NS90A poor idle and beep

Hi there my 1999 nissan NS90A beeps like morse code and idle drops severly to stalling speeds below 400 RPMs. She will stall most times if I do not push the controller to give it more gas when I shift into foward or reverse in other words it will not stay running if I dont not accelerated above idle RPM while in gear.

some observations:

idles fine when in neutral. @900rpms aprox.

compression 125 on all holes.

gas seems ok its been beeping for a few tank fill ups now.

was running fine before this other than the knock thing (see below).

spark looks weak on all holes when tested as per the factory manual, 11mm gap was doable but not a very strong spark, very thin and orange, barly visable in full daylight. not sure how strong this models spark is supposed to look.

engine once in a while will start to knock running at very low RPMS while in gear. below 1500 RPMS (has done this for a long time)

runs fine at all other RPMS including full throttle.

Starts easy when cold and instantly when warm.


I am thinking the beeping is just because the engine is dropping to stalling RPMS and not the engine telling me something is wrong specfically.

Any ideas?

Ignition? Dirty carbs? Link and sync? This is where I am thinking.

Re: NS90A poor idle and beep

The beeper on these is supposed to be either ON or OFF, not intermittent. It's possible that the beeper is coming on/off as a result of low water pressure, due to the engine being at/near stall.

A thorough diagnosis is called for, starting with fuel, and then ignition systems (including link and sync), then checking mechanical items. I would also inspect the LU parts to see if that is the root cause of the knocking. That may well be your whole issue.

Re: NS90A poor idle and beep

Thanks for the reply Paul. I think I will try cleaning the carbs with a rebuild then a link and sync.

I think knocking was the wrong word to use, its more like a running rough condition. The knock is more like the engine bouncing around as if the timing was way off suddenly causing it to run very poorly.