Throttle stumble at small throttle opening

[Colorobo]

So after tuning 5 way to sunday, valves set Raceco specs . it runs awsome  except for a cough at just off idle to 1/8 1/4 throttle at low speeds. At the same throttle position at 40 50 mph nothing. Tps basline at .157 followed doccs guide. except bypass screws are at 1/2 to 3/4. Idle at 1100. I can put the headers with the crossover in front back on. Will it help. Thanks Rob

[gstallons]

 

ok . 

 # 1 the TPS is to be adjusted ( if you don't have the TPS jumper , you can measure at the pcm ) to 0.157 v at closed throttle , idle stop screw backed out & not touching , throttle balance rod unhooked . Then adjust throttle linkage , THEN after everything is PERFECT , adjust the idle stop screw to =.450 v . 

 I have some procedures ( somewhere on this site ) to give you advice on how to do this . Read , read and reread until you understand this . After your epiphany , you will be POd that you made something difficult out of something so easy . 

 Good luck & HTH

[Lucky Phil]

16 minutes ago, Colorobo said:

So after tuning 5 way to sunday, valves set Raceco specs . it runs awsome  except for a cough at just off idle to 1/8 1/4 throttle at low speeds. At the same throttle position at 40 50 mph nothing. Tps basline at .157 followed doccs guide. except bypass screws are at 1/2 to 3/4. Idle at 1100. I can put the headers with the crossover in front back on. Will it help. Thanks Rob

What are Raceco specs? ( 0.004" and 0.006"?)and whats the CO set at?

Ciao

[Desdinova]

I may have some input on this.   I'm so glad a still follow this forum even though I don't participate much anymore.

I had this very issue on my '02 Le Mans.   Now forgive me that I don't remember the exact spot because I solved this over 10 years ago, but either on the ball of the throttle cable where it attaches to the cam, or on the cam there was a bur that prevented the throttle from actually closing 100%.  It was closed about 99.9% but that causes EVERYTHING to do with tuning and the computer to be off just a little because the TPS is at 0 but the throttle isn't.   I don't remember exactly how I finally found this, but once I knocked the bur off, of course it ran like garbage, until I re-adjusted the TPS to where it's supposed to be when closed (I said it's been a while) and reloaded a map for my setup, and I essentially haven't touched it since.  

Hope this helps..   An easy test is get everthing setup as best you can.  Measure the TPS with the throttle closed.  Then take the cable off and measure again.  It should be the same.

[Colorobo]

Raceco specs .008 .010 exhaust. CO at 0.

 

 

[Lucky Phil]

3 minutes ago, Colorobo said:

Raceco specs .008 .010 exhaust. CO at 0.

 

 

Clearances are too wide for a road bike. Set them to what I mentioned above and see how it goes.

Ciao

 

[Desdinova]

59 minutes ago, gstallons said:

 

ok . 

 # 1 the TPS is to be adjusted ( if you don't have the TPS jumper , you can measure at the pcm ) to 0.157 v at closed throttle , idle stop screw backed out & not touching , throttle balance rod unhooked . Then adjust throttle linkage , THEN after everything is PERFECT , adjust the idle stop screw to =.450 v . 

 I have some procedures ( somewhere on this site ) to give you advice on how to do this . Read , read and reread until you understand this . After your epiphany , you will be POd that you made something difficult out of something so easy . 

 Good luck & HTH

YES YES YES !!!!   Now it's all flooding back..   "adjusted to 0.157 v at closed throttle idle stop screw backed out & not touching "  but even with everything backed out, the bur on the mechanism was preventing it from being really fully closed.   

[LowRyter]

I'd advise to keep the RPMs up and to replace the plugs it to gets too troublesome.

[LowRyter]

3 hours ago, Colorobo said:

Raceco specs .008 .010 exhaust. CO at 0.

 

 

.004 int and .006 exh  

loose ain't bad but not that loose

[gstallons]

14 hours ago, Desdinova said:

YES YES YES !!!!   Now it's all flooding back..   "adjusted to 0.157 v at closed throttle idle stop screw backed out & not touching "  but even with everything backed out, the bur on the mechanism was preventing it from being really fully closed.   

Uhhhh , can you explain this word burr and mechanism a little more ? 

[docc]

All good advice.  Although, the idle speed could be further considered. There is no TPS  target value that is critical for idle. Once all the other steps are completed, set the idle speed where you like it. That said, if you are using the bike's tachometer to set idle speed, verify its reading with guzzidiag. I have seen them read 300-500 rpm high. This translates to your 1100 rpm idle being 600-800 (no good!).

A couple other things to check out: First, connect an ohm meter to the TPS and slowly open and close it looking for a jump in resistance, or an open. The progression up and down should be smooth and progressive. Also, even the tiniest intake or exhaust leaks can be problematic. Last year, I found slightly loose vacuum taps ans dried out rubber caps wreaking havock on my Sport's state of tune. Performing a grooming session on your exhaust would be worthwhile. Loosen it all up and de-stress all the joints and junctions making sure they are well seated, tighten in a "star" pattern in steps starting at the heads. IMO, the front crossover just adds more places for exhaust leaks with no known benefit.

[Desdinova]

5 hours ago, gstallons said:

Uhhhh , can you explain this word burr and mechanism a little more ? 

Yeah.. it was a burr... nub, bit, edge, I think it might have been where the cable end hooks into the cam.   The only way to know for sure is to read the TPS with the cables connected and everything (idle etc) backed all the way off.   turn the throttle a few time to make sure it always comes back (by TPS reading) to the same spot.  Doesn't matter what the TPS reads at this point, just make sure every time you twist and let go, it comes back to the same spot.   Then take the cable off.  The TPS should still be at the same spot.  Manually run the throttle cam open and closed... the TPS should always fall to the same reading..      The problem with mine was now that I remember was there was a little burr on the cable end ball.  It was preventing the throttle from closing 100% which isn't really normally a big deal, except when you set the tps because the Tps is expecting you started at 0% open.

 

 

[docc]

Setting the TPS baseline should not be affected by the cable since it is on the left and the linkage rod is disconnected from the right throttle body to get that plate fully closed for the 157mV baseline.

Could affect the idle returning to same place every time, though . . .

[Colorobo]

Thats what I thought Docc. I think it might be a shaft seal. But why only affect at partial throttle opening. I sprayed starting fluid on bottom of Rh TB and it changed . any opinions. Rob

[docc]

Yeah, my shafts are pretty wobbly (and leaky), too . . .  

I even bought a set of lower mile throttle bodies, but got my Sport to stabilize securing the vacuum taps/caps and grooming the exhaust (leaks). Quite surprising to me , actually.