OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines BS 375 sprint still stalling

Hi all,

Still having a problem with a masport I have.

Its running a BS 375 sprint.

The issue is it stalls after a few minutes running.

Starts as normal, easily. The primer bulb sucks in after a few seconds, then within a minute or so it stalls.

why is it creating a vacuum and choking? While im far from a briggs expert, l have worked on a few without issue.

I have done all the serving, oil filter tank clean checked electrics. The running is smooth and normal.

Primer bulb has been changed, check ball removed and tested carby has been cleaned and blown out, new diaphragm and gasket.

Ive touched on this previously with unfortunately no results.

Is there anything ive missed? Has anyone encountered this problem
,if so what was the fix? What is blocked causing this vacuum, as everything appears normal....

Any help would be greatly appreciated.

Mal.

I think that one has a Pulsa-Prime carburetor. The carburetor's fuel pump generates suction on the feed from the long pick-up tube that reaches down into the tank. The primer picks up fuel through that same tube. If the pick-up screen, or the tube that follows it, is blocked, there will be suction in the primer and no fuel feed to the fuel well, which is where the main jet picks up fuel. My guess would be that you have a "floating mass" somewhere in the primary system, consisting of the tank, long pickup tube, fuel pump and primer. After it has been standing, initially the primer works and the fuel pump works, delivering fuel to the fuel well. However at running speed the fuel pump picks up vastly more fuel than when you are priming it, pumps it into the fuel well, and lets it overflow back into the tank. Your floating mass may then be moved by the high rate of fuel flow, blocking either the screen on the bottom of the long pickup tube, or the tube itself with the associated drilling that communicates with the fuel pump.

So, maybe you've missed a floater in the fuel tank, or in the pickup system?

Hey grumpy,

Thanks for the suggestions Yeah its pulsa-prime...

Tanks been cleaned out mesh is clear on the pickup even took the screen off the jet to try. Its just using whats in the reservoir then stalling.

A blockage for sure, but every pipe and gallery seems clear....I havnt checked for a crack in the main pickup, but it still bringing fuel up to prime so i doubt its that....

The prime does take a second or 2 to release after its pushed, not like a victa type, but it does have a tiny check valve so i guess thats normal?

There is another ball bearing in the lower left of the primer chamber, a port block off? Will this or its position have any relevance mate?

There appears definately a blockage maybe mecanical (part inside has shifted?)

Im missing something...

And also not the tank...its too quick too stall and the cap is clear...

Can i burn it now???? Gawn let me lols

I only approve of habitually burning Victa 2 strokes and Kirby Lausons, Blue. You'll have to do this one without authorisation.

Do you have a spare Pulsa-Prime carburetor and tank? I like to swap the whole system over to verify the diagnosis. Then swap the carburetor and tank separately. From what you've said, you'll soon prove it is the carburetor. From the symptoms, you have a sticking intake ball in the primer. People who try to overcome this by shoving things into the hole, usually destroy the carburetor. I can recall Joe Carroll posted on how to unstick the ball a couple of years ago, but I can't find the post at present. Meanwhile someone on another site has recommended filling the well with petrol, and squirting carburetor cleaner into the long pickup tube, then starting the engine, in the hope that the carb cleaner will dislodge the crud the ball is sticking to, by the time the fuel in the well is used up.

Lmao.... I cant burn Frankenturner now gasps* its to shiny! I will just wait until the kirby inevitability blows its self up!

Ok will try that again give it a spray and try sucking it through again...

Btw The check valve is fine it pushes down and back freely and smoothly....the reference was for a ball bearing under that it is fixed in the gallery it sits in, just like the outer ones....just pathway blocks I thought, but wasnt sure of its relevance with my issue. ..

Unfortunately idont have another mate...got a few early carbs and tanks but i dont have the throttle bracket to go with them, and they dont slip under the current throttle linkages....i will try and get one temporarily on just to try....

Thanks mate , ill give it another flush and try and cup the intake a few times while its running and see if that loosens it

Cheers Grumps...ill let you know if it works or unauthorized images if it burns!

I still like my mental image that there is a semi-floating mass behind the ball, Blue. Perhaps if you depress the ball slightly with a probe and hose in some carb cleaner from the front into the cavity behind the ball, you'll break up whatever it is? Don't push that ball far, though: the cavity is tapered, probably to facilitate moulding the plastic part concerned, so once you push it back far enough to stick, I don't know how to get it out.

Success!

I pulled the carb off again,and popped the bulb off. (This check ball comes out Grumpy, oring ball and spring) blew it through all clear, put it back and tested it again...all good.

Disconnected the pickup....AGAIN lols.

OK this is where its odd...you could clearly see through and the gallery's are clear. You can see no debris shade through the plastic. I blow it out again back and forth. ..fine. Now this is the lame part....when i put fuel through a darker shade appears ...hmmm So i get my rod and pass it through and sure enough it moves with the rod. I blow it back out and nothing! Its clear again. So I pass it through and its clear. Ok so to cut a long story short lightly spiked the rod and began running it back and forward and blowing it through....what came out was what appeared to be a ball of hair or fine fibres. My assumption is that when dry it was lighg and porous hence why the air went through freely, but when fuel was put through it became swelled and more dense blocking the tube enough to cause a bigger restriction....like i said im no expert on BS but i usually get sludge rust and particles (or nothing at all) that break up easily when you blow air or cleaner through....This was like a mat of clear hair or fibre all tangled up that could not be seen until wet.

Anyways thanks heaps Grumpy, for steering me back in the right direction, I was about to pack it in....its eating into my Villiers play time lols.

Cheers Mate...A huge help and inspiration as always!

Oh and yeah she purrs now...well roars more like it!

I recently had a similar case here, and I also had a ball of hair like substance in the pickup, this problem arose almost immediately after the mower had run e10 fuel and had been left with a full tank for a couple of weeks, the fuel in my case had also destroyed the diaphragm and primer bulb, luckily for the customer it was a relatively cheap repair.

Most modern fuel hoses are non-transparent, so we don't get the misleading cues that happened in that case, Blue. Floating masses are really difficult to detect except when you flow the fuel fast, and they bunch up in a restriction. In the end they are usually removed by dismantling the pipe at every restriction point, then drying the pipe out and putting compressed air through it. I would say what you did in the end is an analogue of that.

Thanks for reporting back on exactly what was wrong, and how you finally found it Blue. It is a useful case for the archives, in several ways. I'll close the thread.