Overheating Carbs?

[G]

As some of you may know, I've been having some problems with my r6 track bike when it's hot.

It will get to the point that it will only run when on full throtlle and only idle when it is on full throttle... any less and it dies.


I noticed that some pipes weren't connected to my carbs.
It seems that these were coolent pipes. In the hope that these were actually for cooling rather than heating purposes, I took the bypass out and reattached them.

It now seems to cut out even sooner!

Presviously Keith and mark had noticed that one of the exhaust pipes seemed to be cold. I've replaced the sparkplug and coil on that one. However it still seems to be sparking when we have this issue anyway from what I remember.
I've also tried running it with that plug unplugged and with with the plug not plugged in. Ran much better than it does when it has the 'issue'.

I also cleaned out the carbs today; didn't seem that dirty and installed the rubber cover that goes between the carbs and the engins, which I've been told is a heat shield.

Any ideas what the problem is and how I should solve it?

[Barry_M2]

Ever had the carbs ballanced on it? The cold cylinder could be getting too much fuel, which would both cool the cylinder (and bore wash it) and foul the plug.

For you to have to give it full throttle to get it to run would suggest massive overfueling, ie: you need load of air just to get it to go.

[G]

Sorry, should have mentioned. I checked the balance today, it was fine.

When I checked the plug it looked fine. Same as the others as well.

Thanks for the idea anyway .

[Kickstart]

Hi

Never seen a normal bike with carb coolers, just heaters.

Only carb type issue like that would be getting some kind of vapour lock in them. The heat shield may well help with this.

Also check for any missing vent pipes, and possibly a sticking float.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[G]

The floats all looked fine.

With these water pipes attached there are no missing vents, etc.

The way the problem seems to be worse with the coolent (heatent? ) pipes attached seems to suggest it definitely is a Carb heating problem.

Wonder if I could set up a seperate cooling system for the carbs .

[Barry_M2]

[G]

Unfortunately the R6 is very restricted as far as space goes.

It happens more when coming off track.

If it's left to cool for a quite a while it seems to be cool.


However it does happen in other situatuions.

I had run the bike a couple of times today and it had cooled to 41 degrees. Warmed it again to 63 degrees and it died as I tried to pull away.

Previously I think it's had to get hotter before that's happened.

[Barry_M2]

Yeah, I've not really looked at an R6 up close, but space will be a big problem.

As well as getting cool air in there, you will also want to get the hot air out, stop the fuel evaporating (which is what it sounds like). You might be able to raise the float height a mm or 2 to try and stop it running out so quick, but really I think you need to get some sort of ducting to direct some cool air in there.

[G]

That's really not a possibility unfortunately. The r6 is very, very cramped inside (as well as out); there is no where I could get decent ducting through really.

Plenty of other people race with r6s of the same vintage, so I'm presume it is something wrong with mine.

[HurtMePlease]

Sorry my mechanical expertise is limited but how about hunting down some carbs off ebay and exchanging them with your old ones?
____________________
Hear Thy Call..............................
Rs125 (97) <-Sold|Riding->ZXR400L2(92) Yamaha R6(01)

[G]

I would prefer to sort the problem.

I have a (unfortuantely) broken set of carbs. However the jetting is set up right for my current setup, so would be a load of hassle to transfer I reckon.

[Robby]

I'm thinking air leak. Maybe a split along the seam of a carb rubber.

As I understand it carbs get colder the more that passes through them, what with the pressure difference an' ting.

Is this the cylinder with a bit missing from one of the intake trumpets? Could have some valve or seat damage from that.

[G]

[Robby]

Yes by carb rubber I mean the bit between the carb and the block. But if they are ok as you say I'd be inclined to trust them.

Is the mix set up right on the carb? I assume it was set up before you got it. Are all of the small jets (or jet, never had an R6 carb apart) perfectly clean.

Maybe a vacuum pipe not properly blocked off.


Becuase its running ok at high revs I'm assuming its ignition is working fine and its carb is behaving when full open - so the main jet is doing its thing. The problem could be mixture related because an air leak will show itself more at low revs, where air flow is small. At high revs a little extra air won't make a huge difference.

[G]

It seems to work fine until it overheats.

The vacuum pipes seem to be good.
All the jets looked fine and secure.
I blew all the jets out with an airline anyway.

I don't know if the mix is right, but it does seem to run good until it does overheat, suggesting it's not a problem that's there normally.

[sickpup]

Cavitation carb cleaning and then set up on an air/fuel 5 gas meter will give you a good starting point. Strangely I do both at the shop.

A lot of bikes used on the track use a carb heat shield as carbs do overheat.

[bish777]

It sounds that you may have some form of ignition problem, as you say one cylinder is running intermittently. Check the coil to that cylinder is within its impedance specs? Also replace the plug cap whilst your at it.

I had virtually the same problem with my GSXR1100 and the only way round it was to replace the coil.

Also double check the routing to the CDI unit, unplug connection and clean, and give a little squirt of oil.

You need to get hold of a manual to check where all these hoses on the carbs go to? But seeing as they seem ok i doubt they are the problem.
____________________
GSXR1100J

[G]

Was thinking about getting a full exhaust system at some point.. so could consider getting carbs played with then (or even get some new carbs to be setup).

Don't have, well, any money at the mo really, though.

Bish:

I've replaced the plug and coil on that cylinder.

I also tried running it without the plug connected and without it in... it ran fine on three cylinders.
Gonna try two cylinders in a minute.

I have a manual, all the cables are connected correctly.

[G]

It also runs a tad better on just two cylinders than when it's going wrong 'normally'.

I've managed to get it to go wrong on command now (well, almost).

Get the bike pretty hot (around 100 degrees), then ride it up and down the road slowly.

Unfortuantely the act of taking half the airbox off seems to cool it quite quickly.

It does very much look like there's vapour coming out of the carbs.


I haven't tried running it with the heat shield on and the water heating off, so never know, that might sort it .



There also seems to be a bit of vapour coming out of the crankcase breather. Not sure how much there should be as 'standard'. It's enough to be noticeable, but doesn't seem to be leaving an significant oily residue.

I haven't noticed any water in the oil when I've changed it (which I do after every race).

[sickpup]

You misunderstand me.

With the 5 gas analyzer I can individually check the pilot setting on each cylinder unlike a dyno which tends to take an average across all cylinders unless you have the right analyzer attached to it.

I can also analyze the individual intake pressure wave's to diagnose various other possible defects as well as the individual exhaust pressure waves, Yqamaha's have a nut welded to the exhaust downpipes just for this.. This can be done hot or cold and even with the bike being ridden on the road.

[G]

[sickpup]

About an hour to 2 hours labour. Depends on the bike and how much we have to strip off.

We do it on every service.