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Discussion Starter #1
Sometimes my 45,000km '2000 (carb) monster 750 quits running on the vertical cylinder and just runs the horizontal cylinder. Nasty. Simply replacing the vertical cylinder plug gets it firing again.

I'm not an expert or a mechanic, but am doing my best to do all possible Ducati maintenance at home now (M750 is wife's, mine is a Superlight) rather than pay $100/hr - so detailed answers are most welcome. I'm on a learning curve.

* The replaced plug does not look enormously fouled. A little black, but I know it is running a bit rich - jet kit and new needle jet sometime. A good clean makes no difference.
* If I take the plug out and earth it to the engine while ticking the engine over it will show very weak or no spark. A new plug will spark.
* I swapped the coils and ignition 'black boxes' left and right to see if the problem swapped cylinders. It didn't. The problem is still on the
vertical cylinder. (incidentally, problem went away for a little while after that swap, so I thought it may have been dodgy wires or loose connection that I fixed - but it came back)
* I have tried the NGK DPR8-EA9 plugs - same thing after a while. Stock gap.
* I have tried Champion RA4HC (as fitted by ducati workshop) - same thing - gap .6mm. I have just put Champion RA6HC (as specified for the M750 in the haynes manual) to see how it goes but considering the NGK didn't fix it, I'm not sure this will either.
* Multimeter on battery shows 12.45 volts.
* When both cylinders are happily firing there is never any intermittant drop outs, or misfirings or anything.

other info:

* Stock airfilter/carbs - but with termi slip ons.
* not sure if all 750s do it, but this bike is a bit lousy under 3000rpm, shudders at 2200rpm. Figure this is probably worn carbs.
* Got my CarbTune pro (http://www.carbtune.com) yesterday to attempt a carb sync this weekend.

All help/advice appreciated.

Greg.
 

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have you ever tried a compression test? also have you ever pulled off the alternator case off before? there are ignition pickups under the flywheel that could be out of adjustment or bad. just throwing out the possibilities.
 

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Discussion Starter #3
Thanks. Not done a compression test. Sounds like a good idea anyways though.

With the alternator - would that affect the strength of the spark? I need a special tool to get the left hand engine cover off don't I?
 

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i just got done messing with that side of the engine. installed a aluminum flywheel. when i put the new flywheel on i had to re-adjust the pick-ups to the new flywheel gap. to mess with anything on either side of the engine that involves removing the side case covers involves draining the oil, 5mm allen to unbolt case, and maybe new case gasket. i was mentioning this as a last step. it's kind of a PITA.

has there been any maintenance done to the bike recently that may have cause this sudden upset? timing belt, disconnecting and reconnecting plugs?
 

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Discussion Starter #5
Thanks. It has had belts done recently, but it was doing the cylinder dropout before that. The plugs have been swapped a few times, but that is in an effort to narrow the problem down.

I'm afraid I'm still a bit in the adrk as to what could possibly be going on.

Any ideas on how I can test the strength of the spark to see if the coils/etc are really doing their job?
 

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Discussion Starter #6
Bump.

Any ideas out there?
 

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I'm just guessing here, I've never had an issue like this. If it only fouls the one plug it sounds like it has to be a carb issue. I would think all other issues would affect both cylinders. I've noticed mine is real touchy when it comes to fouled plugs, it doesn't take much to make it misfire. I've also heard it's just about mandatory to adjust the carbs after any intake or exhaust mods. The carbs are one area (technically 2) that is easy to screw up and takes a certain amount of experience to get right. I wouldn't trust myself to adjust them so I would recommend you take it to someone with experience with Ducati carbs. Since you've added exhaust and since you haven't had them service in a while it's worth doing even if it's not what's causing the problem.
 

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Have you put your battery on a charger? My M750 drops a cylinder (intermittently), back fires and generally runs like a dog if the battery isn't in top condition. It will turn over just fine with the starter motor, so it SEEMS like the battery is good, but if I put the battery on a charger for a while and try again, it runs perfectly. Worth a try?
 

