Ducati ST4 Starting Problem

[Yorick]

My pal has an ST4 with the 916 motor.

When he first starts it, nothing happens initially. Then it has a cough or two.
Seems to be struggling.
Then fires up OK.

Then starts OK after that.

He's worried that one day it won't start when he's away

I think I remember that this is the way with old Ducatis

Thoughts ?

[KungFooBob]

Starter relay?

Or a sticky solenoid in the starter motor?

When you say nothing happens, no clicking or turning over at all?

[Rockburner]

Are the "ok" restarts after just a couple of minutes of running, or after enough time to get the battery up to charge?

If the restarts are ok after a run, then I'd say it's battery.

If the restarts are after only a moment or two (ie not enough to recharge the battery), then I'd say it's likely fuel starvation when cold - which would indicate a possible issue with the fuel pump, or maybe water contamination in the fuel??

Obviously would be good to get the plugs out when it's cold and see if clean plugs have the same issue (could be just filthy plugs if it's not run often?)

[Yorick]

Starter relay?

Or a sticky solenoid in the starter motor?

When you say nothing happens, no clicking or turning over at all?

Only a split second.

Sort of a slow wurr, wurr, wurr vroom.

[Yorick]

Are the "ok" restarts after just a couple of minutes of running, or after enough time to get the battery up to charge?

If the restarts are ok after a run, then I'd say it's battery.

If the restarts are after only a moment or two (ie not enough to recharge the battery), then I'd say it's likely fuel starvation when cold - which would indicate a possible issue with the fuel pump, or maybe water contamination in the fuel??

Obviously would be good to get the plugs out when it's cold and see if clean plugs have the same issue (could be just filthy plugs if it's not run often?)

Immediately after first starting. Only ran for 2 to 3 seconds.

[Rockburner]

Are the "ok" restarts after just a couple of minutes of running, or after enough time to get the battery up to charge?

If the restarts are ok after a run, then I'd say it's battery.

If the restarts are after only a moment or two (ie not enough to recharge the battery), then I'd say it's likely fuel starvation when cold - which would indicate a possible issue with the fuel pump, or maybe water contamination in the fuel??

Obviously would be good to get the plugs out when it's cold and see if clean plugs have the same issue (could be just filthy plugs if it's not run often?)

Immediately after first starting. Only ran for 2 to 3 seconds.

OK - so the battery is good for repeated startups? That means it's not battery, good (IIRC they only have a small battery).

I'm still thinking fuel supply. Either bad fuel or a knackered pump.

[KungFooBob]

If the start button doesn't make the starter solenoid at least make a click, then I reckon it's that being temperamental. Try tapping it when it won't start.

[KungFooBob]

When he turns the key you can hear the fuel pump prime, right?

[Yorick]

When he turns the key you can hear the fuel pump prime, right?

I'll ask.

[weeksy]

Sounds like the fast idle isn't engaging. Used to be called a choke on a Carby of course, but even on a FI bike at first they had a similar thing

[Rockburner]

Sounds like the fast idle isn't engaging. Used to be called a choke on a Carby of course, but even on a FI bike at first they had a similar thing

Good shout - could well be that - especially if it's controlled electronically and is not a manual lever. (The BMW system has a fast-idle - it's simply a secondary throttle cable. )

[Sadlonelygit]

Double up the earth to the engine
Bfo battery reqd as well
Set tps properly by voltage method
Live at top of big hill!

[mangocrazy]

I seem to remember that Ducatis of that era only had very marginally sized cables from starter motor to battery. Over time corrosion has its dastardly way and the current carrying potential is further reduced. There are folks on the various forums who supply properly sized new cables which make a big difference to starting on the button.

[Yorick]

He just took it for a spin. Fired up OK at home.
But at petrol station it struggled.
Turned over very slow. Not enough to start.
4th go it got going.
Battery is showing 12.8v after ride

He added that the battery terminal got very hot when it's struggling.

And the fuel pump clicks OK when he turns on the ignition

Any more ideas?

Ta

[v8-powered]

As Mangoman says - battery to starter cables. Triumph also had big issues with warm start and that was generally the solution....

[mangocrazy]

Battery terminal getting hot is a sure indicator of high current draw over an inadequately specified cable. Your mate needs to get on one of the Ducati forums or FB groups and start asking about heavy duty battery to starter cables. He'll need both cables (live and neutral) made in heavier gauge cable.

[mangocrazy]

This is the guy I was thinking of - he does high capacity starter cable kits for just about all the more popular Italian models:

https://www.ducati.tech/shop/Exact-Star ... c155257294

I'm pretty sure he supplied a kit for my Falco which dramatically improved the starting, and the bike was only a couple of years old when I fitted them. Your mate might need to email/PM him to see which kit is suitable for the ST4.

[Yorick]

IMG-20240412-WA0016.jpg (136.6 KiB) Viewed 756 times

[Yorick]

He's gonna order leads and relay. He's back in UK in 2 weeks

Screenshot_20240412_163802_Samsung Internet.jpg (297.99 KiB) Viewed 754 times

[Sadlonelygit]

This is the guy I was thinking of - he does high capacity starter cable kits for just about all the more popular Italian models:

https://www.ducati.tech/shop/Exact-Star ... c155257294

I'm pretty sure he supplied a kit for my Falco which dramatically improved the starting, and the bike was only a couple of years old when I fitted them. Your mate might need to email/PM him to see which kit is suitable for the ST4.

Iirc, wasnt the TDM900 relay the cure for many aprilia starting woes. I know we did that on my mates mille and he stopped eating batteries after that.