16 HP vanguard runs rough

[Cdwamsley]

Hi Guys, My Max II has a 16 HP vanguard that wants to run rough and surge and almost stall unless I give nearly full throttle. It seems to happen after a rough bump. Sometimes it straightens up and sometimes not. I have a new gas tank with new fuel, new gas lines, new filter, have cleaned the carb and needle valves, when I put it back together it runs fine until I hit rough terrain and the Max gets jarred around. Does anyone have any ideas, Float sticking? fuel pump problem? I am stumped, and I would like to fix the problem myself, and not have to take to a dealer.

[luffydog]

how does the plugs look? does it have the anti-after fuel device on if it does it might be that it losing power just a bit every so often to make it cut out. might be just the start of a coil going bad. v-twins will run good and smooth one cylinder with out to much notice. have to kill one cylinder at a time to find out which one is bad. lets says you kill cylinder #1 and there is no change you know cylinder #2 is ok. then you kill cylinder #2 and it runs rough or stalls you that cylinder #1 is the prob. just maybe getting gas that has water in it from the tank at times. how about when you go hill backwards and forwards and change? how about it when its under a load does it miss out or lose power?

[Cdwamsley]

OK, no water in the gas, new plugs, not a "fire problem" I did adjust the idle mix needle valve and it did help, still has a little hesitation when you give it the throttle. I don't see any other adjustments on the carb besides the idle screw. Seems to have good power , just not a smooth run at low throttle.

[racerone3]

Chet,
Been trying to keep up with you on here, but this post slipped by me. sounds like the diaphram in the fuel pump may be to blame. I will dig around and see if I have spare that you can try. PM me your address and I will try to get one headed your way

[Jeff t-boss]

These guys (as well as you) have pretty much covered all the basis. The question that comes to my mind is; does this motor have an oil sending unit? If so, it could be weak or faulty. I don't remember if they are normally open or closed, so I suggest starting the engine and unplugging it. If it keeps running, you can try and take the thing for a short spin to see if the problems go away. Or to be on the safe side, remove it and attach an old fashioned mechanical gage to the port and run the engine to see if its building enough oil pressure (1-4 psi). If the oil pressure is OK, then it could be the sending unit. Also, that HP Vanguard is designed to operate on angles less than 15 degrees. Granted, I have had mine on alot steeper angles without any problems. Hope this helps.