1990 Ducati 750 Sport Dellorto Carbs

[jsey]

About a year ago I purchased a 1990 750 sport and proceeded to "clean it up" over the past year. It came in very nice condition and had already been converted to 36 MM Dellorto's. I literally picked it up, drove it home, shut it down, and it was never started agian untill last week. Being unfamiliar with the model I only just realized that the fuel pump was still activated upon starting the bike. It struck me as odd. Any reason to keep it that way? Why not let gravity work it's magic? Regardless, shouldn't the pump cycle off once the float bowls are full? Reason I ask is that the carbs flooded all over the floor then seemed to hold, but constantly run? One other question, it's a tight fit in there for air cleaners, so without a lot of thought I ordered a pair of K&N's that are the same familiar cone shape but only 2 inches long vs the standard 3" that came off the bike. Question is does this approach restrict intake air to a point (1/3 roughly) where it advesley affects performance? Thanks

[jcslocum]

As long as the carbs are lower than the fuel tank, gravity will work just fine for feeding the carbs. Now, is the fuel pump inside the tank like the mid 90's SS?? If it's set up like the later SS then the pump runs all the time but has a return line back to the tank. It works more like a constant flow system but not pressurized. Check this thread in the Paso Forum: http://forums.ducatipaso.org/viewtopic.php?f=1&t=2151

The air filters won't hurt performance but they will not improve it either. In a perfect world, the Dellorto's should vae a velocity stack to help air flow into the carb and then the filter but as you pointed out, they won't fit so use what you have and enjoy the nice HONK from the carbs.

[jsey]

Thanks for the reply John. The pump is in the tank so I guess I'll remove it and see what happens.

[ducinthebay]

You can not remove the fuel pump on the Sport. The steel fuel lines in the tank are brazed in place, and the pick up, without the fuel pump, is half way up the tank. You will get about 50-60 miles per tank. The proper way is to have a T in the fuel line down by the carbs and run it back into the return line on your tank. I would suspect your bike is already set up this way, but its worth following all the fuel lines. If your carbs are overflowing, then your carbs need to be cleaned out and the float needles cleaned.

For filters on your 36 Dellortos, there is a really slick solution. First, get the grey plastic velocity stacks that thread onto the carbs. You can get them from Bevel Heaven, or other outlets for Dellorto parts like Herdan http://www.herdan.com/ . The outside of them is roughly 50mm, or 2inches.

Then get some nice rubber 2" elbows. Here's one from airflow online. http://store.airflo.com/90hl2.html
Add a steel sleeve at the top to adapt to any 2" filter. A bigger filter is better. There's a ton of room above the carbs for airfilters. The intake length also helps with idle and low speed throttle, as it contains the fuel fog, and somewhat acts like a Helmoltz resonator. A smooth intake tract also helps with laminar flow, which improves mixing at mid to higher rpms. Any intake tract before the carb helps making the engine run more civil.

Its still a tight fit, and you will have to trim the elbows a bit to get past the battery, but it will be a lot neater than any other solution I have seen.

The Dellortos don't like to be left alone too long. take the out, clean them up, and run some Sea Foam through them. It will be better after some TLC.

Hope this helps.
Cheers,

[bucbean]

2/24/08

I have alloy velocity stacks (with screens) on my 1990 Sport.....

They are made by Mallossi....but you need to use the short ones....and I don't remember the length (sorry).

I would be very careful with velocity stacks....and "pumpers"....because it creates an opportunity for a fire.

Yep.....burned my Sport up a couple of years ago.

Jeff

[princesnicole]

The air filters will not aching achievement but they will not advance it either. In a absolute world, the Dellorto's should vae a acceleration assemblage to advice air breeze into the carb and again the clarify but as you acicular out, they will not fit so use what you accept and adore the nice HONK from the carbs.

_________________
Aprilaire

[anton88]

Hi, im just in the process of doing a mikuni swap (from original webber). Bought the largest cone air filters i thought would fit, + rubber elbows + aluminium link tubes - it was a frikkin nightmare to get them to fit, but ive done it !

Biggest issue was making everything fit so i could get the tank back on without anything touching the air filters etc. I was worried about using smaller filters and reducing the airflow. Havent had the bike running with them yet, but hopefully soon !

Its a real tight squeeze getting everything in - dont know if same issues with dellortos ?

Will get some pics up for you guys later.

Cheers for now.

Ant.

[anton88]

2 pics with just the mikuni carbs in place = LOADS of space :





with 1 filter unit installed:



Side view with both installed:



Close up of silicone 90 degree bend fitted (but not clamped on) :



Overall view with both filter units installed (took a long time to get the postion right so the filters did not foul on the fittings underneath the tank (fuel vent tube and return tube, plus the electrical inlet thing !):



The inlet diameters of the filters is about 60mm - quite large. Ive positioined them best i can for some cool air flow. Other alternative would have been to re site the battery so the pods faced forward of the carb, but didnt fancy chopping the bike up any more !

[jcslocum]

Those elbows are cool! They initially looked like they are made from wrapping electrical tape.

[btlofrum]

I agree, that's a really slick setup.

My bike's previous owner used Mikunis from a 900SS, and built an airbox out of aluminum. He fitted an SS (or Monster) sized K&N filter. With the exception of the filter being held in with tape, it's a clean look, and seems to work well.

I'll take photos next time I yank the tank. I need to rejet, but probably won't get to it until October.

Ben

[Mustang505]

Hi Ant
i'm right in the middle of doing the same thing. What inlet manifolds (gold) are those? If they are off a monster or something, I might have to make up a pair - is it possible to tell me the length? Have you run the engine yet? Main jet size?

Cheers Clive

[paso750]

If they are off a monster or something, I might have to make up a pair

750 Monster or Supersport (custom anodized as they come silver)

G.

[anton88]

Hi Ant
i'm right in the middle of doing the same thing. What inlet manifolds (gold) are those? If they are off a monster or something, I might have to make up a pair - is it possible to tell me the length? Have you run the engine yet? Main jet size?

Cheers Clive

Hi Clive,
Inlet manifiolds are from a 600 monster - ive just had to open out the tubes a touch where they meet the cylinder head inlets (plus some colourful paint after cleaning ).

Carbs are also from a 600 monster - ive changed the jets to 140 (they were 132.5) and raised the needles another notch - not had running yet, as i'm waiting to fit some new gaskets (valve covers) - may have to do further changes, but thats some way off yet - when its ready for the road, i'll need to get it on a dyno possibly to ensure correct running.

Ducati parts over here are rare/VERY expensive - i just went for the 600 parts as thats all that was available at the time at the right price.

Cheers . Ant