3hp L-head 80202 Briggs Flooding Problem.

[Denny Graham]

So.....restoring an old flathead from Dec. 1988. These were common on some of the early
small mini bikes. This one was left out by the neighbor for the G-man and I decided to try
and bring it back to life. It had a badly pitted intake valve so bought a new one and lapped
it and the old exhaust (was in amazingly good shape) in.
the bore was very good, doesn't look like it had been run much, was off a lawn sprayer I'm told.
It's got good compression now and good spark and has a solid solid fuel tank which has been
soaked in white vinegar over night and flushed.
Next, to address the fuel....The Pulse-Jet carb was soaked in Purple Power cleaner in an Ultrasonic
cleaner then washed in hot water and then all passages (that are accessible without drilling out plugs)
were flushed out with CRC Brakleen brake parts cleaner. This carb does not have a removable low speed
'seat' so cleaning is limited to washing out and blowing out of the low speed 'seat' hoping to clear the ports
into the venturi. A new needle was installed, which, has been set 1 1/2 turns out for the initial starting setting.
The main jet casting and jet that dips into the small well is clear, again delicately probed with tip cleaners and
small wire brushes.
The problem here is, the 'emulsion tube' it is set behind the main jet (which is none removable) so there is no
direct access to the tiny holes in the emulsion tube. And again, this was all flushed and blown out as well as could
be done without drilling out plugs.
Now for the problem. The engine starts but only runs for 10 or 15 seconds never getting up to speed and
with the air cleaner off, you can see that there is much liquid fuel pooling in the throat below the choke plate.
Now that it's flooded and dies, when I pull the plug it's wet. So it's clear that there is WAY to much fuel entering
the engine, and with no way to adjust the high speed fuel delivery on these simple carbs I'm at a loss as to why it's
getting to much fuel.
My guess is that the imbedded emulsion tube is possibly clogged since the holes in it would be extremely
small and this might be a reason that lots of raw fuel is being delivered to the venturi and not being mixed
with air for atomization.
Does this sound logical????
Obviously a new carb would fix it but, a new Pulse-Jet from 1988 would be ridiculously expensive, that is,
if you could even find one, and the object is simply to try and save a good little old engine from the scrap heap
without investing to much into it. Which, so far I've only invested $6 in an intake valve, $10 for a carb kit and
another $6 for an air filter......and 100 hours of labor!!!!
So if there are any 'experienced' small engine experts out there who might have any suggestions, I'd appreciate
hearing them.
Thanks,
Denny G
Sandwich, IL

 

[Hellion]

Sounds like it is a latter generation fixed-jet Pulsa-Jet? This page may shed some light on it for
clarity AND show, among other things, the route of the fuel through the carb as it is pumped from the tank:
https://outdoorpowerinfo.com/repairs/briggs_pulsa-jet_horiz_fixed.asp

That being said, could it be the fuel pump diaphragm? Perhaps it has a bad seal on one of the flapper/check valves causing raw fuel
to leak right into the carb throat? The diaphragm is the main weak point of these carbs.



For anyone looking to replace the whole thing, aftermarket Chinese made Pulsa-Jets are available for under 30 dollars on that popular
auction site (and probably everywhere else and Amazon too). I bought one because the original on a 5 HP was absolutely roached from galvanic corrosion. All the screws (idle mixture screw, etc) were stuck permanently to the carb body.

The replacement carb worked fine and allowed me to flip the garden tiller it was installed on for a decent profit.
Not worth it to me to shell out $100+ for an OEM Briggs carb...

 

[Hellion]

You're lucky I read your post. That is a prime example of a TL;DR (Too Long; Didn't Read) wall of text.

Incidentally, depending on how bad the intake and/or exhaust valves are pitted, they can be refaced with a
valve grinder/surfacing machine in any competent engine shop. I think my shop charged me $10 for both valves.

 

[Denny Graham]

Thanks for the ideas. A bit happened since posting the other day. The original carb was in similar shape as the one
you mentioned. As I posted, there are some inaccessible ports that can get clogged. I put a new fuel pump diaphragm
in the carb rebuild and all appeared to be fine in there, no corrosion, scratches or such. It didn't occur to me that one of the reeds could be sticking, don't know why that would happen with a new diaphragm, other than it's made in China.
With a bit more searching this time, I did find 'that' replacement Chicarb on ebay for $19 w/shipping and tax. That's more
like it. Wish I'd have found that two weeks ago. That's on it's way, should be here this week. So in the mean time, now that I've found a replacement, I think I'll do an autopsy on the original carb just to see if my assumption about the emulsion tube is correct.
As far as 'TL;DR' ya see.....a pet peeve of mine, is when people post one liners leaving out all the details in these discussions and then you have to ask then 49 questions to get the whole picture. I try to say it all at at once so
someone answering doesn't have to keep asking, what about this, did you try that, is that missing, etc, etc.
Oh......and I soon learn that some long threads say nothing and should be avoided. But....others do contain useful information and are worth reading.
So......thank again for the ideas.
Denny Graham
Sandwich, IL

 

[Hellion]

A leaky fuel pump is the only way I can see it flooding or with raw fuel pooling up in the carb.
Now if it was a conventional carb with a float bowl, needle and seat and the fuel was gravity fed, it is
not hard to understand how that can flood.

I agree about posting all the info up front and in the first post. Kudos to you for that.

Let us know how the autopsy goes--this is a baffling set of circumstances (unless it is absolutely elementary and I am having a brain fart)... . .

 

[Denny Graham]

Thanks Robert for the reply. Yeah, I've always been one that wants to know the "Why" when something
happens. I'm gonna wait till I get the Chicarb on and see how it runs before I tear into the old carb.
I'm gonna try not to destroy it but often when they have cross drilled ports they are plugged at the
factory and it's hard to get them apart without causing damage.
I'm 80 and go back to the days when we got Jiffy Kits from the autoparts for our auto carb rebuilds
that came with new lead plugs for those cross drilled holes. Now those was the days when you REALLY
did a COMPLETE carburetor rebuild.
tks agan,
Denny G
Sandwich, IL
ps. Oh yeah....did I already mention? I just finished restoring a 100 year old Sioux valve re-facer that I've had
under the bench for many decades. I tried grinding that old intake valve but the margin was way to thin by the
time it cleaned up. And......new valves are so cheap it's hardly worth bothering with re-facing to begin with.
dg