Engine stalls/bogs with throttle - '99 M900 (Carbed) - Resolved

[CromoMann]

My '99 M900 recently stalled while on a freeway.  I've tried searching through Tech, but I've only found a couple similar cases - one solved by 'dynamite' (Memphis) approach - the other was sent back to their service department without an update to the thread.

Bike will start right up with choke turned on.  Will idle for a while with choke-off. May accept throttle a couple times, but will bog down with throttle and stall shortly after (all of this tested while in Neutral).

Background (recent):
The engine was blipping a little bit and running rough before it lost firing completely.  I had rode it a couple hundred miles the day before without incident (slight rain a couple times during the ride).  I filled up about 15 miles before the campsite - and the bike was parked overnight (usually garaged, but temps in 40's overnight).  My ride then took me about another 15+ miles and the stall described above occured.

The bike was towed home and fired up right away - rode up the driveway and parked (not tested as I was half-a-day late from ride).  

Some Addt'l History:
When I first received the bike, I encountered a rusted tank issue that manifested itself in two clogged float-bowls.  I fixed this about 7 years ago, but having heard some bad things about the 'Cream' kit I used, I focused here first.  The tank drained without issue - no clogs, no sediment in tank (when drained through white t-shirt), internal visual inspection looked good all around.

Steps I've taken with no marked improvement in situation:
I may have had a kink in the 'J' fuel hose between tank and input to fuel filter.  However, I replaced fuel filter and reset hoses without kink.
I checked plugs - horizontal a bit lighter, but both look normal
I checked for back-pressure after stall - no 'gasp' from tank upon opening
Fuel-pump - I read on some bikes when turned on they 'prime the tank'.  I don't hear anything like this, but I don't recall ever having heard this on my monster.  
I also inspected float-bowls and they looked clean (though I did not take apart the carbs completely to inspect jets).  

Bike Mods:
Chopped Airbox
Sil High-mount slip-ons
Rejetted Carbs

Any advice/next steps would be great.  I put nearly thirty miles on fresh tank of gas - not sure if I should replace fuel at this point.
-Mike

[Howie]

You did some good research.  One correction; you have a carbed Monster, mechanical pump, no prime. no whine.  The fuel pump is the hexagon shaped object between the cylinders on the right side.



You also have a vacuum operated fuel shut off (circled).


Either of these could cause the problem.  You can find out if it is one of these by opening your float bowl drains

and seeing how much fuel comes out.

You can get a rebuild kit or new pump from   http://www.sudco.com/CatalogJPG/128.jpg  The pump shown has two outlets instead of one.

[CromoMann]

Thanks for the response and the correction!

A question about "how much fuel comes out" - can you explain what the right amount should look like?

Also - I may have an added bonus - after my first episode with the rusted tank, an inline fuel filter was added between the pump and the carbs.  It's clear, so would I just look for fuel 'flowing' or 'filling' the extra fuel filter?  I'm guessing the suction might pull in the gas while choke is on, but once the larger demand kicks in - it won't keep up.

I'll have wait until after work to perform the next steps.

[Howie]

The added filter will not be full.  No specific amount of fuel that I can put a number on, but not much if the bike is running out of fuel a very little bit will come out.  The float bowls will be close to empty.  I assume you changed the regular fuel filter recently. 

You can also bypass the fuel pump and let fuel gravity feed into the carbs as a test.  The bike should run as long as the fuel level in the tank is higher than the float bowls. 

Oh, there is also a fuel screen in the carburetor inlet that can get clogged.

[CromoMann]

Thanks again Howie - here's where I'm at - yes brand new fuel filter just went in.

One - took the fuel pump out of the equation - connecting the input fuel hose with the outbound hose with a pen housing (high-tech).
Unfortunately - the same symptoms occur with the bike - starts up okay, might rev for a bit, but will quickly bog down with any throttle.

I also took apart the fuel pump - both membranes (one on each side) were intact - without tears (not the crying variety - those were reserved for the make-shift mechanic).  The inner valves of the pump were also working - maintaining single direction flow for each valve.  One thing I noticed - on the vacuum intake (clear) membrane - there did seem to be some 'oily' fluid, but it might have just been some of the old fuel that's come from the intake manifold.  Is that normal?  Is that really oil that I need to replace?

I also opened the float bowl drain screw - once removed - fuel flowed freely out of the carb. I didn't even try to crank it - as fuel was flowing consistently - more than I'd expect both float-bowls to hold (I may have an issue with my vacuum petcock).

I think I found the 'Float Screen' - if it's the inline screen between the fuel line and the pipe that divides/delivers the fuel to each carb.  Mine was not clogged, but it did look a bit deformed (not cylindrical - more crumpled).

Next steps:

I may have gone too far beyond the float drain instructions, but I went ahead and took the carbs apart.  floats/jets/needles and float screen all look decent as far as flow restriction would be concerned.  Before I put the carbs back on - is there anything else I should look at in there?

