Throttle opening adj. 300XS

**Milnejk** · 07-21-2014, 03:09 PM

Trying to determine if my throttles are opening fully. When I look into the throttle body the butterfly/throttle plate is about 3/4 open with throttles full forward. I have no experience with these motors, but my thought is the throttle plate should be vertical at wide open. We are down on power thus searching for help.

I have searched this site and others and no answer yet.If you can help please advise.

John

**davemvegas** · 07-21-2014, 08:36 PM

look at the roller that lifts the butterfly arm. you can see where it travels to wide open.

**Milnejk** · 07-22-2014, 07:40 AM

I am not near the engine, but know exactly what you refer to. The set screws that hold the roller in place are coated with a sealant that seems some one did not want the throttle to be adj.

Do I want wide open/vertical butterfly at full throttle

**Milnejk** · 07-23-2014, 08:56 AM

Still looking for assistance!

**Onetime** · 07-23-2014, 09:45 AM

Is the throttle cable adjusted to allow full travel of the throttle arm?

**Milnejk** · 07-23-2014, 10:33 AM

I have adj. the cables as far as possible without raising idle RPM. With cables fully adj. and throttles full forward, the throttle butterflies are approx. 75% open. There is an adj. on the cam/roller that will change that, but the adj. set screws are sealed leading me to believe that someone (factory?) did not want this changed. My previous experience primarily with auto engines would lead me to adj. the throttle butterflies vertical (min restriction @ WOT). Do not want to damage engines and want to try to solve on my own. If needed I will certainly seek professional help.

**Euroski** · 07-23-2014, 07:21 PM

Will pull the cover off my 300xs this weekend and post a picture. I didn't have to make any adjustments other than connecting the cables,

**Onetime** · 07-24-2014, 10:02 AM

Is your cable pulling the throttle arm against the full throttle stop?
Are you sure it's only opening 75%? The butterfly is usually not adjusted to true vertical. 90-95% of vertical. There is actually more air flowing through at 90-95% of vertical opening. Before you think no way, actually did flow bench tests that proved it.

**Milnejk** · 07-24-2014, 01:33 PM

Port eng. is approx. 1/16" from stop. Stbd. eng. is approx. 3/16" from stop. both can be moved manually to the stop by moving butterfly.
Adj. Cables did not change the throttle opening as best I could tell. Wish I could take a pic, but 3 hrs away from boat. I am certain butterfly is open 75% or less. We are getting 5450 rpm at WOT. Speed 60-61 trimmed out

Boat is 27 Contender twin 300XS turning 22" Bravos. Running 100 gal fuel and two people. No bottom paint and props look like new. Hard Top w/radar & Sat receiver.

This boat is new to us and never had a Merc. before say nothing of a 300XS.

**Onetime** · 07-25-2014, 08:20 AM

Are you talking about the throttle arm stop or butterfly stops"

**Milnejk** · 07-25-2014, 09:01 AM

The stops are on the butterfly shafts. Did not notice a stop on the throttle arm for WOT. there is an idle stop on the lower part of the throttle arm assembly, (down near cables)

**Onetime** · 07-25-2014, 02:15 PM

There is a stop for max throttle on the throttle arm If you disconect the throttle cable from the arm and activate the arm manually see if it goes against the stop and how your butterfly position is then.
Cables should be adjusted so full throttle just hits the full throttle stop of the arm. I don't know what throttle you are running and if it has enough travel to give you full range of throttle.