Carb sync made things worse...

spray____

spray____

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TL,DR;
I tried to sync my carbs and after I got to what I thought was balanced, the engine is running rough and the idle dropped from 1200 to 1000.

FULL
Hey guys, hoping to get some possibilities on what might be going on here.

A few weeks back I was generously given a home-made manometer from a member here on the forums. Last weekend I finally got around to doing a carb sync on my 06 GS500F. I followed this video http://www.youtube.com/watch?v=NYt33GRHzww and got everything apart, with the only issue being I had to remove the airbox + carbs to get at the left side vacuum source. Once the manometer was attached, I put the carb + airbox back together. I noticed some hoses had detached from the airbox when I removed it, so I hooked them back up and started syncing the carbs.

I played with the carb sync screw for a while, and managed to find a spot where the fluid was staying even, so I started putting everything back together. When it came to put the fuel tank vent hose back on, I relized it needed to get routed between the carbs + airbox and fought with it for a bit before getting it attached properly.

When everything was assembled and I started the bike, I noticed it was idling a little low. It had previously idled between 1200 cold and 1500 warm, but it was now hovering around 1000. I figured maybe I accidentally changed the adjustment when I was fighting with the tank vent hose, so I adjusted it back up to 1200.

The problem I'm having now is the bike seems to be running rough. I'm not sure what's going on, but the vibrations from the engine seem to be stronger than they were before I started tinkering. I can feel it the most with my hands down through the bars. So right now I'm thinking there are a few possibilities:

- I messed something up with the hoses. I'm 90% sure I've got everything back where it was, but maybe there is something wrong here
- I didn't have a good seal between the manomter/vacuum source, and it was reading balanced while I actually made it worse
- This is all in my head
- Something totally unrelated to his

I'm planning to take everything apart and try again when I get a chance. If anyone has ideas about likely causes, things I should look for, ect, I would greatly appreciate it. I'd also be open to going for a cruise if anyone who has a lot of experience is open to having a quick look. I'm not suggesting doing the work for me - just confirming that this is not all in my head and having a look + listen.
 
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You cant just do a carb sync. You have to make sure that your carbs are as close to properly tuned on each cylinder, and THEN sync them together. It is very likely your idle dropped if you were just trying to balance the carbs against each other, without regard to how the cylinder itself is running.

What I would recommend is reading up on how to adjust your carbs to get them to idle right on your bike. You wont be able to remove the airbox to do this, as reducing/increasing air flow definitely plays a part in how well the bike runs.
 
He just balanced his carbs. He needs the guide before those ones which teaches him how to adjust the carbs so each cylinder is running as close to proper as possible. Then balance. After that you can chop to ensure each cylinder is running perfectly (its for fine tuning, not "My bike runs badly", and generally I dont bother to chop, I will check the plugs after a good ride and see which way theyre coming up).

Here is a video that goes over the basics (for a car, its exactly the same idea though):

http://www.youtube.com/watch?v=J8ikzcaMWg0

You will probably want to find a step by step if you have never done it, written specifically for your bike though.
 
not sure what you mean by "so each cylinder is running as close to proper as possible"

I bench sync the carbs, this is just so that all butterfly are open the same amount, and you can start with your pilot air/fuel screws (a.k.a. fuel mixture screws) at 2 1/2 turns out from a lightly seated position, then you can follow the methods posted above or follow this one

http://members.dslextreme.com/users/storagecliff1/images/Adjusting_Idle_Mixture_on_CV_Carbs.pdf

not sure what else there is to do....
 
If you watch the video I linked, it tells you exactly what I mean. He just synced his carbs together, who knows if he chose the base as one that was running well, or one that was running poorly. The fact that the idle speed dropped so much after syncing, and the fact the idle got more rough means that the carbs werent set up properly to begin with (properly synced carbs should mean, even at idle, the idle is extremely smooth, assuming this is not a v engine running at like 600rpm). You have to have your idle set properly first, and your mix close before you can start syncing, otherwise you are just syncing the pressure and probably just going to make the bike run worse. Just because the carbs are balanced doesnt mean they are delivering the right air/fuel mix. Its way better for the carbs to be close to the right mix, but slightly different, than really far off the right mix but the same. If you are ever turning the pilot screw more than 1/4 turn during a sync to achieve balance, then most likely you have made a mistake somewhere.

Btw the 2 1/2 turns or whatever from your factory manual is just that, the factory settings. Wear and tear will change the required mixture ever so slightly over time. While the factory settings are always a good base line to start at on a stock bike, it is not a guaranteed correct mix for your specific bike, which is why people can make good money tuning carbs, and why carbs actually need adjustments periodically.

