It's alive... sorta...

[SebringMike]

Folks,
18 months, too many $, skinned knuckles and lots of swearing later, my Sebring is finished.
I am super-excited and proud, considering this is my first restoration.
Thanks to all who have offered guidance on this project.

Only one small hiccup... the carb.
I am using the original Dellorto UBF24BS carb, but have replaced the seals, filter, needle (E19), atomizer(B260) and jet (1486-108).
The bike starts easily, but I don't have control on the idle, nor is there a quick snap off of the throttle.
It doesn't appear to matter what I do with the idle adjustment screw; the idle is high.
The fuel screw also doesn't appear to do much.
While running the bike, and fiddling with the screws, the bike will die after a few minutes of running.

My (uneducated) thoughts are that we are feeding too much fuel into the bike (hence the high idle, and lack of snap-off of the throttle), and then starve the bowl of fuel (revs high, then dies).
If I try to start the bike immediately, it will start easily (as if I've allowed the bowl to fill up again).
Lots of fuel flow from the tank when the hoses are disconnected from the carb.

We think we've checked everything that makes sense, but I'm looking for any hints on any/all things to check.
What would be typical settings for the idle and fuel screws?
The needle is set to the middle clip setting... if that makes sense? Does this sound right?

Thanks in advance,
Mike

[Nick]

Beautiful work! You should be proud — another Ducati returned to serviceability.

I'm sure that everyone on this site is sick and tired of my repeated advice to ditch the stock carb and replace it with a 28mm round slide Mikuni, but if you really want to ride the bike, do it. Or, maybe a 26/28 mm Amal concentric, or any other modern carb you like.
Having said that, I rode my Sebring for quite a while with the stock carb and it worked okay. Not good, but okay. My Diana also runs okay with the stock carb. But the Mic is much better. If you want a pretty bike to park in your garage or take to shows a couple times a year, stock is great. If you want a bike you can ride every day, you're better off with a modern carb. (Sorry, can't help myself.) The Mic will also give you a couple of more HP, because the Sebring is under-carbureted with the stocker.

You didn't mention how you cleaned the carb, but as you probably know, all carb cleaning starts with a complete strip and soak in lacquer thinner. Then blow out with compressed air. Next, confirm that all jets/needles, etc. are as per the manual. Next, check float level (not easy). Once you've confirmed that all the basics are correct. Sounds obvious, but if everything in the carb is as per the manual, the bike's going to run more or less okay. If it doesn't, it's not the carb.

Timing, high tension lead, bad spark plug cap, bad coil, valve clearance, etc.

High idle: 1. is the slide bottoming in the carb or is it hanging up or being held up slightly? You have to have some free play in the throttle cable. That is, the throttle should turn slightly before it starts to lift the slide. When you close the throttle you should hear an audible click as the slide bottoms in the carb. Once you've confirmed that, you can fool around the with idle adjustment.

2. Air leak, either past the sides a very worn slide or where the manifold bolts to the head, or at the carb-to-manifold joint. Wouldn't hurt to check the manifold for flatness.
Maybe try holding the tickler button down and see if that keeps it running. If so, the float level is too low.
Or put some gasoline in a squirt bottle and start the bike. If you can keep the bike running by squirting fuel into the carb intake but the bike dies without it, the carb is not supplying fuel.
Of course, keep a fire extinguisher handy.

Best way to confirm whether the carb is actually the problem, put another one on there and see what happens. Plenty cheap carbies on E-bay or at salvage yards. No need to spend big bucks for a new one. Lots of used Amals out there too.

Sounds like you're almost there. It's the little things that make or break a classic daily rider.

[amartina75]

+1 yes you should consider just putting that in your signature. I saw you had replied to this post and already knew what you were going to say as soon as I read Mikes post.

"I'm sure that everyone on this site is sick and tired of my repeated advice to ditch the stock carb and replace it with a 28mm round slide Mikuni"

Very nice work! Your bike looks awesome. I'm sure you can get it running as good as it looks.
It doesn't matter what carb you have on the bike tuning it is basically the same process. Start with the idle circuit and work your way up. change one thing at a time.
Not having control at an air screw or pilot screw or any idle system adjustment on any carb is a dead giveaway that the bike is not running on the pilot circuit alone. first check for an air leak, and check that your slide isn't too high.
Good luck

[double diamond]

Mike,

Your Sebring should have a flange mount carburetor body. These bodies are notorious for warping at the flange due to over tightening the mounting bolts. The rubber spacer between the head and carb compresses at the mounting bolts and the carb body warps. The warped flange allows an air leak. You can test for an air leak by starting the engine and spraying contact cleaner on the area where the carb body is bolted to the head. The contact cleaner will be sucked into the engine if the flange is warped. You’ll usually get white smoke out the exhaust pipe and a foul smell (do this test outside!). The warped flange also has the unfortunate effect of distorting the slide bore, making the slide stick and wearing the slide. I’ve had good success with correcting this warping by C-clamping the flange side of the body to a thick, flat steel plate and heating the body in a an oven set to 250 degrees. Position the C-clamp over the inlet of the carb body so the pressure is directed to the bore of the body. You might need to position a plate over the carb inlet to get a good clamping. If the body is warped, you’ll find the slide moves in the bore smoothly after the body is trued.