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I'm just guessing here, I've never had an issue like this. If it only fouls the one plug it sounds like it has to be a carb issue. I would think all other issues would affect both cylinders. I've noticed mine is real touchy when it comes to fouled plugs, it doesn't take much to make it misfire. I've also heard it's just about mandatory to adjust the carbs after any intake or exhaust mods. The carbs are one area (technically 2) that is easy to screw up and takes a certain amount of experience to get right. I wouldn't trust myself to adjust them so I would recommend you take it to someone with experience with Ducati carbs. Since you've added exhaust and since you haven't had them service in a while it's worth doing even if it's not what's causing the problem.
Have you put your battery on a charger? My M750 drops a cylinder (intermittently), back fires and generally runs like a dog if the battery isn't in top condition. It will turn over just fine with the starter motor, so it SEEMS like the battery is good, but if I put the battery on a charger for a while and try again, it runs perfectly. Worth a try?

I totally agree with TonyB; on some EFI cars, if the battery is not 1000% there will be a slight missfire across the rpm range...

Regarding the carbs, if you're not mechanically inclined, which looks you are, then adjusting is not that a black science; basically, shut both[mix screw] carbs down while engine running[if you have a big fan use it to have cool air going over motor], then, slowly give gas, slowly, to the front cylinder[adjusting the mix towards rich], give it a couple of quick turns of the wrist[every 1/4 of turn] and what ever adjustment you did to the front, do half of it to the rear; this is how I adjusted a friends carbed M600 a while back and it has worked as of 2500kms, no fouling no missfires...
Forgot, do you have the OEM Mikuni or the Keihin FCR?

Air filter and air filter box? You mentioned replacing the exhaust with an aftermarket one, so, maybe, just maybe, all you need is more air...take the top of the airbox off and go riding the usual distance, if no fouling, then forget the above instructions and get a perfomance air filter and cut the top of your air box...

Have you ever replaced the spark plug wires? Coils? Why not give it a shot and if after doing the carbs everything's OK, replace these parts, maybe with upgraded aftermarket parts and enjoy the bike for years to come.
 

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Discussion Starter #10
Thanks Guys,

I'll charge the battery. Haven't got a charger but now is a good time so it seems! I've put a voltermeter across the battery terminals and it shows a healthy 12.5, but I know nothing about batteries, so I'll give it a shot.

darkmonster620: It has stock mukunis and a stock airbox at this time. When tuning mixture screws, why do only half to the rear?

Update: I worked the entire weekend to remove, clean and refurbish the carbs just in case it was a dodgy carb/jet/needle. While I was at it, I installed a Factopry Pro jet kit and new stainless steel needle jets. When setting the mixture screws to the factory pro recommended 2.75 turns I found that the carb for the dodgy cylinder was 7.5 screws out! I thought I had a smokin' gun.

[While I was at it, I also checked the primary & secondary resistance of both coils (dunno actually what that means, but I was just reading my haynes manual) - both checked out to be okay. Funnily, the haynes manual says that if both those resistances are within range then "the coils will *probably* be capable of correct operation". But remember, I swapped the coils and ignition control units left and right and still the same cylinder was crapping itself.]

Carbs back in. A few quick test rides yesterday, all seemed okay - happiness. Rode it to work this morning. Exactly the same problem as
before - running like a sick goat, and (possibly) it seemed to get worse as the bike warmed up.

I'll be out at lunch today for another test and to stick yet another set of plugs in to start it afresh. If I can get time tonight I'll do (attempt - my first) carb sync using the carbtune tool. Wish me luck.

Regarding the airbox, one of my test rides last night was with a K&N filter and open airbox (I borrowed them from my 900 Superlight) - actually, it didn't seem to make too much difference.

So, next steps,

* new plugs
* carb sync
* battery charge
* also, open airbox for a while.

