GS850 high idle, one more time....

[londonboards]

Yes there can be a big difference between bikes.

Mostly with these bikes, when the cams and valves wear, the gap gets smaller and smaller. With camshafts that have rockers, when they wear the gap gets bigger. If you are having trouble finding a decent gap then you are in trouble.

It is always better to veer on the side of a bigger gap (as the wear over time will make it smaller) in the range 0.0013 to 0.0030 inches (check these measurements for your specific model). I would go for at least 0.0020 all round. The effect of valves not closing completely (if there is no gap to allow them to do this) would have a greater detrimental effect on performance (because compression would be compromised) than if the gap was a little too large, which would have the effect of them being closed for a tiny bit longer than desired.

So, first check before any carb adjustments is always always valves.

Oh and try taking the lead of cylinder 3 and starting the engine.

[bwringer]

To address a few flags that popped up in my brain:

- Yes, the top of the air filter MUST be sealed to the airbox, or it will act like an air leak. Worse, it will draw in unfiltered air. I use a layer of self-adhesive foam weatherstripping on the top of the air filter (obviously, make sure the metal frame of the air filter is squeaky-clean and totally degreased before attempting). It takes a bit of craftsmanship to get the corners right so they don't leak, and to make sure the foam doesn't migrate when you slide the assembled filter unit into place. I also put a little grease on the top of the weatherstripping so it'll slide instead of ripping off when you push the air filter into place.

All the other caveats for the filter apply as well -- make sure it's only very, very lightly oiled, that the foam is in good shape, and there are no leaks. Make sure the airbox is properly sealed so that air only gets in where it's supposed to (through the snorkel and the vents in the bottom) and can't bypass the air filter. Make sure the snorkel on the back of the airbox is installed.

- Every bike is different, and a carb sync on a different bike is meaningless. A bench sync will get it close enough to start the bike, that's all.

- Yes, you really, honestly, truly have to do a valve check completely and the right way on every valve. Sorry, that's the way it is.

- I really wouldn't worry that much about the different throttle butterfly yet. You have a massive air leak, most likely several tight valves, probably a bad petcock, possibly a bad fuel/vacuum line, and maybe a few other odds and ends we don't know about.

- Vintage vehicles require a very different mindset than newer vehicles -- there's NEVER just one problem you can fix and then go ride. You have to find and fix many different issues that overlap in complex and sometimes surprising ways. Fortunately, the path is well-known...

- Carbs can and do re-clog, no matter how reputable the person who cleaned them, especially if you have an old petcock or if the bike sits for several weeks.

- Just to reiterate: YES you MUST do a COMPLETE valve check and get ALL the clearances right. This is not optional.

- Once you deal with the air leak and valve clearances, then you need to check the carb sync. If #3 is way out of line, then maybe there's some sort of difference in the butterflies. I honestly wouldn't bother thinking about the numbers on the butterfly one more second.

- Just a random thought, for which I apologize in advance: you are using proper Viton or OEM o-rings on the carb/cylinder head boots, correct? Regular hardware store Buna-n o-rings will VERY quickly disintegrate when subjected to the heat of the cylinder head.

- Yes, it's well worth the few bucks to replace the carb-airbox boots as well. You think yours are in good shape, but you'll be astonished at the difference if you get your hands on a new set. And it'll make removing and reinstalling the carbs sooooooo much easier.

[Guest]

Well..... clearly I have my work cut out for me!

I am on my lunch break at the moment, and I went to our local hardware store and bought some weather stripping that looks like it'll do the trick. It is 1/4" thick, and made up of two D-shaped moldings side-by-side. I will use alcohol on the metal frame to get it completely clean, then apply just a thin layer of oil on the top of the weather stripping to make sure it doesn't bind as I slide it into place.

As for the carb boots and O-rings, yes, they are genuine Suzuki parts. I'm trying real hard to install factory parts whenever I can.

[Guest]

Well the non-sealed air cleaner wasn't the problem. I installed the weather stripping I bought yesterday and it had zero affect on the high idle.

