Part throttle hiccup

[Dan M]

Unknown, but per my posts on this, under throttle or at higher than 3K RPM, there is NO visible scatter on my strobe. It's as steady as a rock. At fully warmed

 

Same boat I was in before Docc suggested using the timing light way back when to check for scatter. . .I'd always considered using a strobe on an EI motor, well. . . pointless!

 

I hadn't seen this particular post of yours before Ratch, it would be nice to know what 6-7mm converted to in degrees of rotation. Simple to figure with a degree wheel. With the engine off one can "feel" the amount of chain slop by rotating the crank slightly back and forth and feel when the slack is out of the chain by the additional load of turning the cam. It takes a light touch but you can get an accurate read of slack / slop / play / cush (oops, sorry, not trying to start a fight) Anyway, Lets say you have 5 degrees of slack in the chain; that would mean 2.5 degrees on either side of what would be tight. The most the cam will be advanced or retarded is 2.5 degrees. Not much effect on running. Obviously, if you get up around 10 degrees of play (5+/-) you may perceive a slight power loss or somewhat uneven idle. It's pretty hard to say how much timing variation it will take to give a drivability problem but more than 5 degrees of cam retard, I'd be considering opening things up.

 

edit: if a loose or worn chain or gears (or tensioner) will allow the crank to move some degrees independly of the cam you are indeed getting retarded cam timing.

[mfeeney]

Brian; I've the same issue which I noted in this forum a few months ago. My 2004 Le Mans (8500 mi) does this at 3000 rpm regularly once it is completely warmed up. I think it is an electrical problem. The bike has MG Titanium exhaust with the accompanying ECM installed. I was going to try the stock ECM to see if this made a difference. Since you have the same problem I do not think it is a loose ground problem. Sorry that I cannot offer a fix at this time only simpathy!

 

 

 

 

 

quote name='BrianG' date='Aug 23 2007, 06:54 AM' post='127429']

OK... I'm stumped.

 

I have recently acquired a part throttle hiccup that is pretty pronounced and VERY annoying. It almost feels like a backfire, and it is ruining the quality of the MG ride!

 

It occurs while at very low throttle opening and is most pronounced between 2000-3000 RPM.

 

This, together with a very poor idle quality, motivated me to do a "tune-up" last week-end, where I found the valve lash way too tight (0.0015/0.002). Rectifying that smoothed the idle out fine, and elevated the idle speed to about 1500+ RPM. I set the idle speed down to 1000+ RPM and sync'd the throttle bodies. That looked good. I did not set the TPS, or ign. timing, figuring that these items would be unlikely to have changed since the last setting a year ago.

 

I'll check those 2 items this coming week-end, but I'm canvasing the Guzzisti here to see if there is any consensus on the origin of this irritating hiccup thing that I've never experienced before.

 

Any ideas?

[Guest ratchethack]

Thanks for the feedback on this, Dan.

I hadn't seen this particular post of yours before Ratch, it would be nice to know what 6-7mm converted to in degrees of rotation. Simple to figure with a degree wheel.

Simple enough using C = TT(pi) D also, converting C to 360 degrees, but I don't have a good way to measure D without access to the flywheel, and don't know wot the significance in degrees would be any more than in mm anyway?? But as much as 5 degrees at the crank would be a definite concern, and I b'lieve I'm at least approaching the neighborhood!

Lets say you have 5 degrees of slack in the chain; that would mean 2.5 degrees on either side of what would be tight. The most the cam will be advanced or retarded is 2.5 degrees. Not much effect on running.

Mmmmmm, I don't b'lieve this is correct. Nossiree. ALL the chain slack (per prev. discussions and again as mentioned above) results in erratic timing advance (at the crank), and NO amount of slack due to a loose (not worn) chain can cause retard. Think about it. . .

It's pretty hard to say how much timing variation it will take to give a drivability problem but more than 5 degrees of cam retard, I'd be considering opening things up.

 

edit: if a loose or worn chain or gears (or tensioner) will allow the crank to move some degrees independly of the cam you are indeed getting retarded cam timing.

