Power issue mid RPM

Been there done it. Has nothing to do with it..actually made it worse

If this bike ran good back in October and the only change you did to it was install harley mufflers, I guess that is were I would go back to. I would put stock mufflers back on and try it. If all your plugs are white then the problem is affecting all 4 cyclinders at the same time. Usually if carbs are dirty you will always have one or two carbs that arn't to bad and plugs will read different. I am starting to believe problem is outside of carbs, but where.

99.9% sure i have FOUND the problem. I took the TPS off the carbs...set the ohm meter and turned the tps with my finger. Right around 2.0 its cuts out and goes to O.L. After a bit of research it seems the TPS has a break in the linear reading...which makes sense...sooooo....ill let yall know tomorrow

TPS is in...and SAME RESULT...im about to set this thing on FIRE. Still waiting on ECU since they sent the wrong one

TPS is in...and SAME RESULT...im about to set this thing on FIRE. Still waiting on ECU since they sent the wrong one

So here is a thread over on the Delphi forum that sounds much like your issue. I know you have been through the carbs, but this fellow has made an interesting observation, although he has not proven his theory out yet. May be a good idea to keep an eye on his progress.

http://forums.delphiforums.com/vrider/messages/16516/1

Yep! Looks like same issue....I have an ECU on the way tomorrow. So if that does not work i am going to cave in and take it to a dealership.

Idles Fine...Revs Fine...But any load on the motor it completely bogs down...sometimes will fire a few times with the throttle wide open. High in the RPM band it takes off, but not in high gears and low RPM

List of things i have done:

-Fuel Pump

-Fuel Filter

-Rebuilt carbs (New float needle valves, new jets, new diaphragms)

-TOTAL Clean of the carbs (soaked in carb cleaner)

-TPS tests OK

Idles Fine...Revs Fine...But any load on the motor it completely bogs down...sometimes will fire a few times with the throttle wide open. High in the RPM band it takes off, but not in high gears and low RPM

So reading your last post and going back to my first post in this thread see post #5 ,

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.

Are you sure you are not expecting the motor to do something it just will not do, these bikes are not geared to where you can get on the throttle very hard in 4th or 5th gear at slow speeds.

No....this is not a speed thing. Its like someone turns off the gas/ignition....0 power...Its at the same point in the throttle everytime. Comes out of it at high RPM..stumbles for a second then takes off like a rocket.

Would taking a video help at all?

Silly question how is your compression?

Living life one curve after the other. Vroom scooting, thru the countryside.

Have not tested it..assuming its fine. I parked it at the end of October and it was running perfectly fine.

Silly question how is your compression?

 

Living life one curve after the other. Vroom scooting, thru the countryside.

Here is a video I just made. I just cannot tell if this is a fuel delivery or ignition issue? It feels like the timing gets thrown off at a certain point in the throttle.

https://www.youtube.com/watch?v=9AguVmw_m8w

While it never hurts to do a compression check I don't think that's your problem. Low compression usually begins to show up in hard starts. Yours started right up and the starter sounded like it was working against compression.

Most of the electrical doesn't care about load. The ignition module does calculate load from the rpm and TPS. That could be the problem (or bad pickup or TPS sending bad or noisy information). I believe you replaced the TPS. The only thing the ignition module does in reaction to load is retard the timing. Excessively retarded timing makes a kind of unique sound and I don't hear that in the video (although your pipes make my speakers buzz and might mask it). If it's bucking and kicking it's probably not timing - retarded timing runs silk smooth.

Your virgin snow looking spark plugs SCREAM lean.

The way it runs under load is consistent with being lean, but farther up the throttle than I thought the problem was. You're in the mid-range and mostly off the slow jets. You need to be thinking needle jets, jet needles and main jets.

You say you replaced the jets. Did you replace the main jets too and are they genuine Mikuni jets? If they came in a Yamaha package they are. I have run into problems with aftermarket jets.

You also say you replaced the diaphragms. From Yamaha you get the whole slide, so I assume you went aftermarket. What did you use?

That reminds me alot of when my bike had a hair line crack in one of the slides, and a bad diaphragm on another. That is what it sounds like to me I don't know if your slides are the same as mine but just a thought. If the slides aren't moving correctly that could cause it to run lean on one or 2 carbs, I am by no means a mechanic and most of what I have learned on my bike has been from people on this site and by trial and error.

