B&S Nikki carb rebuild problem

[kburns]

Craftsman LT2000
B&S 31P677 0912 G5 Date code 1210257

This lawn tractor looks almost new but apparently sat idle for a number of years. The carb leaked fuel into the engine creating a hydrolock. I've drained the crankcase and flushed it out a couple times with used motor oil. Its been drained again and filled with fresh motor oil, so that part of the problem should be okay.

Now, to the carb. It was pretty dirty inside, so I cleaned it in an ultrasonic cleaner and it came out looking like new. I then installed the B&S rebuild kit #796184. Everything went together just fine even though its a little bit delicate installing the float bowl gasket. After reinstalling the carb and cranking it up, the engine now surges a lot. You can see the governor arm moving back and forth every few seconds from full throttle to no throttle.

A replacement jet wasn't incl'tuded in the rebuild kit. Could that be the problem? I installed a B&S fuel cutoff valve in the fuel line. Could that be restricting fuel flow? I replaced the inline fuel filter with the same B&S filter, so I don't think that would be the problem. What else do I need to check to get this thing running smoothly? Any help would be greatly appreciated!

[Arkie]

You might take a look at this site and Nikki carbs/B&S single cylinder Nikki and look at those steps and see what you might have done or not done.
https://outdoorpowerinfo.com/repairs/

Also keep in mind if the flimsy gasket that is in pic 7 is not good and installed proper the carb float and needle can be good and the carb/engine still get fuel in the oil. (this gasket seals the fuel inlet ABOVE the needle seat. This is often overlooked thinking it's the needle/seat leaking when it's actually the gasket.

Look at steps 6, 7, 8 and about how to remove/install the emulsion tube and it's o rings seals.
Gravity flow uses a RED Briggs fuel filter. White is the wrong one.
Try applying a little bit of choke manually (not with the throttle lever) by pushing on the choke rod while it's surging. If choke helps it's running lean. (not enough gas)
If choke does not help any the Nikki is usually running rich (little too much gas) due to bad o rings on the emulsion tube and/ or the main jet. Both too lean and too rich will cause a surging when using a Nikki carb.
Also try manually holding the carb throttle or gov arm stationery, if the engine don't surge then the governor is too sensitive, if it still surges it's a fuel issue.

Good to see someone else gets to wrestle with the Nikki's surging.
Also when a Nikki carb is operating A ok they will sometimes briefly surge until engine warms up.

Ethanol gas it what kills lots of the Nikki o rings/gaskets.

Also keep in mind that it's not uncommon to get a kit that is not correct for the Nikki you are working on even though it's suppose to fit. (old stlyle and new style Nikkis)
If a Nikki carb you are working on has numbers on the CARB itself, use those numbers on the carb for a kit. Also when looking for a replacement carb take notice of the CODE before and after designated engine codes casually mentioned in the IPL's.

[color=#8000FF]Does the engine hunt and surge at both High throttle and low throttle? (and does your Nikki carb have the adjustable idle jet with the limiter or is it all non adjustable fixed jet???[/color]

[kburns]

Thanks for the reply. I guess I've got a little studying to do.

[hanz63]

I feel your pain. I've had some that I just couldn't get. Assuming the surge is without a load, it can be possible to extra clean out the idle jet passage. New intake seal of course too.

[KE4AVB]

First you need to determine if the surging is carb or governor related. Try adding a little choke to see if it clears up or try hold the throttle vane still to see if the engine smooths out or dies.

If smooths out holding the throttle vane still if governor related. If it smooths out with a little choke it is carburetor related.

These engines can have the idle speed set too low and that will cause surging. Loose main jet will lead to surging. Also idle mixture set too lean will cause surging. Now I have ran also one Nikki single barrel where the idle mixture was unset-able because an idle mixture jet under sized. In that case the idle mixture jet had to be resized. Also that fuel tower o-ring has to be prefect and I have received a handful of them defective from Briggs. Must inspect it well.

If governor related reset the static governor adjustment.

And it was mention the intake manifold gasket could be bad and I have seen that too.

One side note the main jet is PN 699733 and is 1.14mm (marked as 114)