Hi guys, need some carb help

[Jeff Adams]

I just picked up a RATTY 78 GS1000 that barely ran on choke. Cleaned the carbs, new plugs, not firing on cylinder 3. All cylinders have close to 135lbs. I know that's not ideal, but it should run. I have spark in #3, it has 135lbs, had that carb apart apart several times, but still not firing. Getting spark, have had 3 different plugs in, sprayed starting fluid looking for vaccum leak, swapped the boots between 3 and 4 trying to isolate the issue, but the boots all look good. Temp reader shows over 200 degrees on 1,2,4, but less than 100 on 3. I'm running out of ideas on what to check next. Just under 15k on the clock. So what's the obvious thing I missed? It will idle at 1100 now, but you can tell it's not right and only running on 3. Any ideas? Thanks, Jeff

[Brendan W]

Swap the HT leads between 2 & 3.
Have the valve clearances been checked?

[Jeff Adams]

Thought about swapping those, just haven't yet. I thought if the compression was good, the valves had to be ok, is that not true? Thanks.

[Brendan W]

Yes. It's a reflex to go back to basics
Might sound counter intuitive but it often pays to check everything from scratch.

[Jeff Adams]

So you think I need to check the valves?

[LAB3]

He also mentioned switching plug wires between cylinders 2&3, they both fire at TDC in what's called a "wasted spark" system, they fire at TDC whether they're on the power stroke or exhaust stroke. That would help to eliminate any problems with a bad spark plug wires or caps.

As mentioned, start with your basics before deciding to move on to more complex issues, valve adjustments are typical maintenance steps. If you have a manual go through every maintenance item listed in it, by the time you're done you'll have covered most of any issues the bike might have.

[Brendan W]

If compression testing was good enough for valve clearance checking we should all have been doing it years ago

[Nessism]

You might want to check the Newbie Mistakes thread linked in my signature, to see if anything applies.

[chris]

Hi , I have seen cylinders not firing because of carb issues. I would double check carb Blogs , paying close attention to float height. Saying that, I agree with the others in that it is never a waste of time to check valves on a new to you bike.

[Big T]

I'd start with disconnecting and capping the vacuum port on carb Blogs
run the bike on Prime

[duaneage]

Did you try new spark plugs?

[Jeff Adams]

So I bought a parts 750 same year, got it home, put gas in and got it running pretty good. swapped the 1000 cabrs onto the 750 and it ran good, so obviously the valves are the issue. Pulled the valve cover and 0 clearance on the 3 and 4 intakes. I ordered a gasket and tool, not I will have to go thru all of them to see which shims I need to find. Does anyone sell a kit with different sized shims, or will I have to pay $10 each for the sizes I need? Thanks to all the responders, it's a big help. I was on this site 20 years ago when I had my last 78 GS1000. Lots of help, then, too!

[LAB3]

So I bought a parts 750 same year, got it home, put gas in and got it running pretty good. swapped the 1000 cabrs onto the 750 and it ran good, so obviously the valves are the issue. Pulled the valve cover and 0 clearance on the 3 and 4 intakes. I ordered a gasket and tool, not I will have to go thru all of them to see which shims I need to find. Does anyone sell a kit with different sized shims, or will I have to pay $10 each for the sizes I need? Thanks to all the responders, it's a big help. I was on this site 20 years ago when I had my last 78 GS1000. Lots of help, then, too!

Z1 enterprises has them at a reasonable price but you gotta add shipping onto that. You can get them used on eBay too. After just recently doing mine on my Yamaha I really wish I'd have just ponied up the $100 for an assortment since the ones already in there had some wear and my clearances didn't work out when I was done. If you a micrometer or access to one you might save yourself some headaches!

[Rijko]

i use original used shims when i can, they have a slight taper to one side which really helps putting them in.
Aftermarket shims can be hard to put in when they do not have that tapered side ..

Original Suzuki shims are still to be found cheap, just call some former Suzuki dealers (find them in ads in old motorcycle mags for instance) they usually have a bunch and not used them for years.
Recently bought 100 shims for 50 bucks .. came with the original Suzuki tool, too

Many of those 100 were too thick for a used cylinder head.
There is a tool to shorten the valve stems to get in the ballpark again but i prefer to
have the thick shims ground down, any decent machine shop has a grinding table for that.

[Nessism]

A thin shim in the 2.20 range is useful to have. Install that in the positions without clearance, measure clearance, then calculate what shims are needed going forward. Be sure to follow the Suzuki cam positioning method; don't simply point the cam lobe away from the bucket, because you will get more clearance than there actually is when running.

When ordering shims, be sure to get some extras that are smaller than what you calculate. Sometimes they are needed immediately, but if not, you can save them for next time.