Again, I'm not the slightest bit concerned about retarded timing, since this can't happen (per Pete's illustration in the prev. thread). But I AM concerned about anything near 5 degrees more advance (at the crank), on an erratic basis, which (again) would exactly explain (at least to my way of thinking) the symptoms. . .

[Guest Nogbad]

I thought this had nothing to do with mechanical timing of the cam, but is an effect that stems from flutter of the crank position sensor which takes pulses from a wheel on the CAMSHAFT. Hence introducing some inaccuracy in timing within the ECU which is pronounced at about 3 - 4K rpm at neutral throttle.

 

I seem to recall that this is an issue which can be solved by using the Jeffries My15M ECU replacement. My bike has it too, but it isn't annoying enough to get the wallet out.

[Dan M]

Thanks for the feedback on this, Dan.

 

Simple enough using C = TT(pi) D also, converting C to 360 degrees, but I don't have a good way to measure D without access to the flywheel, and don't know the significance in degrees would be any more than in mm anyway?? But as much as 5 degrees at the crank would be a definite concern, and I b'lieve I'm at least approaching the neighborhood!

 

In the earlier post you were looking for what was an acceptable amount of scatter. If there is a spec it is going to be stated in degrees. That is why I think it would be useful to know how many degrees 6mm is. If it converts to one or two than I'd think that would be completely acceptable.

 

Mmmmmm, I don't b'lieve this is correct. Nossiree. ALL the chain slack (per prev. discussions and again as mentioned above) results in erratic timing advance (at the crank), and NO amount of slack due to a loose (not worn) chain can cause retard. Think about it. . .

 

I agree with you here on the matter of only the chain tensioner being bad and then the cam will only be able to be able to advance. What I described was timing variation from a worn chain and gears. If your tensioner is faulty and chain & gears are in perfect condition then only advance can occur. It should be noted though that if the tensioner is pushing the chain way in between the gears, the chain or gears are indeed worn and retart will happen. It all depends on how much play is from the wear of the chain & gears. They certianly do wear and cause cam timing issues. Clearly this is more of an issue the longer the chain and the MG has a rather short one but wear still occurs, hence the need for a tensioner.

 

 

Again, I'm not the slightest bit concerned about retarded timing, since this can't happen (per Pete's illustration in the prev. thread). But I AM concerned about anything near 5 degrees more advance (at the crank), on an erratic basis, which (again) would exactly explain (at least to my way of thinking) the symptoms. . .

 

It certaianly can happen. On OHC motors (again, a rather long chain) with crank and cam sensors I've watched cam timing advance and retard on a lab scope. It is a good indicator of chain, gear, guide & tensioner wear without disassembly.

[Guest ratchethack]

It certaianly can happen. On OHC motors (again, a rather long chain) with crank and cam sensors I've watched cam timing advance and retard on a lab scope. It is a good indicator of chain, gear, guide & tensioner wear without disassembly.

On motors with longish chains, I would agree -- OHC, DOHC, TOHC, desmo, or what-have-you. But that's not important WRT the Guzzzi, nor is it relevant here. Per Pete's description of this, (I repeat) the distance betwen drive crank sprocket and driven cam sprocket on the Guzzi is no more than a few links. This provides NO appreciable ability for timing to retard under any conditions, regardless of chain or sprocket wear. Look, I didn't make this up -- nor would I have likely been bright enough to've thought of it without having the cover off for inspection (which I've yet to do). Pete posted his take on it, that's it, and I reckon he's had more'n a few of 'em apart replacing those lovely timing gears he likes so much . . . The man knows well whatof he speaks here as elsewhere around the old ditch pump motor, and it makes perfect sense to me. . .

[BrianG]

My first inclination was to make sure the sensor hadn't become fouled with debris from the phase (Hall Effect) wheel. So out it came for inspection. The "aperture" was clean as a whistle.

 

My next inclination was to carefully observe under wot conditions the symptoms appeared. Since they NEVER appeared under engine load or above 3K RPM, regardless of ambient or relative engine temp (or any other variances on the road), I was confident in concluding there was ZERO probability that the sensor could be the point of origin, otherwise I'd have some expression of the symptoms under load and/or above 3K RPM.

