Stalling when hot

[Hooptie]

Fuel line is new and clear. Prime makes no difference.

Carbs are great. Valves are great, compression is great.

I know the petcock has to see vacuum to start pulling fuel in the "on" position, so maybe once its running it is able to pull harder than while cranking?

[chuck hahn]

Shouldnt matter. Once its been running you have to assume the carbs are getting fuel to them on PRIme. Its afree flow when in prime, so one would have to think fuel would be free flowing regardless of the petcock being good or bad and whether the bike is cold or hot.

This makes me think theres a flow problem within the carbs themselves. Be it wrong float hts, partially cogged jets, whatever. but the problem is in nthe carbs if you ask me.

If the petcock is flowing a good stream in the prime position, the next place downstream is the float seats and float needles. So, take a rag and loosen all the float drains to see how fast they are draining. Gonna be messy and lots of gas but you need to verify that the bowls are getting good flow and are filling at a rate that is sufficient.

[Gorminrider]

Don't forget air-venting too...the tank cap has a vent -You could crack the gas cap and ride that time period to check...and the carbs have a vent too...

[Hooptie]

Don't forget air-venting too...the tank cap has a vent -You could crack the gas cap and ride that time period to check...and the carbs have a vent too...

Its funny you mention this. There was definitely pressure built up inside the tank. But even after I opened the filler, it still didn't want to start.

[Triam]

When I bought my bike it had a similar problem and it turned out that their wasn't oil getting to the head. This would make the aluminum expand around the steel camshaft which would seize the engine. It would make it seem like a loss of power once warm. If the bike idles under 1,000 RPM then you may be affecting the oil circulation resulting in similar results. Does it lose power if you're riding it around or just if you let it sit idle?

[Hooptie]

It actually runs great. It will crank until the starter has eaten the battery too.

It just dislikes starting right up after being run.

[850 Combat]

If it will crank without firing, but will bump start, it sounds like you are not getting all the electricity to the coils that you need when the starter is running. That could be bad connections in the circuit providing power to the coils, or faulty components in the ignition system providing power to the coils. You might consider checking the voltage at the coils. There is a common modification where a relay can be installed to provide more direct power to the coils. none of mine have needed that, but its common,

Those are cool bikes, I think. Extremely quick in their day.

[Hooptie]

I thought coils too, since they are nearly as old as me. But why would it start every time when it shoot starting fluid at it?

[tom203]

A weak spark can ignite starter fluid easier than gas. When it does this no start, check spark strength- compare it to your cold start spark. Just carry a spare plug, so you don't need to pull a plug

[mrbill5491]

Easy on the starting fluid, you'll wash the oil away from the cylinders, then you'll have bigger problems.

[Gorminrider]

I thought coils too, since they are nearly as old as me. But why would it start every time when it shoot starting fluid at it?

possibly the bike is too lean when warm to start without the extra fumes you supply...so, also check your carb intake boots for a seal (am I wrong to call these manifolds?) and even check the valve clearances... I mean, if it gets beyond the simplest fixes, you must go deeper but get all the simplest idea as noted above off the list first.

You said previous there is "pressure" in your tank . There should not be "pressure" (or vacuum either) when you crack the tank's cap....

[Hooptie]

It was hissing. New cap needed? Where do they vent to?

[Gorminrider]

that'd be beyond my powers of description, right now but my tank cap comes apart..(the plastic cover on the bottom of it has screws...) The idea was to not have all the gas come out of the tank..(at least not all at once) if the bike was dropped...but to allow enough air in to replace used gas and to allow enough air out if the sun warmed your tank, but not so much as to surround your bike with an explosive mixture... so moving the bike to sudden heat from the shade you might hear it.
Thankfully, there is an obvious way to check for problems with venting.

Leave the cap open to see if it helps.

And then too your carbs have vents for the same purpose...ortoo little gas will fill the bowl,or refill it too slow... allowing bike to be started but eventually losing the race to keep up with demand.
These vents are simpler...we know that a bike left too long will dry up the bowls
Checking for spiders building nests in these is about allit takes.

If your tank is a POSITIVE pressure, it might be flooding your carbs. you likely have already but the usual test is to Open throttle wide and try re-starting to test for this.
Also, as another idea.This is a long shot but might indicate sticking floats or needle.
Try the bike with a full tank of gas and a not-full tank of gas.

The pressure on your carb float needles= the column height and the diameter of this "column" =the fuel inlet of the carbs. No more no less, whatever the bends and turns of your fuel line, (within reason!)

anyways these are just ideas to add to others'

[JTGS850GL]

The pressure on your carb float needles= the column height and the diameter of this "column" =the fuel inlet of the carbs. No more no less, whatever the bends and turns of your fuel line, (within reason!)

Actually the diameter of the fluid column has nothing to do with it.
p = h ρ g

where
p = pressure (N/m2, Pa)
h = height of fluid column, or depth in the fluid at which the pressure is measured (m)
ρ = density of liquid (kg/m3)
g = the gravitational constant (9.81 m/s2)


The higher the fluid column the higher the pressure. Wouldn't matter if it was a 1/4" fuel line or a 3 foot pipe. The final unit of measurement is N/M2 or PSI.

A scuba diver measures depth indirectly by measuring pressure. 10' in a pool or 10' in Lake Superior is still 10' or ~4.3psi. This assumes that the density of the water is the same in the pool and in the lake. In GSR terms, it wouldn't matter if you had a 3 gallon L tank or a 5 gallon G tank. As long as the height of the fuel was the same in both the pressure on the float valve would be the same.

[Gorminrider]

The higher the fluid column the higher the pressure. Wouldn't matter if it was a 1/4" fuel line or a 3 foot pipe. The final unit of measurement is N/M2 or PSI.

That's what I said. However
The total pressure in any measure of force you like on the needle is the column height per the area of the needle if you like....which is the area of the carb's inlet that the needle blocks. that is AREA x PSI ....The needle is connected to floats with their counterforce....as in:a flooded float may create issues versus the column height.

Added: If I made the inlet much bigger PSI is the same but will the existing floats hold it back? I say not. so Area is important. And therefore, Diameter.
In carbs it's simplest case, the mass of the fluid, but an air pressure in the tank will skew this as will the walls of a tube in extreme cases... a very small tube and/or a very long one has complications hopefully not important in a Suzuki gas tank and fuel line.