Jump to content

Poor Low Speed Running


Recommended Posts

Hello Guzzisti,

 

I've been troubleshooting unsuccessfully to solve this problem, so any input is greatly appreciated. This is about a 2003 V11 LeMans, 31K wonderful miles.....

 

At a very low throttle opening, the engine spits back, backfires, stumbles. This seems to be independent of engine load or RPM....rather, directly related to throttle position.

 

I first noticed it while the bike had a Power Commander installed. I removed the PC, reverted to the stock ICU. I've done the full set-up for TPS, throttle body balance, etc, per instructions posted elsewhere on this marvelous forum. No differenec, not better or worse.

 

I then re-installed the Power Commander, and the problem is still unchanged. Adjusting the PC low-range mixture to full rich has no effect.

 

I've read on the forum about air leaks in the throttle bodies, but I've all but ruled this out, after close inspection shows no unusual slop.

 

HELP!!!

 

Thanks-

Fred

Link to post
Share on other sites
  • Replies 30
  • Created
  • Last Reply

Top Posters In This Topic

Did you re-map the Powercommander ECU ?Also, have you been fiddling with knobs on the exterior of the PC ecu? The shop that re-mapped mine said to leave them alone. You cannot have any worse low speed problem than mine. The shop that did mine took one shot and cured ALL my troubles.

p.s. My bike's performance went to hell after synchronizing throttle bodies and t.p.s. adjustment. Then the bike was fixed by re-mapping by a qualified technician.

Link to post
Share on other sites

In general, I have not had good luck with adjusting my PCIII with the exterior knobs either. The last time I had a similar problem, I did have cracked intake boots (you can usually see the cracks visually or try spraying them with a little carb cleaner when the engine is running to see if it stumbles fm the cleaner)...but by the time I changed them, I'd jacked my PCIII settings all up with the knobs. In the end, I hooked it up to my computer and reloaded my old settings (with richened low range) and the problem was solved. That's what I'd recommend you do if there is not a place nearby that can set it up for you.

 

Reset your PCIII to your original settings...if that still runs lean at the low end, save it to another file and richen the low band up to wherever the engine runs correctly. In my case, the "richer" program for pipe and airbox mods fm the PCIII website was still too lean in the 3000-3750 rpm range. k

Link to post
Share on other sites

If you have a reputable Guzzi dealer in the area I would take it there to be hooked up to the computer. Sometimes its better to just fork over a little money up frony to find out whats causing the problem than to try adjusting everything sort of blindly. That Guzzi computer is a pretty cool thing, my dealer has one & he just hooks it to the ecu & it tells you just about everything.

Link to post
Share on other sites

Since the issue seems throttle-position dependent only, have you considered the TPS? I don't have anything useful to say on that topic, other than - I know there have been some past threads that looked helpful for troubleshooting/replacing this bit.

 

I haven't tried playing with the buttons on my Power Commander, but as others have said, changing values by using the PC software is very straightforward. I've put a straightpin head into the throttle handgrip, alongside a piece of tape on the housing, marked off in measured intervals. The intervals were translated to % opening by calibrating with the PwrCmder software. When I'm riding and notice a stumble, I note throttle position and rpm, and tweak the appropriate cells at a later date.

 

Good luck.

Link to post
Share on other sites
Hello Guzzisti,

 

I've been troubleshooting unsuccessfully to solve this problem, so any input is greatly appreciated. This is about a 2003 V11 LeMans, 31K wonderful miles.....

 

At a very low throttle opening, the engine spits back, backfires, stumbles. This seems to be independent of engine load or RPM....rather, directly related to throttle position.

 

I first noticed it while the bike had a Power Commander installed. I removed the PC, reverted to the stock ICU. I've done the full set-up for TPS, throttle body balance, etc, per instructions posted elsewhere on this marvelous forum. No differenec, not better or worse.

 

I then re-installed the Power Commander, and the problem is still unchanged. Adjusting the PC low-range mixture to full rich has no effect.

 

I've read on the forum about air leaks in the throttle bodies, but I've all but ruled this out, after close inspection shows no unusual slop.

 

HELP!!!

