vangaurd 18hp hesitation stumble bog issue

[AdrenalineJunky]

I had a 02 max with this motor that ran perfect from idle to full stab and instant repsonse....it had about 70 hours on it when sold. Now my current 03 argo bought it with 70 hours has aboput 85 now and has horrible throttle tip in. Other than that it ides nice and low, and once underway motors is fine. Set the choke on half or so and its fine, so must be fuel related...or weak vac signal. I can see fuel spitting in carb when you stab it as it bogs right out. I pulled plugs thinking gaps were too big, and they were, but new gapped @ .030 made no difference. Carb and all passages and jets have been cleaned properly....was not nasty at all. At this point I'm ready to put a larger main jet in it....but was hoping for input or other ideas from some of you more experienced fellas on here. I also plan to adjust valves but they sound quiet except the very occasional very momentary click clack at idle. Thanks.

Vanguard correct spelling of topic title

[Obsessed]

The fuel tank sits lower in the argo than the max so the 18hp B&S motor is usually short on fuel if it's not running at high RPM or if you attempt to climb a long hill...best upgrade for that machine is a low psi (2-5) electric fuel pump mounted in line on top of the fuel tank...this is a cheap fix at about $60 and will make a big difference with starting, idleing, throttle response and running uphill....you can leave the factory fuel pump in place and use them together (in my experience)

Best of luck

Tim

[AdrenalineJunky]

I have yet to experience any fuel pump issue. I have been up and down very steep banks (although short) with no trouble. This stumble / hesitation is striclty a throttle tip in issue and does so with a full bowl of fuel. Yesterday I adjusted the valves and they were good, only one slightly tight exh on front cyl. I also installed new E3 plugs gapped to .030. I added 5 gals of fresh gas. No change in stumble. I swapped out the main jet from a 100 to a 137 which I had in my collection, nothing closer, and the stumble is much better, but I think it might be too rich @ WOT underway. Still idles like a sewing machine. Perfect. I'm wondering if the gov linkage is snapping open throttle too quick or with some sort of improper ratio of movement? Any thoughts appreciated. Thanks.

[Bazooo guy]

Did you replace the air filter?
When the engine is running and the choke is open will it idle?
Could be the flywheel key sheared and timing is off.
Does it ever backfire thru the exhaust or carb?

[AdrenalineJunky]

bazoo; idles perfect. Update...had to pull the big Main jet...way too fat and killed the power. I put the #100 original back in. The stumble is better after the carb cleaning once the motor is good and warmed up, but its still there....looks like I'll have to live with it. Its been mentioned that these motors without an accel pump are subject to this condition, some worse than others. I dont think its worth getting into a accel pump equipped carb at this point, but it would be nice to see what is available....anyone know of a set-up?

[Tomo]

hi
Vanguard engine weak vacumn siginal to carby will cause engine to suck not enough fuel this inturn causes the bog and or flat spot .
To verify this u have to do a leak down test ,blow by past the rings will stand out
The vanguard rings are narrow and have little depth into piston particularly the top ring this all causes problems for ring seal [short ring life due to poor construction ]
Dependinging upon age etc the hone marks may also be disappearing [wear]

Fit an accelerator pump carby from a 25 hp kohler horzontal shaft 28mm bore
Stock carb has a 26mm bore
Machine up an adapter plate out of alloy ,this replaces the vangueard plastic spacer and then use the kohler thick base gasket as the heat insulator block
Air cleaner is all kohler
U will not be able to use original governor ..

tomo