If you want an example of what I mean, you can crank your pilots out like 4 turns each (assuming they are fuel mix, if they are air mix, crank in, aim for rich because it wont hurt your bike during this "test"), and then sync them together without paying attention to the idle speed, just using the readout on your manometer. You can achieve balance but your mix is way off and the bike will barely run.
 
Not 100% positive, but most sync procedures are done for Idle only. My sync: http://www.youtube.com/watch?v=tuB8k3VHh60 was done as per the shop manual. Even though it an FI bike, my carb Gixxer was the same. I made sure the gixxer carbs were clean and the Idle mixture screws were turned out even. Then hooked up the manometer and adjusted the balance at idle. The R6 was even at idle but not at higher RPM. I assumed it was due to the fuel mapping on the inner cylinders. Your fuel mixture will affect vacuum, that's how you tune a classic holley carb. The leaner you get, the less vacuum you see. I'd adjust the sync at idle or what ever rpm your manual specs (some ask for @ 2,500 rpm).
 
Hey guys, thank you both for the input, links, and videos. Really appreciate it and it made for some good reading/watching.

Didn't realize there was so much involved. I'll admit I'm new to this, and the video I watched originally didn't mention any of this stuff. I actually didn't know before this that my bike even had a fuel/air mixture screw. Thought the only way to change that was to change the jets.

This is, for a newbie like me, fairly complicated and a bit intimidating. I don't have a hard time understanding the theory or the process, but I'm concerned with my limited experience and limited access to the proper tools and environment, that doing anything more than I've already done could yield the same results: the bike will get worse instead of better.

I'm starting to consider paying to have it done by expert. In the end, I might waste a few days of my own time, screw something up, and end up paying for it in the end anyway.

If there is anyone out there who would find this job easy, I'd love to go for a cruise to your garage and pick up some knowledge. In the meantime I think I'll spend some time watching some more videos and reading some more articles about this.
 
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Well you really cannot make it worse, well you can, but you go back to factory specs or a starting base line, and your no further ahead or behind.

it's actually not that hard, but it can be intimidating, if it's an old bike like mine (30 years) you usually find it really difficult to find guys who will work on the bike, so you have to learn it and do it on your own, and if nothing else I at least know it has been done right, especially if it works....

Hope it works out for you, no matter which way you get it done....

Cheers

come to my place, we can get my buddy to bring his Morgan carbtune, and we can fix it right up.....a few beers and a bit of wrenching, what more can you ask for...

and you can get Morgan carbtune instructions right on their site as well

http://www.carbtune.co.uk/inst.html
 
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GateKeeper said:
come to my place, we can get my buddy to bring his Morgan carbtune, and we can fix it right up.....a few beers and a bit of wrenching, what more can you ask for...
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Thanks for the offer - I'd love to take you up on it and obviously I'll bring the beer :). I've had a few thoughts in the last few hours that might stop anyone from being able to do the job quickly:

1) My bike (2006 GS500F) looks like it's mixture screws are covered from the factory when stock. I'll have to look and see if they need to be drilled out. Haven't looked before, didn't even know where they were until this afternoon. Should be able to see them with a little pocket mirror though. http://gstwins.com/gsboard/index.php?topic=58624.0

2) I only got the bike last November, so I've never had the carbs apart to check them or clean them. Should I be doing that before anything else? I've been using the "if it's not broken don't fix it" method so far, (up until the carb sync that is).

What do you think?
 
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Gate-keeper, I would love to join this DIY party if there is room for one more. Got my 91 mc22 last year. It's an inline 4 (Keihin Carb). In pretty rough condition when I picked it up. Did as much of the maintenance I'm comfortable doing. Took the carbs apart, cleaned the snot out of it and toss the parts in an ultrasonic carb cleaner. Sparkles like new and bike fires up fast and runs much smoother. However, it idles a bit rough when adjust to 1500+/-. I have to set it to 2000rpm just to keep it from cutting out. Figured it needed the carbs synced. Just didn't have the motivation to do it. Till now.

Hope I'm not hi-jacking your thread, raydowe :) Bit of a noob on this forum. I don't frequent here often as I do the Aussie forum for it's grey market technical for my particular bike. Would be nice to meet some local members with some DIY expertise. I think I spend more time in the garage with a beer in hand than riding.
 
No problem, I was thinking the same. None of my friends have bikes or live very close so I'm looking to meet local DIYer's too.

Had a look at my bike last night, the brass caps covering the mixture screws are still in place. Will need to get them removed. Thinking of pulling things apart on Sunday and trying to figure out what's going on - unless I lose my nerve that is.
 
