Thoughts on slightly wandering idle

[Guest]

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.

 

[Guest]

"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.

 

[Guest]

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?

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.

 

[Guest]

Thanks Ian, that's real interesting reading... very keen to get into tuning my carbs or at least attempting to. Just gotta track down that mysterious time...

I must agree on a sync too, mine definitely ran better after the sync even without the proper tune...

Oh, almost forgot to say us Aussies were lucky and got adjustable needles too...

 

[Phil]

What is the throttle stop screw? Is this the same as the idle adjustment knob?

I'll be checking the valves once my order arrives from Boulevard with the valve cover gasket. Though I an hoping they all check out since I don't have the tappet tool and I am not quite sure how the zip tie method actually works.

I'll track down some of the Marvel Mystery Oil and see if it makes any difference.

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

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.

 

[tom203]

Idle adjustment knob = throttle stop screw
Putting anything in gas ain't going to lubricate slides- gas doesn't touch them. Closed throttle plates block air , this causes a high vacuum in intake manifold- any leaks can show up then often resulting in random high idle.
Just check your valve clearances to see where they are-this is important, so don't whip out the carbtune just yet. The ziptie is a means of holding the valve open (slightly) to take pressure off the shim so you can pull it out and replace it- it gives you manuvering room.

 

[Phil]

Update

Update

Well I think the wondering idle really isn't the actual issue. After riding the bike for awhile, 20 or 30 minutes, I pulled over and set the idle to where it should be. The bike has been holding this idle fairly well on multiple rides over the past week once it reaches operating temperature.

So the real issue seems to be with cold starting. Like I mentioned in an earlier post the bike starts very weakly with the choke. It will stay on, but hovers under 500 rpms (if its any more/less than 1/2 on it will die out or not start). It also takes a bit to be able to take the choke off, but once it get to that point it runs very well.

I'll finally be checking the valve shim clearances at the end of this week and hopefully vacuum syncing the carbs depending on when the packages arrive.

I will see how it goes after those tasks before I get all excited.

 

[Phil]

Pic

Pic

Figured I should finally post a pic of the machine that is responsible for my golf game falling apart in the past month or so.

https://picasaweb.google.com/lh/photo/uFlfjDBb_3UtbmEZr7A-rdMTjNZETYmyPJy0liipFm0?feat=directlink

The bike is pretty clean, but the picture definitely makes it look better than it does in person.

 

[tom203]

Figured I should finally post a pic of the machine....

The bike is pretty clean, but the picture definitely makes it look better than it does in person.

I've known guys who said that about their exgirlfriends!
At a cold start, you might have a lazy cylinder- not firing right away and forcing the other to do all the work till warm up- this often happens with out of whack valves.

 

[Guest]

That's a nice lookin' machine Phil!

When you said it took a while to warm up, that's what made think of idle adjustment, figured like me you'd adjusted it too soon

+1 on valve adjustments, definitely can be a cause of hard starting.

 

[Phil]

Well the Carbtune arrived yesterday. (It's pretty amazing that something from the UK arrived before my order from Boulevard) I decided to try it out and see how it worked. The Carbtune seems to work great and was very easy to work with. The bike, how it is currently sitting, is pretty close as far as the vacuum sync goes. It was within 2 cmHg.

The Boulevard order should arrive today, so tomorrow or maybe Saturday I am planning on checking the tappet clearances. Hopefully that goes smoothly and I can find a way to get the shims I will most likely need without taking for ever.

 

[Guest]

Yeah Boulevard can be slow... but everything's slow for me over here

Glad you got your Carbtune, and yes I agree, it's a great little unit. It made the carb sync so easy!

 

[Phil]

Update

Update

Well the valves are all adjusted and now in spec, and thanks to tom203 for giving me one of the needed shims!

I am guessing that the valves haven't been checked in quite a long time due to the condition of the gasket which took about 2 hours to remove all the bits from the cover and the engine side. Three of the valves were tight and one was in spec.

I also installed a new petcock, new front pads and replaced the brake fluid.

The difference with the valves in spec is much more than I imagined it would be. The bike started right up with the choke, which now appears to be behaving normally (hopefully that continues), and warmed up quickly, and is holding its idle extremely well now with no wandering at all. It also seems a bit smoother under acceleration which surprised me since it didn't seem to be unsmooth before.

The only issue I have run into with all the work is that the new OEM petcock is slightly different then the original one. The point where the vacuum hose attaches is in a slightly different spot which means my hose is now a bit too short. Slightly annoying but obviously pretty minor.

So big lesson learned, check the valve clearances! Buy the new gasket, buy the feeler gauges, get a dang zip tie (which has got to be on the most simple and brilliant idea) and just do it!

Oh and the whole process really makes me glad that I bought a twin. I am happy to have only had to clean 2 carbs and dealt with 4 valves.

I've known guys who said that about their exgirlfriends!
At a cold start, you might have a lazy cylinder- not firing right away and forcing the other to do all the work till warm up- this often happens with out of whack valves.