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Discussion Starter #1
Hi, I have owned this ST4s since new,it's never started as well as my ST4 did but has always started provided it has a decent batt.It is box-stock.Here's the deal:
When I pulled it from winter storage with the tender on it all winter,batt tests good and it cranks as well as they do, but this time the bike fired and died after running just a fraction of a second.Without switching key-off I tried it again,no fire.I switched key-off and on,fired and died.I keep fresh prem gas and sta-bil in all winter.The fuel pump cycles normally at key-on,bike never loses back-lighting or headlamp as the bike dies.

I remedied this(so I thought) by priming the bike with a half shot glass of fuel in each stack,throttle closed and cranked it,it blubbered and did not fire so I opened throttle and cranked it,it fired and ran perfect except that now I have to put a little input in the throttle to restart hot,which is very strange on an EFI bike.

This brings us to today when it fired and died at the gas station just 3 miles from the cabin before it was even up to full temp( much to the delight of hundreds of H-D riders nearby).I tried to restart with out switching off,no fire,I switched off and on and cranked,no start, so as I was cranking I open the throttle wide-open,bike fires,backfires from exhaust and died. I just trailered it home and have it on the tender to be sure batt is good when I get into it.

My plan,as of now:

1.Figure out how to test fuel pressure
2.Check cranking compression and leakdown due to the backfire from exhaust making me want to rule out an exhaust valve hanging open(Will a Duck one-lung like a Harley?,I suspect they may not have enough flywheel inertia).(I have bought the tool and shim kit and have had good luck up 'till now with adjustment) The bike has 2800 miles since i replaced all the bad rockers,replaced belts,adjusted valves.It has no abnormal sounds ect. while running.
3.Start into the electrical diagnosis although I'm not sure what I would be chasing.


My resources are very limited as the closest dealer is in Denver 350 miles so if anyone who has some solid input could help,I would be forever grateful.I am a long-time Master H-D Tech so i am not helpless,just don't want to beat my head against the wall if someone has the magic bullett.Please avoid conjecture as I am easily confused. Thank You in advance!
 

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Still needs a life.
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12,598 Posts
I had starting issues with my late 02-ST4s which were remedied with the removal of an aftermarket sidestand switch cut-out device which had been installed by the previous owner.
 

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Mr Leakered
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8,815 Posts
Being a 2002, it's right about the age for a split fuel line in the tank. Depending on how much it has split, the motor my run a bit or not at all. Other times, they just pop.

Do you smell fuel when it is cranking?

A bad tank of gas could have clogged the fuel pump or the pump inlet screen. They're easy to check, but you might want to have an o-ring on hand. Check the equivalent parts sticky.

If it isn't fuel related, check for vacuum leaks around the TBs. Do you have an emissions canister? If so and it gets choked with fuel, I've heard that they don't empty well and cause bad starting issues. It is not a well designed fuel catch and generally does more harm than good.

Also, be sure that the vent line(s) between the tank and vert cyl is not pinched.

BTW, there is no need for premium on these machines. They are technically low compression engines. Now, altitude might come into play, but the EFI does have an ambient pressure sensor.

Have a good one.
 

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Also check the block connector under the nose fairing from the alternator to the reg/rec.

What voltage is the battery showing ?
 

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Life is too short to worry !
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I'd bet on a hose and as its easy to check and cheap its a good place to start.
 

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Discussion Starter #6 (Edited)
Also check the block connector under the nose fairing from the alternator to the reg/rec.

What voltage is the battery showing ?
It shows surface charge of 12.8 and will hold good voltage for a short time while cranking,these batts are feeble compared to the bikes I work on but it seems to have good voltage and cranks good,regulator kicks on and off at typical limits,although I am unsure of exactly what the book spec is.
 

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Discussion Starter #7 (Edited)
I will check these items today,looks like some solid leads.Thanks very much,if you come to the Black Hills of SD I'll show you all some killer rides.
 

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Discussion Starter #8
I have found the formed hose from fuel tank to the fuel canister pinched between vertical cyl and tank bottom,also when i blow thru the hose it seems to gurgle a bit as if raw fuel may have collected in it. I presume the function is to absorb fuel vapor from the tank vent so it doesn't escape to atmosphere? If this causes a venting issue,would simply opening the filler neck cure this? I have not witnessed any buildup of negative pressure in tank but do occasionally hear a slight whistling sound from the bike when it's sitting,as-if it's venting.
I have not opened tank yet to look at hoses etc. but bike started with a little priming of each cyl,I let it run to 217 deg and shut down,it restarts normally right now(i left the hose to fuel canister unhooked for now). I hear no fuel spray inside tank at key-on and see no bubbling thru filler neck.,but do hear a slight sound at switch-off that I think is the normal op of the pressure reg bleeding down. I suppose it could be a line leaking down.This bike does not exhibit any runnability issues that I normally see from a fuel pressure issue,as-in it will run at very high speeds(110 to 130 MPH for about 90 miles through the Badlands) and never miss a beat.I am going to get gasket and line and replace anyway,due to age.I have zero confidence that I have found the issue.Thanks for any further input you may have.
 

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Mr Leakered
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You might have. Folks have said that once the charcoal canister loads up, it doesn't purge.

Most folks will ditch them before leaving the dealership. Like you noted, they vent raw gas to the atomosphere anyway. So, what's the use? Put vacuum caps on the TB ports and route the vent line down the engine. You can even purchase a y-connector so that you only have one line to worry about for vent and overflow.

The battery is small for a twin, but if everything is kept healthy, it is sufficient.

Have a good one.
 

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Emissions Canister??

I've also heard strange things about them. Once they fill they never act correctly. Mine works perfectly for the ST4s, as it sits quietly next to the one off of my 999s, on the shelf *smile* looking down at the ST4s from a far........

Cheers,
M
 

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I experienced a similar problem this summer. Cold starts were fine, shut off and restart immediately was fine, but let it sit off for a couple-three minutes and no restart. The engine would crank, catch for a second or two and then cut out. I cranked it until the battery started dying with no joy.

Turned out to be a bad fuel injector. It tested fine out of the bike, but was actually dripping fuel onto the spark plug. A big clue was the fact that a fresh plug would be fouled right away after a few starts. Both injectors were replaced and hasn't been a problem since.

This was all done at a local shop, so please don't ask me for many more details, this is all third hand from the master mechanic there :)

If this isn't your problem, I hope this will help you eliminate it as a source of trouble.
 

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Discussion Starter #12
Seems to be working ok after a good 60 mi run and a dozen or so restarts.Maybe it is fixed.It seems to generally run smoother and accel a bit better,too.I am going to do a few more short trips ending-up back at the cabin.That way if it won't restart,at least I'm in the shade with my flyrod and a cold Summer Shandy.Thanks for the tips!That's why I ride old stuff,by the time it happens to me,someone else has already been thru it.Also,there's no fun in wrenching on your own stuff,during Sturgis, after a twelve hour shift fixin' the heavy iron while listening to full grown "bikers" whine like little babies.....Sorry,fatigue induced tangent.Thanks again!
 
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