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PostPosted: Sun Jul 28, 2019 8:27 am 
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On the street

Joined: Fri May 25, 2018 4:23 pm
Posts: 28
Country: United Kingdom
Bikes owned: 380Gt 750Gt K9GSXR1000 Gt550
Its got electronic ignition fitted starts and runs fine from warm. If left for a few days it won’t start I’ve checked the spark and it’s ok. An old 2 stroke mechanic told me to try prime for starting then move to ON. Its works but why won’t it start from ON in the first place?


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PostPosted: Sun Jul 28, 2019 9:49 am 
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Joined: Tue Mar 10, 2015 12:35 pm
Posts: 497
Location: Wales
Country: WALES
Bikes owned: suzuki gt 550j
It sounds to me that you have a choke circuit problem. The bike should start from cold even after a few days. How clean are your carbs? The choke or starter circuit begins at the bottom of the floatbowl there is an upright brass tube where fuel is drawn up to enrich the mixture. Two strokes need a heavily enriched mixture to start. At the bottom of the brass tube is a small non removable jet which can become clogged by petrol sediment preventing the choke from functioning. Compressed air and or carb cleaner will usually fix that. That tube also has a number of holes near the top to aid frothing helping the passage of the mixture. Check they are clear. The actual choke mechanism has a small piston with a rubber bottom to seal it when it is switched off. When it is lifted and chokes on air is forced down a passage from the air box side of the venturi and as it passes over the hole above the brass tube the fuel is sucked up mixed with the air and fed to the mouth of the carb where it is drawn into the cylinder.
If it is necessary to put the tap on prime after just a few days there could be a problem with the tap diaphragm. The prime is there to replenish the fuel in the floatbowl which has leaked or been emptied.

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98 carb Blackbird and GT550j


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PostPosted: Sun Jul 28, 2019 10:54 am 
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Joined: Fri May 25, 2018 4:23 pm
Posts: 28
Country: United Kingdom
Bikes owned: 380Gt 750Gt K9GSXR1000 Gt550
Thanks for the reply it makes sense need to get it sorted I’m not quite up to carburettor work.


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PostPosted: Sun Jul 28, 2019 12:44 pm 
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Joined: Tue Mar 10, 2015 12:35 pm
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Location: Wales
Country: WALES
Bikes owned: suzuki gt 550j
I would first check that the choke pistons are lifting

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98 carb Blackbird and GT550j


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PostPosted: Mon Jul 29, 2019 1:51 am 
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2265
Location: The Republic of South Yorkshire
Country: England
Bikes owned: 2 x GT550s GT750, T200, TC200
You use prime to allow fuel into the carbs. If the bike has been stood for a few days, the fuel in the floatbowls evaporates so the engine can't start/run. Putting the tap on 'prime' for a few seconds allows fuel to flow into the carbs so the engine can start. The tap is a diaphragm unit which shouldn't allow fuel to flow (in 'on' or 'reserve' positions) unless the engine is running to operate the diaphragm 'pump' in the tap.
Hopefully you have a fuel filter between tap and carbs, so if the pipe between tap and filter is clear, you'll see fuel flow when you turn the tap to 'prime'. As soon as it stops, turn it to on or res as required, or the carbs could flood and cause other issues.
The engine would start after about 20 seconds of electric start being used anyway, as the tap would operate as normal, but easier (and kinder to the starter) to use prime first.
Just use the bike more. The tap and carbs seem to be working as they should.

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PostPosted: Tue Jul 30, 2019 3:15 pm 
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Joined: Fri May 25, 2018 4:23 pm
Posts: 28
Country: United Kingdom
Bikes owned: 380Gt 750Gt K9GSXR1000 Gt550
This is a really helpful post Alan. It makes me think the problem is i'm not using it enough as it usually starts the day after use. With a full time job a wife and a Harley Davidson to also use your probably right.


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PostPosted: Tue Jul 30, 2019 4:57 pm 
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Joined: Thu Feb 16, 2012 11:50 am
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Location: The Republic of South Yorkshire
Country: England
Bikes owned: 2 x GT550s GT750, T200, TC200
Dave Robbo wrote:
This is a really helpful post Alan. It makes me think the problem is i'm not using it enough as it usually starts the day after use. With a full time job a wife and a Harley Davidson to also use your probably right.

