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Hesitant acceleration after carb cleaning

  • Thread starter Thread starter ShirleySerious
  • Start date Start date
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ShirleySerious

Guest
I took my bike to the shop a couple weeks ago to get a tune up and new tires. They cleaned the carbs out and changed the oil and the guy said it should run well now.

Well the past few days, I've been a little antsy with this cold weather and decided to take my bike for a short ride around town. Now it's about 25-30 degrees outside. As uncomfortable as it is for me, I think my engine likes it even less. I give it enough time to warm up and idle at the right speed. When I get the engine up to about 4000-4500 rpms and higher, it seems a little hesitant, like it doesn't want to rev any higher. This is only when I'm moving; when it's in neutral, it revs freely.

Could this be happening because of the cold?
 
If you let it sit awhile maybe your slides have gotten gummed up a bit. Check and make sure your slides are moving freely.
It sounds like an issue with your needle circuit.
How's the charge on your battery?
 
chef1366 said:
If you let it sit awhile maybe your slides have gotten gummed up a bit. Check and make sure your slides are moving freely.
It sounds like an issue with your needle circuit.
How's the charge on your battery?
Click to expand...

Since I got it back, the most I've ever let the bike sit without running is 3 days. Not sure what slides you're talking about, but anything that was gummed up should have been taken care of when they cleaned my carbs.

They also put in new spark plugs and filed down the points and condensors. Bike runs and revs fine in neutral, so I doubt it's the battery (which I keep charged, BTW).
 
Damn, I probably shoulda mentioned that first. It's a 1978 GS550E.
 
Shirley, good to hear that you have had those carbs cleaned. If your mechanic has done the job properly, the reason that you can't rev your engine past 5000 rpm under load, will be because the PO probably has the needle position set too low(lean) and/or he has incorrectly sized the main jets (lean again). This will be more promounced under extremely cold conditions. You need to find out what the needle positions are set at and the size of the main jets. Your mechanic should be able to tell you this.
 
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I can ask the mechanic tomorrow, but he told me when I got it done, that it was running pretty lean, so he adjusted the jets accordingly. I know air cooled bikes don't run so well in cold weather, so this could be part of the problem too.

The only other thing I can think of is when they changed the oil, they used regular oil instead of special bike oil. I'm not sure if this would affect performance as much as it has, though.
 
There's no reason why a fully warmed up bike should not be able to ride properly in 25 degree weather.
Yes it could be improper jetting, but it could just as easily be air leaks. Tons of posts about this.
Do a plug chop at the problematic RPM to see if the plugs are too white. If yes, then it's lean. If they're black then it's too rich at mid-range (maybe the mechanic over-compensated).
That's the problem with taking our older bikes to a "run-of-the-mill-mechanic" - they typically run the bike for a couple of minutes, and if it doesn't stall, they decalre victory! Invariably, the owner ends up have to finish up the half-baked job that the mechanic did.
 
nabrams said:
That's the problem with taking our older bikes to a "run-of-the-mill-mechanic" - they typically run the bike for a couple of minutes, and if it doesn't stall, they decalre victory! Invariably, the owner ends up have to finish up the half-baked job that the mechanic did.
Click to expand...

Half-Baked mechanic, maybe :? ! If the air leaks are ruled out, and the charging system and battery are good, it will be you needle height setting. I had the exact same symptoms when the temps dropped and there were no leaks anywhere (everything from the head back to and through the air box was redone). I raised the needle one position (drop clips one notch) and problem solved. The bike went from 51 mpg to 49 mpg, but no more problems.
 
Assuming the bike is still stock, our air cooled GS engines need to be fully warmed up (several minuets of actual riding) in order to carburete cleanly. The jetting was ultra lean from the factory in order to meet required emission regulations which in turn make the machines quite cold blooded. Because the bikes were so lean to begin with, air leaks cause fits because it leans the mixture even more. The most common cause of air leaks is between the engine and the rubber carb runner boots – if the o-rings on your bike haven’t been changed before, they could well be leaking (or soon will be). Assuming the bike is still stock, there should be no reason to worry about jet sizes – although a little selective richening can reduce the cold blooded tendency. If the exhaust and or airfilter (airbox) has been modified though, the jets will have to be modified in order to get the bike to run properly – Dynojet kits are quite popular for this reason.
 
I called the mechanic (the one who handled my bike was out to lunch) today and couldn't give a good explanation. All he said was that it could be because of winter blend gas, which sounds like horsefeathers to me, and that I should bring it in.

They told me they would replace the boots if they were cracked, and they didn't replace them so I guess they were fine. A visual inspection confirms that. I don't know how to adjust the needles or anything like that, but if it's running a little lean, would I be able to use a little choke to fix that? I'm running pods instead of the airbox if that helps, but that was supposed to have been taken care of when I got the carbs cleaned. This is turning out to be quite the mystery problem.

I'll go try looking at it and playing with the choke, but that's all I can do now.
 
ShirleySerious said:
I called the mechanic (the one who handled my bike was out to lunch) today and couldn't give a good explanation. All he said was that it could be because of winter blend gas, which sounds like horsefeathers to me, and that I should bring it in.

