'99 70 HP Johnson Hesitates

[rjv57chevy]

First I need to say I bought this boat used. The previous owner let it sit for a time but he took it to the dealer and had $600 worth of repair done to the engine(cleaned the carbs, replaced fuel pump, etc) before he put it up for sale. The fuel had gone bad. <br /><br />Anyway, the motor will crank up first crank, idles smooth, a little cold natured but typical for a 2 stroke. It can idle all day long and it runs top end at about 5500 rpm's and runs well. It's when I accelerate under a load (more than one person) it sometimes will go and sometimes it won't. The critical rpm is 1150. When I give it gas if it can make it to 1150 rpm's it will take off. If it goes to 1100 rpms and kinda hangs there it will load up and die. If I turn the wheel so the prop doesn't have to push the whole boat when I accelerate it will take off better. If I'm in the boat by myself it will accelerate okay most of the time. I wonder if the pitch on my prop is too much but the upper rpm's seem to be in the ballpark. It's right where the power band is about to kick in where it has the problem. All the fuel hose clamps appear to be tight also but does have the plastic type. It accelerates with no problem when not in gear. I put new plugs in so I would have the old ones as spares. The stainless prop has a 17" pitch. <br /><br />By the way I'm new here and I don't know all the outboard terms but I know how to work on other types of motors. Thanks for any advice.<br /><br />Lowe 17' Aluminum Boat<br />Rodney

 

[ob]

Re: '99 70 HP Johnson Hesitates

Assuming that the carb fixed orifices and passages are indeed free from restrictions,check to isure that the carb linkage roller is on center and just touching the scribe line on the fiber throttle cam when controls are in neutral position.There's and adjustment screw to loosen and retighten to make this adjustment.If all is well there and if your carbs have idle mix screws ,you may need to open them up a bit more to richen the idle mixture.Tell us what you find.

 

[rjv57chevy]

Re: '99 70 HP Johnson Hesitates

You said a mouthfull. I'll have to pull out the manual and see if I can find the scribe line and what the fiber throttle cam looks like. If I find any idle mix screws on the carbs I'll give them a quarter turn out and see what happens. Thanks for your help.<br /><br />Rodney

 

[ob]

Re: '99 70 HP Johnson Hesitates

Rodney,If you carbs are equipped with idle mix screws ,before you move them,gently seat them clockwise ,counting the turns ,to see where they are presently set at.Open them back up to the original setting and then proceed with 1/4 turn open increments ,then water test, until you find the best setting .Linkage and fiber cam is clearly visible on starboard side of engine with cover removed.Good luck.

 

[boatmec04]

Re: '99 70 HP Johnson Hesitates

Hi Rodney Your carburator adjustment for that model year is 2 3/4 turns out from seat.<br />You also may whant to check your carburator linkage adjustment.To do this you need to loosen<br />the carburater linkage adjusting screws on all three carbs.move the cam follower away from the <br />throttle cam.The follower must not touch the throttle cam in this procedure.Now with all linkage screws loose Verify that all throttle plates are closed.Then apply light pressure upward<br />to the tabs of the adjusting links and tighten first the lower then the upper carb linkage screws.Snap the throttle link coupler shell off the throttle cam ball.While holding the cam follower against the throttle cam move the throttle cam untill embossed mark on the cam aligns with the cam follower.tighten the cam follower screw.While advancing the throttle cam<br />the embossed mark on the cam should align with the center of the cam follower.At this point the<br />carburators will start to open. <br />This Procedure Sincronizes your carburators with your timing. GOOD LUCK I HOPE THIS HELP!!!<br />FROM:boatmec04

 

[rjv57chevy]

Re: '99 70 HP Johnson Hesitates

I looked it over this weekend and see what your talking about. It might be another 2 weeks before I can test it in the water. The carb linkage roller is off by a hair of being perfectly centered with the scribe line when in nuetral. There are idle mixture screws I can adjust. Thanks for everyone's tips!<br /><br />I do have another question about something else I noticed. When I have it full throttle (engine off, looking at the linkages), I can take the carb linkage roller and pull it down even more than the cam is pushing it (one inch away from the cam). I would say at full throttle the carbs are in the neighborhood of being 3/4 or slightly more open. Is this the way it supposed to be? In the water it runs at 5500 rpm's the way it is now.

 

[Walker]

Re: '99 70 HP Johnson Hesitates

Look into the carb throats when you have the throttle fully open. The butterflies should be exactly 1/2 open. If they go past 1/2 open then they are, in effect, closing.

 

[rjv57chevy]

Re: '99 70 HP Johnson Hesitates

I guess I'm used to automobile carbs. I didn't realize (looking at the linkages only) that an outboard carb can go past fully open. That would explain why the carb linkage roller can be pressed down even more. I sure would love to test out everyones tips today but this thing called "work" keeps getting in my way.

 

[rjv57chevy]

Re: '99 70 HP Johnson Hesitates

I made it out to the lake today. Before I left the house I seated all the idle mixture screws and backed them out 3 1/2 turns. The book said 2 3/4 turns but I had it in my head that it was 3 1/2. Anyway, it ran like a champ. I think it is running a liitle rich at idle so I may turn them back in a little. Thanks for all the advice.<br /><br />Rodney