 

Thanks-

Fred

I'm having the same problem, so I replaced the gas and the problem is less but still there . if you find the solution please post it ,and I will do the same.
Link to post
Share on other sites

PROBLEM SOLVED!!

 

The problem was that the RH throttle body was NOT fully closed when I set the TPS to 150mv.

 

The instructions posted on this forum caution you to ensure that the fast idle cam is relaxed fully. However, upon closer examination, I found the small cam roller was still in contact with it's stop, even with the fast idle lever (and cable) fully relaxed. However, the throttle butterfly was still NOT fully closed.

 

There is a small screw on the RH throttle body, head facing downward, that indexes the fast idle cam roller. I released this screw, which allowed the throttle butterfly to close fully. I then tightened the screw so that there was just a very small clearance between the cam roller and it's stop.

 

Then, set the TPS to 150mv, throttle balance, idle set up and air bypass screw set.

 

My bike has been transformed. I suspect that it was never set up properly from the dealer, as it now gets better mileage, and clearly runs stronger, and smooth as glass.

 

Fred Meyer

'03 LeMans

'54 Norton International

'48 Sunbeam S7

'66 Ducati Sebring

etc etc

Link to post
Share on other sites
  • 3 weeks later...

Yep, me too.

 

Excuse the below novel... but I wanted to make sure I covered everything I did... I don't get stumped easily, but this one has me.

 

Or at least similar. Mine can best be described as UNDER LOAD it spits, backfires and stumbles.

 

- I talked to Greg at Moto-International and he had a VERY good suggestion of checking the connectors on the injectors for schmootz. Well I did that, they were clean.

 

- Today I started from scratch. Took off the balance rod, and noticed that like someone else posted, my right butterfly was not totally closed, but in my case it was just a crumb of crud or something..

 

So, to date.. what I have done... and FYI.. I have the VDST software and the PCIII Software.. and everything checks out, or seems to.

 

- Checked the Valve clearance (cold). Hadn't done it in awhile, left exhaust was just a smidge snug, so I made it right. (World settings)

- Adjusted TPS to 150mv and let it lightly slap closed a few times to insure it was at 150mv.

- Hooked up balance rod. Insured TPS still at 150mv

- Sent ZERO map to PCIII (same as disconnecting it which I have also tried in the past to figure this out.)

- Closed bypass screws and hooked up mercury tubes.

- Used left idle to bring TPS up to 500mv

- Started and adjusted balance adjuster to balance tubes.

 

So here's where I am...

 

Vacume is balanced at idle and at high RPM almost perfectly. Idle voltage on TPS 500mv Bypass screws are still closed.

 

So what's the problem you say??? It's idling at nearly 2000 rpm!!!! and...

 

....... If I try to ride it, as soon as I let out the clutch it starts kicking, sputtering, gagging and stalls.

 

I can back the idle down (using the left screw) and at about 200mv the idle is about right. but....

 

.......If I try to ride it, as soon as I let out the clutch it starts kicking, sputtering, gagging and stalls.

 

 

- Messing with removing or adding gas via the PCIII in an attempt to make it worse or better... doesn't really change anything.

- Opening the bypass screws has some affect on idle speed, the right more than the left, but the result, no matter where it idles or why it..

 

 

.......If I try to ride it, as soon as I let out the clutch it starts kicking, sputtering, gagging and stalls.

 

 

I'm stumped, baffled, bewildered, be-bothered and be-mildred.

 

 

Oh yeah, one last and very frustrating thing.. With or without the PC inline or just Zeroed... as long as I'm not "in gear getting ready to take off" I can blip the throttle, rev it up, whatever. It sounds and responds perfectly!!!

 

So to summarize, besides it not wanting to go... With everything set as it should be, Idle at 500mv, Carbs Balanced, screws out as far as 2 or closed doesn't really matter, it idles way too high, and as soon as you put it in gear to go.... it craps out.

 

Making any normal adjustments (left idle screw mainly) to correct the high RPMS... just corrects the high RPM's.

 

I think it's next stop... Moto International, but thought I would post here to see if anyone had any clues of something I hadn't tried.

 

By the way... this started happening all of a sudden. I had been riding it to work everyday, all was fine, then one morning... I started it.. tried to pull out to go to work and couldn't. I also, last week, -Checked/Cleaned/gapped old plugs... no change so put in new plugs as part of this process.