All help and advice appreciated. Keep it coming - this one is not solved yet!

Greg.
 

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Thanks Guys,

I'll charge the battery. Haven't got a charger but now is a good time so it seems! I've put a voltermeter across the battery terminals and it shows a healthy 12.5, but I know nothing about batteries, so I'll give it a shot.
darkmonster620: It has stock mukunis and a stock airbox at this time. When tuning mixture screws, why do only half to the rear?
As I said, this is what I did to a friends M600 with original Mikuni since he was desesperate to ride the bike[bought it online, never saw it,only pics, imported bike, almost didn't run] did what you just did to carbs, except, new kit inside; just cleaned, degummed and when adjusting, after a short/medium ride[10~15kms] it would start coughing, and almost diying while running. I smelled 'unburnt' gasoline, so assumed mix too rich, and proceeded to do as I do in autos with carbs, close the mix screw and open 1/4 turn at the time giving gas to 'purge' the carb in the process; as I said, it worked for his bike, it might work for you. And why only to the rear cylinder? Only the Gods might know the correct answer. Also, I 'modified' his air filter's box top, since it rains mouse,cats and dogs here in Panama, I only opened 5 1.5" holes on the top and 2 on the front, this, somehow also leaned the mix and if from where I got the 'rear=1/2 of front', as said, is working fine on this particular M600.

Update: I worked the entire weekend to remove, clean and refurbish the carbs just in case it was a dodgy carb/jet/needle. While I was at it, I installed a Factopry Pro jet kit and new stainless steel needle jets. When setting the mixture screws to the factory pro recommended 2.75 turns I found that the carb for the dodgy cylinder was 7.5 screws out! I thought I had a smokin' gun.
OUCH!!!! 7.5 out??????

[While I was at it, I also checked the primary & secondary resistance of both coils (dunno actually what that means, but I was just reading my haynes manual) - both checked out to be okay. Funnily, the haynes manual says that if both those resistances are within range then "the coils will *probably* be capable of correct operation". But remember, I swapped the coils and ignition control units left and right and still the same cylinder was crapping itself.]

Carbs back in. A few quick test rides yesterday, all seemed okay - happiness. Rode it to work this morning. Exactly the same problem as
before - running like a sick goat, and (possibly) it seemed to get worse as the bike warmed up.

I'll be out at lunch today for another test and to stick yet another set of plugs in to start it afresh. If I can get time tonight I'll do (attempt - my first) carb sync using the carbtune tool. Wish me luck.

Regarding the airbox, one of my test rides last night was with a K&N filter and open airbox (I borrowed them from my 900 Superlight) - actually, it didn't seem to make too much difference.

So, next steps,

* new plugs
* carb sync
* battery charge
* also, open airbox for a while.

All help and advice appreciated. Keep it coming - this one is not solved yet!

Greg.
*New plugs >>> try one grade hotter....
* carb sync >>> if you have the tools... me, play by ear
* battery charge >>> is a must before carb sync
* also, open airbox for a while >>> liking the growl?

Keep us informed of your findings, we all learn...
 

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Discussion Starter #12
Thanks Carlos/all,

Took it home at lunch.

* Installed Champion RA8HC (hotter plugs - haynes says RA6HC - ducati guys installed RA4HC)
* Exchanged battery with 900 superlight (will get a charger tonight)
* Put on K&N air filter and open airbox lid (also from 900).
* Replaced fuel filter.

*Still* runs like a pig. Off idle it feel really limp and the throttle is imprecise. It'll stall if I don't keep the revs a bit high. Funnily though, on acceleration it feels pretty good.

Both plugs from this morning's ride are pretty black, so it was running pretty rich after the jet kit (hopefully the open airbox lid will assist there - so I'll check the plugs after the ride home this afternoon - might even get it out onto a highway just to see how it feels at that throttle).

You know, I still haven't managed to figure whether it is fuel or electrics. Well, it can only be only of those two I guess!

