Help! Bike Won't Start! Compression?

[jambon]

Hello,
I purchased my 1978 gs750 from her original owner two years ago and she has always run like a top! In september I got a full tuneup from a local motorcycle shop prior to a trip from Portland OR down the 101 in California. The bike sat most of December and January and now it will not start (very unlike this bike).

When I try and kickstart the bike I get little resistance and a sort of swooshing airy sound / feel. No turn over. I replaced all the spark plugs and tried to push start the bike and still nothing. The bike has fresh gas and the battery has a good charge.

The fact that the bike won't turn over with the kickstart leads me to believe I have a compression issue. I am going to borrow a compression tester tomorrow and check for sure.

Is it possible for the compression to go bad on a bike that recently received a tuneup and was running fine prior to a short rest?

Thank you for any and all help!

 

[allojohn]

Checked the kill switch?
Are the carbs getting gas?
Do you have a spark?
Compression is not likely to be your problem.

And welcome to the nut house - we'll get you sorted.

 

[850 Combat]

Sounds like a bad slippy clutch. You are saying that there is no crankshaft rotation when you kick it over, and no crankshaft rotation when you push start it, right? You are not making the pistons go up and down? Try doing it with the plugs out. It would be highly unusual to lose compression on four cylinders at once unless the cam chain has broken or something, which is also highly unusual.

How is the free play in the clutch cable? Has the clutch adjustment been played with at all?

When you say "still nothing" when you push it, precisely what does happen? It can't be "nothing".

Why are you not using the electric start?

If it has an electronic ignition, it won't start easily with a flat battery if at all.

 

[Big T]

Is it possible for the compression to go bad on a bike that recently received a tuneup and was running fine prior to a short rest?

Thank you for any and all help!

No,it's not - compression is a function of the sealing of the piston rings and the valve timing


Have you checked for spark?

Like 850, I don't understand your desciption. To most people, turning over is what the pistons and valves do when they move

 

[jambon]

Thanks you for all your suggestions and my apologize for the unclear descriptions. It has been raining hard since my last post so I have not checked for spark or compression yet (though it sounds like compression is not my problem).

When I use the electric start it makes a kind of werring sound like it wants to start but can't.
When i tried to push start it the bike emitted a sputtering grumble rumble briefly.

With the kick start, there is no sputtering sound of the engine trying to start. Just a hollow "wooshing" sound. Perhaps when I say it's not turning over I mean it is not firing?

I will check for spark tomorrow. If there is no spark, what does that indicate?

The clutch play feels normal and has not been tampered with.

Not sure if this matters but this is the bikes first winter outside as my girlfriend recently moved and I no longer have access to a garage. The bike is covered but moisture still creeps under the tarp.

Sorry to be such a rube.
Thanks!

 

[850 Combat]

Is the battery all charged up? if it isn't, a real small charger should be used. No more than an amp is good.

Where are you?

 

[platinum2]

might be flooded from trying to start it so much, pilot jets might be clogged from setting 2 months,motors are always a pain to get going after setting long periods, try good fuel, turn it over with out plugs let it dry out, clean plugs or replace them new plug are always good, check electrical connections, and give it a whirl

not kidding, 2 months and fuel turned crappy! fuel just isnt the same as when i was a kid, man it was strong potent stuff, now just gets weaker and weaker
dirt bikes atv's all fuel was crap after winter setting!

 

[Big T]

I will check for spark tomorrow. If there is no spark, what does that indicate? The clutch play feels normal and has not been tampered with. Sorry to be such a rube.Thanks!

No spark= new points and condensors, if that's what it has. Pull the plugs and see after this effing storm passes

Hey, everyone's a rube to start with, unless your Dad was Mr master mechanic


And yes, turning over is the mechanical act of rotating the engine. Starting should ensue afterwards. So, it can turn over, but not start

 

[jambon]

Is the battery all charged up? if it isn't, a real small charger should be used. No more than an amp is good.

Where are you?

Battery is all charged up and even if it wasn't at full capacity, the kicker or the push start should have been enough. I am in portland, OR

 

[jambon]

Storm is still raging so I still have yet to check for spark. During the aforementioned tuneup the points where gone through so I feel like they should not be the issue.

the kick start has never just wooshed even when the battery was not holding a charge prior to the necessary wiring harness bypass.

Could this be traced back to a mistake made during the tune up, only to rear it's ugly head several months down the road?

No spark= new points and condensors, if that's what it has. Pull the plugs and see after this effing storm passes

Hey, everyone's a rube to start with, unless your Dad was Mr master mechanic


And yes, turning over is the mechanical act of rotating the engine. Starting should ensue afterwards. So, it can turn over, but not start

 

[Pendulum]

Storm is still raging so I still have yet to check for spark. During the aforementioned tuneup the points where gone through so I feel like they should not be the issue.

the kick start has never just wooshed even when the battery was not holding a charge prior to the necessary wiring harness bypass.

Could this be traced back to a mistake made during the tune up, only to rear it's ugly head several months down the road?

It could be. If the points weren't adjusted properly, for example.

 

[Big T]

During the aforementioned tuneup the points where gone through so I feel like they should not be the issue.

Points can't be "gone thru". They can be adjusted, or replaced and adjusted.

The condensors fail with age, so if the points and condensor haven't been replaced, do that

Who did you work? Roadhawk? Viscious?

 

[jambon]

Points can't be "gone thru". They can be adjusted, or replaced and adjusted.

The condensors fail with age, so if the points and condensor haven't been replaced, do that

Who did you work? Roadhawk? Viscious?

The work was done by Oliver over at Motofactory. Viscious is close to my house, do you have any experience with them?

Ps I caught a brief respite from the rain and checked on the bike. Motor is turning over but i have no spark. And now it's snowing...

 

[Big T]

Nope, I do my own work and I replaced my points for the last time in 1983, upgrading to a Dyna S

OKay, no spark - do you have 12V power to the points?

 

[silverhelme]

No start

No start

Just to throw it out there I just ran across something worth checking. The PO of the 78 750 I just bought went through the same thing. He had no start so he replaced points condensers battery and coils but could not get it to spark. After I bought it I started going through the system with a DM and found no power after the ignition switch. I shot some contact cleaner into it and worked it back and forth a few times and it fired right up. PO said it had only sat 3 months without running and had been stored under a tarp but apparently enough condensation had worked its way into the switch to corrode it. If you don't have one get a DM or a test light and trace your power and see where you have it and don't have it. That will give you the place to fix.

 

[Killer2600]

Just to throw it out there I just ran across something worth checking. The PO of the 78 750 I just bought went through the same thing. He had no start so he replaced points condensers battery and coils but could not get it to spark. After I bought it I started going through the system with a DM and found no power after the ignition switch. I shot some contact cleaner into it and worked it back and forth a few times and it fired right up. PO said it had only sat 3 months without running and had been stored under a tarp but apparently enough condensation had worked its way into the switch to corrode it. If you don't have one get a DM or a test light and trace your power and see where you have it and don't have it. That will give you the place to fix.

I second this advice but to effectively use a DMM or test light you need to know basic electrical. I suppose one can get help with testing using these tools over the internet but I think it's better if one gets assistance in-person if they know very little about electrical.

Also it's been addressed, but I HATE when people say an engine makes the usual sounds (cranks) but won't turn over - It goes against the definition of "turn"

 

[Guest]

If it seems like you don't have compression see if gas leaked into your crankcase from the petcock.
No spark? See if you have voltage at the points with the ignition on.

 

[1948man]

Is the kick-starter drastically easier to kick than it was before? Did you say you did take the trip after the tune-up and it ran okay then?