4 Stroke Question

**2door** · #1 03-06-2009, 05:04 PM

Okay all you 4 stroke gurus, what is this? I have to believe it's a fuel pump that works off of crankcase pressure or vacuum. The tank is below the carb so something has to draw fuel upward.
My father-in-law gave me this Briggs & Stratton 3 HP and said it wouldn't run unless you pour fuel down the carb. He was right. I can't get it to run either. I took that cover off and there is a disc and spring and two small flapper type valves over holes. One hole is open to the fuel tank (I blew air into it and it bubbled in the tank). The other hole goes into the carb inlet to the intake.
What operates the pumping action and what could be wrong with it? The rubber diaphram with the flappers is intact, no holes or rips. Help!
Tom

**Ilikeabikea** · #2 03-06-2009, 05:19 PM

Thats a pulsejet carb. They have a diaphram that pulls the fuel up. Very simple straight forward carb. Norman can tell you how to make em run on Alky........................

Check the diagphram, check the pickup tube and make sure it's not covered with crap or stopped up. You can blow through the gas cap vent and push gas into the carb..................

**2door** · #3 03-06-2009, 07:08 PM

Quote:

Originally Posted by Ilikeabikea

Thats a pulsejet carb. They have a diaphram that pulls the fuel up. Very simple straight forward carb. Norman can tell you how to make em run on Alky........................

Check the diagphram, check the pickup tube and make sure it's not covered with crap or stopped up. You can blow through the gas cap vent and push gas into the carb..................

Did that. Pressurized the tank with air and fuel came up so nothing is plugged, it just won't draw. The diaphram looks good. I'm not sure I want to go the alky route. Used to run an alky altered at the drags but I have no plans to drag race this engine but I'm thinking about that 3 wheeler I have

Thanks Ilikea.
Tom

DOC BOLM · #4 03-06-2009, 07:58 PM

Brigs shows this in their repair book, they say if your engine has been stalling intermittently,remove the gas cap and try to start the engine.If it starts replace or clean vents in cap.HD

**Bikeguy Joe** · #5 03-07-2009, 11:46 AM

Get a re-build kit and thoroughly clean the carb.

My Briggs boat motor has a different fuel pump, but though it looked fine, I had to re-build it... twice in two years.

**Norman** · #6 03-11-2009, 12:51 PM

replace the diaphram its about $2.00 comes with the spring and spring cover disc. take out the main jet if it is the old type and clean out main jet check to make sure the needle is not damaged and the jet hole isn't damaged or plugged. There is 2 small holes behind the main jet blow them out with compressed air do not run a wire into them. take the carb off the tank and make sure the ful pick up tubes are clear there should be small screens on them. clean out the tank and the small resivor that the short pick up tube goes into. make sure that it does not have a hole in it. chack your valves on the engine too a sticking or stuck valve will keep it from running.
Now for the alcohol thing send me your carb and I'll modify it for the fuel it will then be a gas hog and with other mods. depending on how fast you want to go I can mke the engine put out about 18hp and turn up to 9000 rpms. It won't be cheap. over $800.00 for an outlaw engine.
you picture of the fuel pump is correct if I could see the other side I could tell if its a newer carb that you can't adjust the fuel mix on looks to be the older type.
Norman

**2door** · #7 03-11-2009, 06:27 PM

Norm,
Thanks for the advice but I've done everything you've suggested prior getting your reply. I've had the tank off, it was clean as a whistle inside as were the pickup tubes and screens. The engine has good compression, very little to no leakdown so I can assmume the valves are not burnt. New gasoline, new plug, checked point gap and about everything else I could think of but the little bugger does the same thing. Pour a little fuel down the carb and it will burn that off then shut down. Funny thing is there will be fuel behind the diaphram when I pull the fuel pump cover off telling me that it is drawing fuel but apparently its not mixing right or not pulling enough for combustion. I've applied light pressure to the tank and I get fuel to the port behind the diaphram so no plugged passages there. This engine is on a lawn dethatcher that my father-in-law gave me. I don't really have big plans for it but I was sure I could get the thing running, maybe even dethatch my lawn before I pulled the motor off. Rats!
Tom

Creative Engineering · #8 03-11-2009, 08:57 PM

2door:

It sounds like you've covered all bases!

I'm no expert...a few go-carts...mowers.

The engine may be just worn out...like the guys were saying the pump works on a vacuum pulse during the intake cycle.

I think I would do a compression test, and then a cylinder leak down.

Just guessing here...Norm what do you think?

If the engine is worn out, needing a valve job...rings, would that make the vacuum pulse weak enough so that the fuel pump woundn't work?

Maybe pull the head and see if there's a lot of carbon on the backside of the valves?

Jim

**Norman** · #9 03-12-2009, 12:17 PM

I think there is a clog in the carbs fuel system or the small fuel bowl in the fuel tank is holed out changing out the fuel tank to a known good one will solve the problem if the small fuel bowl inthe tank is holed out. he's got to get a new carb diaphragm as if it stiff or a micro hole it won't run
the fuel passages behind the main jet can be clogged and that thing will never run if they are.
If I could get my hands on it I know I can make it run and run right or at least tell him if it time for the engine to take a dirt nap.
I've seen all kinds of problems with these engines some you would not believe and had me stumped worse one was my alcohol engine would run like a scaulded dog then would loose power like the fuel was shut off took a while to figure that one out turned out to be a loose intake seat it would come loose and move with the intake valve shutting off the intake. taking a center punch and peening in the seat then reginding/lappng the intake valve and adjusting the valve lash solved that problem for good.
if you really want it to run mail it to me and I'll fix it charge you only for shipping and what parts it needs PM me and let me know. you could just send the carb and fuel tank as i think the problem is in the carb/tank

I think I an an expert on these engines. big grin

**2door** · #10 03-12-2009, 02:11 PM

Norm,
Thanks for the offer but shipping would probably be more than this thing is worth. Just to recap what I've done.
1. Bought a carb rebuild kit: (new gaskets, carb to tank and carb to intake, diaphram, spring and disc)
2. Confirmed no clogs in pickup tubes
3. Confirmed small resevoir is full, no leaky
4. Confirmed air passes through all ports in carb, behind needle, jet, pickup tubes.
5. Checked compression and leak down. (very good for this little old motor, surprising actually)
6. Filled tank with new gasoline. (Dribbled a little down the carb)
7. Pulled the rope. (engine fired, ran for 5 seconds then died)
8. Repeated item 7 (about twenty times)
9. Went in the house and rubbed Ben-Gay on my shoulder. Drank a beer.
10.Tried step 7 again (same results) Opened another beer.(wife comes out, wants to know why I'm sweating)
11. Tried 7, AGAIN! Runs five seconds then dies...(This thing is p***ing me off)
12. Shoved the whole thing over in the corner and went for a ride on my Chinese 2 stroke powered motorbike.