Ducati 916/VTR trumpet Carb jetting

[Varastorm]

Bit rough this morning after my camshaft swap celebrations, big thanks guys for the support

Thanks for the above needle link Carl, very good read

Like you mentioned many posts ago Carl, I can see myself having to go back to square one on the jetting after the camshaft swap. I just hope the performance gains are going to be worth it.

Back to the Stacks, I feel I have learnt a lot doing this Ducati velocity stack mod & am genuinely shocked about the performance gains better velocity stacks can make on a relatively stock engine. The power run on the dyno doesn't really do it justice & I feel it has greatly improved the performance right across the entire rev range.

If your thinking about a little project with big gains & you can't afford the Dr Honda stacks, I urge you all to consider the Ducati stack mod, its as cheap as chips & it works.

Going to go for a small ride later then drop the oil & filter.

Will update

[Varastorm]

Whilst trawling through many tuning forums searching for the perfect setup, I stumbled over this really interesting paragraph.

One item to mention when dyno tuning is this. RPM does not = CARB POSTION.... and this is where so many dyno tuners fail. For those who have put your machine on a dyno, how long did the bike run once the operator started this operation? 2-3 seconds? max. There is no way you can adjust your idle/pilot or mid range circuits with this type of dyno "pull". Even though the graph/rpm will start out at 1000rpm (or so) then travel up to 10,000+rpm, the throttle position was put at WOT. This is simply how a dyno pull is done. Do NOT confuse the 2000-3000 rpm range on the graph as the Pilot Circuit, and do NOT confuse the 5-7000rpm range as MID RANGE. Cuzz they are not, the entire "pull" was done at WOT, and the only circuit being utilized by your bike was the MAIN CIRCUIT... the rest was just playing 'catch up'. So, if your gonna perform a dyno tune, do it correctly, and you will be very pleased. Let your bike run on the dyno with almost no load, idle to 1500 rpm, and adjust the pilot circuit accordingly. then bring her up to about 5-6000rpm, and adjust your mid range (needle) accordingly. Then, last but not least, WOT, and adjust your main jet for MAX hp/tq.... DONE, and your bike is now fully dyno tuned.....

Right then, I have been working tirelessly on getting the jetting spot on since fitting the VTR cams & now feel that this is the best I can do without a propper dyno run.

It now idles with no stumbling, has no flat spots or jerking & cleanley accelerates to the red line in every gear

What I have found is that these engines aren't too keen on running lean, but run very well rich to super rich & don't show hardly any adverse effects whilst doing so. Apart from crap fuel economy & complaints about eyes stinging due to the overpowering petrol fumes from the exhaust.

The method I used to get the jetting spot on was to start with the original dyno run jetting, then lean it out one jet size at a time until I felt it was effecting the running/performance in that fuelling zone. Then richen it up one jet size & move on to the next zone, starting with the mains, then needle height, then pilot jet, then fuel screw.

There was a lot of trial & error but I feel it was worth it in the end

Here is my finished spec for the Ducati trumpet mod.

Pilot screw
Front------1 3/4 turn out.
Rear-------1 3/4 turns out.

Pilot jets
Front------#48
Rear-------#48

Needles
Dynojet needles fitted (same profile as Std but with the option of different heights).
Front------Clip in 3rd groove from top + 0.7mm washer under clip.
Rear-------Clip in 3rd groove from top + 0.7mm washer under clip..

Mains
Front------#172
Rear-------#175

Slide holes
Std 2 + Dynojet 1
Front-------3 open.
Rear--------3 open.

CV diaphragm springs
Dynojet (short ones)

Air filter
Std paper

Ducati velocity stack mod

VTR cams

TPS
500 ohm's

Porting
Finger porting .
Intake has been (de flashed) cleaned with 180 grit up to the valve guide & intake rubber trimmed tidily for a seamless transition from carb to head.

It feels that the leaner jetting & VTR camshafts give significant power gains over the previous richer carb setting & Varadero cams.

It now pulls very hard to the redline, unlike the Varadero cam'ed engine which did tail off slightly after 7000rpm.

I am now ready to run it again on the dyno & we'll all hopefully see the gains my ass dyno feels, will update

[8541Hawk]

There is only one problem with the paragraph you quoted........

We are running CV carbs, so the whole "It's at WOT" does not apply.
Sure the twist grip and the butterflys are wide open but the slide only opens to the point the vacuum signal will allow.

So it does go through the different circuits during the pull.

Then again I am just a different guy on the net, so I guess the point is don't believe everything you read on the net.

[Varastorm]

There is only one problem with the paragraph you quoted........

We are running CV carbs, so the whole "It's at WOT" does not apply.
Sure the twist grip and the butterflys are wide open but the slide only opens to the point the vacuum signal will allow.

So it does go through the different circuits during the pull.

Then again I am just a different guy on the net, so I guess the point is don't believe everything you read on the net.

Thinking about it, your right, he was on about flat side carbs

Ffs, publicly humiliated again, will this ever stop

[MacV2]

There is only one problem with the paragraph you quoted........

We are running CV carbs, so the whole "It's at WOT" does not apply.
Sure the twist grip and the butterflys are wide open but the slide only opens to the point the vacuum signal will allow.

So it does go through the different circuits during the pull.

Then again I am just a different guy on the net, so I guess the point is don't believe everything you read on the net.

Thinking about it, your right, he was on about flat side carbs

Ffs, publicly humiliated again, will this ever stop

Not whilst you own a blue one....no...