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I am working on my neighbor's Briggs 6.75 HP powered push mower. He had problems with it stalling and not running so he changed the plug, coil, and choke thermostat to see if he could fix it. He then brought it to a local repair place (not a Briggs Dealer) and they replaced the carb with no luck. So I offered to give a look at it.


I have thoroughly cleaned the carb (the repair guy didn't leave the new carb on it) and jet, verified the auto choke is adjusted and working correctly and checked the air gap on the mag/coil. If I pour gas into the throat of the carb I can get it fire off and run as it should. But if shut if off I can not restart it (hot or Cold) without pouring gas into the carb. Without pouring gas in the carb it sometimes will sputter for a few seconds and stalls but never gets up to full RPMs.

I now have put a new primer carb with a primer bulb. If I prime it will do the sputtering thing all the time now. If I hold my hand over the carb and someone else pulls it, I have gotten it start but mostly I still need to pour gas in.


Any I ideas on what to do next?


Poor Compression not bringing in enough gas?
the Compression release getting stuck and not allowing it to go to full compression?

The mower is only 3 years old and does not have hard/ a lot of use.

Rebuild the carb with a new needle/seat, part number 398188. I'll bet the seat has swollen and the float is no long set properly. Here is the procedure I recommend.


Needle and seat replacement.

Remove the carb, and then remove the float bowl. Check the float bowl jet (which is the bowl screw) and make sure the jets both horizontal and vertical are clean and open. Tip the carb upside down and remove the float pin and float with needle attached. Look in the float needle passage and you should see the red float seat at the bottom of the passage. This is where a #5 crotchet hook would come in handy as you need to remove this seat. If you have no hook, but compressed air, you can blow through the fuel inlet and try to pop the seat out. Put your thumb over the passage to prevent the seat from flying who knows where. No air or hook try bending a stiff paper clip to dig the seat out.

I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.

With the seat out clean the passage way with carb cleaner. Now you must find a drill bit slightly smaller than the passage way, to be used to press in the new seat. Apply a very, very small amount of a very light lube to the new seat. 3-1 oil or lighter, to help seat it better. Carefully insert the new seat in the passage way with the rings on the seat down toward the carb body. Slowly and carefully force the seat down with the back end of the drill bit. Once it is seated, check to see that it did not flip and the rings are up. *Next check to make sure that the float does not have any liquid in it. *If it does, replace. *If everything looks correct, attach the new needle to the float and install with the float pin centered. It everything is correct, the float should seat level to the carb body, when looking at it upside down. If everything looks good reattach the float bowl, making sure that both the bowl gasket and the nut gasket seal properly. Reinstall on the engine and test unit. Remember to have patience and take your time. Good luck, but I don't think you'll need it.

PS: *On the side of some Tecumseh carbs you will find a plastic cover. *Under this cover will be an idle jet. *Remove it and check to see that the jet is open both horizontally and vertically. *You should be able to push the old float needle wire through the vertical opening.

Have Model Number, Type, And Code? It sounds like the clearance needs checked on the valves to me atm. Didn't see someone else had posted already. takes me awhile to type. Do what he said first ^ sounds like he knows more about them then I do.

The carb is brand new

Pet982 said:

The carb is brand new

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I would check the Valve Clearances.

http://www.briggsandstratton.com/eu/en/support/faqs/servicing-the-valves

Sounds like the plasic manifold that the carb fits to is cracked or the o ring that the carb fits to is faulty.

This Briggs is an L-head engine. It would be extremely rare to have a valve clearance problem. Pug Made a good suggestion, check the o-ring and intake manifold also.

Thanks for all the tips.

I realized I forgot to tell the engine model # 126T02-0675-B2 and yes its the L(flat) head engine. Between helping my sister out with her network, diagnosing and ordering parts for a Yamaha outboard that I have torn down at work, and this project my brain is on overload LOL.


I was going to ask how likely it is to have valve clearance issues on these flat heads? I will look closely at the intake manifold tomorrow the O-ring is new with the carb.

The intake manifold is not cracked and the gasket is in good shape.

I took the head off and brought the piston to TDC on the compression stroke. I brought the cylinder down about 1/2 inch (1/4 of the way down) on the power stroke and got .005" on the intake and .007 on the exhaust.

Those valve clearances are good, as I posted earlier you have a lean running condition, which involves the carb. I'll bet the float level is set to low, that is why I suggested rebuilding the carb. Yes I know it is new, but just last week I had a brand new one leak like a sieve, you can get a bad one at times.

Rivets said:

Those valve clearances are good, as I posted earlier you have a lean running condition, which involves the carb. I'll bet the float level is set to low, that is why I suggested rebuilding the carb. Yes I know it is new, but just last week I had a brand new one leak like a sieve, you can get a bad one at times.

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Even though when I get it running it will run perfectly? Just to get it run I have to pour gas down the throat of the carb.


I bought a HFT leakdown tester. Could compression be a factor? If not... whats the harm of another tool in the tool chest?

