Engine "knockin/spittin" on low speed..

[frustratedboater]

Guys,
After de-winterize my engine and had some idling troubles. I had replaced the head & water plate gaskets, thermostat, new water pump last season, New carb bowl (corrosion) as well.

I am experiencing very choppy, bucking-type idle. I need to pull the choke knob a little to keep it running in the tank. I had used compressed air in the carb in all the known holes, ports, jets, and still the same! I even took apart the choke and blew it clean. I am assuming that it is carburetion..?..?

I would appreciate ANY help with this.. Thank you!

~FB~

 

[ezeke]

Re: Engine "knockin/spittin" on low speed..

Check that the flywheel is tight and torqued to specs. If it turned it would break the crankshaft key and cause that.

 

[frustratedboater]

Re: Engine "knockin/spittin" on low speed..

ezeke,
I never thought of that and your right! The timing would be slightly off. I will check that. Thanks for the tip!!

 

[tashasdaddy]

Re: Engine "knockin/spittin" on low speed..

what motor????

 

[wbeaton]

Re: Engine "knockin/spittin" on low speed..

Sounds like its running lean. Running better with the choke out certainly suggests it. Have you tried turning out the low speed jet? What motor is this?

Could also be crankcase seals, woodruff key or leaf valves.

 

[frustratedboater]

Re: Engine "knockin/spittin" on low speed..

This motor is an 89' Johnson 25hp. I would adjust the jets if I could, but this particular motor doesn't have that option (both are fixed). There is an adjustment brass/screw needle on the top right side and not sure what that is. I've tried 1 1/2 turn, then 2 full turns, etc. Still the same symptoms.

I did have it looked at a year ago and the shop said it was the choke-pull system and they "knew what it was" It seemed to work fine, but doing the same. Are there replacable o-rings in the choke module?

I saw a timing adjustment screw on the side....would that need adjustment? Could I test any part of the electronics? This really has me...

~FB~

 

[wbeaton]

Re: Engine "knockin/spittin" on low speed..

There is an adjustment brass/screw needle on the top right side and not sure what that is. I've tried 1 1/2 turn, then 2 full turns, etc. Still the same symptoms.

That sounds like your low speed jet. Although, the traditional location for the low speed jet is capped on your carb there is still a jet located on the starboard side of the carb that ends under the welsh plug located on top of the carb at the rear. 1.5 turns is the standard start position. Does it make any difference in running when you turn it? If not you may have to clean the idle circuit.

Your motor has a primer not a choke. If your primer is failing it will leak gas into the carb. This would cause flooding, inability to reach full RPM and rough running. A sneeze and buck like you describe is usually from a lack of fuel not too much. There are a couple o-rings in the primer, but I don't know if they are serviceable. A new primer is about $60.

 

[frustratedboater]

Re: Engine "knockin/spittin" on low speed..

Great! I will double check the adjustment on the top screw. The low speed jet is fixed in the lower float bowl and don't think it's adjustable. I already has a new bowl and jet on the carb. I shot compressed air through while cleaning just to double check before assembly of the carb. Question, what is the idle circuit??

 

[wbeaton]

Re: Engine "knockin/spittin" on low speed..

The fixed jet in the bowl should be the high speed and the adjustable jet up top is the low speed (#14 in the attached diagram). The idle circuit is the path the gas takes at idle. You have to make sure all the passages and holes are clear otherwise it won't idle properly. In order to completely clean everything you must remove the welsh plug (#3 and possibly #4) and spray carb cleaner and compressed air through the holes located in there. You must also remove the jets and everything else and make sure all those areas are clean and clear. Spray everything and blow dry with compressed air. Then reassemble.

 

[frustratedboater]

Re: Engine "knockin/spittin" on low speed..

Wow! Thanks so much. The picture helps--thats my carb. I am convinced that the problem has got to be in that area since everything else is new or sprayed out. I think I had cleaned #3 out, but did not check the #2 passage ways. I am going to pull them both and find the culprit!!

Again, thanks for helping...