Power issue mid RPM

Hey all. Finally got mine back together. Having an issue with power. If I'm low on RPM and give it 40/50% throttle it acts like it's being choked out. The only thing I have done different is throw on some harley stock pipes. Once the RPM gets to a certain point..bam..power is back. I just put new plugs in as well. I did not gap them. Could the plugs be the issue? Bad gas?

The OEM HD pipes shouldn't make any performance differences. Mine would maybe "blubber" a bit more on heavy deceleration. Plugs may be worth a look to make sure gapped correctly to get the most mileage out of them. I thinking more in the direction of carbs. Have you sync the carbs lately?

Sync no...but i did clean them recently last summer.

Sync no...but i did clean them recently last summer.

x2 on plug gap, easy check.

When you say cleaned the carbs, they were removed from the bike? If so they almost certainly need to a good synch. At what RPM does this symptom disappear?

Have you modified the air boxes or added K&N filters? On my 07 after I did a double whammy where I opened up the air boxes after installing K&N filters it would "bog" down at certain RPMs while applying the throttle, then catch up and run fine. First I shimmed out the slider needles on the carbs, but eventually found a set of stock air boxes and swapped the modifies ones out and went back to stock. That cured my problem.

What speeds and what gear are you in when this happens, could be you are lugging the engine down, you cannot e going down the road at 55 mph in 5th gear and quickly open the throttle up on these bikes, they will stumble almost every time, now 3rd gear at 55 mph, crack the throttle, you best be hanging on.

Just a few thoughts.

Keep us posted on what you learn.

Yes i have had k&n on for a long time. I parked it in late October and it was fine. I just ran some seafoam and pulled the diaphragms out and sprayed in some carb cleaner...no luck. Anytime i crack the throttle at low RPM past id say about 30-40% it sputters BAD and acts like its not getting fuel. Fuel pump seems to be ok since i heard it clicking filling itself up.

Have you modified the air boxes or added K&N filters? On my 07 after I did a double whammy where I opened up the air boxes after installing K&N filters it would "bog" down at certain RPMs while applying the throttle, then catch up and run fine. First I shimmed out the slider needles on the carbs, but eventually found a set of stock air boxes and swapped the modifies ones out and went back to stock. That cured my problem.

 

What speeds and what gear are you in when this happens, could be you are lugging the engine down, you cannot e going down the road at 55 mph in 5th gear and quickly open the throttle up on these bikes, they will stumble almost every time, now 3rd gear at 55 mph, crack the throttle, you best be hanging on.

 

Just a few thoughts.

Keep us posted on what you learn.

You said you just got it back together. What did you have apart?

Have you checked the fuel filter?

I replaced that about 3 years back. Would it get so backed up that it would cause this?

I guess the correct terminology would be its "bogging down" when throttle is applied...it sputters for a bit then at a certain RPM it takes off.....

I have not done anything to the fuel system ...i replaced bearings in front and rear including steering stem...did some painting and some other odds and ends

Have you checked the fuel filter?

I replace that about 3 years back. Would it get so backed up that it would cause this?

Not normally, but it is worth looking at I think.

Other than when you roll on the throttle at low RPMs the bike seems to run fine?

Have you checked where the boots from the air box connect to the top of the carbs? Sometimes they are hard to get back on just right and you could have one that is not sealed to the carb throat properly or maybe the clamp is not tight, just some thoughts.

Yep..low rpms taking off its fine..but the more throttle you give the more it bogs down. But when the RPMS pile on, it catches and goes

Not normally, but it is worth looking at I think.

 

Other than when you roll on the throttle at low RPMs the bike seems to run fine?

Have you checked where the boots from the air box connect to the top of the carbs? Sometimes they are hard to get back on just right and you could have one that is not sealed to the carb throat properly or maybe the clamp is not tight, just some thoughts.

When you parked it last October was the entire fuel system treated with stabilizer. It sounds like your pilot jets are partially plugged.

No stabilizer. I did pull the spark plugs again...white as a ghost....its just not getting fuel....going to start with a fuel filter and take off the air boxes and see if the slides are moving

When you parked it last October was the entire fuel system treated with stabilizer. It sounds like your pilot jets are partially plugged.

You're going lean off idle. If I understand right it's been sitting with untreated fuel. It only takes a few weeks to gunk up the idle jets sitting with untreated fuel. It's a bit surprising it idles at all.

Time to clean the carburetors again. Sync them too.

I treat my fuel anytime it might sit for two weeks or more.

If you used a ethenol based gas what MiCarl said holds true. Time to clean carbs.

Does anyone think it could be an ignition issue? TPS?

Anything is possible, but the TPS is not a big failure point on these bikes. You can unplug and put an ohmmeter across it and rotate the throttle. The resistance should change smoothly and linearly...

No stabilizer. I did pull the spark plugs again...white as a ghost....its just not getting fuel....going to start with a fuel filter and take off the air boxes and see if the slides are moving

Does anyone think it could be an ignition issue? TPS?

You already found your own answer.

What Carl said! The coils have been known to go bad, but have you serviced the innards of the spark plug cap yet?? There are 3 tiny pieces inside the boot that can and will get corroded.there is a metal plug that unscrews and inside is a spring (Pay attention here son!) a disc, and a carbon resistive element. Do a search here to find out how to do a resistance check and how to disassemble. Also, you can buy a spark tester to determine if you are getting a hot enough spark. The spark tester is a little plastic box with an adjustable gap and you can purchase these from just about any automotive supply store and only cost around ten bucks. Don't quote me on this, but I think I remember the minimum gap being something like 0.108". Check the Yamaha TM that you can find in the Read Only Technical Forum.

The ignitor box usually does not fail but once again anything is possible...

If once the RPM gets up it has full power and goes, then fuel delivery to the carbs is not the issue. If it was the pump, filter or a clogged line it would not go fine at high RPM.

Ignition issues do not usually pick a mid RPM band to have issues with. It will usually not idle well or fall down at the top end.

The only thing left is dirty carbs. You might get lucky with a heavy dose of Seafoam, or Berrymans if it is really bad, in the tank and then run it where it does not like to run to force it to pull the cleaner thru the dirty circuits, then let it sit for a few hours. keep doing this routine to see if it starts to clean up, the only other option is to tear down the carbs and clean them good.

Thank you for the all the responses..you guys ROCK. When i figure it all out i will post back up!

Got the carbs off. Seem very clean. Going to tear into them this week. I did notice the Diaphragms (when pushing in the slide) seemed to be leaking air? Only 1 seemed very smooth in and out. Could that be the issue?

I revved the engine and they fluttered very bad and it almost died...

They should all flutter pretty much in unison. With the air boxes off the bike will not run that well but should run. When inspecting the diaphragms hold them up to a light and look for tiny pinholes...

Update*** tore the carbs apart...CLEAN. all jets you can see through....i do have a kit and new diaphragms on the way....but now I'm leaning to spark. Do these bikes have anything up front inside the fairing I may have forgot to plug back in that would cause this?

There is a little hose, goes to the left front carb manifold. It's a vacuum hose for the spark advance I think. Often times this one gets cracked. It should have a restricter in it as well if I remember correctly.