Did you remove the pilot jet and inspect it? Your symptoms sound like you may also have a blocked pilot jet or perhaps one of the pilot circuit drillings. The pilot is a tiny little jet located in a drilling off to the side of the needle jet/atomizer/main jet holder. The screwdriver slot in these jets is easily damaged if the jet is stuck, so warm the carb body, soak the drilling in oil, use a properly sized screwdriver, all the usual precautions. Once you get the pilot out, also remove the idle screw and spray carb or contact cleaner in the pilot circuit and air screw circuit. The pilot circuit has a fuel outlet downstream of the slide. If this drilling is plugged, you won’t have a properly functioning idle/pilot circuit. Verify that, when you spray aerosol cleaner into the pilot drilling, that you see aerosol exiting this drilling downstream of the slide. The needle position won’t affect fuel metering much right off idle unless the needle/needle jet are worn but you stated you replaced those.

Ciao,
Matt

[SebringMike]

Matt, Nick and Amartina,
I think you've all hit the nail on the head. Basically I think there are some fundamental issues with the carb, and I've got to go back to basics.

Keep in mind that I want the bike to remain as close to OEM equipment as possible... I'm not opposed to replacing the carb... just not yet!
I'm not looking for performance from the bike... I want it to start reliably and be an enjoyable ride... not set records racing block-to-block.

In researching all of your suggestions, here's what I've found.
The slide is worn, but does not appear to hang up in the bore.
Pilot jet is broken in the hole. More specifically, the slots are gone, so now I have to get it out somehow. Despite the pilot being broken, the circuit is clear (contact cleaner forced through the hole into the intake of the carb).
Flange is definitely warped.
Idle adjustment screw is very loose in the threads. No locking nut, but there is a spring; still an concern for air leaks and self-adjusting.
All fuel circuits appear clear.
I have free-play in the throttle... say 1/8" of cable travel before the slide moves.
I replaced the throttle return spring in the carb with a stronger spring. The slide definitely snaps back into place, with a metallic click when it hits the stop.

Rookie mistake... I completely missed the pilot jet circuit on my initial clean of the carb, so once I've got the pilot jet out, I will focus on ensuring that is spotless.

I've ordered a few parts from Dellorto UK, so in the next week or two I will replace a few more items in the carb.
I will work on straightening the flange, and replacing the rubber spacer.
I will then focus on air leaks first. I did the contact-cleaner test on my BMW once... in a closed garage. Think I may have killed a few brain-cells on that one!

So thanks to you all for you support. I will report back when I've done my next round of trials.

Mike

[amartina75]

Sounds like you have a serious air leak with a warped flange and an old rubber gasket.

I hope someone has a good idea for getting that pilot jet out. I had a one stuck like that once, it has to be the hardest one ever to try to get out. I was unsuccessful, I think that's the only carb that ever beat me.
Good luck
Aaron

[SebringMike]

A long overdue update... she's running reliably!

Had some much-needed additional hands-on help from member jbcollier; timing, valve settings and electrical problems weren't helping out at all, coupled with the carb problems highlighted in my previous emails.

So with that said, I've put 16 miles on the Sebring over the last two weekends; ride for a bit, adjust something, repeat as necessary.

One interesting characteristic that I noted today;
a) bike stood vertically and it idles well.
b) bike leaned to the left, and the bike dies. We assume that the carb is starved of fuel from the bowl.
c) bike leaned to the right, and the bike RPM increases. We assume that the carb is now receiving an ample supply of fuel.

When I say leaned (to the left or right), I mean leaned about the same angle as the bike on the side stand... say 15 degrees?
Handle bars are not turned in any of the above scenarios, so it's not the throttle or choke cable being pulled.

The simple solution is to not lean the bike, but that makes turning corners difficult!

Thoughts on the latest issue?

Thanks,
Mike

[Jordan]

I'm thinking - you have 7 motorbikes and you still haven't figured out that leaning into curves does not cause the float level to change?

[SebringMike]

Jordan,
I understand the physics of the float changing when leaning left or right, however none of the other bikes die or speed up when doing this.
This therefore implies that there is something "unique" about (or wrong with) the Dellorto carb.
Perhaps that's one of the unique characteristics that causes people to throw away the carb!
What I'm trying to determine is if this is normal for the Dellorto... if it is, then at least I know what to expect.
Mike

[Jordan]

The idle speed change when tilting the bike (and carb) when not riding is normal when the float chamber is to one side of the pilot jet.
Carburettors with double floats, one each side of the jets, and circular floats that wrap around the jets, etc don't exhibit the idle speed change when tilted.
Sidecar owners get more benefit from non-offset float bowls than do solo riders, because they stay upright when cornering. With a float chamber to one side, they temporarily run rich when turning one direction, and lean the other. Some 4 wheel cars had a single float, but usually mounted in line with the jets with respect to forward motion, so didn't upset the mixture too much when cornering.