can back it out.
I presume that fuel for the idle circuit flows through this jet first?

I did clean the smaller orifice where the bowl and upper carb meet.

 

[Augoose]

Well I was able to use heat and a very narrow easy out to get the jet out. It was completely clogged. After reading I realized there is a specific tool for this plug, called Orifice plug tool. Whoops.
It seems the rubber bushing around the main jet prevents fuel from coming in and around the reservoir in the middle of the bowl. Due to this, fuel for the idle circuit must go down towards where the bowl drain screw is and then through the orifice jet and then up through the small passageway (smaller red circle) to the upper part of the carb.



thanks again

 

[Vic.S]

Racerone, thanks for the reply.
The idle needle comes to a somewhat blunt point, seems factory with no indication of damage.
I'll check the spark and compression shortly.
I was unaware of the high speed jet at the bottom of the bowl. I just tried to back it out and it is very stuck and it started to strip the screwdriver slot at the top of the jet. I'm going to put a heat gun on it for a bit and see if I can back it out.
I presume that fuel for the idle circuit flows through this jet first?

I did clean the smaller orifice where the bowl and upper carb meet.

The low speed needle should come to a fairly fine point. See attached picture. If it only ends in a blunt tip then maybe the end is broken off and now stuck in the orifice

 

[Augoose]

Thanks Vic. S
I had read on another site (https://www.leeroysramblings.com/OMC_6hp.htm) that the 1965 through 1975 Johnson low speed needles don't have a sharp tip?

I did see in a parts catalog that the new ones are indeed pointed like your image above. I pushed a soft copper wire through the passage and it was clear, so I'm pretty confident that at least my tip is not broken off in there somewhere! Not trying to be argumentative, just posting what I had found for discussion.

In other news, I cleaned up my orifice plug (high speed jet) and reinstalled it. The boat now starts easily and idles, albeit a bit erratic.
I've got a bit of work ahead of me yet, fine-tuning the mixture, checking compression, points, new plugs, etc, but at least the problem for this particular thread with the engine revving up and dying is solved!

thanks to all for the help!

 

[Vic.S]

The picture came from another parts website but it is a listed replacement for the original Maybe the original did not have such a fine pointed tip but if you find it is difficult to set the slow speed mixture you know what might be the trouble

 

[Augoose]

Interesting, the slow speed mixture did seem to be a bit hit and miss, possibly the replacement you mentioned might be the ticket.
Thanks again

 

[69StarcraftJupiter]

Interesting, the slow speed mixture did seem to be a bit hit and miss, possibly the replacement you mentioned might be the ticket.
Thanks again

Reading your original post had me absolutely mind blown. The exact same symptoms you had are what I’m having and I’ve done everything you did but I missed the jet at the bottom of the bowl.
I’ll have to clean it out in the morning.
Did you happen to find out what the cause was? Was it the dirty orifice?
Thanks

 

[Augoose]

After thoroughly cleaning the carb, I determined I was having spark delivery issues as well. After replacing corroded and broken spark plug wires, the motor runs like a top.