Ducati.ms - The Ultimate Ducati Forum banner

1 - 14 of 14 Posts

·
Registered
Joined
·
16 Posts
Discussion Starter #1
My '99 Ducati Monster M750 (carb'd) is currently only on one cylinder. It doesn't even idle, and just barely semi-starts on the horizontal cylinder. I've done a fair amount of examination and trouble shooting and I'm starting to run out of theories! :confused:

A couple of days ago, I replaced the steering head bearings, removed the evaporative emission system (the grey pods on the side), replaced my low-fuel sensor, and replaced some half broken front turn signals a previous owner had on the bike.

After getting the bike buttoned up, I went to take it for a quick ride. After about 100 yards, the bike stumbled and died. It wasn't under heavy load or any hard acceleration. Before, the bike was running great. No pinging or knocking. I walked it back to my house and tried to start it, but noticed that exhaust was only coming out one side.

I've owned the bike for a little over a year now. It has been incredible reliable especially when considering some of the mistreatment (stripped bolts, questionable wiring, and non-existent maintenance) discovered by previous owners.

Over the next few days. I tested just about ever part of the ignition system.

- The pickup coils are within the spec'd ohms.
- I swapped the ignition control units and the problem did not move to the other cylinder.
- I swapped the coil packs and the problem did not move to the other cylinder.
- I swapped the spark plugs and the problem did not move to the other cylinder.
- Both spark plugs are getting a good spark.
- There is unburnt fuel on the spark plug of the cylinder that is not running. It's getting fuel.

Misc things I have checked:

- About 1,000 miles ago I replaced the timing belt. I checked it yesterday, it feels taught and still looks in great condition.
- Put in new spark plugs three months ago.
- When I started to run out of ideas, I disconnected the new turn signals thinking there might be a short in the system. No change.
- About three months ago, I made sure the valve shims were within spec. Any out of spec were brought back into spec.

When I replaced the low-fuel sensor, I drained my gas into a clean bucket. It sat there in the open container for about a day and a half until I was able to source the correct replacement part. Is it possible the gas oxidized?

Any ideas? Other things I can check? :(
 

·
Registered
Joined
·
80 Posts
My brother had a similar problem with his 620 a few weeks back. We were bashing our heads against walls trying to work it out. Plugs, coils and all the electronics were fine. Ended up being a dodgy blocked up fuel filter
 

·
Registered
Joined
·
54 Posts
thats what I was going to suggest too, replace the fuel filter. also it could just be that the fuel hose got kinked somewhere when you put the tank back down.

and one other thing to check would be the vacuum petcock (fuel shutoff) that is mounted at the tank pivot mount, the little silver circular thing. make sure the vacuum line that is connected to that is connected to one of the intake runners. also make sure the vacuum line on the fuel pump is also connected to one of the intake runners.

it definitely sounds like a fuel supply issue, something is causing the carbs to not get enough fuel or any fuel at all, so it has to be something between the tank and the carbs restricting fuel flow.

I had an issue like this at one point too, and it ended up being the petcock was faulty, so I just removed it and put a cap on the vacuum port on the intake runner it was connected to, and connected the fuel line from it directly to the fuel filter
 

·
Registered
Joined
·
16 Posts
Discussion Starter #4
The fuel filter theory is pretty interesting. Namely because it's one of the last maintenance bits that I haven't taken care of yet. Considering the neglect of maintenance from previous owners, I wouldn't be shocked if it has never been changed! :S

I'll swing by the Ducati shop later today and see if I can pick one up.
 

·
Registered
Joined
·
16 Posts
Discussion Starter #6
While that does sound like something I'd do :D , my bike has a vacuum activated petcock. I've always wondered how reliable those are as they age, and have contemplated replacing it with a manual petcock.
 

·
Registered
Joined
·
954 Posts
While that does sound like something I'd do :D , my bike has a vacuum activated petcock. I've always wondered how reliable those are as they age, and have contemplated replacing it with a manual petcock.
:) Just added an extra tap to my SS & not being used to having an accessable fuel tap have forgotten to turn it on a few times... 100 metres down the road the bike has spluttered to a halt. ;)

Is the vacuum hose still in place on the engine? Split diaphragm? Not conversant with the Monster vacuum taps, lol
 

·
Registered
Joined
·
16 Posts
Discussion Starter #8
:) Just added an extra tap to my SS & not being used to having an accessable fuel tap have forgotten to turn it on a few times... 100 metres down the road the bike has spluttered to a halt. ;)
Oh yeah, I've done that with my '75 KZ400 a couple of times :D

I'm going to double check the vacuum line to the petcock after work today. Are there any good ways to check that the petcock is functioning? Besides disconnecting the fuel feed, sucking on the vacuum line, and seeing if any fuel comes out? (There's probably a joke in there somewhere...)
 

·
Registered
Joined
·
954 Posts
Oh yeah, I've done that with my '75 KZ400 a couple of times :D

I'm going to double check the vacuum line to the petcock after work today. Are there any good ways to check that the petcock is functioning? Besides disconnecting the fuel feed, sucking on the vacuum line, and seeing if any fuel comes out? (There's probably a joke in there somewhere...)
That would work!

Your bike would love it too. :D

Leave the fuel tap on, pull the fuel line off and point it into a container, suck on the fuel line & see if any fuel comes out?
 

·
Registered
Joined
·
16 Posts
Discussion Starter #10
Bike runs! Fuel system assumptions were spot on!

Here's what I did.

First and foremost, I got a new fuel filter. I think this was critical. As I've seen time and time again, the previous owner was... well... mechanically and mentally lacking.

After doing some quick research, I found that the original fuel filter was installed backwards. Also, after I removed the filter and shook it, the filter sounded like it had small pebbles or sand in it... When held up to the light, the filter seemed to have a nice coffee color (light roast :D ) inside it.

I also drained my float bowls. With the bowl drains open, I sprayed some carb cleaner down the fuel feed (after the vacuum powered fuel pump). Then I chased it with some pressurized air (from one of the computer dusting cans).

While I was at it, I threw some new spark plugs in it and cleaned my air filter.

Not only does the bike run, but there's zero hesitation on acceleration and the power delivery is very smooth. It also feels like there's a bit more power at the upper end.

Thanks for all the help. :D
 

·
Registered
Joined
·
54 Posts
good to hear!

by the way, for anyone who doesnt know; napa stocks fuel filters for our bikes. part#: 3087

napa also stocks oil filters for our bikes, and they are even chrome plated, but they might blow your motor. I used one and even though it was sealed in plastic like any other good oil filter, it must have had a ton of crap in it because it destroyed my rod bearings; put 1/16th" grooves in both bearing sets directly over the oil ports and turned the oil into heavy metalflake car paint in less than 300 miles
 

·
Registered
Joined
·
54 Posts
The fuel filter was only $8 from the Ducati dealership. I'd probably just stick to that.
yeah that works. I'm up in Connecticut though, and there's only 1 Ducati dealership in my state and its over 2 hours away :( And they dont stock much of anything at all either. the fuel filter at napa is identical in every way and was only like $4, I bought a couple of them so I have spares on hand
 

·
Registered
Joined
·
5 Posts
Hi Guys,

I have this same/similar problem! 99' 750M Monster too.

The front cylinder seems to only kick in after 10 minutes of riding BUT I waited for it to cool down and tested the spark plug and got no spark (brand new plug).

Some how after 10 minutes the spark plugs starts working? My last service was less than 6 months ago.

Any ideas?

Thanks!

Mal
 
1 - 14 of 14 Posts
Top