Gs250t Vacuum Leak Bike wont catch

[jake]

Thank you for the link, I only had haynes manual, this will be very useful.

[Nessism]

Put a towel under the carbs and remove the float bowl drain screws. Several oz. of gas should drain out. If the float bowls are empty you have a fuel supply issue. I wouldn't worry about timing, but you should check the valves. A compression test would be useful too. If the valves are tight the compression will be low.

[Redman]

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ticking over above revbs
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does that mean the engine is turning over on the starter a lot faster (higher revs) than usuall......?

and you say has good spark, and doesnt fire-pop-sputter at all even on starter fluid....?

Have you check compresion? Even just hold thumb over (but not completly) spark plug hole while cranking....?

[jake]

Mechanic said it wasn't compression, and the bike only has 40,000 miles on it. I'm not at the bike right now, but if I recall correctly, I could feel air being pushed out the spark plug hole with my hand above... on both cyliners.

[jake]

the bike once warmed up got to 1300 revs, and had to have the choke on whenever I started it or else it would die... before it stopped completely, the choke was super sensitive e.g. 8k revs, or died

[jake]

power wasnt a big issue either, could get into 6th gear at 100kph easily enough at 8k revs

[jake]

Nessism, I checked the fuel in both carbs 3 times, primed each time and tried to start, and checked the fuel quality on each one, there was unfortunately no water or dirt in any of the fuel I drained from both carbs.

[pdqford]

The fact that this starting issue developed over a period of months, and with 40,000 miles on the clock, I would definitely check the valve clearances. Spec @ .003” - .005” doesn’t leave much room for error. If those valve adjustments have worn down to where the valves are not completely sealing it could act like a vacuum leak as it could draw some of the exhaust side in when on the intake stroke and blow some out the carb on the compression stroke, both keeping the fuel charge from getting in the combustion chamber. I would confirm/set valve lash.

[Nessism]

Compression, spark, fuel. Those are the ingredients to get your bike to run. We have offered suggestions on each of them and you have dismissed them all. I'm out of suggestion unless you are wrong about something. Most of the time when these things occur the problem turns out to be something basic and/or lack of maintenance. Only thing I can suggest at this point is to go back to the beginning and check everything again.

[jake]

It will definitely be the next thing I will check, I'll keep you updated, thank you for all your contributions so far, I will get back to you all hopefully sooner, rather than later.

Thank you.

[jake]

well, everything seemingly but fuel... I'd only had the bike since May, and had only been riding it since mid June... I hadn't even clocked 2000 miles on it and everything beforehand sounded/seemed in good nick... There were no funny noises, or misfires at any rev range, and power seemed adequate given its age... I will check valve clearances, spark plug and fuel quality again regardless.

[Steve]

I have not seen any confirmation of valve clearance verification.

.

[jake]

Hi Steve,

I have not checked the valve clearances as I'm still a relatively new home mechanic, I would hope that when I left it into the mechanics when it broke down that they checked the valve clearances, I will double check with them. I am currently away from the bike, and I have a large work undertaking for college etc... please allow me a couple days to check the valve clearances.

I didn't think to check valve clearances, as there was no loss of power, or misfiring... and the bike rapidly deteriorated in the space of a couple days. Further, there is no fuel entering the piston, so I did not think the problem was ignition or valve related. However as I said, I am new to the game, and I know that the members here such as yourself have far more experience than I do.

Would valve clearances stop fuel entirely from entering the piston or stop starter fluid from catching at all?

Thanks.

[Gorminrider]

Firstly,

I left it into a shop when it broke down, but no-one could identify the problem.

..is highly suspect. These are simple engines ...Perhaps you have "baggage" with these folk or they are not able to help. Find a new mechanic.

....when I have some free time I can clean the carbs etc.

If you are going to work on your own bike, you must take the time to do it. You will need some tools beyond the emergency kit the maker included with the bike. The money you "save" fixing it yourself is best invested in tools.

The usefulness of this forum is BEYOND the basics you will find in almost any manual....fuel,compression,spark. You are advised to get a basic understanding of your engine.

Does anyone know why absolutely no fuel would be able to get into the engine?

the most obvious -fuel supply to the carburetors -the petcock- has been mentioned.

I am stumped as to why the carbs would shut closed completely when there is no vacuum

You should find your engine resists being turned by hand in neutral. This is due to "compression" and "vacuum". If there is no engine vacuum or compression, you have a serious problem. Cracked head, failed or severely maladjusted valves, broken rings etc etc...simply fitting your thumb over the spark plug hole is a simple way of "discovering" vacuum and compression....but a compression gauge is much better.
Checking your valves will inform you of how your engine functions as a "pump". Valves that aren't closing and sealing won'tallow the pistons to csuck fuel in or pump the exhaust away.

again,

I am stumped as to why the carbs would shut closed completely when there is no vacuum

These bikes don't require throttle plate opened to start. When the throttle-plates are closed, the engine vacuum will be greatest ! that is, the main inlet is blocked and the engine must suck very hard through the idle circuit and the "enrichment " circuit. Given the rest of the bike is ok, A no-start condition suggests these passages and jets are blocked, broken,maladjusted.


Do not use starter fluid. Put a little gas on the plug or maybe squirt a little gas through the airbox(remove seat and foam filter- turn the bike over with kill switch off to suck some gas in) Your assumption of the manifold rubbers is probably wrong. Leaking manifolds make the bike run very lean in operation but should not affect starting unless there's some really bad leaks that you can plug temporarily-(grease, tape,gobs of rtv...) Starting is a very rich condition on these bikes.

[Steve]

Put a little gas on the plug or maybe squirt a little gas through the airbox(remove seat and foam filter- turn the bike over with kill switch off to suck some gas in) ...

Unless someone has modified their bike, that is not possible with a GS.

Turning the kill switch to the OFF position also disables the starter.

Now, ... if the bike has a kick starter, you can kick it a bit, but you don't even have to have the key ON, so it won't matter what position the kill switch is in.

.