This started after i put the front and rear end back together. I had not touched the carbs and it was doing the same thing. I used jetsrus for the jets. Yamaha diaphragms. Slides are good. No cracks.

Also it doesnt buck and kick....once it gets into that no power phase it stays there. If i back off the throttle to about 25% it regains power again

While it never hurts to do a compression check I don't think that's your problem. Low compression usually begins to show up in hard starts. Yours started right up and the starter sounded like it was working against compression.

 

Most of the electrical doesn't care about load. The ignition module does calculate load from the rpm and TPS. That could be the problem (or bad pickup or TPS sending bad or noisy information). I believe you replaced the TPS. The only thing the ignition module does in reaction to load is retard the timing. Excessively retarded timing makes a kind of unique sound and I don't hear that in the video (although your pipes make my speakers buzz and might mask it). If it's bucking and kicking it's probably not timing - retarded timing runs silk smooth.

 

Your virgin snow looking spark plugs SCREAM lean.

 

The way it runs under load is consistent with being lean, but farther up the throttle than I thought the problem was. You're in the mid-range and mostly off the slow jets. You need to be thinking needle jets, jet needles and main jets.

 

You say you replaced the jets. Did you replace the main jets too and are they genuine Mikuni jets? If they came in a Yamaha package they are. I have run into problems with aftermarket jets.

 

You also say you replaced the diaphragms. From Yamaha you get the whole slide, so I assume you went aftermarket. What did you use?

Also..thanks for all the help and suggestions! This is very frustrating to me since i can usually figure things out pretty quick. This is just something that is boggling my mind!

Have you tried to run that video scenario with the choke pulled out? I would think that it would run like crap but if it changes the mid-power band it might help with diagnosis.

I have not gone back and read everything you have done in detail but it sure sounds like a lean condition. I just don't believe that changing jet sizes and etc. should have been necessary. I've run all kinds of different mufflers on these bikes with no such problems. Have you actually sprayed around the carb boots and etc. with maybe carb cleaner or something to see if it changes your RPMs and therefore would indicate that you are sucking air? I have that happen once and found that the boots were not seated properly on top of the carbs. I found that I was actually over tightening the clamps and it caused them to slip up a bit on the back side and they were sucking air right at the top of the carbs.

Here is a video I just made. I just cannot tell if this is a fuel delivery or ignition issue? It feels like the timing gets thrown off at a certain point in the throttle.

 

 

https://www.youtube.com/watch?v=9AguVmw_m8w

I notice in your video that you have removed your stock air filter boxes and replaced them with after market units. I might be way off here but try hooking your over flow lines and stock boxes back up. As Goose mentioned them lines need to draw vacuum to work properly.

New computer installed....same result. Im caving and taking it in. Ill let ya know

Wild problem, I'm on the carb wagon, just don't have any definite answer for you...

Try putting the original air boxes back on,,, bet it is that easy! Or restrict the airflow on the cones with some tape to test it out.

I want to thank MarCarl.....Yall can publicly humiliate me now....STOCK AIR-BOXES BACK ON...SOLVED....

Im going to go jump the bridge now for wasting everyone's time.....I guess the airflow is SUPER sensitive:doh::doh::bang head::bang head::bang head:

THANK YOU TO EVERYONE.....

Try putting the original air boxes back on,,, bet it is that easy! Or restrict the airflow on the cones with some tape to test it out.

Congrats for finding the issue, please re-read my post the 5th in this series.

[/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.

QUOTE]

 

Air flow or air volume is very critical.

I would have went to zagger for his suggestion....

Living life one curve after the other. Vroom scooting, thru the countryside.

Late to the party lol

I would have went to zagger for his suggestion....

 

Living life one curve after the other. Vroom scooting, thru the countryside.

Sometimes we're like kids and need to be told more than once.

I really don't think it my fault though, I think Bongo put my brain in gear for this one, I think he mentioned something along this line in another thread, I think.

In the process I think we all learned a lot. I'm going to have to review the thread to decipher exactly what it was that we learned, but hey eh?