throttle srart position 1985 20hp johnson

[Newyota]

New to me 20hp tiller rope start 1985.What is considered the start position on the throttle?Would this be where the decal has a "dot" and an arrow on either side or is that the idle position?.I had just got done reading the post on the starting procedure which was helpful in explaining how the manuel primer worked.I was using that wrong.Did not realize I had to leave it open half way when starting as an enricher even after seeing the picture on the decal.

 

[racerone]

I believe you have to pump that primer unit a few times for near instant starts.---------And ignore the throttle grip.--------Have motor in nuetral and turn the grip till it hits the stop.

 

[oldboat1]

^^like he says.

With the motor in neutral, twist the grip counterclockwise as far as it will go. That would be the standard starting position (fast idle). When you get familiar with it and get it tuned in, it may start at a lower idle position. Use decals just for some reference. It would also be good to put the motor in gear and operate the throttle all the way to the WOT position (motor off) -- want to make sure the timing/magneto plate moves freely. Grease can build up underneath.

A warning on running the engine before changing out the existing water pump impeller -- can break up if old and dried up, clogging the water passages -- makes for a lot of avoidable work.

 

[Newyota]

thanks for the info..I also was wondering about the nylon idle screw that is back below the cowling attatched to linkage.It seems to only act as a stop as far as I can see.It really only prevents you from twisting the handle all the way if you screw it in.Mine is barely screwed in .Is this for setting a trolling speed?I will keep an eye on pump.Hope it holds up.I ordered a new prop that I could have waited on I guess and also, saw that the inner o-ring on prop shaft hub is seeping and the nylon bushing in carb. for the slow speed adjustment is crumbling apart and won't hold the adjustment screw tight.Also, repaired the poor repair of the mouse chewed wires on the stator harnessNew one of those on the way.I still don't know for sure how good this motor is.Went ok last year the few times I used it.And to think the seller said it was in excellent condition when he was selling it.Go figure.

 

[oldboat1]

got a bunch of issues there. On the plastic screw -- it's a throttle stop (idle adjustment screw), like you suggest. It butts up against the throttle control gear. If it's screwed way out, that may be a good sign -- can mean somebody wasn't trying to correct for poor idling. When setting the air mix (carb), I usually back out that screw, then set it when the air mix is dialed in. (Other option is to leave it backed out so the engine can be shut off with the twist grip. If the motor runs really low and slow when you have it tuned up, that might not work -- may need to choke to stop or use the kill switch.)

That bushing you mention sounds like the needle valve retainer. I think a replacement is included in the carb rebuild kit, so you might want to pick up a kit (future rebuild if not needed now). If the needle has worked loose, the standard setting is 1 1/2 turns out from lightly seated, then adjustments from there.

Hope that gets you some of the way.

 

[Newyota]

thanks..Great ifo...The plastic idle screw will not do anything until the roller hits the cam marks anyway unless you turn it way in to where the roller hits the two marks on the cam where it is set to just open butterfly so I m still confused on why bother with it at all other than to keep the twist grip from moving.Thats the only purpose I see of it.What would you say is the minimum turns open for the needle when tuned in?It was running at being open 1/8th of a turn before I had the plastic retainer come apart.I was checking the linkage adjustments also before the retainer came apart and they seem spot on.From what I understand the engine should be around 650rpms when adjusting slow speed screw and in water and in gear?Can I also assume I should be around 650rpms when the roller hits the cam marks and butterfly just starts to open or would I be just passed those marks at those rpms.?

 

[hardwater fisherman]

As olboat said it is the throttle stop screw. It keeps the idle from dropping to low causing a stall. You could use it for slow trolling as well, without having to keep turning the throttle grip. You may need to adjust it depending on air/water temperature Or even maybe altitude.

 

[Newyota]

thanks again

 

[oldboat1]

1/8 turn open sounds a little on the lean side, but may be fine. I usually open to 1 or 1 1/2, then lean it out (clockwise) until it backfires [lean sneezes] or dies, then adjust counterclockwise until the engine slows/stumbles -- final adjustment is the mid point between the two. I usually find that to be 3/4 to 1 turn open from lightly seated, but motors vary. You should find that rpms increase when you set the lean adjustment, and you would use the twist grip to throttle it back to about 650 rpms -- afraid I do that by sound. You need a mix setting that allows you to go into gear without stalling, and also to rev the motor (do that with care if in a barrel -- don't need to hit WOT to test the mix setting for throttle operation. When on the lake, can run to open throttle then check for return to idle -- should not stall.)

You raise an interesting question on the 650-700 idle rpms -- don't think that's with the throttle plate opening (i.e., roller past the cam mark), but not sure. That target idle range is with the motor warmed up and in gear, as I think you suggest, and I'm thinking that would be before throttle up. The starting position would typically be at a faster idle (throttle slightly open), although with a warmed up and well-tuned motor it will start at a considerably lower idle.

(interesting exercise to think through what is done sort of automatically....)

For trolling you can use the throttle stop like Hardwater suggests. There is also friction control that can be purchased if a serious fisherman (operates with a thumbscrew) -- about $30 I think.

 

[Newyota]

thanks for the info.Do you have the throttle roller lined up on the notches while adjusting?Will give it a try as soon as I can replace my needle screw tensioner/retainer and have some nice weather again.I have another question on pressure testing lower unit.If I pump up the lower unit (on work bench) caould I detect a leak in the drive shaft seals without taking the water pump and it's gasket off?Also, can I replace the seals for the shaft under water pump without tearing whole lower unit apart and removing the shaft?

 

[oldboat1]

The seals typically replaced are the driveshaft seal under the impeller plate, and the shift rod seal -- those and the washers under the drain and vent screws.

You can pressure test yourself with a hand or foot pump (not much pressure, maybe 6-8 lbs.) I have a small foot pump that I use for bumpers -- use the inflation needle and a piece of gasket material, and hold it in place in either the vent or fill hole (gearcase drained). With the lower unit removed, immerse in a tub of water and look for bubbles at any leaks. The lower unit is fully assembled for this. You may find that the seals are fine.

The roller is usually adjusted before working on the mix (the link and sync procedure you have probably seen described).

 

[jimmbo]

Those marks/notches on the cam are where the roller is supposed to be just starting to contact the cam. Part of the carb/ignition syncing. At the notches, the carb is supposed to be fully closed. Even when the ignition is fully advanced, the carb will have barely opened. Idle speed is entirely set by the retarding of the spark. Idle Mixture adjustment is for lowest speed idle

 

[Newyota]

Thanks for the help.I do need to replace the oring on the prop shaft housing since I can see fresh gear oil there.Pretty slow seep, but will need addressed and may as well do the prop shaft seals as well since the housing needs pulled.Just another job to do, but does not look too hard.More concerned if I have to do drive shaft seals since the shaft will be in the way.Cross that bridge if I have to and can check those when I do the pump.

 

[racerone]

???---Driveshaft simply pulls out of the gear box.---Install new seals and slide the driveshaft back in.-----Simple job.

 

[Newyota]

thanks-Do the seals need alittle RTV on the edges when putting them in?I thought there was a nut holding the pinion to the shaft.Just looked at parts book and watched youtube video and saw that.Thanks again.

 

[racerone]

No nut on the bottom of the driveshaft in your motor !