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Old 10 November 2012, 06:41   #1
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2000-05 Merc 9.9-15 Throttle cams--Wear

Hi all,

Wondering if anyone has one of the above engines and had noticed either no cold-start throttle adjustment or found the throttle-body cam was not reaching the full point on the tiller model?

Purchased a 2003 Merc 9.9 and tank tested it this summer after the mechanic from the marine company I purchased it from fired-it up just be fore I bought it.

Had a hell of a time starting it and keeping the engine running after cold starting it. The idle was so low it was choking on it's own fumes and the throttle knob did nothing to advance the engine timing or increase the idle RPMs. Had to put it in gear to keep it going until it was warm then it idled low, but fine.
After taking it into the work shop and downloading the merc repair manual for this engine with the throttle specs, I immediately noticed what the problem was.
The (Fast Idle) black-throttle cam to the white throttle-body cam (carb) was not actuating though the outside knob adjustment was working and moving the linkage ahead to that point (black throttle cam).

Checked the spec for the adjustment of the actuator (4 7/8") and was there. Sooo, took a closer look at the black Idle-throttle cam mechanism and noticed it had a ton of free-play preventing the knob adjustment from reaching a point of moving the white carb throttle cam for fast idel. Epoxied the cam contact surface enough to raise it and fixed the no fast idle problem.
But, there are two black-cams which advance the timing as well as the low and fast white throttle-body cam which work-off the same worn throttle cam mechanism.
So, I opened the throttle on the tiller handle full and thought I'd check to make sure the throttle on the carb was opening full.

To my surprise the throttle was 3/8" short of full throttle, again due to the excessive free-play. Had to adjust the spec adjustment arm from "4 7/8" " to about 5 1/4" to ensure the throttle and timing advance opened fully.

The reason I write this is to advise owners of this series of engine, the whole low and high speed throttle mechanism is made of plastic. The two side by side-- black throttle cams located on the starboard side of the engine pivot on a plastic bushing and regular external throttle lubrication is not going to be effective at preventing this wear. I had to remove the 11mm nut and partly remove the bushing and grease it with lithium grease as it was bone-dry.
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Old 10 November 2012, 07:57   #2
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Post a pic to have a look, better than 1 K written words. To reach full throttle on grip, must change cam and probably needs to move advance timming as well ? The 9.9 comes factory restricted that's why it's a 9.9.

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Old 10 November 2012, 10:39   #3
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Yes, here's a pic. I should add, a 9.9 is Not the same as a 15. The Merc 15 has a larger cyclinder displacement.
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Old 10 November 2012, 11:24   #4
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if you have a service manual and strobe light and rev counter, follow the set up procedure in chapter 2C ( I think) it will run and start well.
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Old 10 November 2012, 19:32   #5
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Quote:
Originally Posted by Nightfisher View Post
Yes, here's a pic. I should add, a 9.9 is Not the same as a 15. The Merc 15 has a larger cyclinder displacement.
Yeap, thought it was a rebadged Tohatsu, both 9.9 & 15 are 250 CC, but seems it's a Yam model. That's why asked a pic.

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Old 11 November 2012, 07:05   #6
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Quote:
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if you have a service manual and strobe light and rev counter, follow the set up procedure in chapter 2C ( I think) it will run and start well.
Hi, Thanks for the info. Yes I had read the section and do own the timing-strobe and multimeter. Did the timing check after the repair and adjustment and it was at spec at idle and advancing normally on high throttle.
The problem was starting and normally as with most outboard and inboard engines, cold and warm starting throttle advance, also advance the timing arm hence the engine-timing to more-easily turn over and start engine.

Thanks again.
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Old 11 November 2012, 12:55   #7
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I always used to start two strokes , (except R.N.L.I. forty hp) with the throttle in the tickover position,once it had been set up as per the factory,with factory recommended spark plugs, unless there is a mechanical or an electrical fault I never had a problem
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