Suzuki GT380 poor idle, hard start

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Bront2
Still in the Driveway
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Suzuki 2-Strokes: GT380L, CZ180, JAWA 350

Suzuki GT380 poor idle, hard start

Post by Bront2 »

Hi boys
I am a proud owner of renewed GT380L. All works were done, everything works, but... It is very hard to start engine and idle is very poor. After cold start (about 20 to 30 kicks, I have to also turn idle screw about 3 revs higher) i get approx 4000revs on choke. Than I decrease to 2500 revs by idle screw. Idle is unstable left cylinder has misfires. After small heat on and choke off decrease revs to approx 1500 and engine goes to die. I am on throttle and and idle screw. After stabilizing idle on approx 2000 revs is engine preventet from die. When engine heating up, idle revs goes up, and I still have to decrease idle by idle screw. After full heatup I can stabilize revs on approx. 1500. But after 15sec engine goes to die. When Iam turning throttle to hi revs., engine keeping on approx 3000, than starts to slow decrease, than goes to die. Previously installed ignition Boyer had poor green to yellow spark, so I have changed it to Czech VAPE with 3 sensors and 3 ignition transformers. Spark is Blue-White, fat and satisfactory. Timing is accurate tested by stroboscope. Idle air screws does not have any big sense. Getting bike to move needs hi revs, but after get moved I get satisfactory run. On 1/4 to full throttle I have no any problems. Engine runs smoothly with lot of power from low to max revs. So if anybody have any tip.
Craig380
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Re: Suzuki GT380 poor idle, hard start

Post by Craig380 »

Hi and welcome.

There are some tricks to successfully starting the Suzuki triples. Please forgive me if you already use these tricks - I do not know how much experience you have with these bikes.

When starting the bike from 100% cold, do you turn the fuel tap to 'Prime'? If you do not, try turning the tap to Prime for 10 seconds before you switch on ignition and try to kick-start the bike. This ensures the carburettors have plenty of fresh fuel. The fuel tap does NOT flow fuel in the 'run' position when the engine is not running.

My cold start routine for my 380M was always this, it made no difference if the engine had not run for a day, or had been standing for 2 months:

- turn fuel tap to 'prime' for 10 seconds, then back to 'run'
- lift choke lever
- with ignition OFF, kick the engine over 3 times. Do NOT touch the throttle. Don't even THINK about touching the throttle
- turn ignition on, kick again WITHOUT TOUCHING THE THROTTLE. ONLY use the throttle AFTER the engine has started

I used to let the engine run on choke for no more than 30 seconds, then I would ride away and switch the choke off after 250 metres.

For the poor idling, it sounds like a problem with the pilot jets (blocked or wrong size), or possibly a small air leak around the carb / airbox rubbers. Are the pilot air screws set at 1.5 turns out? Try spraying some WD40 or carb cleaner at the rubbers when the bike is idling. If the rpm increases when you spray, you have a leak.

Good luck, let us know what you find.
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
Bront2
Still in the Driveway
Posts: 4
Joined: Mon May 06, 2019 2:04 pm
Country: Česká republika
Suzuki 2-Strokes: GT380L, CZ180, JAWA 350

Re: Suzuki GT380 poor idle, hard start

Post by Bront2 »

Craig380 wrote:Hi and welcome.

There are some tricks to successfully starting the Suzuki triples. Please forgive me if you already use these tricks - I do not know how much experience you have with these bikes.

When starting the bike from 100% cold, do you turn the fuel tap to 'Prime'? If you do not, try turning the tap to Prime for 10 seconds before you switch on ignition and try to kick-start the bike. This ensures the carburettors have plenty of fresh fuel. The fuel tap does NOT flow fuel in the 'run' position when the engine is not running.

My cold start routine for my 380M was always this, it made no difference if the engine had not run for a day, or had been standing for 2 months:

- turn fuel tap to 'prime' for 10 seconds, then back to 'run'
- lift choke lever
- with ignition OFF, kick the engine over 3 times. Do NOT touch the throttle. Don't even THINK about touching the throttle
- turn ignition on, kick again WITHOUT TOUCHING THE THROTTLE. ONLY use the throttle AFTER the engine has started

I used to let the engine run on choke for no more than 30 seconds, then I would ride away and switch the choke off after 250 metres.

For the poor idling, it sounds like a problem with the pilot jets (blocked or wrong size), or possibly a small air leak around the carb / airbox rubbers. Are the pilot air screws set at 1.5 turns out? Try spraying some WD40 or carb cleaner at the rubbers when the bike is idling. If the rpm increases when you spray, you have a leak.

Good luck, let us know what you find.
Hi Craig

Thanks for initial informations. Instead of my GT380 Iam also owner of old Czech bikes Jawa 350 twin and ČZ 180 single-cylinder. Both two - stroke with very simple carburetor without choke (only overfill button). I have the same experience as you describing with cold start. Both bikes working on 1st kick. Also I am know about necessary procedure with automatic petcock - PRI position to refill carburetors float chambers. And not touch throttle before engine run. Only problem is, that if engine starts cold, on all kicks I can hear several detonations from cylinders, but power is not enough to keep idle. Thats the reason, why I am increasing idle screw. I will enlarge informations about fuel system:
- Petcock is brand new SGP, because original had broken membrane
- Carburetors are original, completely rejeted using some UK sets (main jet, needle, idle jet, float valve, float chamber sealing, throtle valve top sealing) also floats are brand new (Taiwan) due to old floats had corrosion holes and caused carburetors flooding.
- Carburetors rod boots brand new SGP
- Carburetors lever boots brand new SGP
- Carburetors were synchronized before installation according to carburetor original manual
- Idle air screws are on 1 1/4 rotations out

Carburetors are interconnected by new hooses, but I do not understand one circuit. I learned, that one interconnection is for fuel distribution, one is for choke mixture. But there is also third interconnection, where on carburetors is small plastic T-pipe with free outlet. One T-pipe is broken, and instead of hoose connector is only hole. I do not know reason of this circuit. Also boot between carburetors and filterbox does not seal well - you know, this is not possible to buy new one and used part is hard and does not fit well, maybe there is some leakages, but can it be problem? Boots between cabs and cylinders are 100% seal
Craig380
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Re: Suzuki GT380 poor idle, hard start

Post by Craig380 »

It sounds like you have most things covered there!

