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Won't start - Weak compression.

  • Thread starter Thread starter TheRealFatShady
  • Start date Start date
T

TheRealFatShady

Guest
I finally got the title and keys to the bike I bought. Unfortunately, it seems like a bad bike. :mad: 82 1100GL

I drained some gas out of two of the carbs. Turned the petcock (after using penetrating oil) to on/res/prime and none got the gas to flow out the carbs. :confused:

I changed the spark plugs and still couldn't get it to start. Did a compression test and was getting somewhere around 75.

I added oil to retest for compression (assumed the engine was bad; I was told adding oil to a spark plug hole will dramatically increase compression of a blown engine with bad rings) and it actually dropped to around 50.

Any ideas?

EDIT - Forgot to add, I got some spark. Didn't look like much, but I could see it.
 
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Has the bike been sitting for along time? If yes, then put some marvel mystery oil down the plug hole and let it sit.

Have the valves been adjusted yet? You need to do this before messing with the carbs.

Have you cleaned the carbs yet?

Battery fully charged?

What's your voltage at the coils?

Before trying to start the bike, do your basic maintenance first. Don't condemn the bike yet until you've done the work on it.

If you feel like bringing it down to Maryland, I'll trade you my running 750L for it :D
 
Going to look into the routine maintenance a little bit while I'm on this website.

almarconi said:
If you feel like bringing it down to Maryland, I'll trade you my running 750L for it :D
Click to expand...

Hmmm. I wouldn't mind a 750....
 
A couple of things on the compression test:

First, make sure you are holding the throttle wide open. The cylinders need to take in as much air as possible as easily as possible so they can compress it! The battery should be fully charged. If the engine is turning slowly there's more time for the air to escape through the leaks that are always there and that will make your numbers poorer. Those are the two main reasons I could see your numbers going down after adding oil. Crank until the gauge needle just doesn't go any higher.

If you add oil (that's doing a "wet" compression test vs. "dry" without oil), make sure you only add about a teaspoon or so. More than that can artificially inflate your compression numbers, because the oil is displacing the air space in the combustion chamber. Way too much oil can cause bigger problems. Did you check compression across all of the cylinders? Because you've only given one wet and one dry number each.

Obviously since your bike is not running you're doing the test "cold". The typical 90-100psi service limit is a warm motor limit. What 75psi will translate to when the motor is warm is merely speculation - but it will be higher. In any case, there's no reason, if you have 75psi in all four cylinders, that would keep your motor from starting.
 
Throttle wide open. The mistake I made when starting to acess the condition of my new bike was not holding the throttle wide open. The slides controll the quanity of air going into the carbs. Mine jumped 40-50 psi, once I got straightened out. Good luck!

cg
 
I've since been told that BOTH the compression testers I used were broken. Gotta love being given two to use and BOTH are bad. :mad:

I brought the bike to a local home-based mechanic. Within 40 minutes he had the bike started and running.

Apparently all he had to do was rebuild the fuel pump and clear out/replace the fuel line.

He's going to clean the carbs as well to get it running better.

Thanks for all the suggestions
 
tkent02 said:
There is no fuel pump.
What else did this "mechanic" lie to you about?
Click to expand...

That's all he's told me so far.

Could there be something which he simply refers to as fuel pump for lack of better term? Not a 'certified' mechanic, just a guy who happens to know motors a fair amount.
 
Larry D said:
Maybe he meant the petcock.
http://www.thegsresources.com/_forum/showthread.php?t=150388

Maybe he's taking your money........Good Luck.:)
Click to expand...

I was thinking he meant fuel valve. It had been rusted and I needed a penetrating agent + pliers to move it initially. Plus considering gas didn't flow to the carbs when I had the gas on, I'm guessing there was build up in there preventing it from working.

He has quite a few local happy customers. Plus he lives about 1/5th mile away. I'm not too worried about him taking my money.
 
if you're not worried about being taken for your money......i can sell you some blinker fluid so your turn signals work better!:lol:
 
TheRealFatShady said:
He has quite a few local happy customers. Plus he lives about 1/5th mile away. I'm not too worried about him taking my money.
Click to expand...

I wouldnt either. If he knows Bikes and you dont I would make him my new best friend. Mow his lawn for an oil change :). I would tap him for some of his maintenace info. Ya cant take him with you...
 
bonanzadave said:
I wouldnt either. If he knows Bikes and you dont I would make him my new best friend. Mow his lawn for an oil change :). I would tap him for some of his maintenace info. Ya cant take him with you...
Click to expand...

Hmm, I actually do landscaping...

Got it running enough to ride it home. Tried a few of the gears and all seem to work alright. Back brake doesn't respond to well, you almost have to 'pump' it to get it work.

Still some buildup burning off, you can smell it while it runs.
 
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