Needs some help with a 25 hp go devil longtail. I was running it saturday afternoon scouting for a new hunting spot and it ran fine. Then sunday morning when i get to the ramp it started up fine but when i put the prop in the water it bogged down. I put the prop up and let it warm up for a few mintues and then put the prop back in and it happened again. When its out of the water it will run fine and the motor will rev all the way up but when i put the prop in the water the whole thing bogs down and wont push the boat beyond a crawl even with its at full throttle. Does anyone have an idea of whats causing this problem.

I would look for either a cylinder missing, or a clogged jet/ vacuume leak on your carb.

I have a 16hp vanguard go devil and it will run suprisingly well on one cylinder as long as it's not under a load. Put a load on it and it bogs way down.

Carbs will do similar things with a clogged jet or a vacuume leak.

Remember bro, it's a lawnmower engine after all!

1) check fuel lines and bulb for cracks. check fuel filters and change if needed.
2) see if its running on 1 cylinder. pull 1 plug wire at a time and determine if one of the cylinders isn't firing.
4) check for fouling of plugs that would prevent a good spark (blue spark should be able to jump about 1/4 of inch when plug is held close to the frame). White sparks won't ignite as reliably.
3) run small single strand wire through each jet of carb after spraying carb cleaner. run compressed air (about 100psi) through each jet after spraying more carb cleaner. remove float and needle valve to make sure teh needle moves freely.

if you don't fix or diagnose your problem after the above then you likely have an ignition problem which can be difficult to diagnose (either coils or speed advance module).

good luck

I've had the same problem as you are describing and in my case I found that it was either water in the gas or a fuel delivery problem. I make sure I run good, fresh gas in it every time and I put an electric fuel pump on and my rig has never run better! So yes, check for leaks in your fuel line. Check your gas for water. and check your filters and plugs. if those arent the problem then you need to take it to someone who can diagnose your problem more..

thanks guys for the help. im working on the motor right now and it seems to be the left cylinder isnt firing.