There is an interconnection between the carbs with T-pieces, and the hoses from the T-pieces just vents to the air. I think it is some sort of overflow, so that should not be a problem.

The airbox rubber boost is hard to fit correctly even when it is flexible. You could try softening the rubber using one of these tricks:

https://www.youtube.com/watch?v=EnGsllKvheQ" onclick="window.open(this.href);return false;
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
Bront2
Still in the Driveway
Posts: 4
Joined: Mon May 06, 2019 2:04 pm
Country: Česká republika
Suzuki 2-Strokes: GT380L, CZ180, JAWA 350

Re: Suzuki GT380 poor idle, hard start

Post by Bront2 »

Hi Craig

So, probbably I have good track. I have again dismantle whole carbs. First, what I saw was fuel in inlet boot of left cylinder, it always signalize problems with carb flooding. So I have connected only this carb to tank and it does not seal well. After several minutes I have got overflow from bottom of carb. It is interesting. All three carbs I have rejett using new rejet set. But under lens it was possible to see small damage on needle of inlet valve. Bottom of carb with overflow tube is little damaged, because it touched surface of gearbox. Maybe it was caused by vibrations. I have to solve this problem and change inlet valve. Than I will write status. Thanks for your tips:-)

Martin
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Re: Suzuki GT380 poor idle, hard start

Post by Vintageman »

Bront2 wrote:dle is unstable left cylinder has misfires
Hmmm. Would like to hear that ... if it's like "bang" (no firing for time - fuel building up and than bang once it does finally ignite) that sounds more like ignition issue.

Both fuel and ignition have similar symptoms but the bangs sounds (out exhaust for example) heads me towards ignition. if too rich it would bang once or twice then foul plug my guess then I would think fuel... yes lean can cause bang (fuel building in pipe then may fire, but we are talking choke on so not sure it is lean. if pilot circuit OK not sure how it can be lean.

All just a guess.
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Bront2
Still in the Driveway
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Suzuki 2-Strokes: GT380L, CZ180, JAWA 350

Re: Suzuki GT380 poor idle, hard start

Post by Bront2 »

Craig380 wrote:It sounds like you have most things covered there!

There is an interconnection between the carbs with T-pieces, and the hoses from the T-pieces just vents to the air. I think it is some sort of overflow, so that should not be a problem.

The airbox rubber boost is hard to fit correctly even when it is flexible. You could try softening the rubber using one of these tricks:

https://www.youtube.com/watch?v=EnGsllKvheQ" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

So, problem was definitely solved. Yes, it was left carb flooding. Mechanical contact between engine and left carb caused vibrations of carb. Vibrations led to vibrations of inlet valve and wrong level control. As bonus needle of valve got damaged (it is interesting how brass made damage to iron:-), but somebody told here that keyster parts have not good quality). So, I changed inlet valve, readjust float and after installation of carbs I put rubber pad under carb. Result is really good. Start on first kick and stable idle.


Later I will send foto of solution of ignition with components VAPE. It produce hi energy and accuracy sparks.


Thanks to all
Craig380
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Re: Suzuki GT380 poor idle, hard start

Post by Craig380 »

That is good news! On my old 380, the left carb was VERY close to the engine case, but had about 2mm clearance (because of new carb boots).
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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markush
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Re: Suzuki GT380 poor idle, hard start

Post by markush »

Hi!

To balance the weight of the carburetor I hang the carburetor bridge with a spring on the frame. Spring constant and spring elongation are chosen so that just the weight is balanced.
The eyelet on the frame is fastened there with metal cable ties.
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sportston
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Suzuki 2-Strokes: FZ50, GP100, RG125 Gamma, GT380, Bandit 1200S

Re: Suzuki GT380 poor idle, hard start

Post by sportston »

Using a spring to stop the carb vibrating against the engine is an interesting solution. I never thought of that. I ground the chain casing away a few millimetres beneath the left carb, then buffed it so it looked liked Suzuki had designed it that way. I never noticed this problem with the original carbs, only after I fitted GT550 carbs. I am curious; does yours have 550 carbs fitted too?
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markush
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Re: Suzuki GT380 poor idle, hard start

Post by markush »

Hello sportston!

Yes, it has.
The whole story about the "Frankencarbs" is here: viewtopic.php?f=2&t=9585

But with the original GT380 carburetor bridge, the float chamber also had contact with the gearbox housing, and over time, it made a pit in it.

I also use springs to balance the weights of single carburettors at my racer.
(see pics 13+14, from 2008, at this site: http://suzuki-gt250.de/bildernavi/Bilder.php?b=1

Markus
sportston
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Re: Suzuki GT380 poor idle, hard start

Post by sportston »

markush wrote: Sat Jun 22, 2019 1:29 am But with the original GT380 carburetor bridge, the float chamber also had contact with the gearbox housing, and over time, it made a pit in it.
I found the same problem, so I took my dremel to the casing and sanded a dip into it so the carb would not touch it.
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