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Ideas on carb replacement failure

#1

sgkent

sgkent

Have a pressure washer, 20 years old. Briggs 4 hp quattro engine. At the base of the carb are two gaskets/diaphrams where it sits on the fuel tank. The engine is very hard starting. Once it gets going it is fine. The primer bulb will fill will fuel in two or three pumps. In late October 2021 I once again replaced those gaskets/diaphragms and the engine was fairly easy to start. Now it is late Feb 2022, new fuel and once again it is hard to start. Air filter is a green universal one instead of the factory one. After pulling maybe 20 times I removed the air cleaner and tried it again. It started on the second or third pull. Does anyone have any experience with the engines that have the carb on the tank, where they are able to easy start their engine, and keep it that way for years without having to replace the carb etc once a year or two? Also does anyone have any experience where some of the universal air filters are too restrictive and they are the cause of the hard starting?

It is this style carb and tank, and filter. Photos are from the Internet. The filter in this image is the Briggs factory filter. The universal ones are a green dense foam.

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#2

B

bertsmobile1

Remove the cowel & check the long manifold
These are prone to cracking
A small crack = hard starting
Large crack = surging
A badly worn O ring will also exhibit similar symptoms.


#3

sgkent

sgkent

thanks


#4

StarTech

StarTech

Also it can be that the valve clearances are closed up on that 20+ yr old engine as if I remember correctly that series is a L-head [side valve] engine.

Also on the carburetor make sure the base is not warped. They can warp for several reasons. One is heat, another is weight, and a third is over tightening the mounting screws. Then of course if it has that plastic manifold a crack in it.


#5

sgkent

sgkent

working on it now. New carb going in. One unrelated question. I've been cleaning up rust etc., as I go along. I am considering pulling the flywheel off to glass bead the rust off the lamination on the flywheel, then oil it or hit it with a light coat of clear. Any one have ideas on whether that is a good or bad thing? I think I still have some Briggs flywheel tools around here, if not I can get some. Or I could lightly sand the rust but that magnet is so strong I am concerned that the particles will just stick to it. Maybe hit it with compressed air to get rid of them.

Last, I have a Tecumseh air gap tool, is the small Briggs engine air gap about the same?


#6

StarTech

StarTech

Rust does not affect magnetism. Rust however can cause air gap issues. Just use a standard business to set the air gap of coil pack to flywheel. Now rust between coil and its mounting posts does prevent the coil from working.


#7

R

Rivets

No need to clean the flywheel magnets, unless making it look good is what you are after. Won’t affect how it runs. I set armature air gap at .008”-.010” on all engines.


#8

sgkent

sgkent

Thanks. I just set it with the Tecumseh .010 tool, and am waiting for the starter housing to dry as I also cleaned and painted it. I turned the engine over by hand and don't feel a lot of compression so I know it is worn. Just hope this gets it another year or two. It is a 4hp Briggs vertical on a pressure washer that has gotten a lot of use. I replaced the head gasket and followed the correct pattern and torque so I am sure the head is on tight.Either the rings are worn or maybe a tight valve. The exhaust was a lite gray, and the intake carbon, even carbon on the piston so not a lot of oil washing over it. It isn't worth going all the way thru it with new rings etc.. I know when I start the other small motors I own, I can feel the compression better than this one.


#9

sgkent

sgkent

it is back together. Now to get some non-ethanol fuel. I fear that my hard starting issue is low compression. I cannot feel the compression stroke when I pull, however it feels no different than before. We'll see when it is hooked up to water and fuel is added.

40 lbs cold compression on the little 4 hp engine. Guess when I have time maybe Ican pull the head again and adjust the valves in case the exhaust is tight. Never done one of these small motors before so I have no idea what valve gaps I am even looking for. I have no access any longer to a valve grinding machine so I would have to tip them on a grinder if need be. I guess I could check with the local shop to see what they might charge if I brought it to them with the head off.


#10

sgkent

sgkent

Even though I have not starter it, I'll close this thread since no one seems interested. Th exhaust valve was tight so I opened it up to .009". Intake was good at .005" Compression is at 60 psi now. The carb was replaced, the intake manifold removed, cleaned and inspected, the engine cleaned up and painted, head gasket replaced, plug, magneto to coil clearance set to .010" using a Tecumseh coil tool. I was able to compress the valve spring with a thin spanner and then small zip ties going back together to hold it while I slid the retainer in. Spring starter was disassembled and cleaned so it pulls better, the starter thing on top of the flywheel was removed and lubricated. Hopefully once I get some non-ethanol gas it will start nicely. Engine is worn, valve guides worn. It is what it is. If I get another year from it I'll be happy. Not worth rebuilding further as too many internal parts will be worn.


