Yes, I'm a Nikki carb replacer

[hanz63]

I have a bugger of a time with some of these single barrel carbs. I had one on a later twin that I could never get right. That one had a high speed surge that originally was horrible and only got slightly better. They crop up every once in a while on the Briggs singles. Had one on a 33" a few days back for the dreaded surge that doesn't go away. Feels like a low speed issue. On a carb that is a couple years old, perfectly clean, my question is why? I've replaced the whole plastic body and seals at their since I know ya price - only to have to eat it. Tells me the issue is elsewhere. Some claim to know their way around these things. Any tips?

[KE4AVB]

The only surge problems I had the with the Nikki is when either main jet was undersized, the jet's o-ring was bad, or carburetor's idle is set too. Although Briggs don't sell these o-rings separately they are available from other sources.

[hanz63]

You know, I try to think my way through a carb when I'm in there. This last one seemed as though it should be a runner. I just have become somewhat jaded on these. A new one, and up she purrs like a kitten.

[KE4AVB]

The Nikki is a fairly simple straight forward carburetor but things got to be near perfect too. As BGS once pointed out to me about the bowl gasket even a tiny imperfection or nick can cause problems. Now Briggs does try to run the engine too lean at times via using too smaller jets. I personally a few years ago got a whole batch of bad bowl gaskets from my distributor that had a manufacturer's defect.

I have making up own jet pn to jet size chart but it only contains jets that I have ran across. I originally asked here for other members to send some of their info on jets to increase the chart cross reference but one did. Sometimes all you got to correct a lean surge is to go up one or two sizes. When I cant find the correct size I pull out the micro bits while I got a spare jet of the original installed size as a backup.

Early engine manufactures did realized not all engines could run right when identical setups as tolerances added up to make changes necessary. This is why many Tecumseh engine carburetor that were fixed jet have been converted to fully adjustable carburetors.

And I understand that my experiences with the Nikki is not the same as yours. We all have different set problems. Heck right nearly every Stihl mounted cube Zama with built-in primers is driving me nuts as they are failing and due the cost from Stihl it is cheaper to just the carburetor when all that is needed is a new primer base. Probably next year it will be a different set of problems.

Also to check is the intake gaskets as I had one last that actually would sneeze randomly while off load due to an air leak.

[hanz63]

The last one had a wiggy intake seal and bowl seal. Fuels quality? The unit was a little old lady's. Doubt she was dumping a can of slurry in the fuel.

[PtMowerMech]

I'm with you on these Nikki carbs. Especially on the Briggs single cylinders. I've rebuilt so many, only to get that darn surging. Obviously they don't surge when new. So there's something I'm just not getting right on the rebuild.
I suppose some of it could just not be getting that spiderweb of a gasket on properly. The O ring not seated right. Or something.
One thing I've found on those is the float rarely, if ever sits flush, when turned upside down. It always seems to sag.

Since Stens has had these on sale for so long, I've bought about 10 of these I keep in stock and just replace the customers with a Stens. Maybe this winter, I get some more kits and start trying to rebuild the 30 or so I have boxed up. I also have an spare 17hp engine, that's going on a work bench outside, to test them.
Until then, I'll just keep replacing them. Saves me and the customers time & money by just installing a new (good) aftermarket carb.

[KE4AVB]

Yes everything got to be right with these carbs. I have even seen where techs try to run the engines to slow and only a slight idle rpm tweak is needed at times to correct the surging. Plus governors do wear in flyweight areas requiring a static governor is set a little tighter. Something that I have also seen on Kohler Courage engines where a feeler gauge of about .010-.020 is used during the static adjust.

You mention the bowl gasket. Yes they can have defects from the factory, main jet o-rings must be tight, and jet very clean of any wax or oxidation. These jet o-rings are available but just not from Briggs. Briggs rather sell the whole jet assembly.

Personally I have yet to replace a Nikki carburetor in 11 yrs. I have even reworked a couple twin barrel Nikki carbs where the choke shafts pass through worn out by installing new bushings. Yes I had two choke shafts worn completely into on Kawasaki engines. For a part that only moves at startup it shouldn't have been that worn; I would have the throttle would be the one to wear out.

[hanz63]

Speaking of aftermarket carbs, how many do you have experience that run well when installed, and the next year and then the next? I've seen more customers think they've done themselves a favor by fixing it themselves with a Big A special. A few I asked them for their old one to fix up so it ran right. I've not bought a Stens carb so I've no clue if they are the same as Amazon. Some don't run or run well from the start. Some it's like the castings are poor and they flake from the meth and are not usable once they sit over winter. Hopefully I keep seeing CV single carbs because PD sent me bags of float valves for some reason when I just ordered a bag on my stock order. That's another one that aftermarkets I've seen installed are bad news. Maybe I just like the OEM price tags.

The very last Nikki had developed that shotgun surge like you see that some of these have from new, but then they go away in 15 seconds. This one did it through about midrange and didn't go away. The only thing I didn't do is f with removing the welch plug as the carb was so spotless to begin with. This one had more of a slot there in the venturi if I recall. I've had a handful of the Powermore rider carbs too that would stall as they warmed.
I must just be getting old and grumpy.

[KE4AVB]

Mentioning PD which me to the curve for not buying enough parts from them, I wonder if they still got the Briggs 798778 bowl kit at $109 which is way over priced when compared to my other Briggs distributor which has it for under $30 the last time I checked. At that price the related carburetor was only $10 more.

I just couldn't buy Briggs parts from PD at the current time since they only was giving me a 10% discount when the other distributor is at 20% on most of the Briggs parts.

[hanz63]

798778
1
BS, 798778 BOWL-FLOAT

Service Notes: ADD 841653 WHEN REPLACING 499810

Package Notes: ADD 841653 WHEN REPLACING 499810

Add Individual Part Notes
$112.20 List

Here ya go!