Loose idle screws on carbs

[mentalmarine]

Hey,
My father has a Johnson 70hp Seahorse outboard engine (I will get the model number tonight to clarify the correct motor) and he is having problems starting it. I have read the sticky's and have a few things that I am going to try from that, including starting procedures and a few others. However the most pressing issue that I think could be the problem is that the 3 screws that control the idle that are on the carbs are very loose and you cannot tell a difference in performance when you adjust them. Should those screws be that loose?

Thanks,
Landen:

 

[F_R]

Re: Loose idle screws on carbs

Are they actually adjustment needles (sharp pointy ends) or are they machine screws with gaskets under the heads? I suspect the later. Those kind are supposed to be screwed in tight. The idle mixture is via fixed jets.

 

[mentalmarine]

Re: Loose idle screws on carbs

Ok I took a picture of the 3 screws that I was talking about. I also got the serial number, J70ELCRD.

 

[F_R]

Re: Loose idle screws on carbs

Those are not adjustments, just hole plugs. They are to be screwed all the way in, tight (with gasket washers under the heads). The idle mixture is controlled by fixed jets, deep in the hole behind the screws. If the screws are left loose, air will get in around the threads, upsetting the fixed mixture.

 

[mentalmarine]

Re: Loose idle screws on carbs

Thanks a ton! What we did was ensure that those screws were tight. We got the engine started and had it idling fine, then we checked each cylinder. The bottom two when we removed the spark plug wire from the spark plug the engine cut out, so we know those are working fine. When we did the same thing for the top one, we could tell no difference in the performance. So we are guessing thats where the problem is. We used some carbon choke cleaner in to attempt to clean any stuff in the carb, nothing happened. What should we do to get that top one going, or what adjustments do we need to make?

 

[mentalmarine]

Re: Loose idle screws on carbs

I forgot to add that we checked the spark plug and it is sparking.

 

[F_R]

Re: Loose idle screws on carbs

First thing you need to do is a compression check. There could be internal damage to the top one.

Then make sure there is no water getting into the top one.

Then if you are sure the spark is good (jump a 7/16" open air gap), and the spark plug is good, consider the top carb may have a problem.

You do NOT want to run the motor with a fuel problem on one carburetor. If that cylinder is not getting fuel, it isn't getting oil either. If it is getting just almost enough fuel, it will cause pre-ignition and burn the piston or break rings.

 

[mentalmarine]

Re: Loose idle screws on carbs

I will pick up the compression gauge tonight. After reading up some on how to do that test, after taking the plug out and installing the gauge, do I just turn over the engine about 7 times to build up pressure, then take the reading?

 

[mentalmarine]

Re: Loose idle screws on carbs

Just another question, why would it be hard to start up the engine cold? I have to use the manual rope and pull start it, however once it runs for a few minutes you can turn it off and right back on without a hitch?