Couple of questions as I rebuild my bike

DeltaT

Right, coupe of odd things I just need clearing up as I put everything back together.

The crankcase breather on the early ('89) Strada, as far as I can tell from diagrams in the manual, doesn't have a one-way valve of any sort between cases > breather box > airbox. Is this correct? Does it need it?
My bike had a valve spliced in between cases and breather, as you'd expect, and I'm planning on putting it back.

The other thing I'm not sure about... one of the pipes on my throttle bodies has been disconnected and purposefully sealed. Looks like it's been melted and mangled to close it up. Guessing it's some sort of mod to mess with fuel pressure but would what would the effect be, and should I hook it back up?

Any wisdom appreciated!

stafford

The early breather as you say has no reed valve, I run the race bikes one with (into the airbox) the other without (a small K&N filter on the breather box) so as long as your vent is allowed to breathe either is good. Give that later ones have a reed valve how do they drain back? Never had one apart.
The pipe on the pressure valve is the one that vents to atmosphere to allow the diaphragm inside move, not seen this set up before and why it would have been liked to the throttle bodies I don't know. Should be fine as it is.

JSR29

stafford wroteGive that later ones have a reed valve how do they drain back? Never had one apart.

there's a little hole

MarkT

DeltaT wroteRight, coupe of odd things I just need clearing up as I put everything back together. The crankcase breather on the early ('89) Strada, as far as I can tell from diagrams in the manual, doesn't have a one-way valve of any sort between cases > breather box > airbox. Is this correct? Does it need it? My bike had a valve spliced in between cases and breather, as you'd expect, and I'm planning on putting it back. The other thing I'm not sure about... one of the pipes on my throttle bodies has been disconnected and purposefully sealed. Looks like it's been melted and mangled to close it up. Guessing it's some sort of mod to mess with fuel pressure but would what would the effect be, and should I hook it back up? Any wisdom appreciated!

Stafford-- not sure if I understand your first question--- the '89 had a very substantial big cad plated reed valve with input hose from the crankcase and the output hose going to the flat molded breather box under the front of the seat.

I am not sure if you do not consider this a one-way valve. I think it having a stout reed valve is good on these motors.

The vacuum tubing was installed so that vacuum created from down throttle would alter the fuel pressure metered out by the fuel pressure regulator and prevent backfire. It was an early-on debate if this was as good on the track/road as was in theory. I always kept mine hooked up on all of my Corse's-- never saw one omitted from the factory. A number of owners plugged them feeling that it made the throttling more consistent. I never tired it to see.

Foggy 888

I don't think that the vacuum port on the fuel pressure regulator is to prevent backfire on deceleration. It is used on most vehicles from the same time period with fuel injection.
The idea is that it keeps the pressure drop across the fuel injectors constant regardless of throttle position/vacuum. Without it, under high vacuum situations the nozzles of the injectors would be at a higher vacuum while fuel pressure remained the same, causing more fuel to be injected at the same pulse width (same result as running a higher fuel pressure).

When vacuum is applied to the port it lowers the fuel pressure at the inlets of the injectors.

The vacuum hose/port/diaphragm keeps the amount of fuel injected into the motor the same regardless of engine vacuum. It removes one variable that affects fuel mixture and cannot be compensated for by the electronic control of the injectors.

MarkT

Foggy 888 wroteI don't think that the vacuum port on the fuel pressure regulator is to prevent backfire on deceleration. It is used on most vehicles from the same time period with fuel injection. The idea is that it keeps the pressure drop across the fuel injectors constant regardless of throttle position/vacuum. Without it, under high vacuum situations the nozzles of the injectors would be at a higher vacuum while fuel pressure remained the same, causing more fuel to be injected at the same pulse width (same result as running a higher fuel pressure). When vacuum is applied to the port it lowers the fuel pressure at the inlets of the injectors. The vacuum hose/port/diaphragm keeps the amount of fuel injected into the motor the same regardless of engine vacuum. It removes one variable that affects fuel mixture and cannot be compensated for by the electronic control of the injectors.

Hi Brian-- you are most likely correct on this--when this debate came up in the early days most of us knew very little about fuel injection. Does the system work as designed? If so then would you recommend that it be hooked up for the bike to run correctly? I always ran my bikes with it installed.

Mr.R

I personally run with it hooked up on my bike, it was there originally and Webber obviously thought it was needed.
However IIRC? Brad Black had something to say about it on his blog.

Steve R

griff851

So on deceleration when vacuum is increasing it gets less fuel. Makes sense. Back firing usually occurs when things are too lean, so is it possible the old arguments came about with someone suggesting to cure backfiring you disconnect the vacuum line. And Chinese whispers did the rest.

JSR29

Regardless of the theory I'm pretty sure later throttle bodies (916 +) have no vacumn ports connecting to the pressure regulator. The regulator vents straight to atmosphere as the above pic does. Frequently asked, "What connects to this tube?" Answer: "Nothing"

DeltaT

MarkT wrotethe '89 had a very substantial big cad plated reed valve with input hose from the crankcase and the output hose going to the flat molded breather box under the front of the seat.

I can't see any mention of it in the parts manual, but as I say, one had been added to my bike so I'll keep it there as I can't see any reason not to.

I'll leave the hoses as they are on the throttle bodies too, interesting discussion though. Thanks for the responses.

griff851

Just actually looked at the pic. I was wondering in my stupor. ( doing 17hrs days at the moment) where the hose got its vacuum from. Anyway, that's the barametric fuel pressure equalising port. You go up on the alps the pressure get lower so does the air density. You don't need as much fuel and the only way to do it is drop fuel pressure. The regulator is fuel pressure on one side of the diaphragm and spring and air pressure on the other. Reduce tension on the spring or lower air pressure and more fuel pressure will be bled off. QED

You could have it hooked up to a vacuum line and have the fuel map adjusted accordingly I suppose, which would still achieve barametric adjustment.

Ps. That little cover bung comes off and inside you can turn the screw and wind up the fuel pressure for racing etc. Steve mentioned that little handy hint years ago. A lot easier than putting a heavier spring in the reversion. valve.

Mr.R

Just to throw something else in the pot here...
Someone mentioned that the later TB's didn't use this facility.
Didn't the later TB's have air bleed screws as standard? ...and what did these achieve?

My 851/916cc to runs perfectly (it's making 128 rwbhp) using modified (bored out to 54mm) 851 TB's.
Without airscrews and with the OEM balance pipe connected to the fuel pressure regulator.

Steve R

Foggy 888

Ducati eliminated the vacuum hose on the fuel pressure regulator on the 916 and later bikes. Thus leaving the port open, and choosing to keep the fuel pressure a constant value with respect to barometric pressure.
Having the hose connected doesn't make a huge difference in fuel pressure. I would leave it connected, as the bike was mapped to take this into account.

Foggy 888

The throttle air bleed screws allow you to make fine adjustments to the air flow to each cylinder at idle without changing throttle plate synchronization or movement of throttle position sensor. You can set the engine up without them (as you have to do on the earlier bikes), but having them makes it easier to make fine adjustments to airflow and fuel mixture to each individual cylinder at idle.