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runs better with carb cover off?

  • Thread starter Thread starter Anonymous
  • Start date Start date
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Anonymous

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what would change when you put the top carb covers (slide bell crank covers_ back on and make the bike runs worse. then was running so much better with them off during testing and synching?
 
Nothing, as far as vacuum is concerned. The covers are just to keep the elements out.
The throttle valve arms, even at full open position, shouldn't be able to touch the cover.
I have to think you're mistaken about re-installing the covers causing a problem. Makes no sense. Must be something else you did between the end of the synch and vacuum tool removal/button up.
All 4 manifold vacuum port screws tight with crush washers on?
Vacuum line to petcock tight and in good condition?
Fuel line not kinked?
The two floatbowl vent lines clear and not kinked (if running stock air box). If running pods, the vent lines should be removed permanently and vents left open.
Gas tank pinching a plug lead, causing arching?
Were the filters on during the synch? Should be.
Plenty of gas?
 
bazango said:
Keith, why do you say to remove the vent lines?
Click to expand...
It's a requirement in jet kits such as Dynojet. They need to be removed if you run pod filters, especially K&N's. Just don't shoot the open ports with water when washing.
The freer flowing intake and exhaust creates a vortex in the vent lines, it gets even worse on windy days/crosswinds or on freeways. This will compromise the venting. Without adequate venting to the float bowls, the jets won't draw fuel as easily as they should. Fuel starvation will result, most noticable at steady speeds. Feels just like starting to run out of fuel or a hesitation.
A lot of people experience this and try to richen the jetting. Though it IS a lean condition and confused for that, it's really a fuel flow problem. No amount of richer jetting will help, so it can drive people nuts. If they try to re-jet with seperate jets, they don't know about the requirement in the jet kit info.
I try to pass the word around. I've tested for it and it's a fact. My '79 1000 with K&N's, V&H pipe and 1085 pistons, really starved with them on. On my initial re-jet ride, I figured their requirement was baloney, so I left them on. I went down the street and after about 1/2 a mile, the bike started starving so I thought it was going on reserve. It wasn't. I then pulled the vent lines off and the bike was fine. Since then I've told several friends/riders about this and they all notice a difference too.
It DOES matter how free flowing your pipe and filters are. Some people see more obvious results than others. CV carb equipped bikes seem to have a less noticable problem than VM equipped bikes, but I believe they're effected to at least some degree.
 
Wow. I hope that's my issue. I'd heard that elsewhere, and passed it off as "baloney," as you said. I am still skeptical. Especially considering that pulling my bowl plugs results in a more than ample flow of gas. Where's the vortex at that exaggerated flow rate? Still, from what you say, I'm going to try it right away. My symptoms are just as you describe, with no other attributable causes. It is one big mystery, like a ghost or something. Sure hope this excorcises it! Thanks!
 
def a weird one keith/ it def ran rich once those cover were on. i ended up adjusting the fuel pilot screws a 1/2 turn in and it was smooth again at idle. my only idea was with the cover off, it was sucking some air thru the holes in the tops of the slides and when i put the covers on, it wasnt getting any air anymore and turned a tick rich?? weird stuff
 
KEITH KRAUSE said:
The freer flowing intake and exhaust creates a vortex in the vent lines, it gets even worse on windy days/crosswinds or on freeways. This will compromise the venting. Without adequate venting to the float bowls, the jets won't draw fuel as easily as they should. Fuel starvation will result, most noticable at steady speeds. Feels just like starting to run out of fuel or a hesitation.
Click to expand...

Could this also happen on a stock bike? I ask because I have an 81 650G and I have noticed that on my commute home every once in a while I get hit by a hard crosswind, usually from the front left side, and my bike literally dies at 75MPH, just bogs, then pings, then a moment later starts pulling again. I have pulled my plugs and there are signs of detonation. I'd really like to figure out the problem before I toast my motor.

And just to be sure, are the overflow and the vent tubes the same thing?
 
bazango said:
Wow. I hope that's my issue. I'd heard that elsewhere, and passed it off as "baloney," as you said. I am still skeptical. Especially considering that pulling my bowl plugs results in a more than ample flow of gas.
Click to expand...
I'm not sure what you mean by, "pulling my bowl plugs..."
If you mean the bowl drain bolts, removing them and checking how much fuel spills out has nothing to do with determining adequate bowl venting.
This isn't about fuel level. It's about a properly vented float bowl chamber will allow the jets to draw fuel the easiest.
 
Espumoso said:
KEITH KRAUSE said:
The freer flowing intake and exhaust creates a vortex in the vent lines, it gets even worse on windy days/crosswinds or on freeways. This will compromise the venting. Without adequate venting to the float bowls, the jets won't draw fuel as easily as they should. Fuel starvation will result, most noticable at steady speeds. Feels just like starting to run out of fuel or a hesitation.
Click to expand...

Could this also happen on a stock bike? I ask because I have an 81 650G and I have noticed that on my commute home every once in a while I get hit by a hard crosswind, usually from the front left side, and my bike literally dies at 75MPH, just bogs, then pings, then a moment later starts pulling again. I have pulled my plugs and there are signs of detonation. I'd really like to figure out the problem before I toast my motor.

