1972 Mercury 800 Thunderbolt won't idle below 1500 RPM .... Please Help!!

[jacobmeyers]

I have a 1972 Mercury Thunderbolt (800) 80 Horse. I put the boat into the water yesterday to give it a test after purchasing. Drove it over to the dry rack and noticed somethign wasn't right.

What I learned was I have a control shifter and a fast idle lever on my control box. When you are ready to get moving, you bring the fast idle lever down paralell with the bottom of the boat and lock it into place, that will then allow the boat to open up in terms of throttle (as opposed to the lever being up, the throttle is limited).

My problem is, when I bring the fast idle lever back to its locking position, the engine stalls because it won't idle below 1500 RPM. I believe I need to be around 800 RPM when idling. This would be when the distributor cap is rotated all the way back. I could adjust the idle stop screw in, but don't want to be shifting the boat into gear while running at 1500 RPM's.

Can anyone help with this?

 

[Moody Blue]

Re: 1972 Mercury 800 Thunderbolt won't idle below 1500 RPM .... Please Help!!

This is a very helpful post for you to read. It should take care of the problem you are having.

http://forums.iboats.com/showthread.php?t=168855

 

[WYOboating]

I have a 1972 Mercury Thunderbolt (800) 80 Horse. I put the boat into the water yesterday to give it a test after purchasing. Drove it over to the dry rack and noticed somethign wasn't right.

What I learned was I have a control shifter and a fast idle lever on my control box. When you are ready to get moving, you bring the fast idle lever down paralell with the bottom of the boat and lock it into place, that will then allow the boat to open up in terms of throttle (as opposed to the lever being up, the throttle is limited).

My problem is, when I bring the fast idle lever back to its locking position, the engine stalls because it won't idle below 1500 RPM. I believe I need to be around 800 RPM when idling. This would be when the distributor cap is rotated all the way back. I could adjust the idle stop screw in, but don't want to be shifting the boat into gear while running at 1500 RPM's.

Can anyone help with this?

 

[WYOboating]

I know this is a long shot because this thread is 10 years old, but I’m having the same issues with the same motor. Any help to diagnose would be appreciated.

 

[Faztbullet]

Compression test first...

 

[racerone]

Agreed-----Condition of engine is to be determined first.-----Post the numbers.-----Or remove bypass covers to inspect pistons / rings.-------Could be numerous other issues as well.

 

[merc850]

After you've tested the compression try setting the low speed needles 1 1/4 turns out from seated then running in the water in forward see if it will idle down. The idle can be set using the cable's brass barrel - remove the throttle cable and push the lever forward to lower the idle then adjust the barrel to fit into the holder.

 

[aspeck]

I know this is a long shot because this thread is 10 years old, but I’m having the same issues with the same motor. Any help to diagnose would be appreciated.

Please start your own thread instead of tacking your question on to a 10 year old thread. Older threads are for information only or to be reopened by the original poster. When we ask questions on someone else's thread it only brings confusion. Thank-you in advance for reading and following the rules.