Gt550 ignition timeing

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Stevengt750
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Gt550 ignition timeing

Postby Stevengt750 » Mon May 13, 2019 8:56 am

Hi there I have a strobe light with adjustable value on it for the timing and would like to set each cylinder up with the timing marks and wondered how many degrees before top dead centre the timing should be on a 1973 gt550 any ideas would be appreciated also if that works I would like to check and set up the timing on a 1972 750j would that be the same timeing as the 550 or does it have a different value cheers Steve

barney01
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Re: Gt550 ignition timeing

Postby barney01 » Mon May 13, 2019 1:06 pm

His
These bikes have a Fixed timing with no advance or retard. So just set it with timing marks. If you want to you can check the marks are accurate using a TDC gauge. Remember these bikes are not highly tuned so exact timing is not strictly necessary.
NO SMOKE .......NO POKE

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raysunners
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Re: Gt550 ignition timeing

Postby raysunners » Mon May 13, 2019 4:08 pm

Stevengt750 wrote:Hi there I have a strobe light with adjustable value on it for the timing and would like to set each cylinder up with the timing marks and wondered how many degrees before top dead centre the timing should be on a 1973 gt550 any ideas would be appreciated also if that works I would like to check and set up the timing on a 1972 750j would that be the same timeing as the 550 or does it have a different value cheers Steve

I would set it to 0 degrees and go off the marks(pointers)

Stevengt750
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Re: Gt550 ignition timeing

Postby Stevengt750 » Tue May 14, 2019 6:15 am

Thanks for answers as helpful as usual cheers

pearly427
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Re: Gt550 ignition timeing

Postby pearly427 » Sun Jul 21, 2019 3:18 am

O degrees is incorrect, that is top dead center. It will never run right. That will make it difficult to start. All model 550’s are set at 22 degrees or 3.37 millimeter before top dead center. You achieve that using a dial gauge. Buy one, it makes timing these bikes so much easier and accurate. You most certainly can advance or retard the timing. You set your base timing, then once it’s running you can retard timing by slightly turning the base plate to the right, you advance it by turning to the left. That’s the reason why you have 3 elongated slots that hold the base plate on. It allows you to fine tune the timing and more accurately as your not suppose to use the timing marks alone. All manuals state not to use the timing marks alone unless it’s an emergency. As they are all not accurate due to backlash or wear. . A 750 is just the opposite because the points base plate is on the other end of the crank, different crank rotation direction according to the base plate.

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raysunners
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Re: Gt550 ignition timeing

Postby raysunners » Sun Jul 21, 2019 4:18 pm

pearly427 wrote:O degrees is incorrect, that is top dead center. It will never run right. That will make it difficult to start. All model 550’s are set at 22 degrees or 3.37 millimeter before top dead center. You achieve that using a dial gauge. Buy one, it makes timing these bikes so much easier and accurate. You most certainly can advance or retard the timing. You set your base timing, then once it’s running you can retard timing by slightly turning the base plate to the right, you advance it by turning to the left. That’s the reason why you have 3 elongated slots that hold the base plate on. It allows you to fine tune the timing and more accurately as your not suppose to use the timing marks alone. All manuals state not to use the timing marks alone unless it’s an emergency. As they are all not accurate due to backlash or wear. . A 750 is just the opposite because the points base plate is on the other end of the crank, different crank rotation direction according to the base plate.

On a car I would agree, but the timing marks on gt750 are set at the required setting and putting a timing light on will show these marks , if you adjust the light for the correct btdc you will be reading the light wrong

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Alan H
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Re: Gt550 ignition timeing

Postby Alan H » Sun Jul 21, 2019 5:56 pm

I've used the timing marks on GT550s since 1972 when I bought my first J model. I've restored a K and an A since and also have another J in resto. The GT750B that I also run also gets timed to the marks and all run well after.
Using a dial gauge is OK if all the plug 'holes' are vertical - they aren't - so you have to use a bit of trigonometry to work out the angle of rotation unles the head is off so as to do it directly vertical to each piston and then work out degrees btdc (before top dead centre) as Suzuki recommend (+ or - 'a bit'). Or use a dial gauge and a degree disc. Too much faffing about IMO, so just use the marks FFS, then get out and ride it. :roll:
Proof that four strokes are over complicated

barney01
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Re: Gt550 ignition timeing

Postby barney01 » Sun Jul 21, 2019 6:24 pm

And you have to remember these are not highly tuned race engines, they perform well timed on the marks :D
NO SMOKE .......NO POKE

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Harrymail
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Re: Gt550 ignition timeing

Postby Harrymail » Mon Jul 22, 2019 12:57 am

Alan H wrote:I've used the timing marks on GT550s since 1972 when I bought my first J model. I've restored a K and an A since and also have another J in resto. The GT750B that I also run also gets timed to the marks and all run well after.
Using a dial gauge is OK if all the plug 'holes' are vertical - they aren't - so you have to use a bit of trigonometry to work out the angle of rotation unles the head is off so as to do it directly vertical to each piston and then work out degrees btdc (before top dead centre) as Suzuki recommend (+ or - 'a bit'). Or use a dial gauge and a degree disc. Too much faffing about IMO, so just use the marks FFS, then get out and ride it. :roll:

I used a dial guage on mine Alan, but never realised the plug holes are not vertical. It was a faff though, and quite difficult to find TDC accurately. The timing marks were slightly out, but that could be just the inaccuracy of the non vertical plug holes. Think I will stick to the timing marks in the future.

H
1977 GT550A Black
2002 Fazer 600 Silver
1968 BSA Bantam Red

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mizzytheman
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Re: Gt550 ignition timeing

Postby mizzytheman » Mon Jul 22, 2019 8:18 am

Harrymail wrote:
Alan H wrote:I've used the timing marks on GT550s since 1972 when I bought my first J model. I've restored a K and an A since and also have another J in resto. The GT750B that I also run also gets timed to the marks and all run well after.
Using a dial gauge is OK if all the plug 'holes' are vertical - they aren't - so you have to use a bit of trigonometry to work out the angle of rotation unles the head is off so as to do it directly vertical to each piston and then work out degrees btdc (before top dead centre) as Suzuki recommend (+ or - 'a bit'). Or use a dial gauge and a degree disc. Too much faffing about IMO, so just use the marks FFS, then get out and ride it. :roll:

I used a dial guage on mine Alan, but never realised the plug holes are not vertical. It was a faff though, and quite difficult to find TDC accurately. The timing marks were slightly out, but that could be just the inaccuracy of the non vertical plug holes. Think I will stick to the timing marks in the future.

H


Mr Suzuki has already worked out the maths which allows for the inclination of the spark plugs on the left and right cylinders. This is why the centre cylinder is set at 3.42 BTDC (vertical plug) and left and right cylinder 3.64 BTDC (inclined plugs).


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