Gt 550 Cold start Problem

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Dave Robbo
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Gt 550 Cold start Problem

Post by Dave Robbo »

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?
GTandcbr
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Re: Gt 550 Cold start Problem

Post by GTandcbr »

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.
98 carb Blackbird and GT550j
Dave Robbo
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Re: Gt 550 Cold start Problem

Post by Dave Robbo »

Thanks for the reply it makes sense need to get it sorted I’m not quite up to carburettor work.
GTandcbr
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Re: Gt 550 Cold start Problem

Post by GTandcbr »

I would first check that the choke pistons are lifting
98 carb Blackbird and GT550j
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Alan H
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Re: Gt 550 Cold start Problem

Post by Alan H »

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.
Think of how stupid the average person is, then realise that half of them are more stupid than that.
Dave Robbo
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Re: Gt 550 Cold start Problem

Post by Dave Robbo »

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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Alan H
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Re: Gt 550 Cold start Problem

Post by Alan H »

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:
Think of how stupid the average person is, then realise that half of them are more stupid than that.
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Re: Gt 550 Cold start Problem

Post by sportston »

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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Re: Gt 550 Cold start Problem

Post by Craig380 »

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
1976 GT380 - wounded by me, and sold on
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pfg49
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Re: Gt 550 Cold start Problem

Post by pfg49 »

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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Alan H
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Re: Gt 550 Cold start Problem

Post by Alan H »

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.
Think of how stupid the average person is, then realise that half of them are more stupid than that.
pfg49
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Re: Gt 550 Cold start Problem

Post by pfg49 »

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.
sportston
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Re: Gt 550 Cold start Problem

Post by sportston »

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 ... 2749.l2649
Dave Robbo
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Re: Gt 550 Cold start Problem

Post by Dave Robbo »

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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Alan H
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Re: Gt 550 Cold start Problem

Post by Alan H »

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.
Think of how stupid the average person is, then realise that half of them are more stupid than that.
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