Detroit technician in Annapolis area/Idle speed adjustment

[Westfield 11]

The idle on my port engine has begun to stick at 900 rpm when pulled back from cruise. If I blip the throttle it still holds 900. I can push the lever on the engine with the big spring attached (buffer spring?) and it will drop to 800. The previous idle was around 600 and would occasionally stick at 700 or so, but always dropped to 600 when blipped.

I would like to get this fixed and have both idles lowered a bit. Can I do this myself? I have the Gray Marine student manual for the 6-71, but that is my only reference. It does show the procedure, but I have no idea how relevant it is. Engines are 12-71 TIs

If repairing this is above my pay grade, does anyone know of a tech in Maryland who can take care of this?

[dottieshusband]

Danger, danger Will Robinson! The variable speed governor on your engine is a very complex and sensitive item. There are 3 things that could affect the idle speed as you discribe... the buffer screw, the throttle linkage, and the idle screw.. (the rack can hang up as well). None are rocket science... but make sure you have the manual and understand what you are doing. It is DIY, but educate yourself first.

[kelpy]

How long has it been since the engines had a complete tune up? Injectors pulled, cleaned and tested. Racks adjusted. Throttle linkages adjusted. If it has been more than a couple of years, that is where you should start before doing anything else.

[Photolomy]

Out of curiosity, what does something like that cost on a pair of 8v71ti's?

[Boatsb]

Couple o hundred to a thousand depending on how much needs to be done.

Get a good mechanic on it if your not familiar with the process. I have someone come in for that type of work for me because its nor worth the time and cost of tools for a once in 5 years service.

[jim rosenthal]

The technician you want is Tom Hugg, by the way.

[SEVEN]

Hire the pro’s and watch and learn.

[Westfield 11]

The technician you want is Tom Hugg, by the way.

Thank you. I’ll call him tomorrow. The motor had the injectors tested and replaced when they did the compression test about 400 hrs and 18 months ago. The stb motor had the heads done about 125 hrs ago and got a tune then.

[Westfield 11]

Are there any alternatives to Mr Hug? No answer on the phone and it looks like he gave up his business registration in July 2019. MR Power Specialists was his company name as far as I can tell.

[rustybucket]

My gut tells me you don't have any internal engine/governor issues. Do your throttle linkages have full travel? How stiff are your cables?

I would disconnect the throttle cable at the engine and work the throttle manually by hand several times to see if the symptoms still occur.

My guess is your cable is too stiff, or mal-adjusted to allow the return spring to return the throttle to the bottom position.

If you do find it's the cable, the ends of the cable screw in/out to give you more/less cable travel. There is also a set nut that tightens to the cable end to keep in in place. Over time, if not tightened the end can spin in/out reducing or lengthening your cable throw.

So, in a nutshell my troubleshooting method would be....

1. Disconnect the throttle cable(s) at the engine.

2. Manually work the throttle on the engine by hand.

3. If symptoms still persist the issue may be something blocking the throttle lever (dirt, rust, old bolt...etc), internal linkage, governor, injector linkages...etc

4. If the symptoms go away, you either need to adjust your cable ends (at shifter and/or at engine), Adjust/tighten the throttle return spring, or install a new throttle cable.