Pumping Throttle

[brushneckmatt]

Hey guys! Just finished rebuilding a 1994 XP. Have a slight issue I am hoping someone can help me with. When I throttle up to full speed I need to pump the throttle. Sometimes she sits back and then takes off. I want to get a steady increase of horsepower. I also noticed that full speed seems to want to sit at about 3/4 throttle. Any help would be appreciated. Thanks!

 

[POPPS]

You have a fuel delivery issue,,,either the fuel selector, gray fuel lines if you have them..or blockages in the carb,,,its also possible,,,but improbable that your pilot jet is too small or the popoff is too high,,,the latter situation would only apply if someone modified or tinkered with the carbs,,,since the stock jets and popoff are perfect,

 

[brushneckmatt]

No gray lines left. Everything was changed out. The carbs were cleaned and in good shape. I am leaning more in the latter modified situation. Maybe a cheap carb rebuild kit? I will have to get a tester and check the popoff pressure. Thanks.

 

[etemplet]

I'm with POPPS. Once the carb is on the main jet very little else will affect it's operation. If it is dropping off you have a fuel delivery problem. I'd pressure test the system back to the fuel tank. Pay particular attention to the water separater. I've found "new" fuel valves to leak internally, and check for a vent problem in the tank.

Fuel baffles can partially plug and make sure you do not have an "inline" filter installed. Good Luck.

 

[POPPS]

The last time i had this issue,,,i was water testing it,,,had same symptoms,,,ended up lowering popoff,,.they had tinkered with it,,,if you give it throttle from a standstill and it dies,,,the popoff is too high,,,if you have to feather,,,your pilots are too small.

 

[etemplet]

The last time i had this issue,,,i was water testing it,,,had same symptoms,,,ended up lowering popoff,,.they had tinkered with it,,,if you give it throttle from a standstill and it dies,,,the popoff is too high,,,if you have to feather,,,your pilots are too small.

I have an occiliation at full throttle on a 96 XP. It isn't a surge. About once every second or so, Peak then drop. It holds 55mph but I think it will do 57 if I figure that out. Pop-Off is probably 37psi which works well on the 787 GTXs.

 

[Lothsahn]

If the carb kits weren't genuine mikuni, get genuine mikuni and rebuild again. :-(. Aftermarket do not work well.

 

[brushneckmatt]

I don’t really know on the kit. Is there a way to tell? I will pull them and check the popoff pressure soon. I am thinking it is the combination of the 2 I am dealing with.

 

[mikidymac]

If you don't know if they are Genuine Mikuni or not then replace them. Genuine Mikuni will be $50 per carb not including needle ad seat, anything less is not genuine and give you nothing but trouble.

 

[brushneckmatt]

I am going to do that. Mine as well if I have them off anyway. I know my way around them so a quick fix would be nice. Vaca next week but then I will be back to it. I’ll have them shipped from OSD in the meantime. Thanks!