RPM will not increase with throttle movement in drive

[Dishwasherracer]

I have a '79 mercury merc 850 85hp outboard.
We took it out for the first time today and while in neutral and reverse the throttle works perfectly fine (i don't know how high the RPM should be able to go in neutral but throttle works when adjusted) but when you shift into drive the throttle maxes out at roughly 1200-1500 RPM and will not adjust higher or lower from and idle speed.

I removed the cowling and manually adjusted throttle arm and we got the boat on plane nicely. I don't know why the throttle would adjust in every gear but drive then also work by manually using the throttle on the engine itself.

I have spark and compression tested all cylinders the carb lines and fuel filter are clean.
The engine runs smooth with no pops, backfires, roughness or irregular idle.
When in drive the engine is not straining or stalling.

Any ideas? Possibly a broken throttle cable or control?
I have also cleaned and reassembled controls (with a manual) and there were no apparent red flags.

Thank you

I also know very little about boats but I am very mechanicly minded and am capable of doing most tests and repairs.

 

[Texasmark]

Corrosion in the cable or control or something binding/broken in control. Sounds like your engine is not your problem if you can control it with the remote cable disconnected. If you are running original equipment controls, time to renew. Merc Commander 2000 is on sale here. I bought one several years ago, about $250 and if they don't have the cables, Teleflex cables (www for site) has them which I have used....good folks. length is in inches and Teleflex site tells you how to read your current cables and how to order new ones.

 

[Dishwasherracer]

There was no noticeable corrosion in the control but I did notice some rust where the throttle cable attaches to the engine.
There is no noticeable binding, in fact, it seems to move too easily.
I'm thinking it is corroded from what you said.

Thank you!

 

[Texasmark]

Welcome

 

[Dishwasherracer]

A pin in the control was not setting properly so the neutral warmup would not lock out . Fixed now. Thanks again

 

[Texasmark]

Thanks for the feedback. Just indicative of problems trying to answer questions via "remote control". Had I been standing next to you, I could have seen your fast idle raised and solved the problem immediately.

 

[jimmbo]

Just for your info. You do not have a 1979 merc 850. The 850 was made as a four cylinder from 1973 - 1977. It was also made a six cylinder, but that was in the early 60s

 

[Texasmark]

Just for your info. You do not have a 1979 merc 850. The 850 was made as a four cylinder from 1973 - 1977. It was also made a six cylinder, but that was in the early 60s

I had a mid 70's 850 and a little 7 ? of that era. Both had the silver, red, and blue stripe on the cowl that went from fore to aft and at the end fell off like Ranger Cherokee Bass Boats strips. Also Mercury spelled it's name "mercury" just above the stripe and that lower case to start a proper noun bugged me big time. That was one of my best engines. Never had a problem on either.