My next thought is about bad-fuel.  I'm wondering if my coils are losing 'power' - such that the spark might not be strong enough to ignite the bad/weak batch of fuel when the stronger flow of fuel is delivered by throttle.  Once I get the bike back together, I'll put a fresh tank of gas in and see how it runs then.  I think I have an ohm-meter - but I'm not sure I understand plug-wire/coil testing (especially the bit about grounding the plug wire to the cylinder head).

Any other thoughts?

[Howie]

Make sure the floats are set correctly, 14 mm.  High float level could cause the problem too.  Also make sure the starter jet is closed with the choke cable.    Slide diaphragms OK?  Have you checked the spark plugs  for color?  If the gas that came out of the carbs looked and smelled good I doubt stale fuel is your problem.  Yes, you found the float screen.

Usually ignition components fail one at a time and since you have one component per cylinder.  Anything is possible though.  Shade tree checking of spark is simple enough.  Pull ignition wire off spark plug, insert a plastic or rubber handled screwdriver into the terminal cap, hold about .030 from a good ground, crank engine and look for a healthy, blue spark.  Or buy one of these  http://www.autozone.com/autozone/accessories/Great-Neck-Adjustable-ignition-spark-tester/_/N-255s?itemIdentifier=10257  or these  http://www.sears.com/kd-tools-standard-ignition-tester/p-SPM5793246702P?prdNo=22&blockNo=22&blockType=G22

[The Mad King Pepe']

how to play with your carbs: http://www.ducatisuite.com/jetkit.html 

Jokes aside, plenty of good info and photos. Give it a read.

[CromoMann]

Thanks Howie, Thanks Mad King -
More to come - I'll have another once over through all the guts to make sure the carbs are clean and tip-top.  That article looks pretty good - the rest of the project - maybe for another day, but the technique for measuring the float is useful. 

[CromoMann]

Howie - thank you for your notes and troubleshooting suggestions.  The bike is firing up right now - like a champ. If I say that with less than full confidence it's because I didn't end up changing much - even though I did a lot.

In the end, I may have just had a bad tank of gas - as that's the only thing that I clearly changed in the end having taken the carbs off and apart to inspect. 

The first attempt was in taking the bike down to the carbs and confirm fuel was flowing through the system; checking spark plugs; replacing fuel filter; and aligning hoses of all kinks ("J" hose off fuel filter had a slight twist), I started the bike - only to have the exact same symptoms with a bogging engine/stalling after throttle was applied.

The second time I went deeper into the abyss and pulled off the fuel pump, inspected membranes and function (it's like a little heart chamber with two one-way valves and a vacuum line from the manifold to make it 'beat') - checked out okay.  Before pulling pump out - I had already tested the fuel was flowing by bypassing the pump all together - I was just curious how the 'mechanical' pump worked.

I considered replacing fuel at this point, but in my haste jumped into the carbs (In hindsight "[('make the beast with two backs ') x 11ty Billion]") - ...so off came the airbox (and all that entails) and I took the carbs completely apart.

While in the carbs I checked the following:
Float bowls; float hight; float screen - nothing apparently wrong - nothing clogged.
I also checked the main jets and took apart that little stem/tower inside the float bowls... (all I could test was blowing through each channel - 'check')
I then checked the diaphrams for the slides - no tears; seated properly and the slides have full range of motion.

At this point, I felt the only two things I hadn't checked were the coils and the fuel - so I put it all back together yesterday and put in a couple new gallons of gas.  I tried to start it at that point, but it wouldn't fire at all initially.  It had plenty of crank power, but I decided to put in on the Battery Tender and let it sit a while.  Later that evening - I went back out and it cranked right up WITH FULL THROTTLE~!!!  Woohoo.

In summary, I guess the only real way for me to have proven the fuel was the issue was to have the system stable and put the same fuel back in - to confirm the original symptoms existed and then replace with fresh to resolve the symptoms.  Not having done that - I don't think I'm going to head straight out of town on a long journey yet - but if it keeps running strong around town - it won't be too long.

While the lazy side of me wishes that I had at least tried the fuel early on, I may not have had the patience to test that out - I'm not sure how long it would've taken for all the old fuel in the lines/filter/floatbowls would've taken to clear the system.  However, the tinkering side had a good time getting to see the inner workings of the bike (once again) and it was also great to see that the Cream tank liner kit I applied 7 years ago is still working great.

Thanks again for all your help.
-Mike

[CromoMann]

... and having ridden about 80 miles today without any hesitation - confidence is restored.

[monstermick58]

Damn, you figured it out. 

   Here in Oz we have a fuel from Shell (was) called Vortex (now V power) that caused problems liked you have described, in fact a certain well known Ducati mechanic described the gas as 'shit'. Apparently the Gas has a heavier weight and would'nt flow as well as a normal 91 RON fuel, I had to keep applying the choke just to nurse the bike home, back on standard gas and problem fixed.

   But, looks like you have the problem fixed.




                                       Mmick