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Suzuki GS 750 - Won't start and other problems


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Good evening guys!

As the titel already suggest, my fucking GS 750 won't start after me and Nanno put it together last weekend and after many failed attemps i thought about asking you. 

What we (Nanno) did and what is relevant for the problem:

- checked the valves

- set up the timing chain correctly as described in the service manual

- installed a Dynatek S

- checked for compression (quite low actually. 6bar on the cylinder 1-3 and only 4 bar on cylinder 4)

- spark on all spark plugs (NGK)

- sprit reaches the carbs

- Nanno checked the electric, seems to work 

 

The engine turns, but she just won't start. I also tried starter spray but all i got so far were 3 or 4 short "pengs" of the exhaust. Any tipps what my be the cause?

 

The other problem:

I can't put in any gear. It's completly stuck, although i didn't touch the damn transmission. First look behind the clutch cover also didn't lead to new insights. Tried turning the rear wheel and putting in the first or second gear...nothing. Won't move at all. I don't get it, because i worked just fine before i disassembled everything. Any thoughts? 

 

Cheers, Harald

 

20200505_133006.thumb.jpg.08708a096775b7d110339fc6a10883fc.jpg

 

 

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What year 750?

Did you fully strip the carbs, soak or ultrasonic, especially the bodies, then reassemble with new O rings?

If 80 or newer, is the air box on?

If you didn't touch the transmission, did you align the shift shaft teeth to the transmission forks?

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Crap photo of mine. 

 

Your selector shaft doesn’t look to be seated with the selector drum ( resting on the bottom of the casing).

You may have lost the c-clip on the gear shifter side of the shaft and pushed the shaft through. It doesn’t take a lot.

also you may have lost the locating pin between the shaft and the drum.

3B75AC1B-51EE-491D-9591-D391F9F90E34.jpeg

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Posted (edited)

Morning guys, 

thanks for the help! The bike is from 78. I opened the carbs, cleaned the needles with carb cleaner and compressed air and exchanged the old gaskets and valve needles. The airbox isn't on for now. Tried it, but i didn't work either.

10 hours ago, Wilko275 said:

Crap photo of mine. 

 

Your selector shaft doesn’t look to be seated with the selector drum ( resting on the bottom of the casing).

You may have lost the c-clip on the gear shifter side of the shaft and pushed the shaft through. It doesn’t take a lot.

also you may have lost the locating pin between the shaft and the drum.

3B75AC1B-51EE-491D-9591-D391F9F90E34.jpeg

That's it!!! Fixed it and now it's working! Thank you so much!!!

Edited by Hariii
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FFS ! If you tested the compression (cold admittedly) and got figures sub 4 bar i'm not surprised it doesn't run and sub 1 bar its unlikely to ever run! If you did not realise you have greater problems than 'it doesn't run' you should look for another hobby!

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On 5/5/2020 at 6:26 PM, Hariii said:

- set up the timing chain correctly as described in the service manual

- checked for compression (quite low actually. 6bar on the cylinder 1-3 and only 4 bar on cylinder 4)

Did you check the heads torqued down to the proper spec? 

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Posted (edited)
6 hours ago, Jaydee said:

Did you check the heads torqued down to the proper spec? 

Yes, Nanno did that.

 

Actually on eproblem was the Dynatek s. There was a mistake in the prescription and therefore, the wrong coils were connected. After fixing this mistake, i got her to run for a few seconds today. 

https://youtu.be/Ly1rdXojTsE

Check at 1:00...

 

After speaking with Nanno, i guess i will need a different jetting. 

Edited by Hariii
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Please stop grinding away on the starter - if it doesn't start after 5 seconds of using the starter, adjust something or look for something wrong - you'll just kill the battery or the starter or the starter clutch or all 3! And filling the throats with 'easy start' isn't getting it running - all you've shown is that it runs on highly volatile vapour!

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On 5/5/2020 at 6:26 PM, Hariii said:

Good evening guys!

As the titel already suggest, my fucking GS 750 won't start after me and Nanno put it together last weekend and after many failed attemps i thought about asking you. 

