Newbe with v75 problem

[simj26]

Hi there. I'm having a bit of a problem with an ol' guzzi. It's a '92 V75 ex Italian police bike acquired as a non runner that'd been stood for a while. The problem is that it will only run on the left cylinder. I've done all the usual stuff...cleaned and set up the carbs, swapped all the ignition components over to the non running side (no improvement) even swapped the carbs over (no improvement). Removed the head on the non running cylinder to check the valves...they weren't too bad (re ground them anyway) piston n bores are good and compression is good. The one big thing is that the valve timing seems to be out. runs fine on the left cylinder but just backfires on the right. There does seem to be some back pressure through the inlet port at one point during the cycle....which does give the impression the valve timing is out.......but the left cylinder is fine?
 Anyone have any ideas as to the problem......I can't see how you can have the valve timing out on one side but not the other when there's only a single cam? I haven't opened the front casing to check the cam chain or guide yet.
 Any help would be much appreciated. ??? 

[oldbike54]

Could be a bent pushrod , or maybe a flat cam lobe . Yes , a bit of a puzzler .

  Dusty

[simj26]

Checked the pushrods...they're fine. Would one cam lobe deteriorate that badly...on one side only? Must admit,this one is baffling me! ??? 

[Chuck in Indiana]

Checked the pushrods...they're fine. Would one cam lobe deteriorate that badly...on one side only? Must admit,this one is baffling me! ??? 

Sure can, although it is extremely rare on a Guzzi.. it's certainly easy enough to check, just turn it through and watch the valve movement. Report back.

[oldbike54]

Checked the pushrods...they're fine. Would one cam lobe deteriorate that badly...on one side only? Must admit,this one is baffling me! ???  

Yes , baffling . If the valve timing is off on just one side , and the rocker arms and push rods are alright , would indicate a bad cam . Can you verify that the lift is correct on the bad side ?

  Dusty

Edit . OK Chuckie beat me to it , Anyway , yes , what he said .

[simj26]

Thing is, if a cam lobe is worn it would reduce valve lift wouldn't it? Considering that there is back pressure through the inlet port to the carb on part of the sequence...would indicate that the valve is opening longer or at the wrong time? ???

[simj26]

Are any Guzzi cams made up of any thing other than a single unit..ie, a two part cam that's joined in the middle?

[oldbike54]

Thing is, if a cam lobe is worn it would reduce valve lift wouldn't it? Considering that there is back pressure through the inlet port to the carb on part of the sequence...would indicate that the valve is opening longer or at the wrong time? ???

That is why we suggested measuring the lift . Kinda sounds like a lobe has gone flat .


  Dusty

[simj26]

Surely if a lobe has gone flat the valve will open less or hardly at all? Am I missing something here? it is the lobe that pushes the pushrod that opens the valve.....right? The valve fully closed position would still be the opposite of the lobe(whether the original lobe was worn or not) on the cam?
It seems like the valve is actually open either for a longer duration than it should be or opening at the wrong time altogether......I've checked the valves and they are definitely fully closing when they do close but am getting a back blast through the carb....in fact it has actually backfired through the carb a few times If the left cylinder wasn't running ok I'd say definitely the cam timing rather than lift. ??? 

[oldbike54]

OK, let's go back to the beginning . Left cylinder runs fine , right doesn't run at all . You switched carbs side to side , and ignition . Doesn't solve problem . You state the valve timing on right side seems off . Correct so far ?
We ask about pushrods , , they seemed alright , compression seems OK . Still no answer regarding the actual overall lift on the offending side , or an actual PSI compression reading . We suggest a flat cam lobe , you basically say we are wrong w/o doing any test . The overall lift might be fine , maybe the ramp on one of the lobes has gone out of shape . The valves spend very little time at maximum lift . We are talking thousandths of an inch here , hard to discern with the eye . Heck , where is the lash set ?

  Dusty

[Triple Jim]

Also, low cam lift cause by a failed lobe can cause all kind of oddball effects.  Suppose it's the exhaust lobe, and the valve is opening so little that there is still pressure in the cylinder when the intake valve opens, so it puffs out that direction.

[Kiwi_Roy]

One coil with a distributor or 2 coils with two sets of points?
I'm thinking either the wrong cylinder is using the other cylinders points putting one spark 90 degrees out of wack.

Been there, done that with an old Indian.

Use a timing light to check for points opening near TDC of each cylinder in turn.

[oldbike54]

One coil with a distributor or 2 coils with two sets of points?
I'm thinking either the wrong cylinder is using the other cylinders points putting one spark 90 degrees out of wack.


Sent from my shoe phone!

'92 model , doubt if it has points KR .

 Dusty

[Kiwi_Roy]

'92 model , doubt if it has points KR .

 Dusty

I think you're right, Carl's drawing shows an electronic module of some sort with two coils, perhaps it's fritzed but it could be still crossed over. the thing to do is see if ther's a good spark on the non running side.
Roy

[oldbike54]

I think you're right, Carl's drawing shows an electronic module of some sort with two coils, perhaps it's fritzed but it could be still crossed over. the thing to do is see if ther's a good spark on the non running side.
Roy

Yeah , and check the ignition timing also . However , I was working with what the OP gave me .

  Dusty

[Chuck in Indiana]

So.... what kind of ignition is it running?

[normzone]

It's not running.

Well, only on one cylinder.

Oh, never mind me, just wanted to be involved but don't have anything new to contribute.

[oldbike54]

So.... what kind of ignition is it running?

