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briggs needs primed until warmup

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Re: briggs needs primed until warmup

Postby 38racing » Wed Sep 11, 2019 7:03 pm

It's new needle and seat .As per previous post it runs minutes after shutting fuel off so I'm thinking bowl is full . Once it's running fine I'm assuming bowl is full at shutdown of engine and would still be full when starting the next day. But next day requires the priming.
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Re: briggs needs primed until warmup

Postby KE4AVB » Wed Sep 11, 2019 7:07 pm

Now about the float level I have seen some where the level when install is low even with new parts. I have been heating the plastic float hinge to get them level.
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Re: briggs needs primed until warmup

Postby bgsengine » Wed Sep 11, 2019 7:47 pm

KE4AVB wrote:Now about the float level I have seen some where the level when install is low even with new parts. I have been heating the plastic float hinge to get them level.
Walbro 75-570-1 float (I'm 95% sure) - much cheaper (From Power Distributors) and I'm fairly sure replaces 398187 float - May be worth a bit of homework to cross reference Walbro with Briggs & Kohler carb parts , often much cheaper from Walbro. I think they're just a buck or two each, cheaper than the time spent heating and adjusting float levels, no?
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Re: briggs needs primed until warmup

Postby 38racing » Wed Sep 11, 2019 11:03 pm

I should have noted that float was level.
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Re: briggs needs primed until warmup

Postby KE4AVB » Thu Sep 12, 2019 7:18 am

38racing wrote:I'm stumped. The engine is a 12h802 and the carb came from a 12h802. I put carb back through USC then sprayed all passages repeatedly with carb cleaner and compressed air. Still had to continually prime for2 minutes before it would stay running. At that point putting finger over primer bulb hole would cause to falter to point of stopping. When rpm drops with falter the governor opens the throttle but it continues to stop. After 5 minutes of running then putting finger over primer bulb hole causes a slight drop in rpm but it stays running. I'm using original o ring on the intake pipe. Can't think of anything else except checking intake valve clearance. I do have another similar mower just left at dumpster. I guess I could see if I can get it to run and then try it's carb on the problem engine.

This is turning out to be a head scratcher. I never had one doing this as I normally only have two problems with these either primer won't prime due to a warped air cleaner base or the main jet needs resizing. The covering of the primer hole shouldn't cause a problem as most primers used with this carburetor are closed system but the image of the primer does appears to be a vented bulb. Of course I need to check to see if I have the 694395 in stock to have a look see at it.

Curious have you checked the valve clearances? You also mention trying another carburetor. Have you done this and problem remains?
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Re: briggs needs primed until warmup

Postby KE4AVB » Thu Sep 12, 2019 7:23 am

bgsengine wrote:
KE4AVB wrote:Now about the float level I have seen some where the level when install is low even with new parts. I have been heating the plastic float hinge to get them level.
Walbro 75-570-1 float (I'm 95% sure) - much cheaper (From Power Distributors) and I'm fairly sure replaces 398187 float - May be worth a bit of homework to cross reference Walbro with Briggs & Kohler carb parts , often much cheaper from Walbro. I think they're just a buck or two each, cheaper than the time spent heating and adjusting float levels, no?

Yes I think they are the same float and I think I already got the Walbro float in stock here. The problem isn't with the float as much as it is that the seat causes it to be unlevel which why must deform the hinge point to get them level. Even with new seat, needle and float it is still off. At least I don't see many of the engines any more. It just cheaper for the customer to replace the whole mower due other problems.
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Re: briggs needs primed until warmup

Postby bgsengine » Thu Sep 12, 2019 7:44 am

KE4AVB wrote: The covering of the primer hole shouldn't cause a problem as most primers used with this carburetor are closed system but the image of the primer does appears to be a vented bulb.
I suspect you are thinking of the pulsa-prime? All the float carb primers on that type L-Head should be vented, as all they do is inject air into the float bowl to push fuel put the main nozzle, they need to suck in air to the bulb to recharge., Its the pulsa prime that sucks fuel from metering well to push through and inject fuel into carb throat, so they'd have closed system.. If blocking off the vent on the primer changes how the engine runs, I'd be thinking a problem with air bleeds or cracks in carb allowing too much air (or float level or corrosion in a metering passage restricting fuel flow or fuel level)
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Re: briggs needs primed until warmup

Postby 38racing » Thu Sep 12, 2019 8:44 am

bgsengine wrote:
KE4AVB wrote: The covering of the primer hole shouldn't cause a problem as most primers used with this carburetor are closed system but the image of the primer does appears to be a vented bulb.
I suspect you are thinking of the pulsa-prime? All the float carb primers on that type L-Head should be vented, as all they do is inject air into the float bowl to push fuel put the main nozzle, they need to suck in air to the bulb to recharge., Its the pulsa prime that sucks fuel from metering well to push through and inject fuel into carb throat, so they'd have closed system.. If blocking off the vent on the primer changes how the engine runs, I'd be thinking a problem with air bleeds or cracks in carb allowing too much air (or float level or corrosion in a metering passage restricting fuel flow or fuel level)

That's what has me so puzzled. I could spray through every passage in the carb. Just wondering how the warm-up improves it. Maybe tightening at o ring or still something at intake pipe. Next step I think is getting other similar mower running ok and then carb swaps.
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Re: briggs needs primed until warmup

Postby 38racing » Sun Sep 15, 2019 7:57 pm

bgsengine wrote:
38racing wrote:I'm stumped. The engine is a 12h802 and the carb came from a 12h802. I put carb back through USC then sprayed all passages repeatedly with carb cleaner and compressed air. Still had to continually prime for2 minutes before it would stay running. At that point putting finger over primer bulb hole would cause to falter to point of stopping. When rpm drops with falter the governor opens the throttle but it continues to stop. After 5 minutes of running then putting finger over primer bulb hole causes a slight drop in rpm but it stays running. I'm using original o ring on the intake pipe. Can't think of anything else except checking intake valve clearance. I do have another similar mower just left at dumpster. I guess I could see if I can get it to run and then try it's carb on the problem engine.


when carb is apart do you happen to notice if the float sits level? or a bit "up" from level? (low) . If it is "up" from level, then you got a swollen float needle seat and fuel level is too low in carb bowl. (Bowl needs specific level of fuel to reach the fixed jets properly)

I've got another similar engine that runs for long time then just slows down or even stops.plan to open separate thread. Hoping to report that it was a high sitting float. It's level again with new needle and seat. Testing in the morning.
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Re: briggs needs primed until warmup

Postby 38racing » Thu Sep 26, 2019 7:48 pm

Problem solved. Almost embarrassed to tell the solution. I had another donor carb. I put it through UCS. Blew all passages with carb cleaner and compressed air. Installed it without the primer plate and just primed with a spray of carb cleaner. Started and ran perfect. So I had the original carb. I pulled the bowl to again just spray passages and compare to the good carb. The bowl nut main jet did pass cleaner but I noted that the working carb flowed more. So after multi swaps of the bowl nuts it was clear that it wouldn't stay running on that original nut. I guess the jet flow was too lean for a cold engine to run but as engine heated up it would run albeit probably still on the lean side. I haven't thoroughly cleaned the original jet yet to actually try one more time to confirm my theory.
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