Old 8HP "Giant Vac" Stalling When Tilted

[MDetam]

Hi everyone! Hope I'm in the right place -- I've searched everywhere for an answer.

I've got an old (~1988) "Giant Vac" walk behind leaf blower with a Briggs 195422-0751-01 engine.

The problem: Doesn't run consistently at full throttle -- when it begins to die, it seems the only way to revive it is to close the choke and turn throttle nearly off. To expedite or reproduce the problem, angling the blower (or pushing up or down a hill) causes it to die within about 8 seconds. If you tilt it back and it starts to die, you can sometimes keep it running by setting it down flat again. What's strange to me is that depending on the rotations of the hi-speed (main jet) screw, it's sometimes able to keep running for 15-20 seconds at an angle.

What I've tried:
Replaced carburetor (and tried adjusting both hi-speed and idle screws on carb per instructions in owner's manual http://bsintek.basco.com/BriggsDocumentDisplay/msowGQ-K_ny7tH217FzoPu.pdf )
Tried new gas
Small amount of SeaFoam in fuel
Visually inspected fuel filter (screen)
Replaced oil

My question: Am I just not getting the mixture settings right, or is there something else in particular that would cause it to run inconsistently, especially on a hill?

 

[ILENGINE]

It clearly sounds like a fuel issue with the run problems, but lets look at a slightly different direction for a moment. this is an older flat head briggs, that has a problem with floating the valves after several years of use. Lets start by finding out what the compression is, and then think about finding the true problem.

 

[MDetam]

Thanks for the reply.

I tested the compression (with an older compression gauge that doesn't screw into the spark plug hole, but is pressed against it with a rubber cone on the tip). The compression read ~137 psi consistently, tested by pulling the pull-starter.

I also drained the fuel and removed the fuel tank and hose to clean and inspect. They were pretty clean already and fuel ran through the fuel line easily.

Is 137 psi in the right range?

 

[ILENGINE]

If your guage is reading correctly, you don't have a compression problem, so it is most likely fuel related.

 

[MDetam]

The tank, outlet nozzle and hose are clean. What else fuel-related could it be?
Just to clarify, as of today it runs without dying when choke is 90% closed and throttle is ~30% (even when tilted). I've tried making minor adjustments on the carburetor's idle and main valves for hours. Once it seems like it's running great (even for 5-10 minutes), I'll start to push it, and any deviation from FLAT ground (bumps or hills in any direction) makes it die.

 

[jakeamondo]

what replacement carb did you use 390323 ?

Why will my engine run only with the choke applied? | Troubleshooting - Repairs | Search | Frequently Asked Questions | Briggs & Stratton

open link and go to troubleshooting quick reference guide

 

[MDetam]

Yep, 390323. I bought it on ebay New Carburetor for Briggs Stratton 390323 394228 7 8 9 HP Engines Carb | eBay .

Thanks for the link. I read the page and the PDF, and so it appears that the problem resides somewhere in table 8, 9, or 11 but could also be in table 4 or 5 (due to sometimes having black exhaust smoke).

I don't think the issue is related to pre-carb fuel supply UNLESS it's the gas cap, however, I don't think it's the cap because it behaves the same with 1) the cap screwed on tightly, 2) the cap completely off, and 3) partially on. It may not be the proper gas cap though -- it doesn't thread on properly...

I don't think it's an air related issue as it behaves the same with or without the air filter assembled (even after dousing the pre-filter in oil and squeezing in clean cloth).

As an additional note, when the main jet is opened about 2 or more turns, the carb appears to leak a very small amount of fuel either from the lower mounting bolt or the screened hole next to it (vent?).

I'm thinking it could be related to the float in the carb, but it seems unlikely as the problem is the same with 2 different carbs.

 

[jakeamondo]

I had the black smoke issue and the leak from carb after installing new carb. That gasket at the carb was not sealed and gas was actually blowing out when I pulled start rope. tightening didn't help, finally I used permatex permashield fuel resistant gasket dressing item #85420 to seal it. I would fix leak that could be your problem. Sucking air after the carb will interfere with how the gas is drawn into the engine


Remove and inspect the spark plug. A wet plug may indicate over-choking, water in the fuel (see "Servicing the Fuel Tank"), or an excessively rich fuel mixture. A dry plug may indicate a plugged fuel filter (see "Servicing The Fuel Filter"), leaking mounting gaskets on either end of the carburetor, or a stuck or clogged carburetor inlet needle.

black smoke is two much gas and not enough air (running with choke on)

 

[jakeamondo]

another link showing carb bowl vent. Different carb than 390323 same principle

http://outdoorpowerinfo.com/repairs/briggs_large_one-piece_flo-jet_carb.asp

 

[MDetam]

I want to thank both of you (ILENGINE and jakeamondo) for helping me in the right direction. I finally got it working 100%. Without the link jakeamondo provided, it probably wouldn't be fixed. It was, however, a different page on that website that led me to look into the "tang bending" of the float in the carb.

For anyone who may happen upon this with the same problem...
The most recent changes that presumably fixed my issue:
- Bent tang on float so that it sat parallel to the top of the carb lid
- Adjusted clip that connects to the fuel-inlet needle and float tang so that there wasn't as much play. Previously, float would drop (low fuel), but wouldn't pull the needle out to let fuel in.
- Replaced all intake gaskets (incl. carb)
- Replaced spark plug


(still not sure what the problem with the original carb was -- prolly dirty -- oh well... fixed now.)

Thanks again!