Fuel starvation?

[Moyes]

Hi guys

im having some trouble with my bike and I'm after some help.

Bike: 1982 GS550L (cv carbs)

Issue: bike idles fine and will Rev through the full throttle range to red line, but will not sustain this, it will die after about a second at full throttle. If I run it at half throttle it will run fine for about 5 seconds then want to die. If I let it idle for a minute after either of these condition I can get the bike to repeat the issue.

is this fuel starvation?

what I've done:
Checked for any vacuum leaks - none, issue persist
Cleaned the carbs - issue persist
Removed any additional fuel filters - issue persist
Check flow from the tank(peacock set to prime) - appears to be more than enough
check flow into the float bowl - appears to be enough
I believe its jetted right because it will idle fine and will rev though to full throttle, just not for long.
Spark plugs seem to be fine too.

any help would be amazing

 

[tom203]

Are you doing this testing in neutral or on road under load? How's your air filter? Stock setup?

"Check flow from the tank(peacock set to prime) - appears to be more than enough". This plus this.....

" If I let it idle for a minute after either of these condition I can get the bike to repeat the issue."

Maybe fuel bowls are not refilling properly, maybe clogged screens or deceiving petcock though it should run longer than the seconds that you are describing.

 

[DimitriT]

This sounds like a idle circuit mixture problem. It could be due to wrong setting of the idle fine tune adjustment screws or fuel level. It could also be that the carbs are not holding idle well due to being out of sync.

Do you notice the problem getting better/worse as the bike warms up? How does it run on choke?

 

[Moyes]

I've mostly been testing it in neutral on the main stand, but it'll do the same thing on the road, I don't get very far.
at the moment there's no air filter as I've been taking the carbs on an off so much, but it'll do it with and without them.

i pulled out the needle valve and seat and cleaned them, I remove the little filters from them as well to reduce the restriction, issue persist.

It feels like fuel starvation to the bowls, not filling fast enough, but I don't know how to triage this issue or resolve it.

fuel flows out of the petcock and down the fuel lines fine, no vapour lock or restriction, and I've cleaned and flushed all the ports for the fuel going into the carbs.

 

[Moyes]

I don't think it's an idle mixture problem 'cause it'll sit and idle just fine with no issues. Requires a bit of choke to get it started then once warm no more choke needed.

it will reproduce the issue if it's hot or cold, choke or no choke

 

[DimitriT]

You might want to try attaching something like this and watching the fuel level while the bike is running:



http://www.ebay.com/itm/Mikuni-Carb...ash=item3f4ee4f0d7:g:5WsAAOxyf1dTKD80&vxp=mtr

 

[JTGS850GL]

You wouldn't happen to have an inline fuel filter?

Try using a suspended gas tank to feed the carbs. Same setup as when syncing carbs. See if the problem persists. If so, you can probably rule out the petcock. Checking float bowl level with the part that DimitriT showed would verify a fuel starvation issue as well.

 

[tom203]

Make sure your carb bowl vent lines are not restricted somehow - checking with that fuel bowl drain gizmo might show burping.

 

[Moyes]

I did have an inline fuel filter, but I removed it, the tank has been off the bike and higher for most of the testing. If I just open the tap on the petcock fuel pours out at a good rate.

the carb bowl vents are clear

but I like DimitriT's idea. I'm going to need to get me some of those.
we'll see how it goes.

thanks for the help so far guys

 

[Spyderman]

you might have a leak in the vacuum line to the petcock try the prime position on the petcock and see if that makes a difference

 

[Moyes]

Might want to turn down the speakers...

Might want to turn down the speakers...

http://youtu.be/XdNqjIweR5Q

So it doesn't appear to be an issue with fuel delivery to the float bowls
I took a quick video, hopefully you can understand what's happening (might what to turn down the speakers, it's a little loud)

 

[JTGS850GL]

That's normal when you don't have any restrictions on the inlet side of the carbs. Install the airbox and it will run correctly.

 

[Moyes]

That's normal when you don't have any restrictions on the inlet side of the carbs. Install the airbox and it will run correctly.

Really? Omg, I've been trying to work this out without the airbox 'cause it's a pain to have to take off and put on all the time. If that's all it is I'm going to be so be so
ill try it out tomorrow.

 

[Steve]

For a quick check, fold a shop rag in half, hold it over the intakes of the carbs.
If you have a helper, it's easier, but try your throttle tests with the rag in place.

If it works well that way, put the airbox on and go for a ride.

.

 

[Moyes]

Alright cool. The rag trick worked, except now my bike is running very rich.
its a bit of a pain to get the stock airbox on so I want to pose another question.
knowing full well I'm going to be hit with abuse, if I want to run pods, other than rejecting the carbs, what would be the limitations.
because this issue occurs with the pods installed, are they just not restrictive enough or is it just a jetting issue.
there shouldn't be any reason why running pods is not possible, right?
ive got pods on my kz250 and have jetted that so it runs really well.

(let's please put aside the negativity about changing the intake, and assume that I have no choice but to run pods, I would like some assistance in making it work)

 

[JJ]

Alright cool. The rag trick worked, except now my bike is running very rich.
its a bit of a pain to get the stock airbox on so I want to pose another question.
knowing full well I'm going to be hit with abuse, if I want to run pods, other than rejecting the carbs, what would be the limitations.
because this issue occurs with the pods installed, are they just not restrictive enough or is it just a jetting issue.
there shouldn't be any reason why running pods is not possible, right?
ive got pods on my kz250 and have jetted that so it runs really well.

(let's please put aside the negativity about changing the intake, and assume that I have no choice but to run pods, I would like some assistance in making it work)

Get quality pods, if you must run them. Either K&N, or APE (about half the price K&N, and just as good. Don't go with EMGO or any of the cheap brands.

I can't give you jetting advice, as I have never used pods. Others here will have to help you with that. Good luck!

 

[Moyes]

Thanks for the positivity.

 

[JTGS850GL]

You can go pods but like it has been said, pick up quality pods and then look for the Dynojet kit for your bike. If you install the kit then jetting will be much easier. There is a kit for a 1982 550 M Katana (PN: 3314). I'm not positive it will work for your bike but it should. If I'm wrong, then others will chime.

 

[Guest]

Really? Omg, I've been trying to work this out without the airbox 'cause it's a pain to have to take off and put on all the time. If that's all it is I'm going to be so be so
ill try it out tomorrow.

Why are you pulling off the air box so much? Order of operation is carbs off first, then air box. Reverse install is air box first then the carbs. Unless your 550 is the one with clearance issues with the air box and carbs. Also, wanna make sure the rubber boots are soft and flexible, that makes a world of difference in removal and installs.

 

[rudeman]

You need to jet up quite a bit if you're running individuals.