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My Scura has acquired a cough - post TPS adjustment


PJPR01
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A project years in the making...finally tackled it...but not happy with results.

Having finally decided to tackle the TPS setting, despite having no issues, I figured it was time to do the 1 thing I have never done on the Tune up list, after having done absolutely everything else on the list with meticulous attention.   I connected the new Casper cable (so that's how it works...aha!), connected the voltmeter, disconnected throttle linkage and see the TPS is registering 0.350mv...well, that's supposed to be .157...hhm, I wonder why the bike runs well despite that, I ponder.  Thinking, well surely it will run even better when I set it properly!  Premature delusions of grandeur dancing in my head!

Ok, remove the old TPS, look inside, pretty oxidized with some crud, so I clean it out thoroughly, re- connect the TPS, back out the idle screws on both sides so they are not touching the cams, snap the RH throttle several times until it's well and truly seated and get it set on the nose at 0.157mv, and snugged in tight.  All good, put it at full throttle still disconnected from the linkage, and it reads 4.70...sounds like I'm in the right range.  Ok, mission accomplished on the TPS.

Connect it all back up again, remove and clean air screws, blow some throttle body cleaner into the TB's, then set the air screws 1 full turn out each, reconnect linkage, get idle screws touching, bike idling like crap, and tons of flat spots and coughing.  Put a fresh set of plugs in just for fun also.  Cranked it up, idling low, and start adjusting as per the write up here.  Played with it a few more times, getting it nicely balanced with the Carbtune, idling beautifully, air screws 1 full rotation turned out, and I still have a flat spot/cough at low rpm's (1.5K to 3k RPMs') that was NEVER there before.

Disconnected everything again, and go thru each step methodically, recheck TPS with linkage and idle screws backed out, and still seeing 0.157 closed and 4.70 at WOT, hook it all up again, but no change in behavior.  I'm thinking do I have something clogging up fuel lines or something so I take it for a short ride, but not at all happy with the flat spot/cough.

So...decided to buy a new TPS as recommended by Docc...came in a few days, installed it today, and noticeably smoother and I can see it moving in increments of 0.01 easily as I gently tap...so here we go again, set to .157mv and full closure with linkage and idle screws backed out...and 4.70 at WOT.  Figure it will run better, and it does...but bugger all, it still has a cough.

How is it possible that I could have had NO flat spot or cough ever in the prior years of running, with a TPS obviously set at the wrong point, and now with every thing exactly on spec (or obviously I'm overlooking something), I have it idling perfectly, Carbtuned and balanced to perfection at idle and 3K rpm's and I still have a flat spot/cough.  

I even went around and snugged up all the new rubber intake boots 3 clamps each side, snugged up exhaust headers (no movement), connector pipes (2 each side).

It runs beautifully on the highway, but now, every time I come to a stop I know it's going to stumble when I take off again...until I get above 3 k RPM's again.

I know it's not relays, since I had no issues before, no exhaust leaks, fresh rubber, valves set, fresh plugs...WTF?  and just for fun I went and put a fresh full tank of new gas in it...no change.

Back to the drawing board here...surely I'm missing a step somewhere...

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  • PJPR01 changed the title to My Scura has acquired a cough - post TPS adjustment

Bare bones, simplest answer: these steps can't be skipped and have to done in order . . .

The throttle "snapping" method always seemed awful to me. I resorted to holding the throttle plate firmly closed to establish the baseline "closed throttle = 157mV TPS." My best result ever. Be mindful of all of the factors that prevent the "fully closed" throttle plate when baselining the TPS.

For instance, you didn't mention releasing the high idle cam or attending to how much the TPS reading "walks" as it is tightened.

It is a mighty fiddly setting to get "just right" . . . but worth it! :luigi:

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Thanks for the almost immediate reply Docc, I had that thread printed out next to me and followed it step by step several times now.

However, I couldn't see anyway to adjust the high idle screw, so I didn't adjust it at all, I tested it with a screwdriver gently, but didn't seem to even budge, and I didn't want to force it.  Maybe that's part of what's missing, I'm just reluctant to break something here as that leads me down a path of having to source more parts.

With regards to the TPS, snapped or held snug manually, it still reads 0.157mv at full closure and after tightening the screws, it's dead nuts on, so the old and new TPS are not walking anywhere!  They're on a tight leash!  :)

Can you confirm if your high idle screw does turn easily or is it quite stiff?

