Ducati.ms - The Ultimate Ducati Forum banner
  • Hey Everyone! Enter your bike HERE to be a part of this months Bike of the Month Challenge!

1 - 14 of 14 Posts

·
Registered
Joined
·
57 Posts
Discussion Starter #1
Hi gents. As I've mentioned earlier that my '99 M900 has a strange fault like it drives very good for few miles then starts to choke off, back fire and eventually stop. Try to start it again and it's like running on one cylinder. crank the choke up help it run a bit better but eventually die any way. Could it be a vapor lock or something?

Lately I put it in hand of my mechanic who change the spark plugs (didn't help) get one one of the igniter changed (didn't help either but this one I agreed as it has a crack n burnt epoxy suggesting something is burning inside)

Last time I talked to him he mentioned the regulator voltage at idle is a bit off the chart (15-16volts) and now he has personal issue and have to close down his shop. I grabbed two of my bikes back and I have to rely on myself for the moment (as you can see me fixing the leaking fuel sensor myself lol) until I get my new mechanic lol.

So far I start checking from the wiring diagram, service manual:- (with digital multi meter)

the pick ups, both measured 102R approximately.

the alternator coil, some how the previous owner changed it to 3 phase I am not really sure. they measured 0.4R on all three terminal (with respect to each other), measured 11v at idle (ac mode on multi meter with respect to battery ground) 36v at higher rpm (guessing 4000 as my bike has no tachometer)

the rectifier/regulator, Shindengen SHxxx (something I don't remember) I believe it was a 3 phase replacement of the original as it has no charge warning wire (so I planned to build my own scr uC controlled in the next episode) weirdly this time it only measured 11.8v at idle and 12.6v at higher rpm. Could this mean it's actually dying slowly? The wires and the reg/rec are warming up at idle. I check its chassis also connected to gnd. The 40A fuse looks ok.

the igniters, looks like they both conforms to the service manual's checking table.

the high voltage coils, both measured 4.2R primary, 17k secondary.

I also measured the current draw by the bike. At ignition off - 0A good sign nothing 's leaking. ignition on - 3.4A is this normal? idle - 10A noooorrrmal?!?

I tried to find if it's the electrical fault or fuel fault but it could also be others. My next plan is to put a scope in and see the wave form and timing of the ignition and the pickup pulse - try to figure it out why it starts miss firing and running on one cylinder. I might then try to datalog it with the oxygen sensor (see if it's the fuel fault) at the end of the day.

Thanks for your time here. Really appreciated :)
 

·
Registered
Joined
·
1,332 Posts
Sounds like it might just be starving for fuel. When the bike stops, have you tried opening up the fuel cap to see if there's a big vacuum in the tank? How long since you've replaced the fuel filter? What do your plugs look like after it stops running?
 

·
Registered
Joined
·
57 Posts
Discussion Starter #3
That's what I thought. I opened up the gas cap but didn't notice any vacuum. We (me & my ex-mechanic) used to by pass the fuel filter and it didn't help either. Could it be something clogging in the fuel system? He cleaned carbs already.

He said the spark plugs color looked ok. It does look ok to my eyes as well.

I think I should also check the timing and the belt tension at some point.

Cheers.
 

·
Premium Member
Joined
·
5,197 Posts
Belt tension has no effect you are mentioning. It could be electrical mechanical or fuel. most likely fuel or electrical.

I would test to see if you are dropping the same cylinder each time, try removing a plug and see if it dies or keeps running the same.
Change plugs as a broken plug can do this, plug wires as well but start by seeing if it is losing spark when the problem happens. Do not over think this start slowly and hit the simple things first.

I would get it to die and then open a fuel drain to see if you have fuel, or use a clear line to verify it is not a blockage. I had a customers tank un-bond the tank coating and plug the outlet. Test that the fuel pump is pumping, make sure there is gas after the pump. People like to mess with the pumps but they are very reliable.

The 1999 should have been a 3-phase charging system so you should have the right rectifier if you are seeing 15VDC then the regulator is probably bad somewhere mid 14vdc is about right for max. Is the battery working without supplemental charging?
 

·
Registered
Joined
·
57 Posts
Discussion Starter #5
Cheers mate. I don't remember which cylinder is not firing. Will have a look/switch things around as you suggest. Spark plugs aren't likely to be broken as they've been changed but will have a look again sometimes.

Hey. Clear fuel line is such a neat idea. Will definitely go for it. You mentioned the tank drain reminds me I forgot to mention I didn't see any hoses come out of these two (I believe they are drain/overflow line) Might worth driving it with the tank open just to test it. Rough inspection I can see something is blocking in one but not sure which one is which but will have a look into this.

For the charging issue, few month ago my ex-mechanic told me it had 15-16vdc charge voltage and now it's like 12.3v at idle. I charged my battery last night and let it settle for few hours. I took it for a ride this evening it starts out around 12.68v for few miles and it died. Pushed it back home and measured 12.38v. I don't think the charger is normal or is it?
 

·
Premium Member
Joined
·
5,197 Posts
Spark plugs aren't likely to be broken as they've been changed
I have been bitten twice now with brand new spark plugs I installed having a internal break, the plug worked some times and was new. Trust nothing.

At idle the bike should be around 12.5-13vdc but just a bit higher should jump up to 13-14vdc with max (by 3000rpm) around 13.5-14.5vdc. The fact you are reading 12.38 after it dies means it is less likely you are running out of power and that is the problem, the charging may not be right but it is not likely the issue with the bike dying.

