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Discussion Starter · #1 ·
I have a 2001 Ducati Monster 600 with carbs. I cleaned and rebuilt the carbs when I first got it (about 6 months ago).
Rides OK, but I am noticing two things: it fouls up spark plugs pretty quick and it actually doesn't increase HP/Torque when I go wide open throttle under load (say going up a hill).
I put jets in it that were modestly larger than factory spec because it has a full exhaust on it, but since then it's dawned on me that the air in is all stock.
So the factory jets are 37.5, 70 and 132.5 but I think I have 40, 70 and 140 maybe? I left the needle settings pretty much as is etc.
So, I assume the black foiling of the sparks is because it's too rich (this takes a few months of riding to accomplish, but it will get to the point where it won't start unless I clean or replaced the plugs), and is especially rapid and bad if I use the choke for extended warm ups (below 50F).
But... is running too rich and/or having too large a main jet the reason that is kinda bogs down under WOT?
Example: second gear, 40MPH at 5000rpm climbing a moderate incline. Twist the throttle wide open, the bike climbs to 6000rpm and gets a little more oomph, but then cannot really rev higher nor achieve more power/speed. Supposedly peak torque for the bike is around 6000rpm and peak HP is around 8000rpm, but I don't feel much of anything more when I get the bike above 6000rpm, especially if its on an incline.
To be fair, the bike only has like 50hp and 35lb/ft so is this just what a wimpy bike feels like? Or do I need to retune the carbs for better performance?
 

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Yes if it bogs at WOT then it is linked to the main jet. You do have some bleed over from the needle but it is the majority on the main jet. Try dropping back in the stock main jet and see if it runs better at WOT. I would bet three sizes is too much and try it with a 135 or 137.5 if the stock main jet helps the bog. Could be running rich down low too helping with the fouling of plugs. A colortune could help you adjust your idle pilot mixture. I’m not an expect of Ducati carbs so I don’t really know about the air or fuel screw and adjusting, but will help idle fuel mixture. At least it’s better to run rich instead of lean, but I’d still fix the issue.
 

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I agree with bushy, main jets a tad big for a 600, 135 would be better with open exhaust. A quick bush mechanic test, before opening the carbs again.
open airbox and remove filter and leave top lid off, (if possible) , I could do it on my old M900, don't go near any dirt roads, of course, repeat WOT test and see if it makes a difference.
if it pulls a bit better then it's too rich, reduce main jets size.

Avoid extended warm ups with choke on, it should idle without choke reasonably quickly, plugs will foul if choke is over used at starting and warm up.
but then, here in Aus. it's not a cold climate, so maybe you need it.
 

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Discussion Starter · #5 ·
I agree with bushy, main jets a tad big for a 600, 135 would be better with open exhaust. A quick bush mechanic test, before opening the carbs again.
open airbox and remove filter and leave top lid off, (if possible) , I could do it on my old M900, don't go near any dirt roads, of course, repeat WOT test and see if it makes a difference.
if it pulls a bit better then it's too rich, reduce main jets size.

Avoid extended warm ups with choke on, it should idle without choke reasonably quickly, plugs will foul if choke is over used at starting and warm up.
but then, here in Aus. it's not a cold climate, so maybe you need it.
Thank you. The air test makes sense. It's honestly a bigger hassle to get the carbs out then other bikes I've worked on.

I still try to do some riding when it's 40-50F, and it does need run on choke for 2-3 minutes to get to a place where it will idle (roughly), and not cut out. I can of course close the choke and just rev the throttle, but then I am stuck with the bike until it's warm.

When it's above 70F i basically blip it twice with like a 2 second rev, and it's pretty happy after that.

I think the pilot jet is fine. It seems to idle fine and be temp appropriate for air cooled little twin.
 

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Discussion Starter · #7 ·
A quick bush mechanic test, before opening the carbs again.
open airbox and remove filter and leave top lid off, (if possible) , I could do it on my old M900, don't go near any dirt roads, of course, repeat WOT test and see if it makes a difference.
if it pulls a bit better then it's too rich, reduce main jets size.
So I just did this on the exact hill in question. Not a real noticeable difference. Still kind of gets stuck at about 5500rpm going up the hill and not producing additional pull.

HOWEVER.

MY GOD DOES IT SOUND GREAT! You can hear the intake suction, it's growlier, and I think it's even a little more responsive to throttle, especially down low. It frankly runs better in every way with the filter and box removed... not sure it's safe to leave like that though...
 

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70 deg F (21.C) is pretty much winter weather here in Perth. so maybe you do need more choke.
I wouldn't expect a huge difference with airbox removed, just a noticeable one, which sounds like you did, Start by reducing main jets, as Bushy said, 3 sizes over is a bit much.
the pilot jet can be compensated with air idle screws.
I wouldn't recommend leaving air filter out completely, got to keep the dust out. Lots of info out there on mods to airbox etc.
 
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