1988 Nissan 55HP Idle Issues

[Harritwo]

I have a 88 model 55HP Nissan NS50C that I suspect has a vacuum leak on the intake side somewhere. I have a high idle when the engine is running (2000 RPM or so) whether it is running on muffs or in the water. The carbs have been rebuilt, have srayed WD-40 all over while the engine is running and I am unable to locate a leak. The plastic fittings on the reed plate cover were cracked and i attempted to seal them with RTV, I recently was able to purchase some new and have replaced them.

The idle cannot be turned down enough to allow it to idle under 1000 rpms.

Does anyone have any suggestions on where to look for a vacuum leak? Any further troubleshooting tips? What would you recommend as the next step?

 

[Sea Rider]

That's a 2 or 3 cylinder engine. if 3, you need to have a very sharp ear to tune those 3 carbs in a row. Is it possible to install led vacuum testers on all 3 carbs to adjust carbs spot on. So each has its own small intake manifold, right ?

Happy Boating

 

[Harritwo]

It is a 2 cylinder, Obsolete and parts are difficult to find. Not sure about tuning with an LED, i used a handheld tach to set the carbs the best that i could. I am almost positive that is has a vacuum leak, just cannot find it and not sure where to look.

 

[Sea Rider]

So it's a 2 cylinder 2 carbed engine ? A vacuum leak is hard to find as the leak happens inside manifold not outside as if expecting air bubbles forming around manifold while spraying just about anything, Try soapy water, check if some portion is sucked in.

Happy Boating

 

[TwoRivers]

I have a 88 model 55HP Nissan NS50C that I suspect has a vacuum leak on the intake side somewhere. I have a high idle when the engine is running (2000 RPM or so) whether it is running on muffs or in the water. The carbs have been rebuilt, have srayed WD-40 all over while the engine is running and I am unable to locate a leak. The plastic fittings on the reed plate cover were cracked and i attempted to seal them with RTV, I recently was able to purchase some new and have replaced them.

The idle cannot be turned down enough to allow it to idle under 1000 rpms.

Does anyone have any suggestions on where to look for a vacuum leak? Any further troubleshooting tips? What would you recommend as the next step?

Have you checked the timing?