Fagertofta
Hi. My ducati 851, 1989 has rolled 70000 km. The engine has always run smoothly, but lately the engine has begun to go irregular when it is not loaded. I have a very smooth and safe idle speed, and when I load, the engine pulls even and strong. The problem arises when I slow down tex to a roundabout at the road and have even, non-stressing gas, and the engine starts to jerk, which also increases. I increase the gas ending the jerk, and I reduce the gas and the engine brakes stop the engine jamming. No fault is heard from the exhaust pipes. I've had this problem with a irregular engine once a time before, and then fixed it by replacing fuel filter.
Current measures: New spark plugs, clean air filter, new fuel filter, cleaned and controlled injection, replacement of power group amplifier control unit, replacement of I.A.W. Electronic central unit.
Unfortunately no difference!
Able to change or adjust: Pressure Regulator, Absolute pressure sensor, Coil, synchronize injection, Synchronize Throttle Position Potentiometer.
Is there anyone on the forum that can give me information about where to look first?
Thanks, Magnus Sweden
ROB851-999
851 Strada 1992 68000km
Hey,
I'm experiencing similar problems. MOst of my rides (cold engine) It runs fine, also at constant low speed. after a while when the engine is warm it starts.
Constant speed is very difficult, feels like constant misfiring the enigine. also the exhausts bangs now and then (explsions in the exhaust)
I tried swapping the relais in the rear without succes, hope that someone can help.
regards,
Rob
rxs51
My bike has had a similar problem for quite a while and I have tried just about everything I can think of without success - fuel filter and lines, had injectors tested and cleaned, balanced throttle bodies, reset tps, swapped over ECU etc etc but nothing has fixed it and I have just learned to live with it for the time being.
If you find an answer then please let me know what I have missed!
brad black
chain tension/wear, closing clearances, mixture, throttle cable slack?
rxs51
Brad, yes - all have been checked.
It does seem odd that so many early 851s seem to have similar problems and I wonder if it could be something like coils starting to break down under load due to age?
Like others mine is worse when it gets hot.
griff851
A long shot, but fly wheel could be moving.
rxs51
Griff - is there any easy way to check for that?
griff851
Alternator cover has to come off. Has it had a sprague clutch change?
rxs51
Yes, I replaced the sprag clutch at the end of last year but the irregular running was exactly the same before that - it has been a problem for quite some time that I have just learned to put up with as the bike runs fine when on the open road and on and off the gas - it is only really a problem at low speed on a steady throttle opening.
I guess the real answer is to get it on a dyno with a good operator to see what is happening to the mixture but that will have to wait till next year as I am laid up with a crocked back at the moment!
griff851
At what rpm are we talking about here?
rxs51
Fairly low because I try to behave and not upset people going through 30 limits so somewhere between 3- 4000rpm
griff851
Ok. Here's the thing, the old Desmoquattro is a fairly sporty engine. When selling the 4V bikes I use to say two things. First off it's not a Harley. Second, 3 1/2 grand is something you go through in first. I know it's a PITA around town, but they are not really commuting machines.
4K is about minimum, under that the engine is labouring and hence the rough running. There is zip you can do about it. Ideally 4.5-6k around town. Yep lots of gear changes and it sounds like way too revy, but at least it's not labouring and punishing your bottom end and chain. You might want to consider sprocket changes to reduce the 2nd 3rd shuffle if you spend most of the time around civilisation.
And if you do a fair bit of the law abiding town travel, take it out now and again and give it some. Power doesn't really cut in until around 6.5-7k and runs through until 10-11k. So runs to 9k at least through the gears are good for it. I believe it's called the Ferrari tune. 😄
rxs51
Griff, thanks for the comments - made me think about how I ride the bike.
I have owned it for around 20 years but for quite a few of those it was consigned to the back of the garage while I played on modern (and faster) toys. Thinking back I am sure that I used to ride it much harder in my younger days and it is quite possible that it was always like that but I was always a couple of gears lower so did not notice!
Guess I just need to get out and enjoy it the way it is (as soon as my back gets better) - it is still a fantastic bike to ride on open roads!
griff851
No problem, hope you back gets better soon. Lower back? Had one of them for a while.
I know the issue, nearly sort of finished my high comp bevel with kick start only. Problem is I didn't figure on old age making my knees an issue😁 Guess that's what pain killers are for.
Higgins
Engine rough at mid range
Hi gents,
I do have exactly the same "problem" on my 851. (recently buyed).
The bike is 24000km has had a complete engine rebuilt 2000km/2 years ago. Bike is in good shape and was ridden regularly, fuel tank is clean and gas is new.
Check done since aquisition : new spark plugs, fuel filter, all sensors and TPS, TPS adjusted, air intake balanced (new parts from Stein-Dinse) injectors and fuel pressure checked but the bike is still running rough at steady mid range (3500-4500).
I still have to check closing clearance after that next try will be an ECU swap with a modern one (Ignijet) but as a carburettor integrist it is a leap in the unknown😳
Any suggestion will be appreciated
Regards from France
Laurent
brad black
what year is it? bodywork and forks aren't consistant.
if it has soft closing springs that can be an issue in that rpm range, as well as loose closing clearances. what eprom is in it?
it should be able to be made to run down to 2,000 rpm or so nicely.
Higgins
Hi Brad,
Glad to speak with you, thanks for all your verry interresting publications about 888 family
You are right but under her dress this bike is 1989 ZDM851S3 strada.
Standard air filter and open mufflers P7 ECU with "Ducati 851S3-009-" chip
Under 3500 RPM bike is smooth and has a quite satisfaisant idle (of course not as smooth as my 750 sport or my 600SS).
I am far from home (at work) at the moment but i will check closing clearances as soon i will be back, i suppose the return springs are the light original ones.
brad black
be interested in closing clearances if the poor running is just 3500 - 4000.
does it have overly loud mufflers?
Higgins
Hi Brad,
Thanks for your help, the rough range is effectively around 3000-4000 Rpm will check that asap.
The mufflers are pretty loud and the -8 chip seems to be the good one according to your chip list just missing the "B".
I have red somewhere the dash B is an upgrade used to save the sprag clutch by modifying ignition timing could you confirm ? If yes do you recommend this upgrade ?
I suppose it put less advance angle during starting phase ? I have had this mod on my Panhard 24 (french flat twin popular cars and i found it verry usefull).
Higgins
To be continued...
Hi Brad, Hi Folks,
This week I had the time for a complete check on the 851 still runing rough on mid range low throttle.
Valve check : All the closing gaps have been set between 0 and 5/100mm max.
Opening gaps set within 10-12/100mm for intake and 15-17/100mm for the exhaust
New timing belts, injectors cleaned and reverse flushed, new injector filters, caps and o-rings, all new fuel lines. New fuel regulator and air pressure sensor.
Already replaced during last check : irridium spark plugs and plugs wires, fuel filter, air filter, air T° sensor, water T° sensor, new TPS and throttle balance adjusted accordind to your instructions.
Fuel drained and replaced...
My bike is fitted with standard air box and filter, free exhaust (quite loud), 851S3-009 chip/P7 Ecu and light valve springs
I have a solid and constant 2,8 bar (40 PSI)fuel pressure.
Have you any idea ?