 

Thanks for that. I'll pull the sensor and have a look. I've never seen a post here where someone actually found crap on the sensor, though.

 

I wonder if my PCIII is dying,...... again. I had one crap out catastrophically. I'll unplug it and have a go on the road.

 

One thing that's different in my situation is that after the valve adjustment, the idle is rock steady. No hiccupping or attempting to reverse direction as was present before the adjustment. Just the light throttle hiccup at around 3000RPM.

 

I'll also try a number of other power settings just in case I've oversimplified the issue by too much forum reading!!

 

 

Brian, we covered this in some depth in the other thread. I believe he's correct also. Pete suggested that the driven cam sprocket is so close to the drive sprocket that the few links separating them could virtually NEVER result in retarded timing due to a worn chain. I might add that neither would slightly retarded timing result in the observed symptoms. A LOOSE chain due to a wonky tensioner, however, very well COULD -- dare I say WOULD cause the chain to whip and jump erratically, shortening up the normal chain length between drive and driven sprockets by folding back on itself (as they will!), thereby effectively advancing the timing on an erratic basis, which would seem to explain the symptoms perfectly.

 

I read that thread thoroughly now, and what I think you have not taken into account in terms of chain stretch is the "crawling up the sprocket" and then crashing back down that occurs in a worn chain. This is what will eventually cause a "step" on the driven side of a chain sprocket. This would contribute to the ign scatter that has been observed.

 

My point was that chain replacement as a WYAAI issue should be contemplated once you have cracked that chest.. I always replaced a chain twice before replacing chain and sprockets back before I was too sophisticated for drive chains!

[Dan M]

On motors with longish chains, I would agree -- OHC, DOHC, TOHC, desmo, or what-have-you. But per Pete's description of this, (I repeat) the distance betwen drive crank sprocket and driven cam sprocket on the Guzzi is no more than a few links. This provides NO appreciable ability for timing to retard under any conditions, regardless of chain or sprocket wear. Look, I didn't make this up -- nor would I have likely been bright enough to've thought of it without having the cover off for inspection (which I've yet to do). Pete posted his take on it, that's it, and I reckon he's had more'n a few of 'em apart replacing those lovely timing gears he likes so much . . . The man knows well whatof he speaks here as elsewhere around the old ditch pump motor, and it makes perfect sense to me. . .

 

Let's look at a medium-short length chain say like in a small block chevy. There are only a few to several links between gears. When new there is virtually no play in the chain. When worn I've seen as much as 20 degrees in ignition timing variation at idle. This, is as stated above is 10 degrees of advance and 10 degrees of retard. When run up to 2000 rpm or more the slack is pulled out of the chain and what is netted is a very close to a 10 degree retarding of the cam timing. Hell, I can't tell you how many cases I've opened and put the crank at TDC and viewed the cam as several degrees retarded. Have all of these been illusions? Now the guzzi is much shorter and I truly don't know the number of links but even if it is half we still have retard along with advance. It is just to a smaller degree. Unless, of course you are saying that the MG chain & gears don't wear, and the only slack is due to faulty tensioners.

[Guest ratchethack]

I read that thread thoroughly now, and what I think you have not taken into account in terms of chain stretch is the "crawling up the sprocket" and then crashing back down that occurs in a worn chain. This is what will eventually cause a "step" on the driven side of a chain sprocket. This would contribute to the ign scatter that has been observed.

Well, I don't believe I've overlooked anything here, Brian. Eventually can be a long time comin', my friend.

 

Some of Pete's comments (don't know wot thread) led me to expect with some confidence that chain and sprocket wear at 34K miles will be negligible unless something extraordinarily gruesome has happened. Since there are no such indications, I'm ruling out perceptibly hooked sprocket teeth and a "stretched" timing chain. I've put literally hundreds of thousands of miles on a DOHC chain with careful inspection for wear along the way, and no appreciable sign of "stretch" or "hooking" of sprocket teeth -- not to say that wot happened on a car motor necessarily applies directly here, but at 34K miles, I'm confident in placing my expectations with the Pro's with the direct experience.