Hmmm. Drop at least one or maybe two of those.
Bear in mind I'm retired, not married and have only Suzukis.
I have a great soul mate in my (female) partner, who likes pillion seat riding, and I don't like a ploughing attachment on a bike, which may help your decision........ :wink: :clap: :roll: :lol:

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PostPosted: Sun Aug 04, 2019 1:23 pm 
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Joined: Wed Jul 10, 2013 12:04 pm
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Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
Alan H wrote:
You use prime to allow fuel into the carbs. If the bike has been stood for a few days, the fuel in the floatbowls evaporates so the engine can't start/run. Putting the tap on 'prime' for a few seconds allows fuel to flow into the carbs so the engine can start. The tap and carbs seem to be working as they should.

+1 on that. Think the other guy misunderstood what you meant. Alan is spot on.


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PostPosted: Mon Aug 05, 2019 4:55 am 
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Location: Manchester, UK
Yep, another +1. The cold start procedure for my 380 was always:

- fuel tap on 'prime'
- choke on
- two kicks with ignition OFF and throttle SHUT
- ignition on, kick once, don't even look at throttle

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1976 GT380 - wounded by me, and sold on
2006 SV650S - killed by a patch of diesel and a kerb in Feb 2019
2017 SV650 AL7 - naked and unashamed


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PostPosted: Thu Aug 22, 2019 4:01 pm 
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Joined: Sun Nov 01, 2015 8:20 am
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Location: Southampton Hampshire
Country: UK
Bikes owned: GT 550
Alan,

What's the "diaphragm pump in the tap", and how does it work please? I have what I think is a GS550 tap on my GT550, and it won't run on any position other than prime. If I put a vacuum gauge on line between the centre carb and the fuel tap, there doesn't seem to be a vacuum, more like pressure, but a very low reading. Other than that the bike runs fine.


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PostPosted: Fri Aug 23, 2019 12:58 am 
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Joined: Thu Feb 16, 2012 11:50 am
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Location: The Republic of South Yorkshire
Country: England
Bikes owned: 2 x GT550s GT750, T200, TC200
The diaphragm tap works from crankcase impulses as rhe engine turns. There's two spigots on the tap (4 on non-linked carb triple engines) one (or 3) go to carbs, and one to a pipe on the inlet. When the engine runs, this pipe sees suction/not/suction/not as the piston rises and falls and this pressure change causes the diaphragm to move and pump fuel to the carbs. That's why you need a 'prime' position to - you guessed it - prime the carbs - when the engine isn't running (and the bike has been standing for a few days). If the impulse pipe isn't connected, the engine will run weak on one cylinder and the carbs will only get fuel when the tap is in 'prime' position.
If you use the impulse pipe with a gentle 'suck/blow' effort by mouth, petrol will flow when in 'on' or 'reserve' tap positions.
Suzuki liked diaphragm taps and fitted tgem to many bikes in the 60s, 70s etc. No more as injection systems run by electric pump.

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PostPosted: Sun Aug 25, 2019 1:52 am 
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Joined: Sun Nov 01, 2015 8:20 am
Posts: 30
Location: Southampton Hampshire
Country: UK
Bikes owned: GT 550
Thanks for that Alan. Nothing like a bit of over complication on a simple thing like a fuel tap! That accounts for why new ones and the overhaul kits, are so expensive.


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PostPosted: Sun Aug 25, 2019 3:32 pm 
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Joined: Wed Jul 10, 2013 12:04 pm
Posts: 1035
Country: England, UK
Bikes owned: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S
Yes but there are inexpensive alternatives. I recently purchased a new fuel tap for a Suzuki GSX that fits my gt380. It cost me £14 including postage. That is about £100 less than a genuine original!
https://www.ebay.co.uk/itm/Fuel-Petcock-Switch-Valve-For-Suzuki-Katana-600-GSX600F-Katana-750-GSX750F/233188779828?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649


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PostPosted: Fri Sep 13, 2019 3:37 pm 
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On the street

Joined: Fri May 25, 2018 4:23 pm
Posts: 28
Country: United Kingdom
Bikes owned: 380Gt 750Gt K9GSXR1000 Gt550
Craig380 wrote:
Yep, another +1. The cold start procedure for my 380 was always:

- fuel tap on 'prime'
- choke on
- two kicks with ignition OFF and throttle SHUT
- ignition on, kick once, don't even look at throttle


This method works an absolute treat.The bike starts within the first two kicks. I've sacked the electric start from cold as the kick start seems to work better.


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PostPosted: Fri Sep 13, 2019 5:03 pm 
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Joined: Thu Feb 16, 2012 11:50 am
Posts: 2265
Location: The Republic of South Yorkshire
Country: England
Bikes owned: 2 x GT550s GT750, T200, TC200
In that case, sack the battery and fit a Motobatt. Mine goes off the battery every time, first time.
It has to because I fitted a cover over the end of the kickstart shaft so it can't be used.

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