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Mercruiser 140 project- Smoke coming from throttle bolt hole in exhaust manifold

G

gpolkin

New member
I replaced the head, camshaft and waterpump on my 1977 140hp mercruiser(gm block). I am not very mechanical so this has been a challenge. After putting everything together I took it to an auto mechanic to adjust the distributor and set timing. They could not get the boat to idle below 2000 rpms. They told me that either a carburator issues or exhaust leak could cause this. I did not have this issue when the head rusted through last fall.

When I started it up in the driveway I noticed a steady whisp of smoke coming from where the throttle linkage connects to the exhaust manifold. I am thinking this is not good. The bolt hole seems to be roughly 1.5-2 inches deep. I am thinking I should attempt to JB weld the back of the whole and then coat the bolt with gasket sealant when I reinstall the linkage.

Any advice would be greatly appreciated.

Gregthrottle_bolt_hole.jpg
 
An exhaust leak will have nothing to do with the engines ability to idle. It may be better for you to find a good local MARINE mechanic to set this engine up for you.
 
The new mani for 140 / 3.0 has a hole that goes into the intake. Just went thru this with my friends 3.0l. The head went, and we got out hands on a reconditioned head and mani all one piece off a engine that was rebuilt but the block went right when they started it up.

Long story short, any other holes in the mani to the left of your pic, that are open fill them with a bolt. The linkage bolt if you jb weld it in you will never get it back out.

Pull the bolt out use a generous amount of aviation form a gasket on the threads and see if that fix's it.

Make sure there are no other vacuum leaks, spray some wd 40 or carb linkage cleaner around the base of the carb when running and on the linkage if the engine sounds different or runs different you found your problem.

Be aware low compression on one or more cylinders, or a bad wire or plug can cause in this engine not to idle correctly. These new mani's also has a access hole on the top in front of the carb with a square head plug.

Post back the results we will go from there.
 
Thank you very much for this info. Extremely helpful. I will follow these instructions and post back.

Greg





Master mechanic said:
The new mani for 140 / 3.0 has a hole that goes into the intake. Just went thru this with my friends 3.0l. The head went, and we got out hands on a reconditioned head and mani all one piece off a engine that was rebuilt but the block went right when they started it up.

Long story short, any other holes in the mani to the left of your pic, that are open fill them with a bolt. The linkage bolt if you jb weld it in you will never get it back out.

Pull the bolt out use a generous amount of aviation form a gasket on the threads and see if that fix's it.

Make sure there are no other vacuum leaks, spray some wd 40 or carb linkage cleaner around the base of the carb when running and on the linkage if the engine sounds different or runs different you found your problem.

Be aware low compression on one or more cylinders, or a bad wire or plug can cause in this engine not to idle correctly. These new mani's also has a access hole on the top in front of the carb with a square head plug.

Post back the results we will go from there.
Click to expand...
 
Good news. I put form a gasket on the bolt and the boat started right up and ran at 800 rpms smoothly in the driveway on a hose. Bad news- I put it in the lake and ran it around 1500-2500 rpms and after 5 minutes it started to overheat. I will post a separate question on this.

Greg
 
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