WOT adjustment

[bones774]

I have a 1988 350 merc mag engine 260 hp with a 4 barrel carb, last year it was not reaching WOT I thought it was propeller but after removing boat from water I niced when i shifted the throttle to full the butterfly stayed closed. What should i be looking for and any tips on adjustment.Thnaks

 

[Fishermark]

Re: WOT adjustment

when i shifted the throttle to full the butterfly stayed closed.

Are you sure you aren't looking at the choke plate?

At the top, under the adults only sticky, I believe Don has posted a check list for failure to reach WOT

 

[PitchFork]

Re: WOT adjustment

The secondary butterflies are opened up by vacuum that can be tested while on the water. I actually were looking at mine today and they opened up around 2500 RPM.

 

[bones774]

Re: WOT adjustment

i have the mity vac, should be able to vac test while on the hard. i'll take a look.

 

[Bondo]

Re: WOT adjustment

At the top, under the adults only sticky, I believe Don has posted a check list for failure to reach WOT

Ayuh,... I guess you can haphazardly bebop around,...
Or,...
Put Method to your madness by Diagnosing it....

The proper Tools are here at your disposal, If you care to Use 'em....

 

[bones774]

Re: WOT adjustment

Dons sticky mentions it could be "carb problems", if I find it may be the butterflies stuck closed his sticky does not cover that. That requires further diagnosis, I pushed the throttles full WOT and the larger butterfly remained closed, i manually pushed the vac pot and the butterflies still did not open(all while engines is off), it did not look like the way the linkage was set would cause the butterfly to open in any situation.
Thanks

 

[Bondo]

Re: WOT adjustment

I pushed the throttles full WOT and the larger butterfly remained closed, i manually pushed the vac pot and the butterflies still did not open(all while engines is off), it did not look like the way the linkage was set would cause the butterfly to open in any situation.

Ayuh,... It's a 4bbl. carb,... the 2ndaries are Vacuum operated...
They won't move with the motor Not running...

 

[bones774]

Re: WOT adjustment

I pushed the vac pot in manually.

 

[Silvertip]

Re: WOT adjustment

You have an air valve secondary four barrel carb. The secondary butterfly (the large one) opens by demand (less pressure under the butterfly than air going into the carb). They are not even mechanically linked to the throttle. The plate on the front two barrels of the carb is the choke plate. The one under it is the only one operated by the throttle. Physics 101 in play on the secondaries.

 

[bones774]

Re: WOT adjustment

You have an air valve secondary four barrel carb. The secondary butterfly (the large one) opens by demand (less pressure under the butterfly than air going into the carb). They are not even mechanically linked to the throttle. The plate on the front two barrels of the carb is the choke plate. The one under it is the only one operated by the throttle. Physics 101 in play on the secondaries.

Yeah, I understand about the low pressure under the butterfly and yes, the linkage is not mechanically linked, thats what I saw when I manually activated the vacumn diaphragm, so it's working as it should, I'll have to take a better look as the boat is in the water. i'll Work on prop size and pitch.

 

[Bt Doctur]

Re: WOT adjustment

Care to tell us what kind of carb you have, it makes a difference.
Typical Rochester 4MV has a upper plate that adjusts automatically ,the lower plates are your secondary bores,. Those are the plates you check for full opening.
Weber carb:http://www.boatfix.com/merc/Servmanl/16/16B5R2.PDF
Quadrajet:
http://www.florida4x4.com/tech/quadrajet/index.php

 

[deves3000gt]

Re: WOT adjustment

idk about your carb but Rochester 4barel secondaries WILL NOT open unless i am in the water and put the boat under load and even then they only a open a bit for a short burst. that is the way they are suposed to opperate. and i can push the same vacuum thing as yours in and they do what you are saying yours do. I am not saying your WOT problem is not carb related but IMHO it doesnt have anything to do with your butterfly plates.