Thank you!!

P.D.  I'm still scratching my head as to how the old TPS set at 0.350 could allow the bike to run absolutely smoothly however...I mean, that's seriously out of spec...

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The "High Idle Screw" has to be released so that the throttle plate will fully close. That screw would have, originally, been plastered with yellow anti-tamper "witness" paint.

gallery_328_223_536823.jpg

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I just went through this, my bike ran fine, but the air screws had been completely closed & my trim was at -26, I redid the decent basic tuneup with air screws opened one turn,that changed my baseline tune a lot.

I redid it a few times,because I had to re index the throttle linkage to give me more space on the threaded rod part when I dropped it down into position.

I changed my trim to +26

When I finished the tuneup & balance I reattached the existing tank vent T connection to the vacuum ports on the TBs. It ran great,but developed horrible tank suck issues.

Cured my tank suck rough running issues by removing the T tank vent line,changing it to a straight atmosphere vent, & capped off the vacuum ports on each TB.

Was your throttle linkage indexed,so it dropped down smooth with no movement?

What is your trim?

Are your vacuum ports capped?

Did you start off by adjusting the valves as a baseline?

 

 

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8 minutes ago, docc said:

The "High Idle Screw" has to be released so that the throttle plate will fully close. That screw would have, originally, been plastered with yellow anti-tamper "witness" paint.

gallery_328_223_536823.jpg

“Witness paint”, nice Docc :D

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Ok, I'll take another crack at the upward facing high idle screw...hopefully it budges w/o breaking anything and that solves it...it is the 1 step I haven't done.

80CX100:  Many thanks for the comments as well.  My CO is set at +10, it was at +10 before as well, I took it to zero in one of the iterations here and it ran much worse, so I put it back to +10 via Guzzidiag.  I suppose I could experiment and put it +20...easy enough to try!  My air screws were 1 turn out before, and again now also 1 turn out. I tried it 2 times rotated out on both, but 1 turn seemed better at this point.  

I've had a bit of a revelation writing this...I did watch my Carbtune with both airscrews completely removed (you can hear a lot of hissing, but it's interesting to see....my RHS was sucking a bit more until I balanced later on with the linkage connector/white plastic square, so that maybe then the high idle screw is the culprit.

Vacuum ports are both connected via hoses, not plugged, so all good there as I had the tank off a few months ago to replace the intake rubbers, clean throttle bodies, do the valve adjustment and ensure the airbox/new filter and all hoses were good and properly connected and snugged up.  Even took the time to sand and paint my battery tray...not that anyone sees it but me!  

I'm not sure I understand what is meant by throttle linkage being indexed?  Can you elaborate a bit? 

The throttle releases nice and smoothly, no catches at all.  Nothing physically changed from before, but I can see that I don't have it screwed in all the way into the right hand plastic piece as the balance with the Carbtune doesn't require it to be now so I have a few threads now visible vs. the locking nut on the RHS.

Witness paint - there's plenty of that on here from the prior owner...I'm going to have to scrape it off and apply fresh stuff!

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The factory witness paint was a great help finding all the places that need to be messed with! :luigi:

Realize that, if you think you backed the idle stop screws, especially the right, out enough to fully close the right throttle plate for the TPS adjustment, and then find the high idle mechanism is fouling the closure: fully releasing the high idle cam could bring the throttle plate back in contact with the right side idle stop screw that had plenty of clearance before . . .

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Ok...I'm intrigued enough to head back out to the garage again to take a blow torch, I mean screwdriver to the high idle screw tonight and then re-connect the Casper harness and see if the 0.157 has changed once the screw is backed out enough...will pay attention again to the right hand idle screw.

The good news is I've become quite adept at contorting myself sideways to get that little allen wrench into the RHS idle screw...nothing is impossible now.  I can even slip a 0.02 feeler gauge in there to make sure it's truly not touching.

If this solves it...let me know where to send a bottle of your choice of fine liquor!

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42 minutes ago, PJPR01 said:

Vacuum ports are both connected via hoses, not plugged, so all good there as I had the tank off a few months ago to replace the intake rubbers, do the valve adjustment and ensure the airbox/new filter and all hoses were good and properly connected and snugged up.  Even took the time to sand and paint my battery tray...not that anyone sees it but me!  