The "sparky" kind  ;D Sorry  :-[ Good question though , did the SBs run the famous digiplex in that era ?

  Dusty

[sign216]

I think you're right, Carl's drawing shows an electronic module of some sort with two coils, perhaps it's fritzed but it could be still crossed over. the thing to do is see if ther's a good spark on the non running side.
Roy

Yes, the first thing to do is check for a spark on the bad side.  Pull the plug, ground the plug shell to the bike's frame, and crank the engine while  keeping an eye on the plug for a nice blue spark.

Let us know what you find.

[simj26]

Says Moto Guzzi on the electronic ignition pick up plate. Swapped all ignition wiring and tried all combinations..good spark both sides. Looks like I'll have to remove the cam next to have a look.
The right side tries to run but just backfires. Exhaust is clear, good spark,carbs good,no short on ignition wiring, fuel good (use remote fuel tank so no fuel tap issue). This bike has only 30451km (approx 19000 miles) are Guzzi cams liable to wear at that mileage? Someone on the Triumph forum suggested the timing chain tensioner is made of plastic and can break? Sorry if anyone thinks I'm being 'smart' and telling them they're wrong...I'm just trying to gather as much information as possible as I'm not familiar with Guzzi's.....I'm a Triumph man meself! ;)

[Triple Jim]

You don't have to remove the cam to see if its lobes are OK, you just need to measure how much the valves are moving as you crank the engine.  When the lobes get really bad, you don't even need to measure, you can see the problem.

[oldbike54]

Sim , yeah I apologize if I seemed snarky , was not my intention . We are really trying to help , was simply trying to apply the scientific method . It is just so easy to get "stuck" when trying to diagnose a mechanical issue . Assuming anything can be a problem .

 Dusty

[normzone]

I'm putting my money on (let me know where to send it) Dusty and his ignition timing question. Shouldn't you be able to pull both plugs, crank it slowly by hand and witness a spark somewhere near TDC on each cylinder?

[oldbike54]

I'm putting my money on (let me know where to send it) Dusty and his ignition timing question. Shouldn't you be able to pull both plugs, crank it slowly by hand and witness a spark somewhere near TDC on each cylinder?

Thanks Norm , I wasn't the only one who suggested that ... was I ?  ;D We aren't there yet , just in the beginning stages of solving the issue . Besides , RK , Roper , Guzzisteve and Kev m haven't weighed in yet . And where is
Orwig, lying down on the job Wayne , wake up ::) ;D Sure I missed a few , apologies .

  Dusty

[simj26]

Yep done that,and timing looks pretty close (thing is with the pick up plate it doesn't make sense for one side to time correctly and not the other).....need to borrow a strobe light I think (hadn't used mine for 20 odd years and now it doesn't work).

[rodekyll]

So far I've got nothing to add to what's already been said -- run the baseline checklist + the suggestions so far and report back.  I'm no expert on early 90's electronic ignition, but I've got a fair handle on the general 4-stroke theory.  Maybe with more information re: compression, fuel, timing, etc I might have a thought. 

[mwrenn]

 It's been a while since I studied up on small block cams, but I remember there were quite a few issues with cam and lifter wear on the Lario.  I think the V75 has the same head/cam/lifters...
IIRC...the lash would get a little out of adjustment and the it would rapidly wear the lifter...the valve springs were really high tension, so the bike would rev higher without floating the valves...but the increased tension also contributed to rapid wear.  I guess the fix is to go to a progressive spring, like on the newer small blocks...

[rodekyll]

I think the process should start with a bit of systematic observation and recording.

What is the compression/leakdown?
What is the actual ignition timing, and on what stroke does it occur?
What is the fuel flow quality and how was it determined?
What is the condition of the coils/wires/plugs (have the plugs been manually checked and gapped?)
What is the valve lash and how was that determined?
What is the cam lift and how was that determined?

If we think the problem is deep-rooted and out of the ordinary and have no eyes on the bike, then these baseline levels need to be excluded.

Don't care what has been done. Or checked.  You're here because none of it worked.   I do care about heading to the garage and taking an hour to fill out this list with fresh data.  This is how I would handle the broad strokes on anything that came into my shop, and 97% of the problems I encounter are solved by simply a fresh run at systematically stepping down the checklist.  I think the problem will be obvious when the blanks are filled in.  Until then, any diagnosis is speculation.

Humor me.  $0.02

[Kiwi_Roy]

Says Moto Guzzi on the electronic ignition pick up plate. Swapped all ignition wiring and tried all combinations..good spark both sides. Looks like I'll have to remove the cam next to have a look.
The right side tries to run but just backfires. Exhaust is clear, good spark,
[/quote

Thie backfiring was what made me think perhaps the ignition was crossed over, it would fire ok on one cylinder but be 90 degrees late or early on the other. it's not the sort of misstake you would normally make but may be the reason the PO gave up on it, I'm sure it's quite easy to get it mixed that's why you need to check both cylinders.
On the Indian I built up of parts with no point of reference I timed the front cylinder points correctly for the rear cylinder plug, of course the front cylinder was way off because of the uneven firing pattern. It was just a matter of swapping the wires and re-timing.

[Morizzi]

So.... what kind of ignition is it running?

Once again Chuck makes the most pertinent query for the most probable suspect.  ;-T

92 V75. I'm guessing it is a faired Strada.

Do you have a couple of modules like this, probably under the seat?



If so you have the motoplat system. Quite sensitive to poor earths. Clean and check ALL connections. If that doesn't work then swap over the modules and see what happens.

You're lucky. I normally don't help Triumph people.  :P