Problems Reviving '81 GS750L

[beckerc525]

History:

I became the proud owner of a 1981 GS750L last fall. Don't have much history on the bike other than the PO's awareness of charging problems. He also laid the bike down once to avoid hitting a car that pulled out in front of him. I purchased the bike from him shortly thereafter (he moved to CA and didn't want to take it) and put ~300 miles on it, starting it with starter fluid and either jump-starting off my car battery or push starting it down my street.

Once it got cold outside I decided to knock out as much maintenance as I could, assuming that nothing had been done in the last 20 years since I didn't know the bike's history. Here's what I did:

1. Adjusted valve clearances
2. Disassembled carbs completely, dipped in Berryman's for 24 hours apiece, rebuilt (with new o-rings of course) and bench synced carbs
3. Replaced all rubber tubes between airbox/carb/engine
4. Replaced boots (couplers, whatever they're called) at the exhaust joints (i know there still isn't a perfect seal at one joint - either from the PO's wreck or before that the tab on the end of one exhaust tube at the joint was bent badly and preventing the clamp from fitting around the tube so i broke it off)
5. New sealed battery (charged and verified holding charge)
6. Installed brand new Stator & R/R
7. Installed Coil Relay Mod

After I put everything back together, the bike was hard to start. I used jumper cables to connect battery to my car battery to avoid draining the new battery and still took about 5 minutes of turning the engine over before it finally caught. Idled ~2000 RPM for a minute or two, and idle then began increasing slowly. I turned it off, then started it easily and rode around the block to warm up a bit more. In about 2 minutes of riding the idle rose to ~4000 RPM. I'm pretty sure the increasing idle is a result of air intake leak - probably didn't get one of the new hoses connected completely. But that's not the main problem I'm having.

After reading lots in this forum, decided the hard cold start may be a result of incorrect valve adjustment (it was my first time doing it), so I adjusted clearances again, this time to just over .005" to eliminate possibility of tight valves (they measured around .004" when I opened up to adjust the second time).

After re-assembling, the engine wouldn't turn over, even attached to my car battery or even with me trying to turn the 19mm ignition bolt manually with a wrench. The bolt will turn about 180 degrees in either direction and then it's litterally jammed. With all my weight on the wrench it wouldn't go any farther. Seemed weird considering I didn't have a problem turning the engine when I was adjusting the valves the day prior. But after trying to start the engine for about 10 minutes with the starter button, it finally started to turn over a few times and did so for about 5 minutes with no luck actually starting. I even sprayed starter fluid into the airbox in hope that it would help the engine catch but it didn't help. After a while the engine started displaying the previous behavior of only turning 180 degrees before stopping.

I did encounter a little hiccup while adjusting valves the second time - i dropped my tappet clearance gauge into the middle of the engine (where the cam chain is) and it dropped all the way to the bottom. Took 2 hours to fish it out with a tool I fashioned out of a clothes hanger.

My two main questions:

What could I have messed up adjusting valve clearances that would cause the engine to not turn over anymore, even manually? Can too much clearance cause this problem?

What would cause the engine to still have problems cold starting? I expectred it to start up in the 5 minutes the engine was actually turning over completely. Mixture screws (which I turned anywhere from 1 1/4 turns out to 3 turns out while trying to start this last time)? Improperly synced carbs (I have Carbtune but haven't used it yet)? I know both are issues since I never had the bike running long enough to address either but how can I fix either if I can't get the engine to run? I took float bowls off carbs and all were full of fuel so I don't think it's a fuel line problem.

We're getting 4-5 really nice days a week here in Kansas now, and each day breaks my heart a little more. Any advice would be awesome!


Chuck

[Big T]

it sounds like you adventure down the cam chain tunnel changed the cam timing and that's why your engine won't turn 360 degrees

Stop trying to force it- you're bending the valves, a valve is contacting a piston

Fix the cam timing first. If you haven't bent a valve, we can move onto the hard starting

Do you have an airbox on it?

[beckerc525]

Yes I have an airbox installed. Are these bikes supposed to have a box that encloses the air filter? Per the illustrated parts catalogs, I don't think this one is set up correctly since right now there's just an old air filter that connects directly to the airbox intake.

I'll look into checking cam timing. Is cam timing pretty sensitive? In retrieving the clearance gauge, I didn't think I pushed very hard on anaything, it just took a lot of touch and technique to pull it out.

[Larry D]

Yes, there's an air filter box. They are very difficult to find, the lid for them are even harder to find.

Are you sure you used the correct feeler gauge ? Did you use mm or inches ? The correct clearance is .09-.13 mm.....OR .004-.005 inches. I always use a mm feeler gauge.

With tappets, it's very easy to tighten them to far when torqueing down the nuts. They will tighten more when tightening up the nuts. I always leave them a slight bit loose, then when I tighten down the nut, it brings them right into spec. it takes a little practice, but, after a few, you kinda get the hang of it. Be sure to check them AFTER you have them tightened down. It's best to do one, check it, spin the engine with the 19mm wrench and check it again.

[Nessism]

It's not the valves. Leave them alone.

First thing I'd do is check the spark. Pull a spark plug lead off and put a loose plug into the socket, lay the plug against the engine to ground it, and turn the engine over while looking at the spark. You should see and hear the spark jump across the gap. You might want to check for voltage at the coils too - it should be near battery voltage. Lots of us have performed the coil relay mod to get the voltage up where it belongs.

Oh, and the mixture will be off because the back half of your airbox is missing. The bike won't run properly without it so you might want to start searching.

Good luck and don't give up.

