5.7 GS Engine Idle Changes when boat is IN or OUT of the water

cmezzino

Cadet
Joined
Sep 19, 2016
Messages
23
5.7.GS PLKD

Strange symptom I don't fully understand. I can run my boat in the driveway with the muffs on it and it idles fine at @600-700 rpm. I take the boat out and put it in the water and all is fine at first. After a few minutes of cruising, I pull back on the throttle and place the boat in neutral and now the boat wants to idle around 1100-1200 rpm.

I'd read some other forums first before posting this question and I have checked all the cables, the alignment of the cable attachment, return spring on the carb, and all of those things.

Is there anything related to the back pressure on the exhaust that could cause this? Like there is more back pressure on the exhaust once the exhaust is submerged in the water?

Boat runs and performs fine except for the difference in its idle behavior whether it's in or out of the water.
 

GA_Boater

Honorary Moderator Emeritus
Joined
May 24, 2011
Messages
49,038
Yes, exhaust back pressure affects idle. Usually muffs have higher idle and lower idle in the water.

Since you are seeing the opposite when on the water, the next time you float check that the carb linkage is against the idle stop. And the choke should be fully open.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
47,297
most likely the throttle is sticking
 
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