It could be that there was more than one problem. That is, the cylinder that was crapping out may have been doing so because of the 7.5 turns on the mixture - but having that (hopefully) resolved (touch wood), maybe there is another issue.

I guess I've still got the battery charge to try (but as the 900 battery didn't resolve it .. I'm not confident that'll fix it), and the carb sync.

All help appreciated.

Greg.
 

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Discussion Starter #13
Update:

I got home this afternoon and did a carb sync. They weren't much out but I could hear the engine running much nicer as they went into sync. Nice. Pretty easy thing to do for a first timer actually.

I wound back the mixture screws from the factory pro recommended 2.75 turns to 2 turns.

Out for a test ride - pulled like a train. Nice. Still running rich, the plugs were still sooty after the ride, but running a lot better. The carb sync also reduced some engine shudder at 2200 & 3000 rpms. Excellent.

I have a feeling I have been too generous with the jets I used in the factory pro jet kit. Stock pilot jet is supposed to be 140 - mine had 142.5 (just like the fellow at ducatisuite.com - he found his stock was 142.5 also). Kit had a 145 so I put that in. Stock main jet is 132.5, jet kit had 135/137.5/140/142.5 - I went for 140. I think maybe 135 or 137.5 would have been closer to the mark.

I'll charge up the battery tonight and we'll see how it all goes on the morning run through traffic. If it goes okay, I guess I'll have to consider yanking the carbs out to replace those jets and then perhaps take Carlos' advice about starting tuning with the mixture screws in and gradually winding them out. A nice color on the plugs and exhaust would make me a very happy man.

Greg.
 

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Discussion Starter #14
Update:

I think I can close this one now, so for the puposes of sharing I'll summarise.

* Bought bike five months ago.
* Bike sometimes ran on one cylinder. Electrics sorta seemed okay.
* Swapped left/right coil and ignition unit and new plugs. Problem went but then came back on same cylinder - not the coil then.
* Tried different plugs heats. No joy. They all fouled.
* Installed Factory Pro jet kit. Found mixture screw for carb for dodgy cylinder was 7.5 turns out (Factory Pro says 2.75).
* Still ran like crap, but didn't seem to lose a cylinder.
* Battery swap, no joy.
* Airbox/filter swap. No joy.
* Carb sync. No joy.

This is what happened:

* The 7.5 turns thing was running a cylinder waaaay too rich. It caused the cylinder to foul its plug and screw up.
* With that gone, I had introduced another 'running rich' problem when I installed the jet kit which made it run like a sick goat.
* Backing off the mixture by .75 turns then created a quite-lean condition. Huh?
* I rechecked the airbox seals and the rubber seals for carb/airbox/intake. Turns out that the crankcase vent return was not properly back in the airbox, and i wasn't aggressive enough in tightening the rubber seals (everywhere). Tighten those then ...
* Another carb sync has it purring. I even have the right burn colour on the plugs. Nice.

Final config:

* Stock air filter/box with snorkels removed (will probably open this up more)
* Factory pro kit with pilot 145, main 140, jet needle clip on #2, new needle jets.
* Mixture screws 2 turns out (may try 2.25)
* Champion RA8HC plugs (might go back to RA6HC to see).

Thanks for all help and advice. Great to be part of an active Ducati forum.

Greg.

PS. Bike is now ready for the trip to the openng round of the World Superbike Championship at Phillip Island this weekend! .. and it is the wife's bike ... so even better :)
 

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Update:

I think I can close this one now, so for the puposes of sharing I'll summarise.

* Bought bike five months ago.
* Bike sometimes ran on one cylinder. Electrics sorta seemed okay.
* Swapped left/right coil and ignition unit and new plugs. Problem went but then came back on same cylinder - not the coil then.
* Tried different plugs heats. No joy. They all fouled.
* Installed Factory Pro jet kit. Found mixture screw for carb for dodgy cylinder was 7.5 turns out (Factory Pro says 2.75).
* Still ran like crap, but didn't seem to lose a cylinder.
* Battery swap, no joy.
* Airbox/filter swap. No joy.
* Carb sync. No joy.