[Guest ratchethack]

Let's look at a medium-short length chain say like in a small block chevy. There are only a few to several links between gears. When new there is virtually no play in the chain. When worn I've seen as much as 20 degrees in ignition timing variation at idle. This, is as stated above is 10 degrees of advance and 10 degrees of retard. When run up to 2000 rpm or more the slack is pulled out of the chain and what is netted is a very close to a 10 degree retarding of the cam timing. Hell, I can't tell you how many cases I've opened and put the crank at TDC and viewed the cam as several degrees retarded. Have all of these been illusions? Now the guzzi is much shorter and I truly don't know the number of links but even if it is half we still have retard along with advance. It is just to a smaller degree. Unless, of course you are saying that the MG chain & gears don't wear, and the only slack is due to faulty tensioners.

Dan, it looks like I'm just the middleman here and it's time for me to get out o' the way.

 

I recommend fire up the Oracle of Bungendore searchlights over New South Wales with the Mighty MotoModa logo on them tonight, and sit back and wait for the Caped Crusader Hisself to come blazing across the sky and bounding into the Forum to save the day!

[Ouiji Veck]

Sometimes a cigar is just a cigar.

I think it's TBs out of sync...even if you did do them already..

There was a particularly good method posted here somewhere ...

not as good as mine but good. Starting with TPS.

 

You guys will be discussing the gravitational pull of Uranus pretty soon.

(Though the gravitational pull of Myanus may be quite substantial.)

[BrianG]

Sometimes a cigar is just a cigar.

I think it's TBs out of sync...even if you did do them already..

There was a particularly good method posted here somewhere ...

not as good as mine but good. Starting with TPS.

 

You guys will be discussing the gravitational pull of Uranus pretty soon.

(Though the gravitational pull of Myanus may be quite substantial.)

Yes indeed........

For me it's check the PC III and if that's not it....

It's back to the basics/

intake boot integrity/leak check

valve clearance check

TPS check/set

TB balance and idle set

ign timing check... if I can find timing marks in there somewhere.....

 

... then maybe on to the esoteric

 

 

Now I hate to hijack my own thread but..........

 

someone mentioned that a minor exhaust leak could be the culprit here....

 

I don't get that one.... could someone expound on that theory?

[Tom M]

This probably doesn't apply to your situation Brian but...I had a low throttle stumble when my bike got really hot this past spring. I had added a new crossover, drilled airbox lid, and a downloaded PCIII map over the winter so I knew there was a possibility I would have to do some manual map tweaking. I tried to note exactly where the stumble was then I looked at the map that I was using. It was leaner than stock in that rpm/throttle area so I added 5 points to a few cells and tried it for a week. Better but not perfect. I added another 5 points after that and my lean cough is gone.

 

Check your map in the area where you're having the problem. If it's significantly leaner than stock you might want to bump a couple cell values up and see how it feels. To me it's like lowering the clip on the slide needles in the carb days, but now I can do it on the PC instead of getting the tools out

[Dan M]

Dan, it looks like I'm just the middleman here and it's time for me to get out o' the way.

 

I recommend fire up the Oracle of Bungendore searchlights over New South Wales with the Mighty MotoModa logo on them tonight, and sit back and wait for the Caped Crusader Hisself to come blazing across the sky and bounding into the Forum to save the day!

 

 

I'm still thinking his problem is a lean misfire. I had a similar symptom, seat of the pants made me think lean, I confirmed it being lean just off of idle at low throttle opening on the EGA. Bumped up fuel slightly in that zone on the PCIII and problem reduced, I'm thinking more time to fine tune it and that will be the end of it. Impossible to say if he has the same trouble without diagnosing. I wouldn't recommend he does the same because lean can be caused by several things. The root cause of the trouble should be identified before he's is sent off chasing anything, let alone pulling the timing cover.

I respect Pete's experience with the MG mill, and he's likely to have most all of the answers, but I'm sure he'd agree it's tough to diagnose a problem over the internet. If you open up enough engines you learn not to say that anything is impossible. Seems you've got your problem diagnosed, parts bought and ready and you haven't even opened the case yet. You may get lucky my friend and I hope you do, but buying parts on theories is usually the wrong way to go about it.

