Hey everyone,
2000 M750.
For several months, I ignored the fact that the exhaust smelled ridiculously rich. (Famous last words...) Then, last month, I packed up for a multihour ride, only to have the bike sputter black whisps of smoke and bog down on the highway merely 25 miles into the ride. (Small blessing, I guess.) Got her towed home.
- Pulled the carbs. Cleaned them surgically.
- Cleaned the repeatedly wet n' fouled plugs... Probably need new ones, but these were just installed prior to the attempted trip, darn it...
- Float needles nice n' springy. Bowls currently set to 13mm (per DucatiSuite method of measurement) I have read 12 is considered "stock" by some, and that FactoryPro suggests 14. We're splitting the diff. Open to thoughts on that.
- Replaced main jets
- Replaced all gaskets and o-rings in the carbs
- Idle mixture screws set to 3 turns out
- MotionPro carb balancer to arrive any day now
- New belts installed prior to the fateful trip
When I last tried to start her up, she fired up, only backfired out the exhaust like the 4th of July for about 20 interminable seconds. Discovered the hoses that vent to those little gray airboxes each had 1 significant crack. I've trimmed and reattached the now crackless hoses at the little black air filters with vacuum connectors and flexible plastic cement. They aren't re-installed yet. But I digress.
After the backfiring ceased, (this was prior to discovering the cracks) I restarted, adjusted the idle, gave her some healthy revs, and rode her around the block.
She took off like a champ, until I shifted into second, and gave her throttle.
That's where she lugged and bogged; I was practically wide open and she barely got to 3300 RPMs.
How much â€" if any of that â€" was a set of cracked vent hoses?
Before I get her all back together again, I wanted to toss this story into the ring. And with that, I await the brilliance of the assembled throng. :)
Check the needle jets (emulsion tubes). If they seem at all oval change them.
Thanks for the quick response, Howie.
Needle Jets are good. Nice and round. Not egg shaped.
How many miles on those needle jets? Are they the bronze coloured type? The oem needle jets can wear in as little 5 to10,000 miles and you may not see it. I would replace them with hardened Factory Pro parts if I was overhauling the carbs. I would set the floats at 14mm while I was in there.
Hopefully you may just have a carb flooding issue and a use of the search function will provide the reasons for it and a number of solutions. There are a few threads on this issue which should help. Just enter "carb flooding" and a great deal of info appears.
Koko is correct that visual inspection may not pick up worn needle jets. If you are going to take them apart anyway this would be a good upgrade. DO recheck float height. I had Factory Pro jets with DynoJet needles in my old 750. The new owner is still riding with them trouble free, oh maybe 30+K miles.
Take a look at your fuel filter.
Thanks, Blackout.
I failed to list in my original catalog of maintenance that a brand-spankin' new fuel filter has been fitted.
That did make a world of difference.
She also has HICAP starter cables from MotoElectric. So starting, when she doesn't have fouled plugs â€" is absolutely instantaneous.
If I remember correctly, changing out needle jets is a matter of pushing that white, circular plastic piece through from the guts of the carb...
Can someone walk me through it so I don't screw something up? :)
Perhaps an order from Factory Pro is a good idea.
And another question â€"
If I install new Factory Pro needle jets, does it follow that I need to replace the jet needles, too?
Check the vacuum line to the fuel pump for holes. Also, +1 on replacing carburetor vent lines. My winter hard starting problems disappeared after that. I ignorantly always thought it was battery.
What type of fuel tap do you have there? Vacuum fuel taps cause trouble and people replace them with a manual tap.. Was it both plugs fouling? If so then the vacuum tap hasn't sprung a leak into one of the cylinders via the vacuum hose, but it is worth replacing with a manual tap which can help deal with carb flooding.
The domed bolt in the float bowl secures the needle jet, jet holder and white slide frame to the carb body. The notch on the needle jet has to line up with the pin in the jet holder upon reassembly. The parts are delicate although it requires some hand force to push the needle jet out/in. The dome bolt is thin gauge, so be careful both ways.