This is what happened:

* The 7.5 turns thing was running a cylinder waaaay too rich. It caused the cylinder to foul its plug and screw up.
* With that gone, I had introduced another 'running rich' problem when I installed the jet kit which made it run like a sick goat.
* Backing off the mixture by .75 turns then created a quite-lean condition. Huh?
* I rechecked the airbox seals and the rubber seals for carb/airbox/intake. Turns out that the crankcase vent return was not properly back in the airbox, and i wasn't aggressive enough in tightening the rubber seals (everywhere). Tighten those then ...
* Another carb sync has it purring. I even have the right burn colour on the plugs. Nice.

Final config:

* Stock air filter/box with snorkels removed (will probably open this up more)
* Factory pro kit with pilot 145, main 140, jet needle clip on #2, new needle jets.
* Mixture screws 2 turns out (may try 2.25)
* Champion RA8HC plugs (might go back to RA6HC to see).

Thanks for all help and advice. Great to be part of an active Ducati forum.

Greg.

PS. Bike is now ready for the trip to the openng round of the World Superbike Championship at Phillip Island this weekend! .. and it is the wife's bike ... so even better :)

Greg,

glad you're back on the road with no issues, was glad to help....keep on ridin'...But use your own not the wife's.....
 

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Hi Greg, I have a 98 M750 (stock carbs) that has done 130,000 klm and still going strong when I bought it had done only 8,500 klm and after say about 1 yr it started to run rich and fowling plugs and cylinders cutting out, tried a couple of things like you but in the end I had it dyno tuned and found that the bottom end was rich and the top end lean and after re jetting all good. so I would suggest getting it dyno tuned.
Cheers
Jack
 

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Discussion Starter #17
Hi Jack,

Thanks for the advice. The bike is still not quite perfect, so the dyno may be an option when I run out of patience! I priced having someone do that locally and it was over $800 so it's not a cheap option.

May I ask what jet sizes you ended up with and what needle clip position?

Did you use a Factory Pro kit or a Dynojet? or something else ...
 

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Hi Greg,
$800.00 for a dyno tune is a **** load of money it should about $200, I have just got back from a 4,500 klm ride to Phillip Island we went on all the twisty roads we could find. The duke went OK but for a small electrical fault (corroded wire) after the fix all good.
Getting back to your problems, when my bike was running rich and fouling plugs the dyno tune showed the bottom end rich and the top end lean with stock jets,
the only jet change was the main a little bigger I do not know the size the needle was dropped one position (three from the top) the float height lowered and idle mixture adjusted.
Another problem I have had was the horizontal cylinder running rich and spitting out raw fuel on start up, I first thought that it was a carby problem but found that it was the vacuum operated pet cock under the seat the diaphragm had failed and fuel was draining into the intake manifold, replaced pet cock.
Hope that all helps

Jack
 

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Discussion Starter #19
Hi Jack.

Thanks. Good info. Been to the World Supers at Phillip Island then eh. Same here. Might have seen you there! We were at Siberia.

Just had the bike out for the weekend for about 1200klms. It ran well, no fouling, good colour on plugs. But, still not perfect and I think some more adjustment needed. Back down one on the pilot jet, probably on the main as well, and recheck float heights and then mixtures. I promised my wife I would have another 2 'adjustment' sessions on it and if it still wasn't like she wants it (it is my wifes bike) I'll do the dyno/shop/tune thing.

Back to Phillip Island on Monday for the Vic Ducati club ride day, so I can test it on the track. Life is soooo sweet sometimes. :)

Greg.
 

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Discussion Starter #20
Forgot to ask. Was it a Factory Pro kit you used? (just making sure that when talking about the needle/clip position we're talking apples and apples).
 
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