And just to be sure, are the overflow and the vent tubes the same thing?
Click to expand...
Removing the float bowl vent lines should not be necessary on a stock bike. If you removed the stock air box lid, that can change things though. But you could have kinked or semi-plugged vent lines or vent passages to the float bowl chambers. If you're not the original owner, the float bowl vent lines could even be too small or been replaced with longer ones causing more resistance to adequate venting. Anything that can cause just a small loss of maximum venting can cause the problem. Check them for the above problems. You should be able to blow into them too see if they are clear. Though you can't really know if they're 100% clear, you can at least test them that they both have the same resistance when you blow into them. These checks are the best you can do without taking the bowls off or cleaning the passages.
The float bowl vent lines and float bowl overflow lines are not the same. The overflow lines are under the bowls. The vent lines come off the side of the carb and are routed under the seat. Different carbs have the vent port at different locations. Should be a brass nipple pointing upward, similar looking to the vacuum nipple for the petcock.
If your problem only happens or is most noticable with crosswinds, then I believe poor venting is your problem. If you have removed the air box lid or modified the air box with extra/larger holes, then you may have to remove the lines as you would for pods.
Fuel starvation can certainly cause pinging and the rest of your symptoms fit too.
 
Though you can't really know if they're 100% clear, you can at least test them that they both have the same resistance when you blow into them.
Click to expand...

Are these the vent lines we are talking about?
http://www.thegsresources.com/images/carbs/003_T1_2 VENT.jpg

If so, then I am sure they are clear as if it is cold an humid in the morning (all Summer in San Francisco!) then I have to gently blow into the those tubes to get it to start. If it is warm out, it starts right up. I did the complete carb rebuild a few months back and the bike runs good, but just feels like it is a little starved for fuel when I 'get on it' or need to accelerate at 75+ MPH.

Thanks for all the help Keith.
 
Ok, I'm just curious as to how you found out that blowing into that tube would make your bike start! :lol:
 
I found it on GSresources....naturally!

I bought the bike and ended up hosing the carbs because of rust in the tank. After cleaning them, but not completely rebuilding them, the bike would be really hard to start.

Searching the forums led to a post about blowing into the tubes (insert fellatio jokes here) and I tried it and it worked. Rebuilding the carbs and getting the floats set helped a lot, but if it is really foggy and cold, it still won't fire right up.

I still don't know exactly what the problem is now that the carbs are clean, the floats are set and the battery is new, but at least it runs pretty well.
 
All carbs are a little different, but those do look like the float bowl vent nipples. Just don't confuse a vent nipple for a vacuum nipple.
I don't know what blowing into them would do to the carbs to make starting easier.
The only thing I can think of might be a stretch but, it's possible your blowing into the bowl chamber may disturb/displace the fuel level just a little. The fuel level may "go up" the sides just a little and down in the middle. The float valve then could drop a little and admit more fuel, raising the fuel level (and richening the mixture too.) This could obviously help the bike start better on a colder/foggy day. Just .02" or so in higher fuel level could make a difference.
 
Also, Espumoso. Your first post said your problem is just during crosswinds. But it now sounds like you have a fuel flow problem or lean condition. Could be a lot of things.
 
Thanks Keith. The crosswind/bog-o-thon happened again today on the way home. Hit an area where there is a strong crosswind for about 1/2 mile and the bike just bogged along then started pulling again (couldn't hear if it was pinging b/c I wear earplugs for the commute).

Earl mentioned something similar when I talked about blowing into the vents; said it should move gas into the carb throat, richening it. I guess I'll have to adjust the floats *again* :) and raise them a little more. It is kinda strange though. When it won't start in the AM, it will almost always catch, the RPMs will go to about 3K for about 1 second, then it dies. A quick puff in either tube and it starts right up. What surprises me is that even 1 second at 3000 RPMs isn't enough to keep the gas flowing. The upside is that I'm getting really good at removing and installing the carbs. The bad thing is the airbox is getting harder and harder to get sealed on the carbs.
 
Is this line the only vent to the outside of the bowl? If so, wouldn't blowing into it force fuel out through the jets? That would sure prime the pump!

Anyhow, I wanted to enter the info into this thread that removing the fuel vent lines solved the strange mystery "running out of fuel" with a full tank that I have been trying to figure out for over a year. I checked everything possible, and the bike ran great, but still died if I tried to cruise over 60. I pulled the vent lines like Keith suggested, and the problem just disappeared! Amazing. And this happened even when my bike was bone stock. Airbox... the works. So I suspect this may be a problem for a lot of folks with mysterious "carburetor" issues.

Thanks!
 
I'll be checking this possiblity out soon on my '80 GS550L, as I've had this "mystery problem" for years, and have even missed out on several weekend trips over the years because I didn't trust the bike to run properly...

I'll let you know what I find...

Regards,
Steve 8)
 
Thank you to all that helped with this issue. Kudos Keith Krause!-Pete '80 1100L
 
bazango said:
Anyhow, I wanted to enter the info into this thread that removing the fuel vent lines solved the strange mystery "running out of fuel" with a full tank that I have been trying to figure out for over a year. I checked everything possible, and the bike ran great, but still died if I tried to cruise over 60. I pulled the vent lines like Keith suggested, and the problem just disappeared! Amazing. And this happened even when my bike was bone stock. Airbox... the works. So I suspect this may be a problem for a lot of folks with mysterious "carburetor" issues.

Thanks!
Click to expand...
Glad to help! :)
I once made a topic here about removing the float bowl vent lines if you're running pods or a modified airbox, and most members seemed to think I didn't know what I was talking about. I guess they figured it couldn't be that simple. :roll:
A lot of people have gone nuts trying to richen the jetting to eliminate it. Can't be done! That's why I mention it now and then.
 
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