Ducati 450 help needed

[Knutsonbm]

Hello all,

I have a 1971 Ducati 450 (non-desmo) and I need some help since this is my first single that I've every really worked on.

The bike starts but doesn't like to idle and fouls out plugs very quickly unless I hold the throttle nearly wide open (which is enough to blow your eardrums since there is just a straight pipe......no silencer). It has a new PHF32 Carb, but the intake manifold is some custom piece made by the previous owner.

I don't know where to start in trouble shooting so I'm looking to you to help me even understand what questions to ask....

So first, what would you need to know to help me help you solve my problem?

Thanks,
Brandon

[JimF]

My knee-jerk reaction to a quick fouling bike is that the carb is jetted wrong, probably way wrong.

A secondary cause could be if the float bowl was overfilling, due to a float that sinks or a float valve that doesn't stop the flow of gas. Usually if this is the case you will see fuel seep out from the top of the float bowl. Look for signs of that.

It's pretty easy to take out the float and dip it in water to see if it floats. To test the float valve you can push the float needle into the valve seat and then try blowing air into the gas supply tube. You shouldn't be able to. If the carb has a tickler, make sure the tickler is not stuck in the position where it is holding the float down. If the carb has a choke or enriching lever, make sure that it is in the off position as any of these things would feed too much fuel to the carb inlet.

By looking into the possibility of the float bowl failure or the choke/enriching being stuck, you might either find your problem or eliminate them from consideration before you have to spend money on new jets.

The thing I would do if I though all of the above was OK would be to carefully disassemble the carb and remove all the jets while making notes what jets are in there. You might then find someone on the list that is using the same carb and they can tell you what jets they are using. That will give you a pretty good starting point for jets to buy. Meanwhile soak the carb in carb cleaner. When it has soaked for at least a day, clean all air passageways with some of that dental "super floss" if you can feed it through any of the passageways.

If no one has the carb you just have to buy lots of jets and use time and patience. You first get the idle jet right, where the bike runs at idle and does not foul the carb. Then the pilot and then the main. It's a lot of needles and carb disassembly and changing plugs. You get to be fast at it though. We can get into that later if you have to.

Jim

[Nick]

To the good advice above I would add:

1. Strip carb completely and soak in lacquer thinner for about an hour, then blow compressed air through all orifices.

2. Since someone went to the trouble to put that carb on the bike it's quite possible that the carb is already jetted reasonably well.

3. Be sure you understand exactly how the choke operates. Obviously, if the choke is open when it's supposed to be closed.....

4. Turn air screw all the way in until it bottoms, then turn out 1 and 1/2 turns. That should be a good starting point. Assuming you eventually get the bike running okay, final adjustment to the air screw can be done as follows. Withe the engine idling, turn the air screw in and out slightly until you get the best/highest idle, then readjust idle as needed.

5. If you don't have a manual, get one.

6. And if all else fails....Put a Mikuni on it!

[Ventodue]

<snip> It has a new PHF32 Carb, but the intake manifold is some custom piece made by the previous owner. I don't know where to start in trouble shooting so I'm looking to you to help me even understand what questions to ask....

Hi Brandon,

As you probably know, that's not the carb the factory used. Your bike originally came with a Dell'Orto VHB 29. So in terms of jets etc, there's no factory specifications to refer to.

Have a look around the forum and you may find some guidance from others who've retro-fitted a PHF32. Otherwise, to give you an idea, here's what the Spanish-built Ducati Vento used:
Needle: K3
Main jet: 150
Idle jet: 55 (or 58)
Atomiser: AB 265
Slide: 50 (alternative 40).

HTH

Craig

[double diamond]

The PHF32 has an accelerator pump installed on the rear of the carb body. It’s activated by a ramp on the slide that pushes on a plastic lever that pivots on a pin held in the top cap. This lever in turn pushes on a diaphragm in the accelerator pump assembly. Every time you lift the carb slide, the pump squirts fuel into the intake tract. This may account for the rich condition you have observed. To get your carb tuned where it will run without fuel fouling the plug, remove the lever that activates the pump. The engine will run fine without it. Does the carb have a lever operated starting circuit or cable operated? If it’s a cable, make sure the starting circuit piston closes all the way when in the “off” position. Also, PHF Dellortos have a selection of starting circuit jets available for tuning the amount of fuel that is metered when the enrichment circuit is open. You may have a starting circuit jet that’s too large if it’s drenching the plug with the circuit open. The float arm should be level with the gasket surface of the carb body when the fuel valve closes. Position the carb body horizontally when you check this so the weight of the float doesn’t compress the spring in the needle valve. Then, hold the carb upright with the fuel line attached and the bowl off. Open the fuel tap. Gas should flow from the fuel valve. Push up on the float, fuel flow should stop.

Dellorto UK has a good exploded drawing of the PHF:

http://www.dellorto.co.uk/product-categ ... phf-parts/ (then click “view diagram”)

and suggested standard jetting: "Standard Jetting 507Slide K9Needle 260AB Atomiser 125 Main jet 63Idle jet BF1Idle emulsion tube 35 Pump jet 65Choke jet 250Float valve 7450.1 Floats – 8.5 grams"

Hope this helps.

Matt

[graeme]

Suggest removing the pump lever as has been suggested.
A small pin can be pushed out of the plastic lever and the lever and spring will come away.
Suggest jet / slide and needle sizes the same as a Darmah. You can get these specs off the web.
Plug NGK BP7HS

This works for a good starting point

Graeme

[Knutsonbm]

I really appreciate everybody's responses, since i just moved a crashed Ducati 1198 into the space where I was working on the 450, it will be a few days before I can get to everybody's suggestions (maybe a few weeks depending on what I find and what works or doesn't work)!

Y'all are awesome!

Thanks