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Anyone experience a CLUNK when starting?

  • Thread starter Thread starter Sokocanuck
  • Start date Start date
S

Sokocanuck

Guest
Hello everyone!
Hopefully everyone survived the Winter and is back on the road.
My bike (1980 gs750) has NEVER been a good starting machine since I've owned it. Likely to do with the pods that came with it (airbox is being shipped to me as I write this) but I have a concern about the starter.
Has anyone here experienced a audible CLUNK noise when their bike is trying to start? Clearly something is up that I need to fix, I'm just not great at diagnosing these things.
So far I've been told it could be my...

- starter motor
- start clutch/ Sprag
- flywheel

I'm going to take it apart this weekend, but does anyone have some tips for things I should look for?
I tried the search feature but I didn't really get the answers I was looking for.

Thanks!
 
It depends on what the noise sounds like, if you could post a video it would go a long way to getting the right help. It could be as simple as needing a new battery. A low battery will make a god awful sound when starting the bike sometimes.
 
First thing I would do is jump the starter motor with a car battery direct to the motor supply post and the crank case. Good idea to wrap the + lead clamp in something in case it strikes something. If the clunk is gone, provided the battery is good, open off all the power leads from the battery to the solenoid, on to the motor and back from the crank/frame to the battery negative. Inspect them carefully for corrosion at lugs and the crimps, clean everything back to shiny metal and try again.
It may be that the starter motor is not seeing full battery voltage and is getting kicked back by a compression stroke.
If that doesn't improve matters, take out the starter motor, clean the brushes and the comm.
Only after having exhausted the electrical possibilities start pointing fingers at mechanical bits.
 
Check the two bolts at the rear of the starter to be sure its bolted down tight. Its that or the starter clutch needs some attention. Youll need to get the proper rotor puller. Take the crank bolt that holds the rotor on out, use the puller to get the rotor off and youll see 3 bolts holding the starter clutch on. Remove those bolts and clean the holes and bolts with carb spray to get any oil off them. Use GREEN loctite and retorque the bolts.

Next, take the gear and check the bearings for servicability. When reinstalling, you get the gear inserted into the starter clutch by setting it against the dowels and use a push and twist motion to seat it. Hold it all together and slide it over the crank end. RED loctite the crank bolt in when you reinstall the rotor. New gasket and button it up.

Another thing that will make a clunk..and the starter clutch be fine..is a going bad starter motor or battery. What happens is it will snap the starter clutch out real quick for a second and then when the battery and starter are under a load they hesitate a second before cranking good Sort of like a bump...secondary pause..then she cranks normally kinda deal. So, you MAY also be looking at the age of the battery...they do loose thier ability to supply good cranking amperage as they age...even though they will take and hold a charge!!
 
Alright, thanks for the tips guys.
I'll be taking a look on Saturday so I'll post an update on what I find out.
I'm not sure if the battery is the issue, but it could be. It's new but seems underpowered.
I used the vehicle match and it said this one at the closest place I could grab one.
http://www.canadiantire.ca/en/pdp/motomaster-powersports-battery-0271007p.0271016.html#.VVSf5vlVhBc
It takes a while to turn over when it's cold, to the point that that selonoid by the battery heats up massively.
 
Well if thats going on...you need to adjust the valves first off. Bad adjustments are associated with that symptom. Valves dont close tightly and the cylinders are hard to get fired off.

Second question....did you do the carbs?? If so how..be specific in details as to what you did. When was the last time the bike has ran..has it been sitting a while as of late???

Has a gauge sync been done on the carbs???


What I am trying to impress here is that there are several things that must be right as they all work in concert to assure good performance.
 
Air leaks in the intake maniifold orings are also a major problem with GS bikes. Basically give us a run down on what youve done..some background history of the bike and what you know about its maintenance history. This will greatly help with some better diagnosis.

The more detailed info we have the better.
 
