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PostPosted: Wed Oct 10, 2018 9:41 pm 
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Around the block

Joined: Wed Aug 22, 2018 10:55 pm
Posts: 58
Country: USA
Bikes owned: GT100, GT500
I have checked that there is spark on both spark plugs.
The bike has not been started in many years.
When I acquired it was non-running.

I would like to find out why bike is not running.

Where should I start?

Seller showed me that compression on one cylinder was 90 ( lbs/sq in.?)
How much compression should be?

Also, I have rebuilt carbs,
What should be the settings on air-screw, idle screw etc?
could this be causing bike to not start?

How do I confirm that the carbs is not the culprit?

Thanks.


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PostPosted: Thu Oct 11, 2018 1:09 am 
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Expert racer

Joined: Mon Dec 01, 2008 2:52 am
Posts: 1155
Location: Manchester, UK
The cold cylinder compression reading doesn't mean much: compression can only be accurately checked when the engine is fully warmed up. That said, 90psi when cold shows that the bike does have some compression, probably enough to get it started. When hot, compression should be at least 120psi with no more than 10% difference between the two cylinders.

Can you smell gas when trying to start it? If you can, fuel is getting through. It's worth noting that with the Mikuni carbs on Suzis, do NOT open the throttle when using the choke to start from cold. Only tweak the throttle once the engine has actually fired.

About the sparks. Does your bike have Suzuki's PEI electronic ignition? If so, these can fail so that while you still get a spark, it is delivered at completely the wrong time, way after the piston has passed TDC - which means you might get an occasional pop or fart from the bike, but it won't run. You can check this using a dial gauge to see when the spark is actually delivered.

The only cure is repair or replacement. The good news is, Rex's Speed Shop can fix these in the UK. http://www.rexs-speedshop.com/epages/es ... oducts/GT1

_________________
1976 GT380 - wounded by me, and sold on
2006 SV650S. It's got cams, and valves, and stuff


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PostPosted: Thu Oct 11, 2018 1:53 am 
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To the on ramp

Joined: Tue Mar 10, 2015 12:35 pm
Posts: 427
Location: Wales
Country: WALES
Bikes owned: suzuki gt 550j
+1 on the above. Just two other things to say. You say you rebuilt the carbs I hope you used genuine Mikuni and not Keyster, I would measure the compression myself as you only have the PO's say so. Remember cheap gauges are not so accurate.

_________________
98 carb Blackbird and GT550j


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PostPosted: Thu Oct 11, 2018 9:48 am 
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Around the block

Joined: Wed Aug 22, 2018 10:55 pm
Posts: 58
Country: USA
Bikes owned: GT100, GT500
GTandcbr wrote:
+1 on the above. Just two other things to say. You say you rebuilt the carbs I hope you used genuine Mikuni and not Keyster, I would measure the compression myself as you only have the PO's say so. Remember cheap gauges are not so accurate.


1. Sorry I should have said I have 'partially' re-built the carbs. I took them apart, cleaned pilot jets, main jets,
replaced gaskets, freed up choke plunger, replaced needle jet and seat on ONE of carb, NOT both.
I should replace needle jet and seat on the other carb also. Planning to put order for these.

2. Compression was measured before me, and it showed around 90 on one cylinder. Other cylinder was not measured.

Thanks.


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PostPosted: Thu Oct 11, 2018 10:29 am 
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Around the block

Joined: Wed Aug 22, 2018 10:55 pm
Posts: 58
Country: USA
Bikes owned: GT100, GT500
Craig380 wrote:
The cold cylinder compression reading doesn't mean much: compression can only be accurately checked when the engine is fully warmed up. That said, 90psi when cold shows that the bike does have some compression, probably enough to get it started. When hot, compression should be at least 120psi with no more than 10% difference between the two cylinders.

Can you smell gas when trying to start it? If you can, fuel is getting through. It's worth noting that with the Mikuni carbs on Suzis, do NOT open the throttle when using the choke to start from cold. Only tweak the throttle once the engine has actually fired.

About the sparks. Does your bike have Suzuki's PEI electronic ignition? If so, these can fail so that while you still get a spark, it is delivered at completely the wrong time, way after the piston has passed TDC - which means you might get an occasional pop or fart from the bike, but it won't run. You can check this using a dial gauge to see when the spark is actually delivered.

The only cure is repair or replacement. The good news is, Rex's Speed Shop can fix these in the UK. http://www.rexs-speedshop.com/epages/es ... oducts/GT1" onclick="window.open(this.href);return false;


>>Can you smell gas when trying to start it? If you can, fuel is getting through. It's worth noting that with the Mikuni carbs on Suzis, do NOT open the throttle when using the choke to start from cold. Only tweak the throttle once the engine has actually fired.

I do NOT smell gas while trying to start.
I understood that I am NOT supposed to open throttle when starting from cold.