The cap open test will let you know if the tank is not getting air to replace the fuel used but will not help with a plugged tank/line or filter. If you have a carbureted bike then the pressure is low and it is usually less likely to have a issue from low pressure systems. Can you make the bike have the problem on the sidestand without riding it? if so you can make a temporary fuel supply to the carbs and rule out the tank and pump (gravity feed from a bottle).
 

·
Registered
Joined
·
7,104 Posts
Make sure your fuel lines aren’t kinking when you put the tank down. Make sure fuel lines are not routed too close to a heat source. I have to say, this sounds as if it may be an ignition issue. Carry a spare plug, when the trouble starts use it to check for spark while still hot. Make sure you ground the plug against the head.
 
  • Like
Reactions: Hamster749

·
Registered
Joined
·
57 Posts
Discussion Starter #8
Cheers mate. You would have known this model has a kinking fuel line as hell. They route everywhere pass the cylinder heads for few times if not more lol. But will do like what you said see if anything I can get away with this.

Not sure about your grounding plug though. You mean to check if the sparks are all right when it died? So, I just take off the spark wire, connect to a spare plug, ground the spare plug to the cylinder head and crank the engine up see if I get the sparks?

I have been bitten twice now with brand new spark plugs I installed having a internal break, the plug worked some times and was new. Trust nothing.

At idle the bike should be around 12.5-13vdc but just a bit higher should jump up to 13-14vdc with max (by 3000rpm) around 13.5-14.5vdc. The fact you are reading 12.38 after it dies means it is less likely you are running out of power and that is the problem, the charging may not be right but it is not likely the issue with the bike dying.

The cap open test will let you know if the tank is not getting air to replace the fuel used but will not help with a plugged tank/line or filter. If you have a carbureted bike then the pressure is low and it is usually less likely to have a issue from low pressure systems. Can you make the bike have the problem on the sidestand without riding it? if so you can make a temporary fuel supply to the carbs and rule out the tank and pump (gravity feed from a bottle).
Cheers mate. Ok. I trust you. will definitely check the sparks.

I agree with you the charging might not be an issue but I would guess when the bike about to die, the voltage would be significantly less than (static and already recovered)12.38v as it draws almost 10 amp running and with not enough juice from the reg/rec. Will hook up small volt meter see what the voltage we get when this symptom occurs.

You reminded me again my mechanic used to take the tank and the filter off and feed it with the bottle and brave enough he went out for a ride. He said the bike died just outside the city skirt. Not quite sure how he managed to get back to his shop though.
 

·
Registered
Joined
·
7,104 Posts
You need real double wall fuel line that will strongly resist kinking. Single wall or clear plastic line can collapse when hot if bent too tight and will melt through in seconds in a fire. Don’t use it.
 
  • Like
Reactions: Hamster749

·
Registered
Joined
·
57 Posts
Discussion Starter #10
Cheers mate. Will definitely have a look into that.
 

·
Registered
Joined
·
57 Posts
Discussion Starter #11
An update this evening. It turns out the high side of the regulator/rectifier issue is infact the one to worry about. Not the low side. I measured the battery around 12.6v then get it started. I let it idle for about 10 minutes. The voltage actually rose to 13.8v and was going up. As I blipped the throttle, The voltage went up. Sometime pass 17v. Held the rpm to around 4000 and it almost hit 17v so I would guess a lot more at red line so I would't risk. Something is not right ain't it?

Should this contribute to the symptom? What will be bad to the system from the excess charge voltage?

At the end of the test today(raining today so no test ride), the bike don't die. It just keep idling nicely.

Any thoughts? Cheers.
 

·
Registered
Joined
·
57 Posts
Discussion Starter #12
Good news gents. About a week after my last update, I have put a transparent hose just after the vacuum pump. I can see the fuel behind the pump but the engine was still choking. Then I put a longer transparent hose looping it up so the high point of the loop is higher than the carbs (I guess) to let the gravity do the feed. At the first time I can see the fuel rush in but has a difficult time passing the loop. The engine was still choking but after the loop was filled for about half a minute, a miracle happened. It ran smoothly. I mounted a small volt meter and went riding around town and back without any issue - problem solved, it was starving of fuel(pheww)

- How can we check if the pump is working properly? Should there be a range of fuel pressure the pump produced?

The clear fuel line allow me to see there was some debris left just behind the pump. It looked like some sort of sand so I don't think fuel filter is doing the job.

The regulator is probably bad as well. Under cruising speed It is from 12.6v and keep rising pass 15v so I have to turn on the main light then it is well in the range. There is no go for prolonged mid or heavy acceleration I have to back of the throttle unless the voltage will shoot pass 15v. Time to build a uC-SCR regulator on my next episode then.

Thanks a lot guys. I really really appreciate your help, time and effort. All of you.
 

·
Registered
Joined
·
7,104 Posts
I’m not thinking your fuel loop is a good idea. Just a spot to trap air in the line. I’m not familiar with the vacuum fuel pump on your bike but my experience with other vacuum operated things tells me they aren’t very good or reliable. The debris could be the pump falling apart. I’d find a way to measure output. Make sure the vacuum line going to it is good, or replace it, before you test.
 

·
Registered
Joined
·
57 Posts
Discussion Starter #14
Cheers mate. Was suspecting the vacuum hose as well. Cant see any air in the hoop though after running it for a while it was flooded nicely but sure it will come off when the vacuum pump is sorted.
 
1 - 14 of 14 Posts
Top