What we (Nanno) did and what is relevant for the problem:

- checked the valves

- set up the timing chain correctly as described in the service manual

- installed a Dynatek S

- checked for compression (quite low actually. 6bar on the cylinder 1-3 and only 4 bar on cylinder 4)

- spark on all spark plugs (NGK)

- sprit reaches the carbs

- Nanno checked the electric, seems to work 

 

The engine turns, but she just won't start. I also tried starter spray but all i got so far were 3 or 4 short "pengs" of the exhaust. Any tipps what my be the cause?

 

The other problem:

I can't put in any gear. It's completly stuck, although i didn't touch the damn transmission. First look behind the clutch cover also didn't lead to new insights. Tried turning the rear wheel and putting in the first or second gear...nothing. Won't move at all. I don't get it, because i worked just fine before i disassembled everything. Any thoughts? 

 

Cheers, Harald

 

20200505_133006.thumb.jpg.08708a096775b7d110339fc6a10883fc.jpg

 

 

Are you sure you did the compression test correctly?

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Actually, i did it not correctly. Nevertheless it should be enough to get the GS running...Unfortunately, this is not the case, even after i cleaned the carbs completly, changed the sprak plugs to Bosch, installed the air filter box etc. She just won't start. Next thing to do is check again the timing of the valve timing, the tappet clearance and the ignition timing. Honestly, it's quite frustrating at the moment.

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Hang in there.

It is probably something small or stupid. 

Re : timing the valves.

On my very first solo full engine rebuild... almost 30years ago i was 100% sure i got the cam timing perfect. Just like in the manual. What can go wrong?

During my final check - before setting the valve lash - i noticed i had not only swapped the inlet cam with the exhaust and also phased them 180 degrees off. Luckily i never rotated this engine as i still needed to install the tensioner. ( this was when i was still a spotty teen of only 17 )

i still remember my thinking error.... inlet is on the front...of the bike :| that it also was the place where i attach the exhaust headers to never raised any doubt. 

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when spinning it on the starter make sure it "sucks" through the carbs and "blows" from the exhaust. If not you've probably swapped the camshafts around like @Blubbersays, with the same symptoms you described earlier.

But I doubt it would be easy to make that mistake since the GS has the tacho drive on the exhaust camshaft doesn't it?

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Thanks for the help guys. Very much appreciated. 

Today i spent again hours on the motorcycle. I may should note, that i'm doing all this tasks pretty much for the first time. Quite exciting too be honest, but also difficult. 

Turned out that the valve timing was completly off. Getting it right was really hard, don't know why. The camshaft and the camchain were quite a bitch and getting the right position seemed impossible at some times :D But i think i got it in the end. Well, i hope. 

Next i checked the clearance and this was completly off. I think we may made a mistake, when we were putting  in the shins...5 out of 8 had more than 0,08 clearance, one 0,08 and two had less than 0,03 (almost no clearance at all). 

3 hours ago, Captain Chaos said:

when spinning it on the starter make sure it "sucks" through the carbs and "blows" from the exhaust. If not you've probably swapped the camshafts around like @Blubbersays, with the same symptoms you described earlier.

But I doubt it would be easy to make that mistake since the GS has the tacho drive on the exhaust camshaft doesn't it?

Jep, it does. And no, i did't swapped the the camshafts. Well, maybe i would, but fortunately Nanno did it the first time and all i had to do was correct the timing. 

 

Man, it won't get boring at all the next days. Lucky me^^

 

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So, today i managed to get her running, but only on 3 cylinders. After trying different things out, it seems like my intake pipes (Nr. 17) https://www.cmsnl.com/suzuki-gs750ec-1977-b-usa-e03_model34282/partslist/BLCK0001.html#.XrrD_BMzY1I need to be replaced. Whenever i spray some brake cleaner on them, the engine turnes up and cylinder 3 gets finally as hot as the others. I know it's still a long way, but i was so damn happy to hear her roar for the first since i saw her :) Next i will correct valve clearance, get new intake pipes, snyc the carbs and then i can finally do the wiring. 

 

By the way, here is a short video of her running: https://youtu.be/wHRLTVCdFnQ

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On 5/6/2020 at 5:37 AM, Hariii said:

Morning guys, 

thanks for the help! The bike is from 78. I opened the carbs, cleaned the needles with carb cleaner and compressed air and exchanged the old gaskets and valve needles. The airbox isn't on for now. Tried it, but i didn't work either.

That's it!!! Fixed it and now it's working! Thank you so much!!!

 

 

I now have an issue, after this happening to me, any imfo on how you fixed this may help me, please.

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