[beckerc525]

Larry,

I'm pretty happy with my valve clearances the 2nd time around. I was pretty meticulous, used a set of .004"-.005" (.09mm-.13mm) tappet clearance gauges (each gauge has .004" gauge on one side and .005" on the other side), set the clearance a bit on the loose side, tightened tappets really good, checked clearance again (I'd say the clearance was still a bit loose, probably .006"-.007" but I wanted to err on the side of loose to eliminate the possibility of tight valves keeping me from starting the bike when cold), turned the engine and checked again, and then dropped my clearance gauge down the cam chain shaft... Is the main drawback to loose valves a noisy engine? If so, I can live with that for now - I just want the bike to start. Are there any other problems associated with loose valves?

[beckerc525]

Ed,

Thanks for the encouragement, I needed it a lot - last night I was the closest I've been to wanting to just quit and sell this thing. Will the air filter box need to be specific to my year and model or do you know if several years/models of GS series of bikes use a common box? My first reaction is that it'll need to be from a 750 since the air filter box for, say, a 1000 will need to be different to accomodate different mixture requirements of the larger engine but that's just a guess. Thanks again

[Nessism]

Ed,

Thanks for the encouragement, I needed it a lot - last night I was the closest I've been to wanting to just quit and sell this thing. Will the air filter box need to be specific to my year and model or do you know if several years/models of GS series of bikes use a common box? My first reaction is that it'll need to be from a 750 since the air filter box for, say, a 1000 will need to be different to accomodate different mixture requirements of the larger engine but that's just a guess. Thanks again

I suggest using one of the various on-line parts fishe (such as found on alphasports.com) and look at the various part numbers to see if there is agreement between different models, thus showing compatibility. Also check ebay since there are photos for you to see there. It shouldn't be overly hard to find the airbox you need, but it may take some time.

Regarding your carb rebuild, did you hold up the pilot jets to the light to make sure they were open? Spray carb cleaner though the choke tubes to make sure they are open too? Critical details like this are important even if you soak the parts like you did.

Good luck and keep going...


Edit: checked the air box part numbers for you and the second generation 750 and early 1100E shared the rear airbox part number. That should open up your search.

[Larry D]

The air filter box is from '80-'82 750 L's and '80 1100 L's. The fische I looked at listed "E's" from the same years...but, I'd double check that.

If it were me, I'd get the valves as close as I could. I wouldn't leave them loose or tight....but, that's just me.

Get a multimeter and check voltages. I'm guessing you have one since done the coil relay mod. The Stator Papers are in The Garage section on the main page.

Where are you ? You may have a member close by that's willing to take a look.

[DanTheMan]

The 180 deg turning then lockng up sounds like your cylinders might be hydro-locked with fuel. Pull the spark plugs then turn it over by hand. If that works then you'll know your float vales are leaking by and flooding the cylinders. Do you have the fuel shut- set to RUN or PRI? That can be the cause of hydro locking. Of course, trying to force the starter to turn it when it's stopping like that can fry the starter as well.

[JimWilling]

As with what Dan said, maybe your petcock diaphragm is shot, and you've got fuel leaking down the vacuum line into your #2 carb, and then into your engine, causing hydrolock. My experience is with a GS650, but if the carbs are the same, this may be an issue.

[beckerc525]

Thanks for all the suggestions. Got a list of things to check when I get the time.

I'm always very careful to set the petcock to ON since the PO left it on Prime for about a month after he wrecked it. He told me he addressed the problem of getting all the fuel/oil mixture he'd then created out of the bike and I just took his word for it. He's a friend of mine who I also helped replace the old petcock with a new one right before I bought it so I'd be surprised if that's bad already. This one has seen <400 miles.

I wouldn't be surprised if I damaged the starter relay. In the several minutes I was using it to try to turn the engine over when it was locked, the rubber cap covering the starter relay bolt started melting. That's when I stopped trying to turn it that way.

[beckerc525]

And I'm in Wichita, KS

[Big T]

And I'm in Wichita, KS

Okay, add that to your profile. There can often be someone nearby who may help you and/or go riding with you.

So, on to diagnosis:

1. Pull all 4 spark plugs
2. Remove the ignition cover (small one on the right)
3. Use a wrench or socket on the big nut and rotate gently clockwise

A. Does it turn and spit out liquid? Turn it a few more time to pump out as much fuel as possible. Then, leave your spark plugs out to dry the cylinder. Change your oil and filter to remove any gas in the oil. Get a new petcock

B. Does it still lock up? Check BassCliff's site for the proper cam timing alignment. There are marks on the ignition rotor and cams that need to be in the proper positions.

let us know what you find

[beckerc525]

Pulled the plugs, engine still locks at about 90 degrees each direction. No fluid came out of the spark plug holes during the little turning I could do.

As for checking cam timing - I'm unable to turn the engine so that the #1 arrow on the exhaust sprocket is aligned with the valve cover gasket surface. The arrow is about 45 degrees below where it should be. Problem is, I can't rotate it up to horizontal as the intake cam sprocket locks when it's 45 degrees below. Likewise, #3 arrow on intake sprocket is about 45 degrees clockwise of vertical at this point. Is it possible to completely remove the cam chain from one of the sprockets so I can try turning them independently? Or is that not a good idea? Does the cam chain guide pull out completely? I'm afraid of damaging the rubber end by pulling on it too hard. This would probably be easier with BikeCliff's tutorial but I couldn't find it.

Side note: Petcock was changed after we drained and replaced the fuel and oil before I bought the bike. I've also since done another oil and filter change. 400 miles on the new petcock with oil/fuel where they should be. Still think it could be a problem?