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I have a B&G 25HP Twin engine. I rebuilt the engine last year due to broken piston/connecting rod. Ever since the rebuild I can't seem to set the Idle/Running RPMs properly. For this engine I believe they are idle@1750, running @3600. The springs are in the right place and the governor arm has been adjusted properly. What happens is the following. I set the running (full throttle) RPMs to 3600 by bending the spring arm, then move the throttle level down to idle and set it using the idle screw on the carburetor. When I go back to full throttle the running RPMs vary between 3200 and 3400 and the engine sputters and backfires. I can see the governor arm moving rapidly back and forth while it's doing this and I'm assuming that this action is causing the engine to sputter like that. I then reset the running RPM back to 3600, and engine runs smoothly. When I go back to idle mode the cycle repeats. I now have the throttle hard wired to full throttle and I'm running it at 3600RPM all the time. Which I guess is ok for getting the job done, but I'd rather have it setup properly. I used the original springs and governor when I rebuilt the engine. Any ideas?

If the engine is surging or "bouncing on the govenor" the mixture is wrong. Set the high idle at 3600 then slowly move the throttle control back to the low idle position. Does the engine at some point start surging? Does carb have an idle mixture screw? If you hold the carb butterfly against the idle stop does engine run smoothly? Are you sure you do not have an air leak in the intake between carb and heads?

Need the engine's model and type numbers.

A lot the v-twins uses a governor idle setup and the tuning has to done a particular way.

Also did you do a static governor adjustment before even attempting to tune the carburetor?

This engine does not have an mixture screw, only idle screw. I did set the governor lever with engine off. I would appreciate if you can send me the correct procedure. Unfortunately I can't get to the tractor right now to give the model number.

I think the engine model number is 407577, does that make sense?

Well that brings it down to few specs. But that number comes back a 22 hp Gross engine series.

Being an Intek.

Tnx for that, I knew I was missing something. I'll get back to the forum with the complete engine model in a few days.

I got the right engine model from the valve cover. It's 445777-0154-E1.

I still can't get it to run properly. As I mentioned before my engine model is 445777-0154-E1 and I've since found out running RPM should be 3300 (not 3600). I can set idle RPM as per instructions above, but setting running RPM to 3300 causes engine to sputter. It runs ok at 3600. See video here (note that idle RPM is set a bit high on video)

Does anyone out there have any suggestions? Thanks for your help.

At max RPM, have you held the throttle still in one position? If so does it still make that popping sound? It soulds like it is popping back thrun the carb like a burnt or leaking intake valve.

Yup, I did that and it still does makes that popping sound. I'm afraid you might be right and I need a valve job or maybe it's a worn out cam. Though I don't understand why it runs smoothly at times for a few minutes, usually at the higher RPMs.

I found the valve lash setting to be a bit high around 0.008 so I reset all of them to 0.005. Engine now runs smoothly and backfiring stops. However once the engine gets warm and under load, backfiring starts again, thought much reduced. I don't understand this, when the pushrods get hot they become longer, so the valve lash will get smaller, shouldnt I set it to a higher value to compensate?

Had a new to me Briggs twin Intek that was spitting, acted like valves. Checked valve setting and then thought maybe valve seats or ????
Could not get valve/valves to leak using leak down test and manually pushing open the valves with the push rods off. finally went to the Nikki carb.

I have seen Nikki carbs have those symptoms. Very strange that a carb will spit back and act like a valve. Sometimes on the dual throat Nikki's you can watch down the throat of the carb's intake and see which throat is doing the spitting. I've also seen them dual throat type cause one cylinder on a twin to be completely dead.
Is your Nikki a dual throat type or the single throat type?

I bought a replacement Nikki clone carb to replace a spitting Nikki awhile back (less than $20 and the clone did not spit back, just would not idle smooth. I used parts from the clone into the OEM Nikki and got a good run, mainly used the internal O rings, gaskets and the two little jets with the o rings. During testing the non-spitting clone carb indicated to me that it was the OEM Nikki carb that was causing the spitting and not the valves on the Briggs Intek OHV so I went to carefully checking and replacing the internals inside the bowl section ONLY on the OEM carb using parts from the clone. BUT do not expect to take two Nikki carbs that appear same on the outside but be different on the inside. I just got lucky that day. Not all Nikki's are the same internally for transferring parts and pieces.


I've also used some of the lesser priced clone Nikki kits from flea bay and repaired OEM Nikki carbs. Here is couple of links on flea bay just to give you an idea of the lesser priced kits for single throat and dual throat Nikki's. I noticed that some of the needle's in the kits would cause a high float level when installed but the Nikki carb still worked ok (float would not set level when the kit replacement needle was installed) I purposely tested just to see if carb worked ok with the high float level and got a good run test.
Summary: From hands on experience. Nikki carbs will cause sputtering and spitting back on Both single cylinder and twin cylinder Briggs engines. (and both the single throat and the dual throat Nikki's)
and it's usually the rubber gaskets and o rings inside causing such.
The OEM Nikki kits are quite expensive. As compared to the old Walbro carb's Nikki carbs SUCKS BIG AIR. I think ethanol gas PROBABLY also reduces their life span.

Carburetor Rebuild Kit Master Overhaul For Briggs & Walbro LMT 5-4993 698781 | eBay



797890 Carburetor Overhaul Kit For Briggs & Stratton 791230 799230 699709 499804 | eBay

Here is a single throat Nikki kit on Amazon

If digging into a nikki carb always replace the tiny o ring(s) on the main jet(s). Number one problem with those carbs

Hammermechanic says:
If digging into a nikki carb always replace the tiny o ring(s) on the main jet(s). Number one problem with those carbs

Very true and keep a heads up when removing the bowl and then placing the carb up right. I've see the little jet missing, just evaporated. It's laying in your lap or on the floor because the itty bitty o ring is bad and let the jet fall out of the plastic emulsion tube..

