mariner 40hp Idle speed and HT leads

Hello people

Hoping for some advice.....?
1985 Mariner 40hp 2 stroke, 2 cylinder twin carb

Idle speed seems quite high as when going into gear its a bit grindy and just sounds like it needs to be slower.

The screw stop on the flywheel is already screwed out so much so its not making contact. Cant seem to find any other adjustment other than turning in the mixture screw on each carb to slow the idle but its a fine line between slowing it and the engine stalling. 1/4 turn either way makes a big difference.
How many turns out should the mixture screws be?

Mine are 1 1/4 turns out now from 1 1/2, it idles slower but seems a bit more lumpy ticking over. Thinking there must be a better way to reduce idle without cutting air mixture?


Also can i replace the ht leads on this model without replacing the coil ? they look like they are sealed into the coil?


thanks

make sure your throttle plates are close together, at idle.You could have one throttle
plate open more then other one. This will make your idle speed stay high
....Disconnect your linkage been the carbs.
Restart see if idle comes down

Steve

Adjust throttle cable !!

thanks for the ideas.
i have a vaccum gauge that i use on my carbs on my motorbike but i dont think there is anywhere i could attach them on these carbs to check they are both drawing the same air, so will revert to measuring if there is any gap when the butterflys are closed.

The throttle cables dont seem to have any adjustment left but will have a closer look i think.

No vaccum gauge is use on 2 stroke, only setting up fourstroke. Just disconnect are between carbs when engine running, see if idles down

Steve

Right. The butterfly(s) on the carb(s) is not closing all the way.

Jeff

i disconnected the carb link but the idle remained the same. When the throttle is opened to maximum the top butterfly isnt quite as horizontal as the bottom one which is horizontal. however from idle when twisting the throttle tiller the engine revs a bit before the butterflys begin to open so i am assuming that they are both fully closed at idle as not opening until half throttle.

I tried to tighten the throttle closing cable so the fly wheel stop touches the adjustable screw stop pictured in my fist attached picture. Not sure how much more adjustment i can make on it. i have undone the lock nut and then screwed the adjuster out, away from the lock not to show more thread.

Also adjusted the link rod to the carb butterflys from the acc cable spindle so that the buterflys are fully open now as before they werent opnening as much! this shouls enable top speed where as before i think it wouldnt have maxed out.
where can i download a manual from? or buy one?

adjusted the rod to the flywheel magneto so that the twist grip closes this a bit more and its moved the throttle stop screw into play now so hoping it should have lowered the idle enough to use this for adjusting.
will run it up tomorrow and check.

anyone know the original propellor diameter and pitch of these motors?

Start lookung for air leak.When engine running take a bottle of gas with more oil mix.Start applying on motor in diff places , and see if RPM's come down.One more thing make sure trigger is coming all the way back

Steve

i adjusted this link rod pictured so that the fly wheel returned further in the direction it goes when decelerating so that it lowered the idle and the throttle stop was now useable.

Just wondering where the neutral position of the fly wheel is and if its possible to damage anything by moving it clockwise til the idle speed lowers.

Or should i let the flywheel settle in its natural position thats determined by the springs inside it?

Didnt find any leaks by spraying fuel round the engine.

Where do i attach a rev counter as i think i need to determine what its idling at really.
Want to lower it so i doesnt clunk into reverse. Forward is ok no noise but reverse is a bit noisy, is that normal on these engines? my 25hp tohatsu is noisy going into reverse but ok forward.

You need to set up the spark advance stops as per a workshop manual, you also need to set up the throttle linkages as per a manual. Blindly messing with ignition stop screws on a 2 stroke will at best create a badly performing engine, at worst melted pistons. These twins are VERY sensitive to ignition advance, especially at low speeds.
So to recap, buy a workshop manual.

just ordered a manual off this site.
hope it covers the bits a i need. gonna reset everything as it was and see how the engine idles when in use. the chap i bought it from said he had it serviced by a marine shop and they set the carbs up? got a receipt for it but not sure how good they were as they set them up without having the throttle stop anywhere near useable!

Yes, you really need the ignition spot on before you can even consider adjusting the carbs! These twins don't have as many cylidners as most outboards, so when they go out of tune, they run really badly very quickly.
As you may have found out, most dealerships have no idea on how to set up an older outboard (and they consider 5 years old an ancient engine not worth their time).
I personally have a lot of time for the Mariner/Yamaha twins like you have, good, solid engines, plenty of them used (always keep an eye out and buy spares engines for $200 or less), parts are definitely still available too.
If you flush these engines after use and keep the maintenance up, they go forever! My boat had a mariner 40 like yours on it for years as a workboat, it went waaay past 2000 hours before it was stolen and recovered without the engine. Now it wears a Mariner 60 which is still of the Yamaha twin family.

thanks typhoon.
good to know the engine has earned a good reputation. Am mechanically minded and having looked at all the connections and how they work there was just no where else to adjust the idle other than bringing the ignition advance/retard screw stop into play. My manual has been shipped so i am looking forward to finding out how it should be.
Was the idle on your mariner 40hp fairly high and did it make a bit of noise going into reverse? i had it idling at what sounded a comfortable speed but the noise in reverse made me think it was idling a bit too high. PLus i like to be able to adjust it once the engine has warmed up.
Its a Seloc manual so i hope its comprehensive.
Yamaha seem to be the name when it comes to marine engines. I have a friend who gets towed into big surf and they only use yamaha jetskis as other makes have cause them some trouble in 40ft surf!!
thanks

No, the Mariner twins can idle fairly low. It will all become apparent once the manual arrives, there are a lot of interrelated adjustments to make, throttle stop is one of the last! So if the other adjustments are off, you have no chance!

bought the workshop manual and adjusted the timing as per the book and it was a fair way off what the book says to set it to.
I bought a tiny tach rev counter in order to fine tune the idle speed but the tiny tach doesnt show any reading and its the second one i have had so until i can get a fix on the revs i have adjusted it to where the engine feels happy idling.