I haven't adjusted the valves but I haven't heard the symptomatic "tapping" noise while the engine is running, but maybe that could be an issue too.
The issue with the carbs is a unique one....it came with pods...and wasn't rejetted, etc. The ratios are off and it gets hot and won't go over 110km/hr. A whole other kettle of fish which I hope is solved by the airbox that I ordered.
The carbs have been cleaned and synced though.
The bike sat for about 8 months before I bought it and then I ran it for about 5 months and then put it away for Winter. All the issues are carry-overs for last year, so it wouldn't be the most recent sitting that did anything to the bike.
I know it sounds like a nightmare but the engine sounds good when it's running and it only have 2,700 miles on it so I thought it would be worth tinking with
 
My bet is it needes lots of updated maintenance first before throwing money at the battery and electrical.

Brendan..note he says it cranks and cranks before starting cold. well with the maintenance done ( valves within specs, good intake orings, a good air filter thats not clogged, carbs properly cleaned AND synced to the running engines requirements ) the bike should be choked and a few roll over and it should be running...not cranking and cranking. His comment is a HUGE HUGE red flag!!!
 
chuck hahn said:
Air leaks in the intake maniifold orings are also a major problem with GS bikes. Basically give us a run down on what youve done..some background history of the bike and what you know about its maintenance history. This will greatly help with some better diagnosis.

The more detailed info we have the better.
Click to expand...

Unfortunately I don't have any history of the bike. I bought it from some kid who tried to make it into a cafe races and gave up half-way through (presumably for the same problems I'm experiencing)
All I did was bought new plugs, battery and rectifier and cleaned the carbs and synced them to get it going. Gets around fine in the city but is useless on the highway.
As I said, once it gets started, it runs smooth in 1-3 gears but is garbage in 4th and 5th. This is my first old GS so I have no idea how it's suppose to feel in 1-3, though.


Brendan W said:
Shouldn't be getting hot. My money is on bad connections.
Click to expand...

That's possible, the wiring was a mess.
And when I say the selonoid gets hot, I mean smokes and melts the rubber skin on it....but that's also after trying and trying to get the bike to turn over.
If the bike is warm, I don't experience all these starting issues (though it's still not perfect)
 
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There IS NO sypmtmatic tapping noise to properly adjusted vavles!!! Wherever you got that from is bad info. There is some tapping from cam walk and tahts just life as a GS engine.

So last year you didnt address any issues. So did YOU PERSONALLY do the carbs or a "shop"? or are you taking the previous owners word for it???

So back up the bus and do all the maintenance yourself AGAIN and that includes the carbs per the tutorials on Bikecliff Website. Do the valves, Put in new intake orings. Get it all done and the bike will be another animal when youre done....
 
Soooo, you're not going to like this but I'm pretty sure it's just a boot between the carb and the engine. Like....slips on and is tightened with a band-clamp. I don't think there is anything that can take an o-ring. Seem like that could be a big issue? lol
I never thought of it as an issue. I just thought it was part of his dumbass modding.
 
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Here is the bike. Notice the intake boots....
 

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Close up of the intake
 

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Sokocanuck said:
Close up of the intake
Click to expand...

There are no orings associated with those intake boots. When the clamps get old they lose their ability to tight down properly. If the boots are hard and cracked, new boots and new OEM clamps. How are you supporting the rear of the carbs?
 
chuck hahn said:
Air leaks in the intake maniifold orings are also a major problem with GS bikes. Basically give us a run down on what youve done..some background history of the bike and what you know about its maintenance history. This will greatly help with some better diagnosis.

The more detailed info we have the better.
Click to expand...

mrbill5491 said:
There are no orings associated with those intake boots. When the clamps get old they lose their ability to tight down properly. If the boots are hard and cracked, new boots and new OEM clamps. How are you supporting the rear of the carbs?
Click to expand...

There was nothing there before and they flexed like crazy so I just installed a single bracket in the middle that attaches under the seat.

So where do the intake o-rings go?! Or are they not used for this bike? Should I change them to the type that uses o-rings?
 
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