[Burque73]

My 850 for the longest time had a high idle issue. Started fine, ran for a short time fine but ten minutes later when I stopped it would rev to 1500+ rpms. I can't say for sure what the cause was but it's gone.

What's changed? I had the pilot or mixture screws at 1.5 turns out which are now at 2.75 turns. Changed carb boots and O-rings, vacuum synched carbs, adjusted valves to all the same clearances .064mm, clipped a bit off the plug wires and changed plugs, replaced the R/R with an SH775, cleaned electrical connections and added single point ground, sealed the airbox and filter basket on top and then ran the snot out of it. 5k miles later it's stable at 1100 rpms every time it runs.
Oh, I tell it goodnight every time I shut the garage. Maybe that's it! just kidding... but I'm thinking it

[Guest]

Tonight, after I reinstalled the air filter with the new weather stripping, I left the choke completely off - AND the bike hadn't run in three days. It started instantly and raced immediately to 3000 RPM. Something is way off, and I really don't think it's anything to do with the installation. I have removed and reinstalled the carbs several times by now, and there's just not that much to it. So this weekend I'm going to pull them back off and bench sync them and see what happens.

And I'm also going to do another compression check; the #3 exhaust pipe is slow to warm up, the bike spits and sputters when it's running, and there is an intermittent metallic clanking sound coming from the vicinity of the clutch/right-front of the engine that has me worried.

[jlyon40]

I had a similar problem with my 81' 850g recently and with mine when it first started it would idle low and then when the bike warmed up it would jump to 2500-3000. I fixed mine by getting a new airfilter and also get some weatherstriping tape that I got on amazon for less than $10 to make sure the side covers and the top of the air filter were air tight. I also had to bring my idle adjustment screw down a little bit and now she's running fine, no problems after warming up or anything.

[Guest]

I had a similar problem with my 81' 850g recently and with mine when it first started it would idle low and then when the bike warmed up it would jump to 2500-3000. I fixed mine by getting a new airfilter and also get some weatherstriping tape that I got on amazon for less than $10 to make sure the side covers and the top of the air filter were air tight. I also had to bring my idle adjustment screw down a little bit and now she's running fine, no problems after warming up or anything.

Hi. Thanks for that input. I've done all of that on my bike. Nothing. So the next thing is to try spraying carb cleaner on all the air connections to see if I can spot a leak. And if that doesn't find it, there's nothing to do but pull the carbs back off and start inspecting them closely for issues.

[eil]

While I'm not as much of an expert as some gurus around here, I have managed to get my 850 running great. Like they say, you won't get very far only doing some of the maintenance. Since we both live in the same neck of the woods, I'd be willing to stop by and offer a hand. I have everything needed to dial in valve clearances (minus the gaskets and maybe some shims) and do a proper carb sync. PM me if interested.

[Guest]

Woo hoo!!!!! I found the problem! Apparently, all four of the throttle butterflies have to be perfectly flat. After a vintage bike mechanic in Austin, TX ("Chris" at Limey Bikes) told me that before you bench sync your carbs, you need to make sure all four are able to make a perfect seal around their perimeter - at the same time. When Charles (from Ypsilanti) was here a few weeks ago and we were inspecting the carbs, we noticed the the #3 had a few dings on the edge, so I filed those down gently and made the edge as smooth as I could, but I did not remove the valve from the carb so that I could inspect it closely. So a few nights ago I pulled the carbs - again - and did a really close inspection to see how well they valves were able to seal; #1, #2 and #4 were perfect, but the bottom of #3 showed a fair amount of light through it. So I removed the valve from the shaft so I could see it from the edge, and sure enough, it was a bit "potato ship-y" around the edge, and there was evidence of having been mistreated by a PO. Luckily I had another one on the way from Ebay and installed it tonight. Eureka! Charles has graciously loaned me his CarbTune Pro, and I've got the four cylinders close, but I suspect there's still room for improvement.

I'm convinced that this is a really unusual situation. I mean, how many people run across a warped butterfly valve? So along with all the great advice about checking for vacuum leaks, too-tight throttle and choke cables, etc, be sure to check your butterfly valves for flatness! Hope this helps someone.....