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Ask Jeff G. Your Own Question
Jeff G.
Jeff G., Marine Mechanic
Category: Boat
Satisfied Customers: 4728
Experience:  42 years experience, Certified Master Technician, All Major Outboards, Sterndrives, Hi-Performance
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We have spoke before. I have a 120 hp force outboard (by

Customer Question

hey Jeff we have spoke before. I have a 120 hp force outboard (by Mercury)1997. I just recently rebuilt the entire power head and I went to fire it up for the first time today and it toke a minute but then fired up. Problem is after about 3 seconds of running it jumped in rpm and began to idle very high!!! Now I am familiar with the engine intimately but as for linkage adjustments on the carb I am at a loss basically I need to tune it. But not sure how. 160 Larson flyer 1997 with 120hp force by Mercury outboard 1997
Submitted: 1 year ago.
Category: Boat
Expert:  Jeff G. replied 1 year ago.

Couple of things.

Make sure the control cables or linkage is not sticking.

Check the throttle shutters in the carbs are closing all the way.

On the side of the carbs is a flat link arm. They are adjusted by a small screw and flat nut. Loosen the screw. Move the control to neutral/idle. Move the carb linkage to allow the carbs to snap shut, they are spring loaded. Check the throttle plates are closed. Snug the adjusting screw so both close at the same time all the way.

the carbs are now synced.

On the towershaft, the rod that controls the throttle just to the side and rear of the carbs is a curved throttle cam. At idle the grooved line should be next to the roller on the carb linkage but not opening the linkage. Adjust as necessary.

At the top of the towershaft is the connector to the timer base. make sure this isn't binding.

Try these things and post back what you find.


Customer: replied 1 year ago.
All is synched I have a little bit of play in the rod but the play doesn't effect the carb movement. I attached two photos so u can see what I am looking at
Customer: replied 1 year ago.
I do have some gas leaking out of the bulbs on the carbs top and bottom one. And my little Manual pump on the gas line will not tighten up I can just here it keep dumping gas ibto the bulbs
Expert:  Jeff G. replied 1 year ago.

Don't worry about the primer bulb not getting hard.

The rpm is controlled by two things the timing and the fuel ratio to air.

Things that will cause higher rpm are, advanced timing, air leak, lean idle mixture, carbs partially open.

Have you checked the timing on the engine?

Customer: replied 1 year ago.
No I haven't done the timing didn't even think of that. Just wanted to fire her up to see if she ran.
Expert:  Jeff G. replied 1 year ago.

I'll bet the timing is too high at idle.

Customer: replied 1 year ago.
How do I set that?
Expert:  Jeff G. replied 1 year ago.

Look at the bottom of the towershaft the adjustment screw is there. Time it in the water with a timing light. There should be a decal with the specs on the engine.

Customer: replied 1 year ago.
It was the fuel air screw. I have an idle now but I had a small piece pop off it was a hose 1 of 2 that feeds from the side of the block there are four square panels on the side of the block which have hoses that all intertwine and lead to two hoses that go to front of block with little screens on them well one broke and I don't j ow what there called
Expert:  Jeff G. replied 1 year ago.

You are referring to the recirculation hoses. If one breaks then you are getting extra air into the engine.

Do you have a good idle now?

Customer: replied 1 year ago.
I have a great idle at 700 800 and yes one of those fittings broke and is spitting exaust and oil out at the bottom
Expert:  Jeff G. replied 1 year ago.

You should be OK then. Once you put the boat in the water set the idle speed so it stays running in gear but as low as possible. Probably about 900 to 1000 in neutral. Set the idle mixture as lean as possible without any back fires or popping where it still can accelerate and get on plane.

Customer: replied 1 year ago.
Now my issue is water. I can't get the pisser to work I rebuilt the impeler kit and everything that all is good but idk what else it could be I had a guy say a dry block won't let water threw until 3200rpmz another one say flush it backwards
Expert:  Jeff G. replied 1 year ago.

Forget the dry block nut case!

When you installed the lower unit where you sure to get the water tube in the midsection indexed properly?

You can put a garden hose on the water tube and turn the water on and see if there is a blockage. Check the fitting where the indicator tube connects for blockage.

Customer: replied 1 year ago.
I don't know what your talking about so I'm guessing no. I though after the impeller casing it was a straight shot up to the block. Didn't known anything about " indexing properly"
Expert:  Jeff G. replied 1 year ago.

There is a tube in the midsection that goes into the output tube of the water pump. If they are not connected then no water to the block.

Customer: replied 1 year ago.
Hmmm that's seems to simple lol. I have water coming out of the prop would i still get that if the tube wasn't connected? And is it a fixed tube or like a rubber tube? Only reason I ask is because I didn't neccisarly look when I put it back together and it all slide back into place without fuss.
Expert:  Jeff G. replied 1 year ago.

Metal tube.

Customer: replied 1 year ago.
What is the small piece inside of the impeller it is metal. It was sitting on the plate when I pulled the Cassing up the shaft.
Expert:  Jeff G. replied 1 year ago.

The impeller key? Goes on the driveshaft and the impeller slides over it. Without it the impeller won't turn.

Customer: replied 1 year ago.
I had that piece or something metal fall out of the Cassing and I could not find it anywhere inside the lower unit I figured it was a rubber seal
Customer: replied 1 year ago.
That would be my problem
Expert:  Jeff G. replied 1 year ago.

Let me know how you make out and don't forget to rate! Thanks

Customer: replied 1 year ago.
I have a new problem a big problem. I fixed the water pump and went to crank it and it started up fine and as I was waiting for the water pressure to build up I noticed it was coming out of the head gasket. I took it apart real quick or stleast yanked the head off to clean out the Pistons and I had water in all 4 I dried them out the best I could and put everything back together. I noticed my water line was clogged and fixed that. Now everything is dry and unclogged but it won't crank back up
Customer: replied 1 year ago.
Posted by JustAnswer at customer's request) Hello. I would like to request the following Expert Service(s) from you: Live Phone Call. Let me know if you need more information, or send me the service offer(s) so we can proceed.
Expert:  Jeff G. replied 1 year ago.

Did you require a phone call?