1mm on the floats makes a difference, but shouldn't foul plugs like you are describing.
What needles you running?
If by "fuel tap," you're referring to the fuel cutoff... it has the stock vacuum cutoff as pictured here: http://www.ducatitech.com/bikes/m900_fuel.jpg (http://www.ducatitech.com/bikes/m900_fuel.jpg)
Forgive the noob question here, but, there are three lines running to that vacuum tap. I've only ever seen a straight on/off valve with a pair of in / out ports. Can you point me to what I should be installing?
Both plugs were fouling; horizontal was worse.
Needles are currently stock. However, thanks to you guys, I did place an order for a "Fresh Start" carb kit from Factory Pro, today [clap]
[thumbsup]
That fuel cut off valves often give trouble. One line is the vacuum line to the manifold and needs to be plugged when fitting a manual tap.
Have a good read of the threads on carb flooding via the search function. A manual tap helps with that occasional issue. Try our sponsors first, but Motion Pro and mower shops have in line taps that you can fit in a spot that lets you get to it easily even while riding. The early oem tap bolted to the frame but that bracket was later removed. It was a good set up with a big tap knob.
Just remembered, bogging can occur when the slide diaphragms are not located and seated correctly. Check that the slides lift when you rev it by looking in the airbox.
Slides were lifting beautifully during that previous ill-fated run around the block. I remember checking before fitting the K and N cans.
I will check back in after the stage III Fresh Start kit from Factory Pro arrives.
If I wanted to by-pass my fuel vacuum, what would you suggest I use? I found this one from MotionPro, but it says it isn't recommended for bikes over 200cc.
http://www.jcwhitney.com/motion-pro-universal-petcock-valve/p3074455.jcwx?filterid=c51113d59394y2000u0j1 (http://www.jcwhitney.com/motion-pro-universal-petcock-valve/p3074455.jcwx?filterid=c51113d59394y2000u0j1)
I'm sure Motion Pro make other fuel taps with more capacity.
I believe Parts Unlimited offers some too. Easy to find at most bike shops.
5/16" in and out should do it.
Make sure you are not using high octane fuel unless engine modified. This can cause fouled plugs on these tame motors.
OK gang, the nature of my post now changes from "bogging down" to "how does this newbie set up this carb?"
With the sole exception of float needles (which were clean and springy) and breather tubes (which had slits near the ends but I trimmed and rejoined using plastic vacuum connectors) everything inside is new thanks to a rebuild with a Factory Pro kit.
- Pilot jet: #45
- Float height: 14mm (purchased and used Factory Pro's cool little black measuring tool)
- Needle clips set at 2nd position from top as per FP spec
- Main jet: 142.5
- Fuel screws: 2.75 turns as per spec
She started immediately without any priming, and with no choke, and hovered around 900-1000 RPMs
Turned on choke, to little if any change.
Cranked up idle screw 'til she hummed around 4000 for about 45 seconds, then turned off choke
Back to around 900 - 1000 despite a roaring choke
What do you suggest next?
I have the Factory Pro tuning guide, but of course, you have to have her up to a proper 1300 idle before you can take her out and go through those steps...
Also have a new Motion Pro carb balancer, but assume that is the final cherry-on-top step?
1300 is a little high for a Duc idle. The idle will likely hang if you set it at that number. I'd look for something around 1100, and then synch the carbs.
The rest of your info will come from riding the bike. It's hard to really tune a bike at idle.
Quote from: ducpainter on October 28, 2016, 07:17:02 AM
1300 is a little high for a Duc idle. The idle will likely hang if you set it at that number. I'd look for something around 1100, and then synch the carbs.
My question is â€" do I just keep on twisting that idle screw 'til it gets to 1100? Like I said, with choke, it was at 4000, which to my experience is really quite fast.
After turning it quite a lot to get it to where it is (900-1000) it would bog a little bit when I'd try to blip the throttle.
So I'm wondering if there's another adjustment to be made somewhere else to get the idle nailed before I try to ride it.
I've never ever tuned, much less rebuilt a carb before. This is all new territory. :) Thanks for your patience, everyone.
