Hello everyone!
So in actually having some problems when it comes to the synchronization of the carburetors in my 1993 GS500E.
I just finished what is almost a complete overhaul. I even adjusted the valve tolerances by changing the shims to meet the specifications(around 0.05mm in each valve).
When it comes to the carburetors, i place the mix screw 2 and a half turns out, if im not mistaken that its the stock setting.
WIth a feeler gauge i left both butterflies in the same position.
I mount everything, start the bike, and i can say all works "fine", i let it warm up, and it can idle at around 1100 rpm without a problem.
Now the fun part, i want to try and sync both carburetors, probably whit the feeler gauge trick they will be fine, but i really want this bike to work the best it can.
I build a DIY sync tool with 2 bottles, some tubing and all of that, probably all of you knows how that thing work already. It doesnt have any leaks, tested it and can even hold some pressure with the air compressor.
Anyway, when it comes the time to sync both carbs, after letting the bike warm up, i shut it off, place the hoses, start it, and never manage to get both bottles at the same level. And after some minutes, the bike can start revving really high or just die and not start anymore.
What are the actual steps for syncronization of carburetors? What im doing wrong? Can someone help me out?
TLDR:
If feeler gauge synch (can be verified by eyeball to a bright part of the sky, not the sun) and its equal, but when vacuum gauges are applied it is different you have one of these 3 - Intake leak, exhaust leak or poor compression in the low cyl.
Now poor compression could be a tight valve or something worse.
A pair of equal compression cyls will pull the same vacuum, unless the intake has a leak.
Cool.
Buddha.
Sorry I managed to read some parts of it, its late and I'm getting sleepy.
But the 2.5 turns is actually 3 turns and for mix screws not synch screw.
Cool.
Buddha.
OMG you cant synch 1 carb. Synch = both butterflies are equally open and move the same way up and down.
Toss the feeler gauge, pull them off look at a bright cloud from the air filter side and fiddle the synch screw - the one between the 2 carbs till the light crescent you see from the bright cloud is equal.
The 2.5 turns is mix screw ??? Is it on the bottom side ? Put both of those at 3. 2.5 is factory setting and it sucks.
I'm terrified now that you said you've done a complete overhaul.
Cool.
Buddha.
Quote from: The Buddha on January 14, 2023, 09:43:51 PMOMG you cant synch 1 carb. Synch = both butterflies are equally open and move the same way up and down.
Toss the feeler gauge, pull them off look at a bright cloud from the air filter side and fiddle the synch screw - the one between the 2 carbs till the light crescent you see from the bright cloud is equal.
The 2.5 turns is mix screw ??? Is it on the bottom side ? Put both of those at 3. 2.5 is factory setting and it sucks.
I'm terrified now that you said you've done a complete overhaul.
Cool.
Buddha.
Sorry, maybe is the fact that im not native English speaker, but i do not understand what exactly are you talking about. When i said that i place the mix scew 2.5 turns out, im talking about both mix screws that are located in the botton part of the carburetor. The ones that in US come blocked with a brass insert.
Aaah OK both mix screws have to be 2.5 (or 3) turns out. Yes. But the synch screw is between the 2 carbs visible from the top. Small phillips head screw. Look at a bright spot and see what the crescent's look like under the butterflies. If they're equal let it be. If not, turn that screw one way or the other till the crescent's are equal.
Cool.
Buddha.
Quote from: The Buddha on January 16, 2023, 08:33:47 AMAaah OK both mix screws have to be 2.5 (or 3) turns out. Yes. But the synch screw is between the 2 carbs visible from the top. Small phillips head screw. Look at a bright spot and see what the crescent's look like under the butterflies. If they're equal let it be. If not, turn that screw one way or the other till the crescent's are equal.
Cool.
Buddha.
Thats correct, but if im not mistaken, the vaccum that one cylinder can generate can be different from one to other, thats why people use the tool to check the differences and tune it
If the cyl to cyl vacuum is that different that your tube method is needed vs the eyeball method, you need a engine rebuild. Because while you can have as low as 100 psi cold compression and still run great you cant run anywhere near fine if the difference is 10psi. I had a bike that was 100psi in both. That was the smoothest bike I owned (of the 17 GS'es). It was pretty low on power and would top out at ~90 and use a qt of oil in 300 miles. But it felt like a 4 cyl. It also had 48K of which I put 40K and I learnt all my mechanical skills on. I should have rebuilt it and kept it instead of selling it in 2005.
Cool.
Buddha.
If you can afford it, I would spend the $50 - $100 on a cheap sync tool with vacuum gauges. I also did a DIY sync tool and it was much harder to get right. When I finally used a Bikemaster Carb Sync tool it was much easier. The DIY tools are often too sensitive because you don't use enough tubing so you kill yourself trying to get the levels the same when they are actually close enough.
I disagree with The Buddha that a bench sync gets you perfectly in sync. Any bike with some mileage will have differences in the cylinders and valves that cause the vacuum to be different but not enough to need a rebuild. Bench syncing using a needle or feeler gauge just gets you close. Then you fine tune the sync with a vacuum sync tool.
I think the issue is that your DIY tool is too sensitive so tiny differences are showing up as big differences in the DIY tubing tool.
Quote from: Bluesmudge on January 18, 2023, 10:21:44 AMIf you can afford it, I would spend the $50 - $100 on a cheap sync tool with vacuum gauges. I also did a DIY sync tool and it was much harder to get right. When I finally used a Bikemaster Carb Sync tool it was much easier. The DIY tools are often too sensitive because you don't use enough tubing so you kill yourself trying to get the levels the same when they are actually close enough.
I disagree with The Buddha that a bench sync gets you perfectly in sync. Any bike with some mileage will have differences in the cylinders and valves that cause the vacuum to be different but not enough to need a rebuild. Bench syncing using a needle or feeler gauge just gets you close. Then you fine tune the sync with a vacuum sync tool.
I think the issue is that your DIY tool is too sensitive so tiny differences are showing up as big differences in the DIY tubing tool.
My man, thank you. Probably this is what im gonna do, get a sync tool and save me a few headhaches.
I was really confused with what Budda was telling, because i always thinked what you said.
Again, thank you. The DIY route was a fun experiment, but in the end, using the correct tool is always the answer.
Have a nice day. :thumb:
This bike vibrates a good bit. And if the vacuum vs eyeball synch is something you can feel while riding, its a good bet that you're well out of the spec for differential compression between the cyls. I think its like 14 psi or ~10% right. You'd have to be well out of that range to be able to feel the eyeball synch vs vacuum synch.
Cool.
Buddha.
I've actually got this tool but haven't done it for 6 or 7 years, a reminder that I've been a bad boy and I must get around to it.