1980 seahorse 70 bottom bog - Jetting?

[trxxx250r]

Hi, I have a Johnson 70 (j70elcsa) and I can't get rid of the bog when I stab the throttle.

J. Reeves wot timing, idle timing is 4* approx in water in gear, synk & link perfect, carbs have been gon thru TWICE and there is no doubt clean and set up properly. Spark is strong at 7/16ths blue. Compression 120psi x 3 identicle.

The local Johnson dealer/shop who are capable long time johnson techs tell me that if the carb throttle arms have become loose (excessive play in the bore) over the years it will suck air and cause this from a lean condition. They said the fix is to increase the idle and off idle jet sizes by approx 10% or about 2 jet sizes. They said they have to do it all the time. I took the carbs down to them when they were apart and the tech said the arms were loose enought to cause this and the bigger jets were the only way to solve this short of new carbs.

Is this common and will richening the jets solve it?

If so, should I drill them with a jet drill kit or buy new ones (expensive).

oh, also, yesterday when I took it out to test after some tuning, when it was cold, like sitting for 10 minutes it would take off pretty good with little bog but then after running for a few minutes I would stop and then nail it and boggggg having to fether the throttle to get it going.

Thanks for any help, been working on this for 2 months now as a new boat owner.

 

[boobie]

Re: 1980 seahorse 70 bottom bog - Jetting?

Seeing the mtr is 33 yrs old your dlr may be right. Let him try it and see what happens.

 

[pn]

Re: 1980 seahorse 70 bottom bog - Jetting?

a couple of things to try before you lay out the dough. make sure theres fuel in your bowls before you gun it, just to see(should be a drain screw), or pump primer bulb while boggy, easy tests, its always hard to gass it with no gas readily available. if theres a manual choke you could close it off a little which should richen your mix and you should take off. or block off your carbs somehow...i suggest checking your fuel flow before opening up any jets.

 

[trxxx250r]

Re: 1980 seahorse 70 bottom bog - Jetting?

Seeing the mtr is 33 yrs old your dlr may be right. Let him try it and see what happens.

Well whatever I end up doing, I will be doing the work. Besides the shop owner (not well liked) says he will not drill jets for liability reasons although the head tech said that's what I need to do and they do it often.... Geez... Anyway, I've looked into the exact drill sizes I need and If I go 10% bigger on the idle jet which is currently a 57 (as per service manual spec) I will need a No. 52 drill which is 0.0635 thousandths and will get me approx 10% bigger jet I.D. Off Idle currently 37 will need a No. 59 drill at 0.0410.

Please correct me if my math is wrong or I'm missing something. I would consider buying new bigger jets but OMC offers very little range and I don't see the sizes I would need available.

Thanks for chiming in, boobie!

a couple of things to try before you lay out the dough. make sure theres fuel in your bowls before you gun it, just to see(should be a drain screw), or pump primer bulb while boggy, easy tests, its always hard to gass it with no gas readily available. if theres a manual choke you could close it off a little which should richen your mix and you should take off. or block off your carbs somehow...i suggest checking your fuel flow before opening up any jets.

I'm going out tomorrow to try a few last things and I will try your suggestions, pn, good advice, thank you. If nothing solves it, I'm drilling jets.

 

[trxxx250r]

Re: 1980 seahorse 70 bottom bog - Jetting?

Well I went out today and nothing changed in terms of the bog...

pn, I didn't check the drain screws on the bowles because I didn't have time to take the air silencer off but from my experience as a mechanic I seriously doubt that would be the issue as the motor never has trouble starting and never starves for fuel wide open. If there were fuel flow problems it seems to me that would not be the case. Maybe I'm wrong as the fuel pump works on strange vacuum pulse system.... All I know is it never starves for fuel when it being consumed at at a high rate, no visual fuel leakes either, btw.

Anyway I thought trying the partial manual choke was a good Idea and made sense, although the local tech shook his head and said that wasn't the way to do it... Anyway, I tried it at a couple slight closures and it made things worse, actually, I think it kinda fouled my plugs...

Bottom line at this point, I have to crank the idle adjust screw in to the point where I'm at, at least 8* timing at idle in gear to keep the motor idling/running properly. I actually loosened the roller off the cam so the butterflies would be fully closed and then pulled the timing arm out of the retainer and advanced it all the way at that point and it didn't make that much difference. This is with the motor in the water in and out of gear. I'm trying to isolate the problem.

It seems to me that if I can't get strong or high idle with the butterflies shut and the timing at wot timing, there's a problem! This is where the suggestion that the carbs are leaking air at the throttle arms therefore causing a lean condition seems to make sense. If there's not enough fuel being vacuumed then the motor will not be able to rev or operate correctly.

I don't know, I'm at my end after today. This bull**** has taken all the fun out of my new boating experience.

Btw - After talking to one of the local tech again today and him reitterating I need bigger jets..... Another tech walked in the roon and he yelled out, hey mike, what do you do when you have a Johnson 70 bottom end bog? Within about a second he popped off, bigger jets! Lol... Apparently these guys have seen this over and over.

Just wanted to see what some of the obviously extremely knowledgable people on this forum's thoughts were on this problem.