Id back the fast idle, with choke, down to about 3K. 4K is unnecessary. Are you sure you're turning the correct screw?
Then, I'd synch the carbs. You turn the other screw up there to accomplish that, with the Motion Pro synch device attached.
Once you get them synched, you might need to play with the idle and fuel mixture screws a little, don't be afraid to open them to 3 turns.
Finally, you'll adjust the idle speed screw to obtain a hot idle around 1100...then ride it.
That's super-helpful. Thank you.
I'll start with backing out the fuel / air screws to 3 turns, apply choke, start 'er up, and back down the idle to 3k.
Then we'll see if she'll settle to 1100 or so, and break out the MotionPro sync tool.
Have you checked the diaphragms for fine cracks? My M750 was bogging a bit due to that. \\
JM
Quote from: pneumadeux on October 28, 2016, 08:20:30 AM
That's super-helpful. Thank you.
I'll start with backing out the fuel / air screws to 3 turns, apply choke, start 'er up, and back down the idle to 3k.
Then we'll see if she'll settle to 1100 or so, and break out the MotionPro sync tool.
You're jumping the gun on the fuel screws, but it won't do much harm.
LATEST UPDATE
Cranked the idle screw down so the "hot idle" is right at 3000.
Slightly adjusted air / fuel screws so the non-choke idle is 1100 / 1200.
Used the Motion Pro sync tool and adjusted the carb sync screw to perfect balance.
IMPORTANT TO NOTE: Several times while these adjustments were being made, the bike would stutter / cough a little, and a few times, it backfired into the carbs, and once or twice, a small backfire out the exhaust. After getting everything synced, no stutters, tho.
Took the bike for a ride around the block â€" and blargh... it was like riding her through 3 feet of mud. No pull. At all. Struggled to get her RPMs up.
Thoughts?
I am still curious if my work with the carb breather hoses (cutting out the old splits and cuts, and joining the hoses with vacuum connectors) hasn't somehow restricted airflow to the detriment of the bike.
You joined the carb breather hoses? :o I must have missed that.
That won't work. They should have those little filters and be separate.
No, they are still separate.
When originally disassembling the carbs the two breather hoses displayed cracks down by the little filters. So, I cut the hoses so I could illuminate the cracks. In order to keep the hoses at their original length, I used little plastic vacuum connectors to rejoin the cut pieces. That means the inner diameter of the hoses is smaller where the connectors are. I have been concerned that reduction in diameter is impeding performance. To be honest, I'm not entirely certain what the function of those breather hoses are.
Those hoses vent the area above the diaphragms to atmospheric pressure. The filters are to keep dirt out. See if the diaphragms move as easily when throttle is applied hoses on and hoses off. If not, the filters may be clogged Doubtful, but worth a try.
Thanks very much for that. I absolutely know for certain that they are not clogged, because before rejuvenating them and getting them all spliced and sliced together, gently blowing by mouth allowed flow.
The air hose that connects to the carb from under the fuel house goes to a breather pod but doesn't have a filter. Does this serve the same purpose as the others?
Meanwhile, I still have a bike that when I opened up the throttle on the straight road leading to my house after yesterday's round trip around the block, it simply had absolutely no pull. What jets do I need to change? What adjustments do I need to make?
Taking the factory pro instruction sheet literally that came with the kit, since the bike had such poor pulling power with the throttle opened up, going to install the next larger size main jet.
Stay tuned for details.
You're chasing your tail IMO.
There's no reason that a bike that was running OK would suddenly need a larger main jet just to rev.
Something is wrong, and you've missed it.
Have you tried a new set of plugs, or are you still running the ones you fouled and cleaned?
Oh the little things...
Thank you for the simple encouragement to replace the plugs. They were fouled.
I did up the main to 145, adjusted idle, and tested her.
Omg.
New bike. Front end coming up throughout the range. No surging at idle even after 30 minutes of hard riding. Will be testing her for 2k - full throttle snap later to make sure floats are nailed and no bogging.
Thanks for all the thinking.