Anyone consider mounting fan on their carbs?

[JTGS850GL]

Hmm. Thing is the plugs look fine. Not wet or fouled. I can get it to keep running a bit if I hold the throttle open. So it's probably not the coils. What else could it be.

Have you verified spark when it happens? Strong and blue? Have you tried to turn the petcock to prime?

Not saying that you couldn't have boiled the gas out of the carbs but it should be as simple as turning it to prime unless the heat is so high that the fuel vaporizes as soon as it gets into the carbs. That would be very unlikely since the inrush of cooler fuel should be able to get things back down below the boiling point.

I'm still a bit concerned about what other things may be getting MUCH hotter. Just seem to me that the engine temp would have to be WAY above normal operating temps if things are getting hot enough to boil and keep on boiling fuel from the carbs.

Anyone else have this happen?

 

[Buffalo Bill]

Just reminds me of my own 550 problems.
I think I traced a similar problem down to the electrical system, then on down to bad crimp connections, poor connection to the battery ground.
Once it stalled on the highway and that turned out to be the main glass fuse sliding sideways out of the holder.

 

[Gorminrider]

from the tank which will be MUCH cooler

but not so much on a hot day with sun beating down on a (black?) gas tank while the bottom is being warmed by the engine? I'm not saying Dimitri doesn't have a mechanical issue but can anyone say there is no viable scenario on these bikes that involves a hot day in desert traffic? True, I haven't heard it mentioned as a common issue but one wonders....
it seems to me... having a carb enrich itself (flood) bubble gas out of carb passages on a hot day has happened to me on old cars. And I'd have to floor the throttle to get her started.
Any smoke when your bike does start, Dimitri?

 

[DimitriT]

but not so much on a hot day with sun beating down on a (black?) gas tank while the bottom is being warmed by the engine? I'm not saying Dimitri doesn't have a mechanical issue but can anyone say there is no viable scenario on these bikes that involves a hot day in desert traffic? True, I haven't heard it mentioned as a common issue but one wonders....
it seems to me... having a carb enrich itself (flood) bubble gas out of carb passages on a hot day has happened to me on old cars. And I'd have to floor the throttle to get her started.
Any smoke when your bike does start, Dimitri?

No smoke. I let it sit for two hours and it started right up on the first crank.

 

[DimitriT]

Have you verified spark when it happens? Strong and blue? Have you tried to turn the petcock to prime?

Not saying that you couldn't have boiled the gas out of the carbs but it should be as simple as turning it to prime unless the heat is so high that the fuel vaporizes as soon as it gets into the carbs. That would be very unlikely since the inrush of cooler fuel should be able to get things back down below the boiling point.

I'm still a bit concerned about what other things may be getting MUCH hotter. Just seem to me that the engine temp would have to be WAY above normal operating temps if things are getting hot enough to boil and keep on boiling fuel from the carbs.

Anyone else have this happen?

I haven't verified spark but I did try to turn the petcock to prime. If this happens again I'll have a spare spark plug handy.

 

[Guest]

Any fuel that's "boiled away" will vaporize and leave the float bowl via the vent lines. As the fuel level drops is will be replaced by fuel from the tank which will be MUCH cooler then the fuel in the bowls. Even if the fuel is completely boiled off in the carbs, it will still be fed by they tank if put in the "prime" position. I can't see any way that the engine would be stalled and not be able to be restarted for a long period of time unless something else (probably electrical) is inhibiting it.

The vapour leaving the surface will go out that way; the fuel in the idle passageway will probably not head 'down and out'. It's going to take a lot of vapour leaving to make much draw of new fuel.

 

[DimitriT]

Any chance this could be a valve clearance thing? I checked the clearances and they were within spec but a few just barely. Do we know if the exhaust valves get tighter or looser as it gets hot.

 

[tkent02]

I think they get tighter, but I haven't ever checked them cold and then hot to find out. Are yours on the small or the large end of just barley?

 

[DimitriT]

I think they get tighter, but I haven't ever checked them cold and then hot to find out. Are yours on the small or the large end of just barley?

There were a few which measured .03 or .04 mm.

 

[JTGS850GL]

The valves clearances do close up as they get hotter. You might be onto something.

 

[tkent02]

,03mm should be fine, unless that was a while ago and it's gotten tighter since.

 

[Sandy]

I can't imagine taking 15 minutes to synchronize carburetors. Hell, five minutes is a stretch.

Agreed for sure. I hook up the gauges and run it until slightly warm, set a high idle and get everything ready before I pull the tank to check what needs adjusting. Then pull the tank, carb tops if VMs, restart and sync and most times I don't even have to hook up an auxiliary tank. Only if they're way off I may need a fan and extra fuel supply. If the engine is too hot you wouldn't be able to set your mixture correctly anyway so might as well shut it down for a while to cool off.

 

[mikerophone]

Ive occasionally toyed with the idea of mounting a small fan to blow on my oil cooler while in traffic. So far its never made it past an idle thought....

This thread has rapidly moved past the point where this is as relevant, but years ago I wired 2) 12V computer case fans to the tranny cooler on my 4Runner. When the A/T trans light kicked on trailering a heavy load up in the mountains during summer, I would switch them on and cool the trans down as soon as possible. I too have considered doing the same with the oil cooler on my 83 750ES.

Temp gauge doesn't seem accurate and now that it's getting to 100F in SLC already, note to self...I need to remedy that.

I'm no expert in tuning carbs either, I have the long screwdriver tool and even a fancy remote gas tank and a big fan, but not the carbtune. I just use 4 bottles with ATF in them connected to 1/8" air lines and man is it sensitive! I also can't do it in 15 minutes. One day I will have the carbtune and be able to bang them out like the pros do.

 

[Guest]

The valves clearances do close up as they get hotter. You might be onto something.

Have you measured this? Usually the aluminum between the camshaft and the valve seat expands more than the steel parts, except for when the exhaust valve gets really hot, and that's over long before the valve cover comes off.

The old rule was that if the motor was quiet and there was good compression when cold, the valves were probably close enough; if you had low compression that came up when the motor warmed then the valve were too tight. In this case, idling shouldn't get the exhaust valve very hot, compared to high speed where it has so little seat time.

 

[tom203]

I think what could happen is that fuel boils in carbs and we get a bubble somewhere in the network of tubes and pipes which keeps it from spitting fuel into the airflow. At least that's my 25 cent theory.

My fuel injected jeep behaved like this when electric radiator fan failed to turn on ( faulty computer or sensor) - when shut down, residual heat boiled fuel in lines and it would not start till it cooled down implying that fuel pump could not repressure the lines due to residual gas vapor in system

 

[JTGS850GL]

The old rule was that if the motor was quiet and there was good compression when cold, the valves were probably close enough.

Great way to have burnt valves. Ole GS's don't take kindly to tight valves.

 

[Guest]

Great way to have burnt valves. Ole GS's don't take kindly to tight valves.

It was an old rule and not one of mine; but it implied that the clearances increased with temperature, which was the question. If they decreased with temperature rise, then they start out pretty small.

 

[Rob S.]

Shut the bike off. I do this with my car too

My '68 Camaro - no power steering, no power brakes and the cassette player worked without the key (also no A/C). In downhill traffic jams, it ran better with the engine off!