Thoughts on slightly wandering idle

[pete]

Over oiling can make it run rich, you shouldn't be able to squeeze any oil out, it should basically just be damp.

[tom203]

maybe you mentioned this already, but............. have you disturbed the carb boots to cylinder head? Those o-rings might be calling for attention- they need to be temp resistant- ordinary hardware store ones won't survive long. PO might have been in there already. 80 degrees inland- just like august, but lake temp is 55 degrees !

[Phil]

The o-rings on the boots are brand new. They came from the guy on here along with all the carb o-rings. I got out and rode about 90 miles. The bike did great. The idle still wandered but it was pretty random. Sometimes when I came to a stop it would idle perfectly fine, sometimes it would be about 2k. Sometimes when it idled at 2k there would be slight clunk sound and then it would idle normally. I have no idea what that was about.

maybe you mentioned this already, but............. have you disturbed the carb boots to cylinder head? Those o-rings might be calling for attention- they need to be temp resistant- ordinary hardware store ones won't survive long. PO might have been in there already. 80 degrees inland- just like august, but lake temp is 55 degrees !

[sicnarf442]

I *really really* need to find a way to get some time with my Colortune. I've learnt to ride around it for now but it's not nice on the clutch having to ride it so much when it bogs off idle

Pete, Let us know how the Colortune works for you. I've read that a limitation is that you can only use it to indicate conditions at idle. At higher rpm's the bike needs to be on a dynamometer to reproduce engine under riding conditions.

Francis
Austin, Texas
1980 GS450S

[tom203]

Hooray for "bike did great" -a reward for your efforts. The clunk sound is odd- other than clutch that is; when you do valve clearances, check how cam tensioner works to make sure its happy.

[pete]

I wonder... is your throttle cable lubed and routed properly? And is the throttle mechanism on the carbs able to move freely and spring back fully and easily on its own? Is the throttle tube turning freely and easily in the right control block? I'm wondering if one of those is the cause of the erratic idle and clunk...

As for the carbtune, I had one very brief go with it at idle, but yes, technically what you've heard is correct and at the various throttle openings you will apparently get slightly different readings with a load as opposed to just revving while stationary in neutral or whatever.

I'm hoping to use the poor man's dyno... foot on the rear break in 6th to simulate some load.

I'm also hoping (once I get it close) that I can get it on the dyno mainly just to make sure there are no really lean spots that are likely to cause me grief.

The place I got my tyres from had a dyno and charge $100 for three runs with AFR, and I figured that will be worthwhile peace of mind once I've got some tuning done.

[Phil]

"Clunk" might be too strong of a word. It made a noise I have heard many times in a car, but I am not sure how to best describe it.

Anyhow, I am starting to get frustrated with starting it. The choke seems to do almost nothing. After I had cleaned the carbs back in early December it started perfectly with the choke. (I even tried starting it below freezing in the winter time and it started up with no issue) Now when I start from total cold, with the choke half on it struggles to stay on and I have to give it some throttle to help it stay on for about a minute or so. If I move the choke much it will die out.

Hooray for "bike did great" -a reward for your efforts. The clunk sound is odd- other than clutch that is; when you do valve clearances, check how cam tensioner works to make sure its happy.

[Phil]

The cable and throttle mechanism appears to work well with no issues. The throttle tube turns easily and returns back to place fully. That was one of my thoughts as well.

I wonder... is your throttle cable lubed and routed properly? And is the throttle mechanism on the carbs able to move freely and spring back fully and easily on its own? Is the throttle tube turning freely and easily in the right control block? I'm wondering if one of those is the cause of the erratic idle and clunk...

As for the carbtune, I had one very brief go with it at idle, but yes, technically what you've heard is correct and at the various throttle openings you will apparently get slightly different readings with a load as opposed to just revving while stationary in neutral or whatever.

I'm hoping to use the poor man's dyno... foot on the rear break in 6th to simulate some load.

I'm also hoping (once I get it close) that I can get it on the dyno mainly just to make sure there are no really lean spots that are likely to cause me grief.

The place I got my tyres from had a dyno and charge $100 for three runs with AFR, and I figured that will be worthwhile peace of mind once I've got some tuning done.

[pete]

"Clunk" might be too strong of a word. It made a noise I have heard many times in a car, but I am not sure how to best describe it.

Anyhow, I am starting to get frustrated with starting it. The choke seems to do almost nothing. After I had cleaned the carbs back in early December it started perfectly with the choke. (I even tried starting it below freezing in the winter time and it started up with no issue) Now when I start from total cold, with the choke half on it struggles to stay on and I have to give it some throttle to help it stay on for about a minute or so. If I move the choke much it will die out.

Hmmmm... choke not working right.

So, hard starting can mean valve adjustments required, but if you need to have throttle and choke like that... well the choke is an enrichener on these carbs to give it more fuel, so to have to open the throttle is not right... however I'm not sure what that could mean except maybe the mixture screws aren't optimally set? I can't remember but have you checked your valve clearances? How about a carb sync? Sorry if you've been through that already, getting a tad tired here...

[Phil]

The idle mixture screws are currently at about 2 1/2 turns out. I haven't adjusted the valves or synced the carbs. The parts are on order to complete both of those tasks. It does make me wonder a little about the valves since the starting issue began after actually riding the bike. Since this past November when I bought it, it was only in the garage running in neutral as I was working on it.

