rpm's drop

[wills89fj1200]

When in 4th gear or 5th and full throttle, the engine accelerates fine until 5500 rpms, then drops to 5000.  The drop is very noticeable.  Then it picks back up and accelerates fine.  Seems like maybe an ignition problem but not sure.  What could it be.

[FJmonkey]

When in 4th gear or 5th and full throttle, the engine accelerates fine until 5500 rpms, then drops to 5000.  The drop is very noticeable.  Then it picks back up and accelerates fine.  Seems like maybe an ignition problem but not sure.  What could it be.

I can't help myself.......Maybe a limp wrist?.....Just for fun, had to shoot on this one, no harm intended.

[wills89fj1200]

Lol

[turbocamino]

   I'll have a stab at it ..if your saying that you are keeping the throttle in the same spot and its losing RPM or bogging down....it may certainly be a carb related flat spot due to a jetting issue.

[wills89fj1200]

Just rebuilt and jetted Carbs so I don't think so.  Also in 3rd gear and lower it does not drop.

[Harvy]

Just rebuilt and jetted Carbs so I don't think so.  Also in 3rd gear and lower it does not drop.

hmmmmm...interesting!

My '91 started to do the same thing at around 6000, then evenually it would not run past 6000. It wasn't the carbs. I replaced plug caps and leads, but it didn't get any better. I eventually bit the bullet and bought a Dyna2000 ignition system, Dyna coils and plug leads and boots.

6000 comes and is left behind very quickly now!

I'm not saying its the same as your symptoms...... but its either carbs or ignition and if you have done the carbs correctly, you are left with only 1 choice.


Harvy

[racerman_27410]

what jetting ? 

adjustable needles ? what position ?

did you also replace the needles and emulsion tubes ?


Murphy's law # 2    ..... the last thing you touched is probably the thing causing you trouble.


KOokaloo!   

[Pat Conlon]

Murphy's law # 2    ..... the last thing you touched is probably the thing causing you trouble.    

LOL Frank, This is sooooo true...

What did you set the float heights at?  Quick, you should know the answer....I bet you didn't check them huh?

Lower your floats, they're too high. According to the Factory Pro folks, the Mikuni CV's are notorious for having high floats which is normally not a problem, that is until you run fatter jets. ...yea, I bet a jelly donut on the float heights.

[racerrad8]

Here is the float height setting; http://www.fjowners.com/index.php?topic=3592.msg30781#msg30781

I do know he just install the parts I sold him and was instructed on where to install the needles and the jetting is correct. (from memory...117.5, 40.0, adjustable needles)

It might be worth checking the carbs one more time for proper settings & adjustments, but after that it is off to the ignition system. Make sure the vacuum hose for the ignition advance is good and does not have a hole which will allow the timing to retard due to a loss of vacuum.

Randy - RPM

[Dan Filetti]

Make sure the vacuum hose for the ignition advance is good and does not have a hole which will allow the timing to retard due to a loss of vacuum.

Randy - RPM

I was thinking the same thing.  It's at higher RPM/ stronger vacuum that it makes a difference.

Easy thing to check.

Dan

[wills89fj1200]

The jets that might need adjusting would be the adjustable needles.  Randy said that I might have to go down 2 or 3 clips.  I set it on the 2 nd down from center.  But at that high of rpm could that really be the problem?  I thought the needle key was for like 1/4 throttle.  I could be wrong.  This is not a big problem either, bike runs good but only does this in high gear with throttle wide open.  Really don't need to be in 5 th gear at 5500 rpms anyway since its just a little over the speed limit, LOL.  Thanks everyone, ill try the needles first then go from there.

[carsick]

  It's at higher RPM/ stronger vacuum that it makes a difference.

Owner states full throttle at 5500. Shouldn't be any intake vacuum to advance the ignition given those parameters. If this were a cruise condition I would agree with the vacuum advance statement.
What happens if this point is passed at less than full throttle? Get on a different carb circuit with less throttle opening. Run through that range with a little choke on, figure out if it gets worse/better, is it rich or lean? WOT is using the main jet and float level to meter fuel. Needle is out of the picture by then. To actually lose RPM is pretty severe at WOT, can you hear/ feel a misfire?

[Pat Conlon]

The jets that might need adjusting would be the adjustable needles.  Randy said that I might have to go down 2 or 3 clips. 
I set it on the 2 nd down from center........  

You set it 2nd down from the center? Really? Would you mean that you set it on the lowest clip? 2nd down from the center?

[wills89fj1200]

I meant I'm down one and can go one more clip down.  What vaccum hose do u guys mean to check?  Still have a lot to learn, first bike I've owned or worked on.

[RichBaker]

Should be 2nd groove from the top.... you're too rich on the needles.  

The pilot jets and mixture screws(also idle air correctors) affect closed throttle to ~1/8th throttle, pilots and needles affect 1/8th to ~3/4th throttle, mains start affecting things ~1/2 throttle or so, and are fully in at WOT.... more or less, there is some overlap.