Throttle sync problems

[drswift]

Help!

My '04 dual spark RT had been running very rough for the last 3K miles. I just did a typical 12 mi. tune up and when I tried to balance the throttle bodies I kept getting totally disperate Big Brass Screw settings from left side vs. right. I'm now at 1/2 turn on the right and 3+ turns on the left to get closest to zero on the meter.

 

I pulled/cleaned and switched the ingectors and the BBS with no change. Coil sticks were replaced about 10K ago.

 

I'm suspecting TPS problems. Any other suggestions???

 

(My bike sounds almost just like what DonW was dealing with in his post from earlier today. Surging, rapid rpm drop at startup to the point of knocking and stalling.)

[cycleman]

Have you checked for any vaccum leaks? Take an unlit small propane bottle ( one used for sodering etc ). With the bike running pass the opened propane bottle around both intakes, throttle bodies. If the idle speeds up you've located the site of your vaccum leak.

 

Odd that it would just start running rough like you describe. Had the bike been stored for any length of time?

[drswift]

Bike gets run a lot. I have not tried checking for vacuum leaks. Will probably useWD40 instead of propane.

 

I'm also going to try the TPS "zero-zero" cable adjustment tomorrow.

 

 

[Haynes]

Getting right back to basics, are you sure that your throttle cables both have free-play while you sync with the brass screws?

[drswift]

Not much, but some.

[T__]

Dave, when you are doing a TBI balance you are just matching the pressure drop (vacuum) across the throttle plates.. That means things like TPS or injectors have no effect on the TBI balance..

 

With the big discrepancy you are showing on the BBS side to side that usually points to a problem with either the vacuum measuring device,, or a vacuum leak on the side with the screw turned in farther,, or coking of the throttle bores around the throttle plates,, or a problem with a throttle plate not totally shut (TBI cam not hitting the throttle stop)..

 

What are you using for a manometer? Any chance the hose or hoses to your manometer have a slight vacuum leak.. Have you tried switching sides on the manometer hoses?

 

On using WD-40 to find vacuum leaks.. The new WD-40 has the formula changed so it doesn’t burn like the original did so it is no longer a good thing to use for finding vacuum leaks..

 

 

Twisty

 

[Jerry Duke]

Could your cables be old and stretched?

[Michaelh]

Dave,

had the same problem a few years ago, PITA to be sure. Mine turned out to be tiny fine pebbles and a little road tar on the cable cam wheels that changed the throttle settings in small but meaningful ways. Look at the pulley wheels and clean. Good luck

[mrduck]

Went thru the same thing awhile ago, check your stick coils. One of mine went bad and I had the same problems! 04 RT

 

 

Don J

[Peter Parts]

snip

 

I'm also going to try the TPS "zero-zero" cable adjustment tomorrow.

 

 

With BBSs off like that, likely something is awry. A little bit off is normal. Hey, easy to forget what's connected to your vacuum ports - can be loose at the port or downstream. I always run with a TB balance line - a controversial subject, eh.

 

Idle stop is a TB factory calibration, not to be messed with without good cause and tech sophistication. Betcha a lot of machines have messed up TB idle stops because people think it is a normal adjustment like with carbs.

 

The cables, BBS, and idle stop are three variables you need to solve with two equations. Which is reason to ride with dual vacuum gauges under load.

 

You can explore imbalance of the butterflies by looking closely at vacuum balance at idle and the first increments off idle. Funny swings happening?

 

For sure, as Twisty1 says, always test your tools by switching sides with the TwinMax or vacuum gauges or better, just testing with a tee-fitting.

[Peter Parts]

Dave, when you are doing a TBI balance you are just matching the pressure drop (vacuum) across the throttle plates.. That means things like TPS or injectors have no effect on the TBI balance..snip

 

Twisty

 

I always thought the post-butterfly vacuum was partially reflecting the burn and other downstream cylinder effects. Is that wrong?

[drswift]

With the help of a great m/c gearhead friend of mine we did a reset the TPS, and balanced throttle stops on both sides. The right side was way off. We balanced the throttles off idle and across a wide range of rpms.

 

Checked for vaccum leak with a can of propane with nothing to show.

 

Our best guess is that there was 1.) not enough play in the cables, 2.) a big fault in the right side stop was causing me to try to compensate with the BBS.

 

We got it running great, but will have to wait until tomorrow to do a good road test and check out the surging at speed. For right now it purrrrrrs!

 

Thanks for all the great imput.

[Deadboy]

Great news!

[Peter Parts]

With the help of a great m/c gearhead friend of mine we did a reset the TPS, and balanced throttle stops on both sides. The right side was way off.

snip

 

Right.

 

Why was the right side "way off" and so the BBSs were way off, as you said earlier?

 

Somebody read all the stuff about doing a zero=zero and tried it and, as I suggested, couldn't do it accurately enough to replicate the factory setting?

 

That's my guess.