 

Miles

Link to post
Share on other sites
air leak between the TB and manifold? are you SURE everything was backed off when you set the baseline to 150mv? has the "crumb of crud" returned?

 

Checked for airleaks, actually went around checked everything for anything loose. Found a couple exhaust bolts that needed tightening, but nothing affected the overall outcome. Checked the boots. Cleaned the throttle bodies.. and yes double checked they had full travel.

 

I've pretty much done everything I listed twice (except checking the valves only once) once last weekend, then once this weekend.

 

I'm thinking a sensor, the injectors or the ECU itself as disregaurding the high idle, the consistant theme is "when loaded."

 

Even tried an experiment of keep the RPMS over 2000 and feathering out the clutch and as soon as there is a load, it craps out and I can't even use the throttle to keep the revs yet. Yet in neutral... I can pretty much set the idle to whatever I want and using the throttle, pick an RPM and it runs smooth as silk. Responsive and smooth.

 

-mkb

Link to post
Share on other sites

plug wires! or the caps.. see if they are screwed in to some blueish copper wire instead of nice clean copper. I once stalled out in the middle of south Dakota with a bad plug wire... worked fine on low power but cut out under load. are the wires tight into the coil?

ROLL4DX-06.jpg

Link to post
Share on other sites

Just did an experiment and it's lack of really positive result may be telling in itself.

 

(I really didn't mean to hi-jack this thread, I thought the usual "oh, just do this little-known-thing" was going to be a one line answer from someone and I'd be all set....) I did re-check the plug wire and coil connections.

 

Anyway, just for giggle I decided to back off the left idle adjustment and set the idle by ear using only the right side idle adjustment, which at this point was not engaged (used a .002 feeler guage to insure it was just... almost touching, but not). Both bypass screws all the way in.

 

- So it started as usual, then holding the throttle to keep it from stalling I adjusted the idle stop screw until it idled nicely.

 

- At this point, rolling on the thottle just a little caused the usual backfire spit'n nonsence... so..

 

- I started with the right side bypass and just started turning it out in 1/4 turn increments, bliping the throttle between and it almost stopped backfiring and spitting. I had to back off the idle stop a little as the more I turned out the bypass, the higher the idle.

 

- The right bypass is now out about 2.5 turns, the TPS is showing about 270mv and it sounds like it's ready to ride, with just a little girlie-burp as I open the throttle.

 

- I try adjusting the left bypass in the same manner as the right, but it has little to NO affect at all on anything. Doesn't affect the idle, the burping, nothing.

 

- So I try to ride it this way... no joy. Stall, cough cough.

 

- I put the merc tubes back on, and in nuetral, it starts, and the carbs are balanced.

 

There are other forces at work here. I have worked on this and other bikes before, and this one is throwing me a serious curve ball. If I had the extra cash I would get an O2 stick. It also almost seems like the "timing" is off, allthough that doesn't really apply and really odd part is over 2000 rpm, it's fine.

 

 

So far (with an earlier omission)

- The popping and spitting seems to be on the RIGHT SIDE almost exclusively.

- The LEFT Bypass screw has little affect on anything.

- The Carbs balance.

- Smooth idle and running can be achieved with a myriad of combinations of idle and air bypass settings, some that probably shouldn't work.

- The TPS voltage seems very consistent and smooth, however 500mv causes the idle to be WAY too high, no matter what else is done.

- With the TPS at 500mv both the VDST and PCIII software indicate the throttle is just shy of 3.5% which is about right too, so it doesn't seem like anything is faking out the ECU or the PCIII and also re-enforces the TPS seems to be operating correctly.

 

Sensor? Injectors? Voodoo? This has all the marking of something really simple, that just needs to be found.

 

-mkb

Link to post
Share on other sites

if the oil or air temp sensor thinks it's really cold wouldn't the computer spray more fuel into the mix? and that would stall it out when ya turn the throttle open? could explain why it idles nice w/a tps reading of 270?

OR, after setting the idle stop screws, did you just stick the link rod back on or did you "set" that too. if you just hooked it up maybe it opened one of the butterflies slightly?

Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

×
×
  • Create New...