30HP 2 stroke Mariner throttle setting advice

TomKat · 30 August 2011, 22:55

Hi

Stripped my carb after the engine oiled the plugs and after putting back together the tickover was too fast so I adjusted the throttle mech and cable now it does not open up fully! Any advice on setting these things up? there is a max limit screw but it does not even come close to contacting it. The throttle rolls into the fist cam on the side mech but does not roll on over if you know what I mean - I can by hand push it further and ran with the cover off and manually pushed to WOT tonight to see if I could wake board behind it!

Any advice appreciated, engine is 1989 and I believe it to be a rebadged Tohatsu.

Cheers

TomKat

TomKat · 31 August 2011, 00:00

just read this http://www.rib.net/forum/f36/upratin...2-a-25933.html

will check timing marks tommorrow.

9D280 · 31 August 2011, 09:15

Be very very careful about advancing the spark without proper instrumentation.... I had a rebuild as a result of the previous owner doing that where he / she hadn't noticed the broken spark plug lead & decided to fiddle with everything....

Sounds like you might either need to find the adjuster in that mechanism, or as happened to my prehistoric Johnson, check the follower isn't meant to have a roller on. Mine dropped off (rather bizarre design held on with an O- ring!) and so the follower shaft was about 3/8" too close to the cam. Net result - stalling at idle (throttle closed) and at WOT ran equivalent to about 3/4 throttle.

Thankfully a simple 6 turns of the follower - throttle plate adjuster screw & relative normality resumed. Problem is if the roller is missing, the adjuster will likely not have the capacity of taking out the slack due to the missing link as well (which it sounds like you may have discovered already?).

TomKat · 31 August 2011, 21:13

Thanks 9D280.

Worked at it tonight and its very weird... its as if the throttle mechanism does not have enough stoke, all I am doing is adjusting the throttle cable lenght (timing looks OK to me so left well alone althoough in the post referred to all he really did was screw the WOT throttle limiter out to allow the full movement of the mechanism if I am reading it correctly). Anyway on mine to get WOT I have to adjust the cable so that when it returns to what should be idle it is about 1/8 open. I dont really see any way of adjusting the remote throttle assembly so am puzzled as to how it ever worked. Maybe WOT was never acheived but boat felt slower last night than on previous occasions (rev counter stuffed so no way of knowing for sure).

Any ideas?

9D280 · 01 September 2011, 10:14

Can you force it back to idle? (I'm thinking missing return spring)

Any chance you could post a pic, coz otherwise I'm second guessing what your mechanism looks like. My guess is the throttle cable from remotes or tiller will directly move the coil plate under the flywheel, and there is a cam arrangement with a roller that operates the throttle from the movement of the coil plate carrier.

Throttle cable throw can be adjusted on some of the aftermarket things by smply moving the business end to a hole further form the pivot. If you have a generic (i.e anyone's name on the box!) single lever mechanism, it may be worth having a deeper dive look inside - My old Yam 703 was as loose as a loose thing on it's 15th pint, and a new set of plastic bushes improved things immensely.

TomKat · 01 September 2011, 22:23

Pics are awkard, spent the night stripping building up and re stripping! Definately not enough stroke in the throttle mech. There is like a floating plate that the cable is anchored to and it moves about 30mm. If I contrain it I easily get the stroke I need so working on a way of restraining it. Very awakward 1 armed access to it so tried some 4mm rope - it came loose, then some cable ties inexplicably they lossened!

Will go out agin for another while! Project boats are good in theory but I am not sure that I am enjoying this!

9D280 · 02 September 2011, 09:19

Option 2: Serial Number?

I could then look at the microfiches & get my head round the mechanism.

Poly · 02 September 2011, 09:27

TomKat,

Am I reading this wrong:

- You serviced the carbs and had too much idle speed. So then you adjusted the idle speed by playing with the throttle cable.
- Now the throttle cable either won't give you WOT or won't go back to "idle" depending how it is set?

My guess is you shouldn't have tried to compensate for the incorrect idle speed by moving the throttle cable - is there not a screw on the carbs to set the idle speed?

TomKat · 02 September 2011, 21:47

Polwart, your reading it right, after the carb clean the engine idle was very high, in order to reduce it I had to adjust the throttle cable lenght as the minimum stop no no longer worked. When I did this the engine could not acheive WOT.
To me it looks like the throttle stoke was never enough, hopefully test tomorrow will confirm this.

Fixed fuel leak tonight so just the tacho and fuel gauge to sort out now (got some on eBay on their way!). Also bought a 2hp aux just in case!

Cheers for the help.

m chappelow · 02 September 2011, 22:12

If the roller outer goes soft or is worn on the small shaft it rides on ,it can sometimes cock over and it wont then ride /go over onto the second part of the cam ,and it suprizing how little wear will effect the timing set up ,as 9d280 says new bushes will help a great deal too.
you dont think it could be drawing air through the cab/ manifold gasket or seal when you reasembled that perhaps would cause the fast tickover .

Locozodiac · 03 September 2011, 02:10

If you find the pics not to match is because Tohatsu, Mariner models doesn't use throttle cable, just rods throughout the entire throttle/carb system. That engine is probably a disguissed Yamaha model made for Mercury/Mariner.

TomKat · 03 September 2011, 22:52

Its all rods, just my bad decribing powers! Tested my bodge today and all seems OK!

Cheers for all the help chaps.