I have a highly modified 1987 10th anniversary low rider and I am having a problem. In 1st and 2nd gear it runs up to 7000 rpm and as soon as I grab 3rd 4th and 5th it falls on its face like it is starving for fuel and I know that isn't the problem I have ruled that out and put in a new single fire ignition module in and no change . Maybe the coil ?

 

Clutch is slipping

 

do you have the stock petcock? if so there is a good possibility you're starving

 

How did you rule out the fuel? what carburetor......?

 

Gas cap vent clear?
Scott

 

^^^^^
Gas cap vents can be a real pain and you never think about them

 

I don't have a pet **** I run a ballvalve1/2 inch and big fuel lines also ,i took bowl off and watched the fuel come into the bowl and the float and fuel flow was good also cleaned all jets . I run a super e with thunder jet . Alreadd checked the gas cap . And no the clutch isn't slipping . When a clutch slips you can still Rev the bike up I've blown a few clutches so I know how they act . So you all have anymore ideas

 

Seeing that you have a E carb, the next time it happens immediately shut off the fuel valve and shut down the motor. Pull over and pop the float bowl. It's easy enough on an E.
Does it happen if you only take up to 6 k?
I don't think your ignition will cause it. I still believe it's fuel related. What's your jetting, including the thunder jet and are you using an external air bleed. If your running it that high in the rpm range (in which i don't recommend) you might have to install an external air bleed if you don't already have one and you should also plug the bowl vent that is open to the face of air cleaner. I believe on the S&S web site there is documentation on how to convert to the external air bleed.... Or you can call their tech support....

One more thing. If your are going to consistently push the motor to 7k i would suggest bringing it to a reputable Indy (one that's been around since the shovel days) to dyno tune your motor...... Otherwise it probably won't last as long as you would like it to......

 

1/2" ball value? I'd like to see a pic of that. spark plugs? main jet? air breather? sometimes a venture stack placed sideways the air flow will create a suction and prevent air from entering the motor. leaky intake? exhaust pipe?

 

Doubt you are running to 7K. If you are running a tach, you might want to check it. Either way, you say highly modified FXR. What motor and cam? Chain drive? Gear ratios?
You say falls on its face in upper gears....does it bog? Sputter? Sound fine but just isn't pulling up there?
Not enough info here, but if this is a big motor, the E may be be not able to pull enough air at higher geared, higher speeds and is running out of air to pull any harder as motor demands increase. In other words, first and second gear, at those slower speeds, the air velocity, AFR is nice, but motors air demands at higher speeds are not met.
Other possibilities are running out of fuel at high speed demand. Not fuel flowing from tank to carb, which you have already verified is working, but too small of a main and TJet.
Other possibilities are trans and final drive gearing. You bang first and second, it's pulling nice and hard, but the rest, once you shift are too low numerically and its fighting uphill to pull strong.
Have you tried it with different levels of fuel in the tank? Any chance your ball valve isn't working properly? I have always run petcocks on my modified motors.
It sure has the symptoms of vapor lock or fuel starvation, but hard to tell on the net.
Electrical is a possibility (coil-inspect for cracks), also a loose (bad) plug wire, sparkplug, loose battery cable (fine at low speeds but high rpm vibration loosens it and cuts power intermittently to the motor), or loose wire or ground.
A good dyno session would be in order as said.