78 intruder bogging after half throttle.pls help b4 snow hits!!!

[danmiller369]

the sled was running great. i ran it hard for 5 hours straight. going 55 threw old bean feilds hitting drifts on the golf course and it ran flawlessly. we took a break and on my way home i noticed it bogs after half throttle.

i checks all fuel lines and they are tight. also checked the airbox connection to the carb and that seems normal too. the gas cap seal was out of line a bit and straightened it out. we have no snow as of right now so i cant really test it. should i just change the plugs and wait for this snow storm to come through or check something else?

[jimvw57]

There should be a vent under the dash that sometimes gets pinched off, should be open.  Also should be a weight on the end of the fuel pickup tube in the tank.  could be a carb needle and seat leaking or has dirt in it, that will make one cylinder flood out and bog until it burns clean.  Possibly snow sucked into the airbox, or a worn belt... I'm sure there are other ideas too. 

[danmiller369]

inside the fuel tank there had been no hose or weighted pick up since I've owned it. the carbs look greasy for some reason but again the lines look and feel tight. the lent line looks clear.the belt is fairly new(this year). the air box was clean.

how do I check this needle and seat? also the boots from te carb to the engine will need replaced soon. would that cause this?

[jimvw57]

It could, Once they warm up, they might start leaking. Any air that gets in besides what comes through the carb will be just air. That will cause the motor to run lean, which makes it run hotter (oil helps cool; these things down) Higher temps will melt pistons and cylinders in a hurry.  Also can cause hard starting if they leak bad enough.

Leaking needle and seat in a carb will cause flooding when you try to start them warm (after they have been sitting a short time) but may not be noticed on a cold motor (say overnight) as it usually takes the choke or primer anyhow. Also if the anti-siphon valve isn't working, a needle and seat failure will drain the gas tank.
my 4/6 has a bad needle and seat  right now. When I shut it off, I get a small amount of gas leaking out and then it stops. (drains the line from the fuel pump to the carb)  it then starts hard with one cylinder flooded and no gas in the lines.

[mswyka]

Check your compression when the engine is warm.  I had the same experience on my 79 the first year we got it before we put in new pistons and rings.

[danmiller369]

well my lines have fuel in them. could a fouled plug cause this? also what range should my compression be? or can I just do the good old thumb over the spark plug hole compression test?

[jimvw57]

Compression below 100 PSI is not good.  120 is about the norm on an older sled. he main thing is to see if they are within 10% of each other If not, you could have a problem. Make sure you block the throttle wide open and pull it over until it stops getting higher.

Fouled plugs or once plugs are flooded can cause issues. best to replace them with new ones.

[jimvw57]

When the hose fell off inside the tank on my Invader, I had problems once the fuel level go below about 1/2 tank. it tended to slosh around enough on corners and hills to the point where the pump would suck air.

[bryan_damone]

A leaking needle and seat can be identified by attaching a small piece of tubing to the fuels inlet. With the carb upright, you should be able to blow air through the tube with your mouth. Flip the carb upside down (closing the needle valve) and you should not be able to blow air through the tube. If you hear air moving with the carb upside down, your needle and seat are leaking. If it is a very minor leak, you may only experience flooding problems when the fuel tank is full as there is more pressure head on the needle valve.