 

This probably doesn't apply to your situation Brian but...I had a low throttle stumble when my bike got really hot this past spring. I had added a new crossover, drilled airbox lid, and a downloaded PCIII map over the winter so I knew there was a possibility I would have to do some manual map tweaking. I tried to note exactly where the stumble was then I looked at the map that I was using. It was leaner than stock in that rpm/throttle area so I added 5 points to a few cells and tried it for a week. Better but not perfect. I added another 5 points after that and my lean cough is gone.

 

Check your map in the area where you're having the problem. If it's significantly leaner than stock you might want to bump a couple cell values up and see how it feels. To me it's like lowering the clip on the slide needles in the carb days, but now I can do it on the PC instead of getting the tools out

[Guest ratchethack]

Seems you've got your problem diagnosed, parts bought and ready and you haven't even opened the case yet. You may get lucky my friend and I hope you do, but buying parts on theories is usually the wrong way to go about it.

Of course, Dan. And I generally agree that for the DIY moto maintenance guy, buying parts on spec without first thoroughly completing a hard diagnosis is NOT ALWAYS the best approach. It's a principle I've followed many times meself. But each situation is unique, isn't it, and there are always trade-off considerations, n'est-ce pas?

 

Look, you're free to disagree with me and I welcome the challenge -- sincerely. I have no need wotsoever to justify wot I'm doing to anyone at any time. But just to clarify since we've been so far down this happy little game trail together in this thread, here are some of my trade-off considerations that I've thrown into the salad bowl that I've partially described above:

 

1. I've learned to trust the experience of the Pro's on this Forum very nearly without exception, including yourself. As I've mentioned many times before, without their willingness to put the most valuable thing they've got as professionals on the line every time they post (that would be their credibility), this little Tech Forum here wouldn't be worth dog spit. Thankfully, a few of 'em have decades of precious experience on the Guzzi. Thankfully (Part II), they're willing to share it. I hope that every such effort comes back to them in spades in terms of rewards (in many cases I'm sure this amounts to nothing but personal satisfaction at having provided value to others free of charge), and to some degree I reckon it does, or they wouldn't be doing it.

 

2. I figure I've had enough experience with the Guzzi donk myself, and a heap of other various motor-vehicular contraptions besides, to place some faith in my own diagnostic ability. Combined with #1 above, this generally makes for a basic pro-active maintenance capability that I confidently put up against any unknown service shop with a phone number and a shingle hanging out front with a name and address on it. In the case of chasing my own symptoms as described above, I've done a fairly exhaustive analysis and have put together a pretty solid diagnosis, I think, largely based on the process of elimination.

 

3. As mentioned before, I'm a big believer in maximum up-time. When approaching any Guzzi work (I've always done 100% of all my moto work on 12 bikes) I like to have every part I'm likely to need on hand before I take it off the road, if possible. Generally, I like to have it apart and back together in one go, rather than the common shade-tree mechanic approach of, "take it apart and THEN start hunting for parts, it could come back together eventually." On this plan, for example, doing most of the work myself, I was able to complete my own transmission recall with only 2 days off the road with no wait for parts and ZERO out-of-pocket cost. Others with the same trans recall took their Guzzi's to their dealer and waited up to 6 months, and in a few cases, longer. For a few of these, as posted here, there were many more months of continuing problems afterward, including multiple return trips to the dealer.

 

4. If a tensioner cost many hundreds of dollars, I'd be more inclined to hold off buying one until I had the chaincse opened up. But the tensioner was only $26 USD from the boys at Moto International, who were kind enough to throw it in with an order of other stuff and ship it out in advance of my need.

 

Hey -- if it turns out I was WRONG in my diagnosis, it's cost me a whopping $26 USD for a spare tensioner and front crank seal that I'll keep in the workshop cabinet with the pile of other spares in there waiting for a time when I'll surely use 'em all in the spirit of max up-time. There's an outside chance I'll have enough time this weekend. I'll surely post back with the results, and might have a photo or 2.

 

OK by you?