pressure regulator and return line

[Turin]

I'm remedial and maybe I'm missing something. I bought the holley 12-804 regulator. fuel comes in from the bottom and has two outs. (no return port) I plugged one of the outs. The functioning out is fitted with the T joint, and I stuffed a 55 idle jet into the return line end. I also put an AC jt in the hose to keep the idle from shooting out and getting into the tank. So far so good... but I only a get constant 3 psi fuel pressure when I completeley pinch off the return line. Otherwise it bounces between 1.5-2.5. Do I really need to have the return line hooked up? I did a search already and read 10 pages worth. The only thing I found is that some 750s didn't have a return port at the back of the tank. I also saw that my fuel line set up may not be standard. Petcock to filter to pump to regulator, all in one straight line. Only one T was in the entire set up for the return. Thanks for any suggestions.

[jayh]

Hi Turin, There is no need for a return line to the tank,with the holley reg.Just straight from pump/filter ,in the bottom of regulator and out one side at the top to carby,with other side blanked off.

The return line with the jet inside was ducati's rather crude attempt at dropping the pressure from the pump,but didn't take into account real world variables such as debris in the fuel,blocking the jet, or varying pressures from different aged pumps etc.
Jay.

[Turin]

Thanks Jay. That confirmed what I was thinking. BTW, I went with your 55 idle, 185 AC , 170 mains. still have mucho tuning to do. how many turns out are your mixture screws if you don't mind me asking?

[jayh]

About 2 1/2 turns each should be close,What air cleaner/exhaust system do you have ? Jay.

[Turin]

I've got staintune mufflers and a K&N air filter w/ the stock air box. She's running, albeit a little rich at the moment. I definaetly see what you meen about the pump cam. I'll probably be busting out the dremel in the near future. -T.

[jayh]

I just updated the weber 'what if 'thread for you,I'm looking forward to someone verifying my results,any questions just ask. Jay

Almost forgot,the staintune and k&n should have you very close to the right jetting.a couple of other things that made a noticeable improvement to mine were doing the ignition relay mod and fitting iridium plugs got all but the slightest miss gone

[Turin]

I'll be more than happy to verify your results. Dyna coils and a relay mod are my next step. I was going to do the work myself, but I may get the local Ducati specialist involved for fine tuning. Throw the kitchen sink at her I think you are spot on about the pump cam. After tweaking on her for days now, the carb just dumps in a bunch of fuel after 3000 rpm, no matter what other tweaks I try, besides removing the cam. That got rid of the flooding Thanks Jay

[jayh]

Turin, Have you ridden the bike to test it,as you will get different results than just free reving it,you don't want to take to much off the cam or you will get another flat spot !!!!,cheers Jay.

[paso750]

The return line with the jet inside was ducati's rather crude attempt at dropping the pressure from the pump,but didn't take into account real world variables such as debris in the fuel,blocking the jet, or varying pressures from different aged pumps etc.

I don`t really think it can happen that the return line jet can be clogged as the debris would have to be quite big. It would have to pass a mesh filter and also a paper fuel filter to then also go through the fuel pump. If that happens it`s not Ducatis fault.
I think the return line to the tank is needed. It`s specially in situations when the float chamber is full. The backpressure in the fuel line will put more load on the fuel pump. It could also happen that fuel is pressed passed the floater needle. Quite franky I don´t know how often that happens when the engine is running and you`re actually riding. It would happen if you switch the ignition on and not start the engine (which of course one shouldn´t do as this could damage the CDI modules).
What I`m wondering about; the engine requires a variable amount of fuel depending on its load. The electric fuel pump delivers a constant pressure so the fuel chamber/floater has to equalize this. Would the return line add to this effect ? I`m talking about the return line to the tank not a slope in the fuel line. Any thoughts ?

G.

[jayh]

G. I don't like being misquoted,it's misleading to others who havn't read the entire thread.You should have included the part about the holley regulator,perhaps you missed it ? Blocking off ducatis crude attempt at a fuel regulator,would be stupid unless you were fitting a proper one ! Anyways I stand by the words quoted,100% no truer words have left my keyboard

Mine was blocked when I removed it,I didn't really pay much attention to what had blocked it though,but it could have been any number of things,a piece of rubber from the fuel line,or pump manufacture springs to mind.Carburettor jets get blocked even in their proper enviroment,it's Murphy's Law.Regardless of that, the pressure regulator should not allow the pressure to rise high enough to cause any trouble,and if a contaminant does find it's way into the system, the holley fuel reg will keep on working and let it flow through to the filter in the banjo of the carby,That's why they put a filter there too. Jay

[paso750]

Actually I didn`t mention the pressure regulator as I don`t think it is really relevant for what I mentioned about the return line. I`m not commenting on the pressure regulator which is definetely the right thing to have with the Weber so I`m currently disregarding it. I just think one should have a return line also when using a pressure reg. No intention to misquote you btw !
I`m currently working on an ST2 engine equipped Duc with Keihin 41 FCRs. The bike has an almost identical twin. Both bikes suffered from flooding carbs. They didn`t like being kept at idle or riding in traffic as this would result in a noticable amount of fuel in the engine oil.
Compression is just fine and the Keihins on one bike are used and on the other brand new. The floater needle was checked, the floater was checked for any cracks where it could fill up with gas but it`s all fine. Then a return slope was added to the fuel line as the tank has no return and the problem was solved.
These bikes don´t have an electrical fuel pump but an underpressure pump which should not generate any pressure higher than what comes out of a Holley fuel pressure regulator.
So my personal experience is pro a return line/slope even though it may also depend on the engine or carb. The advantage is there even though it may generally work also without one.

Regarding the fuel line disintegrating. I didn`t think about that. That could definetely happen if the fuel lines are not changed every couple of years. I already had that with brake lines which clogged because they were dissolving internally. A good reason to use transparent fuel lines, not those textile braided ones

G.

[jayh]

G.It could be related to the vibrations of the L twin at low speeds,vibrating the fuel in the float chamber,both my pantah's flood at idle / low speeds,but I've checked the float levels many times and they are correct,I just put it down to being a 'ducati dellorto' thing and don't leave them idling or running at low speeds if I can avoid it.Oh and I ALWAYS carry a spare set of plugs and spanner on me.Ducatis,youv'e gotta love em

[paso750]

both my pantah's flood at idle / low speed

Ever tried a return slope ? It did help the bikes mentioned. You never know.

[Turin]

Hey Jay ! I took her out last night to tiddle around a bit, but couldn't get on it because the tires are absolute fossils and the ride was squirrelley at best, tires sliding and spinning. Avons, sprockets, dyna-3 coils, belts, and maybe some hi-comp pistons are going in this week. I have a buddy who is a well known duc tech here in Arizona (and used to race a Paso... had two of them!). I'm having him go through the whole thing. He's pretty enthused about digging in to it. After it's tuned, we'll attack the pump cam I think that having a pro do the work would be a better verification of your pump cam mod, than me doing it. I'm a mediocre mechanic at best.

[jayh]

Great Turin, Can't wait for you to get it back,you won't be able to wipe the grin off your face for a week,just go easy on the cam after you move the ramp back to about the 10mm mark,a little at a time and test ride each time from that point,one other thing that is important is to warm the bike right up as the tune changes quite a bit from cold to hot 20 mins- 1/2 hour riding.Quite often when tuning mine I would hop on it and ride after a quick warm up of course,and it would be smooth as silk,but after 15-20 mins the miss would start to become evident again,especially when taking off and moderate acceleration in first and second gear.This is a sure sign that you are still rich on the cam. Jay