Nissian 90 Low speed miss or vibration

[dlbryant1]

I have a Nissian NS90A that I and working on. This boat idles ok under no load and runs STRONG from 2000rpm's and up. This thing will shake the whole boat from just above idle til 1500 to 2000 rpm. Tried cleaning carbs. The only thing extra I noted it smokes a lot, and I read about a fuel pump diaphram problem. Has anyone else had this problem.<br /><br />Thanks <br />DAVID

 

[TOHATSU GURU]

Re: Nissian 90 Low speed miss or vibration

Whats the compression on all three cylinders and are you sure you have ignition spark on all three?

 

[dlbryant1]

Re: Nissian 90 Low speed miss or vibration

120 psi all three. Good spark. Clean all three carbs again today and resyn. Looked at RPM close miss starts at 1000 and goes away at 1500.

 

[TOHATSU GURU]

Re: Nissian 90 Low speed miss or vibration

While the engine is running, pull the spark plug wire off of each cylinder one at a time. It sounds like you are only hitting on two cylinders.

 

[dlbryant1]

Re: Nissian 90 Low speed miss or vibration

Tried pulling wires. Change was about the same for all three.

 

[TOHATSU GURU]

Re: Nissian 90 Low speed miss or vibration

That puts it back on carbs or a mechanical problem.

 

[rickdb1boat]

Re: Nissian 90 Low speed miss or vibration

What shape is the prop in?? Propshaft??

 

[dlbryant1]

Re: Nissian 90 Low speed miss or vibration

I have talked to a couple of people who said it could be when the transition from idle circuit to the main circuit. Nature of the beast? Older unit wore, loose.

 

[TOHATSU GURU]

Re: Nissian 90 Low speed miss or vibration

Nope. There is a transition bubble, but it does not last 500 RPM's.