Possibly things have become more out of wack as its actually been used?

Luckily it seems to run well outside of this as it has zero issues lugging my 280 lbs around as fast as I would care to go.

Hmmmm... choke not working right.

So, hard starting can mean valve adjustments required, but if you need to have throttle and choke like that... well the choke is an enrichener on these carbs to give it more fuel, so to have to open the throttle is not right... however I'm not sure what that could mean except maybe the mixture screws aren't optimally set? I can't remember but have you checked your valve clearances? How about a carb sync? Sorry if you've been through that already, getting a tad tired here...

[tom203]

"Choke" system behaving oddly. As I recall, you said your tank looked good inside, but maybe with all this riding around something has made its way to fuel bowls blocking "choke" pickup hole (very bottom of bowl). Can you drop fuel bowls without pulling carbs on this bike? If so, I'd poke/blow this circuit out. Usually enough fuel gets pulled up here to cause high idle at cold start. If bike is running well otherwise, I'd look here.

[Phil]

I might be able to get at the bowls. I really don't want to pull out the carbs entirely since its such a wrestling match to get them back in after. If only Suzuki had designed the area around the airbox so you could move it back like an inch more. Then it would be fairly easy.

"Choke" system behaving oddly. As I recall, you said your tank looked good inside, but maybe with all this riding around something has made its way to fuel bowls blocking "choke" pickup hole (very bottom of bowl). Can you drop fuel bowls without pulling carbs on this bike? If so, I'd poke/blow this circuit out. Usually enough fuel gets pulled up here to cause high idle at cold start. If bike is running well otherwise, I'd look here.

[tom203]

.... If only Suzuki had designed the area around the airbox so you could move it back like an inch more. Then it would be fairly easy.

Yeah, some of these models are no fun for carb removal- if my starter motor goes, my carbs need to come off to replace it.
You could try a dose of Seafoam, making sure it sat in bowls overnight, but poking and blowing is more conclusive.

[pete]

The 450 airboxes are an absolute nightmare... one reason I have K&N pods...

I can easily remove the float bowls on mine while in place, and the allen head screws make it simple.

If you didn't replace yours yet, do it. It's a million times easier to get an allen key in there than a stubby philips screwdriver.

You should be able to check the float bowls out pretty easily and while I haven't tried it yet, with the tank off I reckon I could get the slides out as well.

[IanF]

sticky slides?

I didn't read all the posts, but I'll throw in $0.02.

Do the valves first. Carb tuning is meaningless if the valves are tight and the risk of burning one is great. Do the valve adjustment first. Listen to the wise men who have kept these bikes running for 30 years for more. I'm not one of them but Mr. Nessism is

First some background: GS450 carbs are set up super lean at the factory and many people have spent a lot of time trying to fine tune them so the bike is tractable throughout the rev range. If you figure out how to do that let me know. My PO eliminated the little nylon spacers in the carbs to raise the needles, effectively richening the mixture at 1/4 to 1/2 throttle openings. This had the effect of making the bike easier to ride around town, putting around with the revs under 5k. It also reduced mpg to around 48-50mpg city. This is the only way to adjust the needle height in the BS34SS carbs, unless you have some aftermarket needles. Needle height will affect throttle openings from 1/4 to 1/2 open where the main jet begins to take over. The problem with this mod is that while the bike was easier to ride around town trying to ride at a steady 65-70 mph on the freeway at small throttle openings would not work. The bike would surge and pull its rocking horse act.

Putting the carbs back to stock made it more tractable on the freeway but it no longer has the nice low end torque at 3k to 4k rpm. I've just learned to downshift and keep the revs around 4.5k-5k so there is power available when needed.

Sorry, this got long! So, the probable reason your idle is not stable is that the throttle stop screw is open too far and the vacuum controlling the slides is not getting shut off enough to allow the slides to close completely. There also might be some stiction happening in the slides. I would try backing off on the throttle stop screw a bit. The pilot screws should be somewhere between 1.5 to 2.5 turns out. Any more than that would be on the rich side. I would also try 2 or 3oz. of Marvel Mystery Oil in a full tank of gas. This will lube up the slides a bit.

Vacuum leaks either at the intake boots or in the carb diaphragms themselves can also cause unstable idle. It is mission critical that the boots and o-rings between the intake boots and cyl. head are fresh, viable rubber.

Carb sync is important and some will say that vacuum sync is the only way to do it, but I have never done it and my bike runs pretty well now. Having only two carbs greatly simplifies carb sync and I'm sure it is far more important on the 4 cyl. bikes. What carb sync does is ensure that both carbs are pulling equal amounts of vacuum at any given throttle opening. It can't be made absolutely perfect. What works at idle doesn't work at 4k rpm or 7k rpm. So one has to decide where in the rev range the most smoothness is desired and sync at that rpm. Out of sync carbs cause roughness and vibration more so at high revs than at idle. Bench syncing should be close enough to be able to tune for a decent idle.

I'm sure there's something else I haven't thought of, but those are the basics. The airbox can be wrestled back about two inches which gives you just enough room to get the carbs out. It's not easy but practice makes perfect. I had to replace the trumpets inside the airbox too because they got beat up from a few too many carb removal/replacements.