Gs 550l 1980 running on cylinders 1&3 only.

[Guest]

Just started the bike after a top end rebuild ie. new rings, cam chain, valve seals and valve refurb. The carbs were stripped and cleaned with new needles and seats. Float heights set as per tutorial on this site. When I start the bike it runs fine on cys. 1&3 but cys. 2&4 wont run. Thought it might be a spark problem but all cys.are getting a good blue/white spark so there seems to be no problem there. When I checked the plugs on 2&4 they were dry suggesting a carb issue. Removed carbs and all seems fine. The bowls on 2&4 were full so fuel is getting that far and vacum taps cant be a factor as the vacum is blanked off as I'm using a jury rigged container with an on/off tap on the fuel pipe. Just plain stumped at this stage,has anyone come across this problem before.The bike sounds like a lovely twin at the minute but seeing as Suzuki went to the trouble of making it a four I think the least I can do is get 'em firing.

[roeme]

Compression is OK?

Since the plugs came out dry, drop a teaspoon of gasoline into the cylinders and check if they're firing after that. If they do, the carbs weren't done correctly.

If they don't, it's either compression or spark.

[850 Combat]

Your two coils are supposed to be hooked up so that one fires on 1 and 4, and the other fires on 2 and 3. Is that how yours are hooked up?

[jdvorchak]

time to go back to the basics. While seated on the bike the cylinders are numbered 1 2 3 4 from left to right.
First make sure your coils are wired to the correct cylinders. On most Suzuki the left coil wired to 1 and 4 and the right side coil to 2 and 3.
Check the end to end resistance of the plug wires. Ohmmeter in the spark plug end of both wires on each coil. Should be about 22k ohms.
Remove the spark plugs and plug them back into the plug wires. Lay them on the head so the lower screw part touches the head. Ignition on and run/stop switch in run. Spin the engine with the starter and confirm you have spark on all four plugs.

[Grumpy]

Thanks, I tried the petrol down the plug hole trick and yes the cylinder fired up fine so the carb would seem to be the problem. The lead to no. 2 cylinder was shorting against the frame, only saw it as the light in the shed was off. Odd as the plug leads are new but there it is. Would I be right in thinking that the idle jet is the first place to look.
Thanks again.

[Grumpy]

Yeah, all plugs sparking well and hooked up properly. Looks like the carb is the issue. Thanks.

[Steve]

Carb sync?

When you had them on the bench, before putting them on the bike, you should have done a "bench sync" to get them close enough to start and run.
After they are on the bike and running, do a vacuum (dynamic) sync to get them perfect.

It sounds like carbs 2 and 4 are simply not open enough to let fuel into the cylinders.

.

[Grumpy]

Carb sync?

When you had them on the bench, before putting them on the bike, you should have done a "bench sync" to get them close enough to start and run.
After they are on the bike and running, do a vacuum (dynamic) sync to get them perfect.

It sounds like carbs 2 and 4 are simply not open enough to let fuel into the cylinders.

.

I'll take the carbs off again and check out the jets and synch the four before I try and restart. I'm getting very good at taking the carbs off and putting them back on at this stage.😊

[Steve]

A "bench sync" is rather easy to do. Just turn the idle speed adjuster so there is barely a sliver of light at the bottom of the throttle, then adjust all the others to match.

Here is what you will be looking for:


Note the sliver of light at the bottom of the throttle. This is actually a bit too much for a good sync, so turn the idle screw to make it a bit smaller.
Adjust all the others to match. Snap the throttle a few times to get everything to settle in, re-check the slivers of light.

.

[Grumpy]

Many thanks Steve you are a gentleman. I was just searching the site for info on a bench sync when I saw this post. It's 6.30 pm here at the minute so it's time to head for the shed.

[Grumpy]

Just an update, synced the carbs, closed the idle screws fully thrn turned back two and a quarter turns. Refitted the carbs and it fired up on all four cylinders immediatly. Running just a little bit lumpy on tickover but as I'm running pod filters getting it dead right could be fun. I'll have to buy a set of vacume guages and see if I can get it 100%. Thanks for the advise folks.

[hillsy]

Do you have all the vacuum ports sealed up? I did that once on a 750 - balanced the carbs but didn't put the port screws back in....took me a while to work out why it wouldn't idle