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Author Topic: WTF! on,off,prime?  (Read 1842 times)

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Offline Hush

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WTF! on,off,prime?
« on: December 29, 2008, 01:44:13 AM »
OK might need some help from the USA guys here, I'm redoing a wee Suzuki GS400L for my partner and as they seem to have sneaked into NZ as imports via USA you fellahs may know more than I about them.
For one, the bike starts very easily with full choke but wont let you take the choke off or she dies, it aint the carbs as I've stripped them and its all good.
I have found that if I sart the bike with the gas tap on PRIME it revs straight up and then I can take the choke off and return the gas tap to ON or RESERVE and I'm away riding.
Is this normal? I mean does one have to PRIME the carbs everytime, if so all good she can get used to doing that, if not I have a problem some where!
Also fork oil, I just put new seals in the forks and when it came to adding oil the book said 600cc's like how many mils is that?
What is a ball park figure for fork oil, half a cup? half a litre?
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Offline mark

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Re: WTF! on,off,prime?
« Reply #1 on: December 29, 2008, 02:42:23 AM »
It has a vacuum-operated petcock for lazy folks. Prime should only be needed when the carbs are dry. On or reserve as appropriate.

600cc=600ml.


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Online SteveD CB500F

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Re: WTF! on,off,prime?
« Reply #2 on: December 29, 2008, 02:50:59 AM »
"Prime" forces the fuel tap open when there is no vacuum.

Sounds like your bike is running lean when cold and needs the extra choke.

Fork oil - 600ml sounds an awful lot for a (relatively) small bike.
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Offline Hush

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Re: WTF! on,off,prime?
« Reply #3 on: December 30, 2008, 12:48:04 AM »
Thanks for the replies guys, will delve deeper into the fork oil issue.
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline mystic_1

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Re: WTF! on,off,prime?
« Reply #4 on: December 30, 2008, 12:55:17 PM »
Check/replace any vacuum hoses, could have a small air leak there.  This could keep the vacuum petcock from opening fully when starting.

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Offline bryanj

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Re: WTF! on,off,prime?
« Reply #5 on: December 31, 2008, 06:42:03 AM »
And dont leave it in the prime position when stopped, seen many bent suzuki conrods from that
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Offline Hush

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Re: WTF! on,off,prime?
« Reply #6 on: December 31, 2008, 07:47:14 AM »
Yeah found a sump full of 7 year old gas from last owner when he left the tap on prime, gas plus oil equals something akin to diesel!
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline MickeyX

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Re: WTF! on,off,prime?
« Reply #7 on: December 31, 2008, 01:36:59 PM »
It sounds like the same petcock as I had on my Suzuki Savage. I would replace the vacuum line first. If it is still not running on "ON" from start up, then I would think about rebuilding or replacing the petcock. They do have a tendency to leak or just end up with a bad diaphragm inside. While there, I would also check the tank fuel filter if it has one. I've had a clogged one in the past that gave the same type of symptoms.

good luck.
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Offline Hush

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Re: WTF! on,off,prime?
« Reply #8 on: December 31, 2008, 10:43:52 PM »
Cheers Mickey, I've already done the filter thing but the gas line might need replacement.
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!

Offline BeSeeingYou

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Re: WTF! on,off,prime?
« Reply #9 on: January 01, 2009, 11:51:22 AM »
I don't know this bike but if it has vacuum petcocks there are a couple of things to check if they are similar to the Yamaha petcocks.  The vacuum diaphragm has a plunger that has an O ring on the tip that stops the fuel flow when the engine shuts down.  If the bike has sat for a length of time the O ring sometimes sticks and the vacuum is not strong enough to pull the plunger open.  Often the O ring is damaged when pulled open from this condition. The other common problem with these is the "whizzer" valve, a rubber disc behind the lever that gets torn up when operated after not being in use for a long time.    Lack of use for long periods of time are the main causes of problems with these vacuum petcocks.  A punctured diaphragm is less likely but possible.  A vacuum petcock that has been idle for a long time and is stiff to operate should be taken apart and have the o ring and whizzer valve inspected.  Don't force the lever.
« Last Edit: January 01, 2009, 05:16:46 PM by srust58 »
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Offline Hush

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Re: WTF! on,off,prime?
« Reply #10 on: January 02, 2009, 12:03:12 AM »
Cheers for that 58, I'll get a new "O" ring and do an inspection of the whole area when I get a moment.
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I think the thing I most like about motorcycling is the speed at which my brain must process information at to avoid the numb skulls who are eating pies, playing the ukulele, applying make-up etc in the comfort of their airconditioned armchairs as they make random attempts to kill me!!!!!!!
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