BTW, one silly thing I am doing: Right now I do not own a spark plug wrench, so I have just tightened spark plug as much as I can using fingers! Will this drastically affect starting of bike?

Also I I have yet to put back the air filters on both carbs. Will this make bike not starting?

On one of the carbs, I have not been able to replace needle value and seat.
I am thinking of ordering one soon.
I have cleaned carbs from inside, cleaned pilot jets, main jet, replaced gaskets, freed up seized choke plunger
on one carb, cleaned up gunk from inside of carbs, replaced both carb boots, replaced needle valve and seat on ONE carb.
Since bike has not been started in many years, i suspect dirt from fuel tank may have got into carbs,
so I plan to cleanup carbs one more time, just to make sure.

>> About the sparks. Does your bike have Suzuki's PEI electronic ignition? If so, these can fail so that while you still get a spark, it is delivered at completely the wrong time, way after the piston has passed TDC - which means you might get an occasional pop or fart from the bike, but it won't run. You can check this using a dial gauge to see when the spark is actually delivered.

Yes, bike has PEI ignition.
I am not getting even occasional pop.
Do I need to buy this dial gauge right away or should I rule out other possibilities first?

Thanks.


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PostPosted: Thu Oct 11, 2018 11:30 am 
Offline
To the on ramp

Joined: Tue Mar 10, 2015 12:35 pm
Posts: 427
Location: Wales
Country: WALES
Bikes owned: suzuki gt 550j
Finger tight plugs will not seal the cylinder and will drastically reduce compression which is already suspect. No air filter fitted will make the air/fuel mixture very weak. How did you clean the carbs? Best way is in an ultrasonic cleaner but if not use carb cleaner spray in every orifice you can and if possible blow through with compressed air.
When you have the air filter attached and the spark plug tight kick bike over if no start take plug out is it wet?

_________________
98 carb Blackbird and GT550j


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PostPosted: Thu Oct 11, 2018 5:49 pm 
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On the main road

Joined: Sat Sep 05, 2015 3:14 pm
Posts: 133
Location: southeast pa
Country: us
Bikes owned: GT
GT500-2stroke wrote:
Do I need to buy this dial gauge right away or should I rule out other possibilities first?

Do not buy a dial gauge, instead you should use a timing light on a GT500.
The GT500 has marks on the stator plate and engine case you simply line up when bolting down the stator plate, the flywheel also has a mark on it that should line up with the mark on the engine case when using a timing light.

I would check carbs again, and when you think they are clean, clean them again, there are small passages that are hard to get clean, including the choke tube that is found in the fuel bowl, it pulls fuel from the bottom of the bowl, this is especially hard to get clean.

Are you getting fuel to the carbs?

_________________
76 GT185
77 GT250
77 GT380
76 GT500
73 GT550
73 GT750
74 GT750
71 T250 scrambler
75 T500 cafe


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PostPosted: Fri Oct 12, 2018 10:52 am 
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Around the block

Joined: Wed Aug 22, 2018 10:55 pm
Posts: 58
Country: USA
Bikes owned: GT100, GT500
Craig380 wrote:
The cold cylinder compression reading doesn't mean much: compression can only be accurately checked when the engine is fully warmed up. That said, 90psi when cold shows that the bike does have some compression, probably enough to get it started. When hot, compression should be at least 120psi with no more than 10% difference between the two cylinders.

Can you smell gas when trying to start it? If you can, fuel is getting through. It's worth noting that with the Mikuni carbs on Suzis, do NOT open the throttle when using the choke to start from cold. Only tweak the throttle once the engine has actually fired.

About the sparks. Does your bike have Suzuki's PEI electronic ignition? If so, these can fail so that while you still get a spark, it is delivered at completely the wrong time, way after the piston has passed TDC - which means you might get an occasional pop or fart from the bike, but it won't run. You can check this using a dial gauge to see when the spark is actually delivered.

The only cure is repair or replacement. The good news is, Rex's Speed Shop can fix these in the UK. http://www.rexs-speedshop.com/epages/es ... oducts/GT1" onclick="window.open(this.href);return false;


Thank you and other members for your support!

The engine finally fired up yesterday!

It was my mistake ( due to lack of experience and or knowledge ), that I assembled the needle valves incorrectly!
I did not realize that needle valves were incorrect until i inserted finger and found out that needle valves were both
3/4 up at the lowest throttle position! Both of them were not sitting at the bottom,
which raised red flag and I decided to find out why.
Opened up the cap and found that the notch in the carb body and sliders were not correct because right side was mistakenly inserted into left side and vice versa.

The I swapped needle valves and re-tried and after first few kicks engine showed signs of life!
Which it had never done before.
Who knows after maybe a decade this bike was being re-started!

Now need to work on carb settings.
Bike does not stay running at this stage.

It fires up and then dies down.

I do not have air filter boots on still.

Thanks again!


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