Johnson 6R74 won't stay running

[Canoe2]

I've been working on getting a 6 hp johnson resurrected and I think i have an issue with the high speed circuit or fuel pump. I can spray fuel in the carb throat and it will fire, if I close the choke and pull several times it will run briefly then die with gas visible in the carb throat but won't stay running. Is there a method to test the fuel pump to rule out that as a problem or do i need to somehow clean out the high speed jet. How does one do that in that it is pre-set high speed jet? Any help would be greatly appreciated. Thing seems to want to run and it is so close it is starting to drive me nuts. Thanks.

 

[oldboat1]

If you are unable to start it, it's not the fuel pump (primer bulb should get your going, and the fuel pump should keep your going). You likely need to rebuild the carb. You can try adjusting the idle mix before taking off the carb, just to see if it's an adjustment issue. Lightly seat the needle, then back it out about 1 1/2 turns and see if you can get it running at that initial setting.

 

[Canoe2]

I was afraid of that, i have already had the carb apart, and have the needle set at 1 1/2 turns. Guess I need to have another go at that. I have a brand new in the box 9.9. carb from the same era, could i swap that in? I suspect not. Another evening in the garage i guess, not a terrible thing i suppose. Thanks.

 

[oldboat1]

Well, if you haven't tried to dial it in, I would try that. Try an initial setting of 1 turn out. If that works, adjust leaner until it wants to stall, then back it out. Maybe you have messed with it already. I would stick with the 6 hp carb. Did you do anything to the h.s. jet? I normally leave them in and soak the bowl, rather than risking buggering them up. But need to soak everything metal, and physically clean openings with straw from a broom or soft wire -- then spray with carb cleaner. I just eyeball the float height, and have never had a problem. Some of the kit needles have the littler rubber tip, which is fine -- but need the little clip with those or they can stick in the seat.

 

[Canoe2]

Yup, have done a bit of fooling with the low speed needle without a good result, i do have the rubber tipped one from the kit, but i did use the clip. I will give it another good soak and then try the wire trick, I just blew it out with the cleaner last time and it was a pretty nasty mess when i first got in there so something still lodged in there is certainly possible. Thanks, will post results when i get some

 

[oldboat1]

yeah, have to pull off the expansion plug on the top and really get after the idle passages under there, and thoroughly clean out the needle housing too if the carb was pretty messed up. Make sure the needle opening/orifice up there in the carb body is open. Sometimes an old needle tip can be jammed in there (rare, but happens).

 

[Canoe2]

Well, a nice long bath in carb cleaner and bit of fine wire solved one problem, reassembled the carb, started up on the second pull, ran in the barrel fine but doesn't want to throttle up. Seems i have to tinker some more with the points as it is dropping the lower cylinder. Pretty sure i have seen a tutorial or two on here about that so time for some research. Thanks for the help!

 

[oldboat1]

Sounds like progress from here! Points are a good bet. If you did some magneto work and replaced wires, check the spring connectors in the plug boots -- need a solid contact with the wire core. Coils?

 

[Canoe2]

Could are new and once I can pry my 15 year old assistant from his computer I will see if it can jump 5/16 on the bottom cylinder. Coils and worse are new I will see how the spark test goes and then recheck that spring connector. Getting closer is always good I figure.

 

[Canoe2]

Well, apparently the 6 is more interesting than the computer, jumped 5/16 no trouble so it must be in the timing. The timing marks don't seem to be helping and neither does the high mark on the cam so I guess I need to break out the multimeter?

 

[oldboat1]

yup. And good luck with the 15 yr old. (It gets better....)

 

[Canoe2]

To be fair if I had the same luck with the motor as the kid, that thing would be running great. Fingers crossed on both counts.

 

[oldboat1]

stepped on your post -- sounds like you are doing fine.

​If your spark is good, I would suspect the carb on the '74 (again -- sorry). Guessing of course, but think I would suspect an obstruction in the nozzle.

[edit. link and sync, if you haven't done that. and....idle mix adj again after the last cleaning. May be a little lean this time -- throttling up part of the test in setting the mix.]

 

[Canoe2]

well, I went through the carb again and i am some puzzled. I have it running on both cylinders now (apparently I did miss something in the carb) but it still doesn't want to throttle up in a meaningful way. I also have noticed that adjusting the low speed is having no effect on it running, though i did go behind the welch plug and clean that out previously. Kind of leaning to the link and sync but i believe i have the carb beginning to open at the mark on the cam follower, though i can only do it by peering through the cowling with the low speed needle removed. Is there a better way to do this that i don't know? Edging closer, thanks again

 

[AlTn]

couple of things..the idle mixture needle setting should have an obvious effect on the idle...too lean it will sneeze and die. too rich it will load up, cough, etc. then die...there's a passage on the carb body that runs from the bowl to the well that the mixture needle enters < same well that the core plug seals and the 3 small idle holes feed the rear of the carb throat behind the throttle butterfly > that passageway needs to be extremely clean. With the carb off the motor, scratch a mark on the carb body directly in line with the roll pin on the butterfly shaft when the shaft is completely closed and when the shaft is exactly horizontal in the carb throat scratch another mark. Carb mounted, motor in gear link and sync done...can you see looking at the movement of the roll pin, that it begins to move on the cam mark and will become horizontal when the throttle position is at wot?...that's what you are trying to obtain....start out with the idle mixture needle 1 1/2 turns out from a light seat then adjust with the motor warm, at idle, in fwd gear, and pushing the boat...those motors are known for idling very smoothly at low rpms

 

[Canoe2]

Well, that's way easier than how I was trying to do it. Looks like the carb is coming off again. Thanks much

 

[Canoe2]

Well, i think i may have figured out my problem. couldn't get my throttle to align with the open/close settings in the carb, which was a bit confusing until i had a look at the seized powerhead sitting on the bench. When i swapped over the new powerhead, i used the same newer carburetor, which had a different cam follower, and a different cam. Now my carb appears to want to open correctly though it is too late to run it tonight. I will post the results tomorrow when i get it in a barrel. Closer and closer...thanks again!

 

[oldboat1]

I'm not sure what parts you are using, but cam followers on a '74 carb would be solid, where others will use the roller on a round shaft. Additionally, newer throttle cams may be plastic, some with an adjustment screw on the h.s. end. (And the plastic cams break.)

closing in on it, sounds like....

 

[Canoe2]

Yup, turns out that once the cam follower and throttle cam were correct, the thing runs great, idles down and throttles up. Thanks to everybody for all the help, would have been turning in circles for ages otherwise.