I proformed a leak-down test and that seemed to have checked out. The gage was a little touchy but the cold engine seemed to have 20% leakage (buy the rings, the muffler and carb was quiet.)


I contacted where I bought the new carb from to see about another one. But something tells me I am missing something mechanical in the engine as, if the repair place was truthful. They claimed they put a new carb on it also so that would make 3 carbs so far.

The carb is set too lean for starting, that is why you need to pour in extra fuel. Three things will cause this. 1. An air leak at one of three places. O-ring between carb and manifold, cracked manifold, gasket between manifold and block. 2. Auto-choke not operating properly to close the air horn during starting. 3. Fuel in the float bowl not at the proper height, causing the need for a higher than normal vacuum needed to draw the fuel into the cylinder.

Another new carb came in today and I installed it. Its still doing the same thing.



The new carbs are a primer type and when I push the primer, a squirt of gas squirts up the main jet. When I pull the cord itsometimes sputters for 5-10 sec. but never gets up to full RPM. I can put it 10+ times in a row with no sputtering, when I check the plug it does have gas on it but not soaked

https://www.briggsandstratton.com/n...nemanuals.html?searchrequested=126t02-0675-b2

adjusting valves correctly is very important, you have to be on correct stroke, both valves closed & rocker arms loose, 1/4" past TDC on B&S engines, you can remove spark plug & rotate engine by hand on top screen above flywheel, gently place a screwdriver in spark plug hole to let you know when piston is at TDC, if rocker arms are tight & valve is open rotate engine 180 degrees & check for rocker arms loose to TDC then 1/4" past & adjust valves.

Can I ask why its now a primer instead of auto choke?
If I remember right both systems use a different coil which might cause your problem.
Also cylinder head will be different.
Also have you checked the flywheel key as it could be sheared and timing may be out?

pugaltitude said:

Can I ask why its now a primer instead of auto choke?
If I remember right both systems use a different coil which might cause your problem.
Also cylinder head will be different.
Also have you checked the flywheel key as it could be sheared and timing may be out?

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I check the key it was slightly off but the key looked all in tact. when I put it back all lined up and it still would not run.

When I first started messing around with it and got it to run when priming it I decided to try a new primer carb on it. When I looked up the parts for the model / s numbers a P/N was listed to both types of carbs so I decided to give the primer carb shot. The air filter had the bulb spot plugged and I added the bulb.

All other parts appear to have the same numbers correct me if I'm wrong that's why I'm hear to learn things. How are/ why would the heads different? Air Flow?

The valve clearances measured within spec when putting the piston 1/2 way down the power stroke(combustion).

If the key is even 1/2 a mm off then timing is off. Replace the key if it is not perfectly square.

Pet982 said:

I check the key it was slightly off but the key looked all in tact. when I put it back all lined up and it still would not run.

When I first started messing around with it and got it to run when priming it I decided to try a new primer carb on it. When I looked up the parts for the model / s numbers a P/N was listed to both types of carbs so I decided to give the primer carb shot. The air filter had the bulb spot plugged and I added the bulb.

All other parts appear to have the same numbers correct me if I'm wrong that's why I'm hear to learn things. How are/ why would the heads different? Air Flow?

The valve clearances measured within spec when putting the piston 1/2 way down the power stroke(combustion).

Click to expand...

So your problem could be the air filter back plate.
If it is autochoke, where the gasket fits will be flat.

On a primer back plate where the gasket fits it has a channel for the air to go when the primer gets pushed.

Could it be this?

pugaltitude said:

So your problem could be the air filter back plate.
If it is autochoke, where the gasket fits will be flat.

On a primer back plate where the gasket fits it has a channel for the air to go when the primer gets pushed.

Could it be this?

Click to expand...

No the backing plate does have the horseshoe channel. All I had to do was take the plug out and put in the bulb. When I push the primer a squirt of gas does shoot up the main jet.

Could the compression release system be screwed up?

Pet982 said:

No the backing plate does have the horseshoe channel. All I had to do was take the plug out and put in the bulb. When I push the primer a squirt of gas does shoot up the main jet.

Could the compression release system be screwed up?

Click to expand...

No nothing to do with compression release.

Is it pushing up enough fuel when priming?

The back plate was common for warping and air would escape as the gasket was not completely sealed.
Add another gasket.

Sometimes you can get what looks like fuel coming up the emulsion tube but all its doing is going back down when you let go of the primer.

I believe enough gas comes up and yes I did have to double up the gasket to get a good seal there.


Another part. If I get it going with pouring gas into the carb and let it run for 5 min or so and shut it off, it will not start again without putting gas into it. I am at a loss.


could somehow it jumped valve timing? but when I did a leak down test if I held the blade in the front to back position(TDC) it would seal the cyl. slightly before tdc air out the exhaust (compression release). and after it was sealed too.

I'm at a loss Original auto choke carb had a 48hr chem dip soak and it does the same thing too. did not throw a needle and seat at it though.