They told me they would replace the boots if they were cracked, and they didn't replace them so I guess they were fine. A visual inspection confirms that. I don't know how to adjust the needles or anything like that, but if it's running a little lean, would I be able to use a little choke to fix that? I'm running pods instead of the airbox if that helps, but that was supposed to have been taken care of when I got the carbs cleaned. This is turning out to be quite the mystery problem.

I'll go try looking at it and playing with the choke, but that's all I can do now.
Click to expand...

Two things:
1) If they didn't rejet for the pods, your problem will continue.
2) The "winter gas" is another way of saying, "We don't have a clue"!
Do not run with the choke circuit as a moderator for a lean burn condition!!! Either buy the book and fix the problem yourself, or take it back to the "horsefeather" dealer, and pay them the big bucks to have a tech who wasn't even born when these bikes were king of the road, slap parts at it because he isn't sure what to do with it.
WOW...I'm starting to sound like my father............. :shock:
 
You'll never get it to run right at all RPMs by chasing the problem with choke settings.
You really have only two choices at this point.
1. Keep on paying "mechanics" to screw up your bike.
2. Bite the bullet and invest the 30-60 hours it's going to take you to learn and fix your bike. There are tons of posts on this site (some by me) that give very good avdice, geared towards newbie mechanics, for your specific problem, and for many other problems typical of our older bikes.

I suspect that the amount of money you've already shelled-out to "mechanics" already has far exceeded the cost of the tools you would have needed to do the job yourself.
Yes, the time/effort investment is significant, but well worth it, if you intend to ride for years to come.
If you don't know what a plug chop is or how to test for air leaks, you can find that info here.
 
I don't have the patience to learn how to fix it myself. Sorry, that's just how I am. As bad as the mechanics are, they know a hell of a lot more than I do about this. My philosophy is if I don't know what I'm fiddling with, it's best to not fiddle with it. To clarify my condition:

When the bike is moving in gear, it hesitates past 3000 RPMs. When I pull the throttle back all the way, the engine goes below idle speed. Something's fishy with this, so I don't outright suspect the carb settings. Here's where it confuses me, though. When the bike is in gear with the clutch pulled in or in neutral, it revs higher with no problem. I propped the bike up on the center stand and ran it through the gears as if I were actually riding it. It revved just fine then.

So I'm thinking it has something to do with having a load put on the engine. They changed my oil with regular motor oil, instead of motorcycle oil for a wet clutch. Would you recommend changing the oil again using bike oil this time?

UPDATE: I called them again and they want me to bring it in and leave it overnight. They said they can't legally take it for a test ride until April 1st, but by then it'll be too busy. Too bad the only way to see that there's a problem is to actually ride it. They keep giving me the runaround and can't spot the problem they were supposed to fix in the first place. I have no frickin clue what could be the problem.
 
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Sorry for the double post but I just made a discovery. I took a look at the carbs and saw that the tubes that used to connect to the vacuum vent were gone. There is just the brass nipple exposed with no tube. I don't know if this is significant relating to my problem, but I know that the mechanic took it off.
 
Oi.

Your mechanic is an idiot. The stock jetting is just fine on a GS550 with the airbox in place. He should not have rejetted. All your bike needed was to have the pilot jets cleaned and the mixture screws cleaned.

Did he tell you what jets he installed? If he didn't, you're up the creek untill you find out what he put in there.

What prompted you to file your points? By filing them you have changed the timing of your bike. Your timing will need to be reset now.

Right now, you need to clean, and reset your carbs back to their stock settings. (this is REALLY Easy to do.) And make sure your timing is set properly. This isn't 30-60 hours of work, it's more like 3-6. You'll be amazed when you see just how simple it really is.
 
He didn't give me too many specifics, but I can try to repost what he wrote on the order sheet.

"Cleaned & synced carbs, cleaned points and set timing, replaced tires & tubes, changed oil & filter, replaced plugs, checked brakes, adjusted & lubed chain, checked cables, checked & adjusted clutch, checked exhaust & air filter"

It looks like an overall thorough job, at least on paper. He jetted it because I have pods, not the stock airbox.
 
That was perhaps a little harsh.....but on an older bike you are worth learnign to be your own mechanic...or at least know enough to ask the kind folks in here for a hand after using the 'search' feature :-D

I can understand you may not want to spend the time to learn... I bought my bike this last year... I have been doing my own rebuild on it this entire winter...started out to fix the oil leaks...ended up needing an entire overhaul, cleaned carbs, de-rusted *as best I could* gas tank..new fuel lines...replaced exhaust...list goes on...

anyway...idea is I have learned more in the last few months than I knew I was capable of understanding...if you have the desire to learn, put in the time... you may not get it right the first time but big deal... you try.. make mistakes learn and move on.

I'll be extremely satisfied with myself knowing when my bike comes back to life *hopefully this month* it will be the result of the hard work and effort my friend and I have put into it.

Good luck to you
 
I'm not sure which hose was left unconnected, but this could be most of the problem. Start the bike and put your finger over the exposed nipple. If it draws vacuum this is your prob. Then you have to find where it connects on the other side and hook it up. Do you have a vacuum operated fuel petcock? Are they the nipples on the manifolds for carb sync.? Or might be just vents.

Also, did you have this prob before you brought it in? Were the pods on before or did they install? If they installed them, even if they did rejet the carbs I highly doubt they got it right without test-ride. this would cause your symptoms also.
 
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