#11

R

Rivets

I hope you’ll let us know when you get it running.


#12

sgkent

sgkent

a little hard to get the new dry carb to suck fuel, but once it was going it ran nice and strong. I'll let it sit a few days and see how it starts then. Has a random rattle under load at 3400 but none with no load at 3600. Could be the pump or who knows. It probably hasn't had this much compression in a long time. Could be the starter release too clanking a little because I oiled that so it would have a bit more drag than the dry ball bearings. If so that should work out quickly. Could also be the exhaust valve. The stem was carboned up and I cleaned that up.Lots of guide wear so I am sure it is moving around a little. DIdn't sound serious, came and went as I opened the pressure wand.


#13

Ericcburson

Ericcburson

sgkent said:
Have a pressure washer, 20 years old. Briggs 4 hp quattro engine. At the base of the carb are two gaskets/diaphrams where it sits on the fuel tank. The engine is very hard starting. Once it gets going it is fine. The primer bulb will fill will fuel in two or three pumps. In late October 2021 I once again replaced those gaskets/diaphragms and the engine was fairly easy to start. Now it is late Feb 2022, new fuel and once again it is hard to start. Air filter is a green universal one instead of the factory one. After pulling maybe 20 times I removed the air cleaner and tried it again. It started on the second or third pull. Does anyone have any experience with the engines that have the carb on the tank, where they are able to easy start their engine, and keep it that way for years without having to replace the carb etc once a year or two? Also does anyone have any experience where some of the universal air filters are too restrictive and they are the cause of the hard starting?

It is this style carb and tank, and filter. Photos are from the Internet. The filter in this image is the Briggs factory filter. The universal ones are a green dense foam.
Click to expand...
Ive found that some carburetors actually fit nicely together backwards or 180’ off.


#14

sgkent

sgkent

Ericcburson said:
Ive found that some carburetors actually fit nicely together backwards or 180’ off.
Click to expand...
physically impossible with this one


#15

sgkent

sgkent

Success and failure. The pressure washer runs fine. Really strong and steady. Starting is another story. It has been sitting about 5 or 6 days. It has a new factory carb. When I press the bulb to prime it there is no resistance. If I press six to ten times quickly it will get hard, then 3 presses and the engine will start on the first pull. If I try to start it before the bulb gets hard, you can pull and prime all you want, but it won't start. I would think that the fuel should not bleed down from the primer bulb but what do I know.


#16

Scrubcadet10

Scrubcadet10

these carbs are prone to warpage along the base where they meet the tank. 2 gaskets then the diaphragm *might*work... im not sure.


#17

sgkent

sgkent

carb and gaskets are new. How would that affect fuel bulb bleeding down?


#18

R

Rivets

Sounds to me like you have an air leak. When you press on the primer bulb, you are applying pressure on the fuel in the tank, forcing fuel up the pickup tube. Definitely could be that the tank is warpped, allowing air to leak between the carb and tank. You can check this by putting a thin coat of dish soap around the carb base and push hard on the primer. Any bubbles mean a leak. Doubling up on the gasket might help. Where a new tank is not an option, I’ve sealed this area with silicone sealant. Must remember not to spill gas here, as it will damage this seal. Also could be a bad primer bulb, even though it is a new carb.


#19

sgkent

sgkent

the cap leaks fuel a little when I turned it over to change the oil. Are you saying the cap is supposed to be a one way valve that holds pressure between when it runs?


#20

Scrubcadet10

Scrubcadet10

I don't think Mr. Rivets said anything about the fuel cap... ?


#21

R

Rivets

No, the cap is vent, that’s why it leaks.


#22

sgkent

sgkent

Scrubcadet10 said:
I don't think Mr. Rivets said anything about the fuel cap... ?
Click to expand...

...you are applying pressure on the fuel in the tank,
Click to expand...


so how would the fuel tank hold pressure unless the fuel cap was involved, right? Either the bulb sucks up fuel, or it pumps up the tank applying pressure to push the fuel up. Which is it? Why does the fuel bulb bleed down?


#23

R

Rivets

The primer doesn’t hold fuel. Right now I can find my link to Briggs pulsa/prime carb operation. If you would google search “how does a Briggs pulsa/prime carb work” you will find videos on your carbs operating principles. I’ll keep looking.


#24

sgkent

sgkent

this is probably the one you refer to. I'll take a look at the diaphragm to make sure it is seating properly. Will also check the tank carefully.


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