I have a 99 Softail that I recently purchased. It sat up for a while why the guy was deployed. When I got it it was hard to start when cold and was popping when you got up in the RPMs. the mods it has is

Cam (unknown specs)
Dynatek S6 Ignition
Dual Exhaust
Screamin Eagle intake
the guy I bought it from had everything installed by a shop and tuned.

When I got it I
Cleaned the carb including all the jets (had crystallized gas in the bottom of the bowl) the jet sizes in it are 45/185
installed new Petcock and drained all fuel and refilled (93 octane)
New Fuel Line
NGK iridium plugs (gapped to .040)
New Plug Wires
***** Out primary bearing and seal
changed all fluids and filter
cleaned tappet screen
cleaned and oiled air filter

After cleaning the carb and all the other maintenance the bike runs very strong and pulls very hard through all the gears and through the entire RPM range. the popping is gone however when it gets to around 90mph and just flattens out like its out of fuel. It does not pop or anything just goes completely flat. I can up shift and it is still flat.

I don't usually run 90mph but I know that it should run that or faster so I want to fix whatever the issue is so the bike is right.

Can anyone shed some light on what may be the issues with this?

 

I don't think my 09 Heritage runs much faster than 90.
I've had it at 100 once, but even that took some time.

Hows it run up 80?

Is there a reason to run it faster than 80 mph?
Not a good reason.

 

It runs up to 80 very strong and up to 90 very strong and then it like when it hits right around 90 it just goes flat.

No there is not any reason to run it over 80 except for that if it should run over 90 and there is an issue I want to get it fixed so that everything is running correct on the bike. Also if there is a problem I do not want to let it go and then it possibly gets worse and wont go over 80, 70, 60...etc.

 

probably nothing to do with your issue but NGK irridium plugs should be carefully gapped to Gap: .032" (0.8mm) as per manufacturers spec. your cams could be the culprit as far as limiting your speed to 90 MPH

 

Maybe the gearing somewhere was changed?

 

What you describe sounds like hitting the speed governor on a car, but I am not aware of HDs having one. They do have a rev limiter though. What rpms are you hitting?

 

Check your gas float in the carb. It may need to be adjusted. It may be set too lean.

 

What rpm are you running at 90? Could be gearing. My 07 will run 110 pretty easy and still seems has a little left. That's of course with no head wind..

I'll check tomorrow since I need to get up on the highway to get where im going, but if I remembered correctly I'm running 2600-2700 rpm between 75 and 80.

 

if under all other circumstances the bike runs strong then I would have to lean toward gearing or cam choice of the previous owner. if it is set up for low to mid range power without thought to top end the rev limiter could be kicking in at those speeds . that being said,I know absolutely nothing and that was a total guess. it sounds good though :-).

 

Try it without the air filter. I went through the same thing on a Kawasaki that sat for a few years. Drove me crazy. Did everything you did and cleaned the filter twice, no change. Took the A/C off, easily got over 100.