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raydowe said:
Thanks for the offer - I'd love to take you up on it and obviously I'll bring the beer :). I've had a few thoughts in the last few hours that might stop anyone from being able to do the job quickly:

1) My bike (2006 GS500F) looks like it's mixture screws are covered from the factory when stock. I'll have to look and see if they need to be drilled out. Haven't looked before, didn't even know where they were until this afternoon. Should be able to see them with a little pocket mirror though. http://gstwins.com/gsboard/index.php?topic=58624.0

2) I only got the bike last November, so I've never had the carbs apart to check them or clean them. Should I be doing that before anything else? I've been using the "if it's not broken don't fix it" method so far, (up until the carb sync that is).

What do you think?
Click to expand...

the covers could come out easy without drilling, use a drywall screw and pull the plug out, or if really stuck, you will need to drill, don't go deep, less than 3mm

you can also try some seafoam, or gasline antifreeze in the tank to clean up a bit, check your rubber boots for cracks as well, or loose clamps, air leaks can cause you issues as well

just some thoughts...
 
Klubjunkee said:
Gate-keeper, I would love to join this DIY party if there is room for one more. Got my 91 mc22 last year. It's an inline 4 (Keihin Carb). In pretty rough condition when I picked it up. Did as much of the maintenance I'm comfortable doing. Took the carbs apart, cleaned the snot out of it and toss the parts in an ultrasonic carb cleaner. Sparkles like new and bike fires up fast and runs much smoother. However, it idles a bit rough when adjust to 1500+/-. I have to set it to 2000rpm just to keep it from cutting out. Figured it needed the carbs synced. Just didn't have the motivation to do it. Till now.

Hope I'm not hi-jacking your thread, raydowe :) Bit of a noob on this forum. I don't frequent here often as I do the Aussie forum for it's grey market technical for my particular bike. Would be nice to meet some local members with some DIY expertise. I think I spend more time in the garage with a beer in hand than riding.
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did you replace all the O rings, they can cause all sorts of issues, and as above, check the boots for cracks and leaks
 
When i synced my gs500 i did it at idle just like yours i did not sync to cylinder first and she came out running real pretty after. Start easy

Check the carb boots are sealed nice

You should get access to your mixture screw to adjust , very possible thats the problem

Have you opened your carbs up and if so did you pay attention to all the o rings?

It has to be an air leak or a hose connected to the wrong place

My $0.02
 
cbcanada said:
When i synced my gs500 i did it at idle just like yours i did not sync to cylinder first and she came out running real pretty after. Start easy

Check the carb boots are sealed nice

You should get access to your mixture screw to adjust , very possible thats the problem

Have you opened your carbs up and if so did you pay attention to all the o rings?

It has to be an air leak or a hose connected to the wrong place

My $0.02
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Haven't had a chance to do anything more yet, but I'm hoping to soon.

I will definitely have a look at the boots. I had a bit of a rough time getting everything to seat together again, although in the end I thought I did. Maybe I was wrong. Again I'm pretty sure I got all the hoses back where they are supposed to be, but I'll probably sit down with a diagram and go over everything to make sure it's right, and there are no leaks.

Haven't opened up carbs yet, although I'm considering doing it. Bike has been well used, and I wouldn't be surprised if it's never been opened (especially considering the mixture plugs are still there).
 
Update for those who are interested.

Got around to ripping things apart again on Sunday. I've been studying diagrams of the airbox, carbs, and all the associated hoses since my last attempt. Had more confidence this time, and figured if I'm going to take it all apart again, I might as well open the carbs and clean them out. Got lucky, and everything went back together without any leftover pieces.

Ripped out the brass caps covering the idle mixture screws. They came out fairly easily. One thing I found was that one was 2 turns out, the other was 3 1/4. Seems strange that they would be so different from the factory. They spin fairly easily, so maybe one had loosened over the last 6 years under the cover? Anyway, I set them back to the baseline 2 turns.

Bike seems to be running a bit better now, and seems to have a bit more power, although that could be the placebo effect. I still want to do some fine tuning (adjust idle mixture and try the manometer again) but in general I feel a lot better about things now.

My guess as to what went wrong was a bad fitting somewhere, probably the seal between the airbox + carb, or carb + head. Didn't see any problems while taking it apart, but I wasn't really looking. It was however a bit of a pain to get back together, so I could have easily had a bad seal there.

Seems to have a bit more power now, although that could be the placebo effect.

Only problem I ran into was when reassembling, my reserve fuel line broke right off at the tank petcock. Lost about 1/4 tank of gas before I managed to pinch it off and yell at my wife to come out and close the petcock.
 
I believe so, or at least very close. The idle is much more smooth than it was, or at least it seems that way to me.

Even when it was bad, it wasn't terrible - it was just more rough than I thought it should be. Someone more experienced might have smacked me in the head and told me to stop wasting my time, but the idea that something might not be right was bothering me more than anything.

Either way, now I know the carbs are clean, I can easily adjust the idle mixture, and I got to play with my tools this weekend.
 
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