 

I'm not sure I understand what is meant by throttle linkage being indexed?  Can you elaborate a bit? 

 

My bike had apparently spent it's whole life? 6K kms with the tank vent line T'd  off to the vacuum ports on the TBS,for whatever reason,when I changed the baseline tune up settings,it didn't like it.

I cleaned out the 2 gas tank vent holes by the cap iirc 6 & 7 o'clock with small wire & eliminated that T and the hoses connecting the TB's,capped the ports off with vacuum caps,eliminating that wildcard completely.

I'm not sure indexing is the proper term,but the first balance set up I had was perfect, but when I replaced the throttle linkage rod,in order to get it to snap into place smoothly with no right or left movement,the plastic cup on the end of the threaded rod at the right TB had only a couple of threads into that cup,I wasn't comfortable with that.

I disconnected the whole rod (circlip on left side don't lose it btdt lol) buried the threaded rod completely into the plastic cup on the right side,readjusted the white knob on the left,so when I reattached the threaded rod linkage,I now had lots of threaded rod buried into the plastic cup when it was adjusted to snap into place with no movement on the throttle linkages.

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80CX:  Got it now, I fully understand what you're referencing now.  Ok, no issues on this side, it's got about 1/2 inch of thread going into the black threaded cup...all good there!  I figured it was just as easy to spin the rod off, even took advantage to put a little white grease into the threaded plastic cup to make it a bit easier to turn.

Luckily I know this whole cough is related to the TPS setting, since the bike was running great after I had done all of the other work a few months ago and had never had a cough since I bought the bike back in 2016, I just had the need to tinker with this last piece to see how it was done as the manual TPS adjustment is so different and somewhat archaic compared to my two other CARC bikes where we can reset it via Guzzidiag.  Good learnings all the way around playing with this and I feel good about putting a new TPS sensor on as it certainly looks like an original one there now, plus I was able to clean out all of the crud that gets into that TPS housing reservoir.

Hopefully I'll have good news to report shortly this week once I get the adjustment done and time for a ride sometime during the week.

Thanks all...much appreciated!

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Now, this potential issue is noted in the Decent Tune-up, IIRC, but make certain the TPS is not fouled (or too close) by the fuel return line/hose and its clamp the regulator.  The TPS is engine mounted while the regulator is frame mounted, so a bit a clearance between is desirable . . .

I hope this solution still qualifies:

"If this solves it...let me know where to send a bottle of your choice of fine liquor!  " :drink:

 

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On 1/23/2023 at 1:58 AM, PJPR01 said:

... disconnected throttle linkage and see the TPS is registering 0.350mv...well, that's supposed to be .157...

Hi,

350mV is in the range you would see if the TPS is not fully closed. If it ran well with this setting and not so after changing to 157mV then my guess is that you did not remove all the stops keeping the TPS from being fully closed.

Much success in resolving the bug.

Cheers
Meinolf

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Danke sehr Meinolf and Docc...you are both 100% right (as usual!).  The learning continues here in the well illuminated Houston garage!

Indeed, late last night I was able to loosen the right hand high idle screw and sure enough that enabled the throttle body to close completely...so when I read the voltmeter again it was then sitting at approx 0.100 less than before when I thought it was fully closed.  Reset everything to 0.157mv, snapped it a few times, came back to 0.157 and at WOT was registering 4.78...so that's a good sign!

I proceeded a few more steps, got it started again (it did sound smoother) but it struggles to idle without some inputs.  After getting it to stabilize and warm up I checked again the CO Trim, sitting at +20, so that seems fine (maybe I should try +26), air bleed screws are 1 full turn out, high idle screw is just "nudging" the cam, and both LH and RH idle screws are not touching (0.02 feeler guage slips in just fine).   Will get at it again this afternoon at a break.

So much fun!!

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I can't remember the base v but, the 0.157v is the # you want to adjust the throttle plate to from fully closed. IDK how to find this procedure I posted here some time ago. I do remember , EVERY step is critical and you follow EVERY step to a T. 

 I hate getting old ! I can remember an event at 1 1/2 yrs.old , the 1st day of school. all my 1sts. but I cain't remember where I laid my car keys.

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