Some of the kit's do not even have these little o rings. Some of the Nikki clone kits lately have the little jets and may even have the little brass jets.
Some places have just the little Nikki o rings by themselves for like $4 or more each. I try to look carefully at pictures of the kit on-line to see if I can locate them as being in the kit.

I bought a 20 pack of the o rings

I fix most 2 barrel nikki carbs with a kit like this.

I been getting these from Kawasaki under pn 92055-7013 for 0.62 ea (packages of 5 ea) until the last price update (10/30/22) were they just went to 0.70 ea. Either way they are very tiny and you work where the air isn't moving as they are easily lost.

Also one other thing is when removing the fuel make sure you don't the jet in the first place.

Hammermechanic and StarTech:

Have you guys seen a Nikki produce the spit back in the Briggs Inteks that makes one think that valves are not seating?
I've isolated the Nikki engine spit back right down to the carb internals on more than one engine. (not the engine or external manifold leaks.

Strange: How them Nikki carbs can act sometimes.
Also seen them dual throat type produce a completely dead cylinder on the twin engines.. No fuel at all getting to one cylinder. (each throat of the dual throat Nikki is isolated from the other so if one side clogs not fuel)

Good info about source for Nikki o rings and twin kit you guys posted. Them Nikki OEM kits and OEM carbs are too expensive for me to put on a old engine.
Thanks for the info

I know a lot people say these carbs very hard to repair. To me they are not. I even have install bushing where the throttle and choke shafts have badly worn the carb bodies on the Kawasaki engines on JD ZTRs.

The last one I installed a bushing in was so bad that it took me using a schedule 80 1/8" brass pipe to make the bushing out of.

For cost it all depends on the customer here and the equipment condition. I can have in the shop a 22 yr old machine that looks like new and then a have 1 yr old ZTR that looks it been in a war zone.

Another big problem is that people don't replace the flat o-rings on the intake manifold and they have air leaks. The OEM get hard and compressed and the cheap AM swell from the ethanol. I stock a dozen of them as i change a lot of them.

Biggest problem Next to the jet o-rings on the 2 bbl carbs is the tiny passageways under the w shaped plate. Ultrasonic cleaner usually gets them clean but the carb cleaner spray guy usually miss them.

Thanks for your help folks. I just cleared the first snow of the year and the tractor ran smoothly, no backfires or sputtering, valve adjustment must have fixed it. Coincidentally the RPM gauge stopped working, this is the digital type with the sensor wire that wraps around the spark plug wire. Not sure if related, the sensor wire is well insulated to prevent any possible arcing but I thought I'd mention it, might help someone else in troubleshooting.

amentac wrote:
I just cleared the first snow of the year and the tractor ran smoothly, no backfires or sputtering, valve adjustment must have fixed it.

Thanks for the comeback.

Hammermechanicman said:

Another big problem is that people don't replace the flat o-rings on the intake manifold and they have air leaks. The OEM get hard and compressed and the cheap AM swell from the ethanol. I stock a dozen of them as i change a lot of them.

Biggest problem Next to the jet o-rings on the 2 bbl carbs is the tiny passageways under the w shaped plate. Ultrasonic cleaner usually gets them clean but the carb cleaner spray guy usually miss them.

Click to expand...

Yes those o-rings need changing during carburetor service. I had one engine to come that was sneezing at idle because of a bad square cut o-ring. On the V-twins the same problem except you can have the area where the carburetor mounts to warp especially when the tech over tighten the carburetor mounting screws but heat does it too.

On the most recent repair of a v-twin with dual barrel Nikki. It called for the 695241 manifold superseded to in my case 797503. I used the 595606 instead and the only real difference was the 595606 had the stud for the auto choke spring. They also used a new o-ring design. It was well worth to try anyway at the cost difference for both me and my elderly customer. I will use this from now on.

May have already mentioned this. I usually just add a paper gasket (not really paper, it's a automotive gasket material about 1/16 inch thick) over the old intake manifold o rings. Sometimes these paper gasket material come in a kit in addition to the intake o rings. I trust the thicker intake gasket material more so than the rubber o ring for a good seal.

I save them plastic intake manifolds when sending the engine to the salvage. (after seeing the replacement prices)
Some plastic intakes for the single cylinder Briggs Inteks are specific to the type of air breather required.

That what someone did here then they tighten down the screws so tight that spacers had cut right the gaskets and I could see light through the area. Still wasn't sealing.

Wow, Bubba must have used a big impact driver.
Some of them plastic intakes have a steel sleeve through the bolt holes to limit the tightening and prevent breaking the plastic so no really need in trying to do the extra leverage, it's just distorting things.

And them kind of people get to vote.(at our expense)

Things sealed by O rings should have some wiggle when tightened because you are trying to SLIGHTLY compress the O ring so that the parts have some relative movement as they heat up to account for different amounts of expansion
Most British motorcycles used this from around 1960 on
The US distributors invented a tool to straiten the flange which US mechanics warped because they over tightened the mounting nuts and that was even after the factory changed to a very lightweight split washer and a 1/2 nut .
O rings must have a solid FLAT surface to seal against
Putting a paper gasket under the O ring defeats the whole system
Aussie distributors had a similar problem but we ended up fitting a soft composite gasket and deleting the O ring so the gasket extrudes into the O ring hole .
I fix a lot of power torque engine that are "impossible to start" simply by doing the 10 year maintenance and replacing the 4 O rings that are not obvious which go hard thus stop sealing