GS450 Carb/Petcock leak, still not starting

[Guest]

I've been rebuilding my 1980 GS450 and finally got to where I could start it. Unfortunately, I couldn't. After replacing gaskets and fuel tee in the carbs, they're still leaking, though not nearly as much. Fuel is slowly collecting on the bowls and dripping down. Two bowl screws are able to spin without tightening down any more, making me think they're stripped and therefore the gasket isn't clamping down. The bike sounds like its trying to catch, but the spark plugs are pretty dry, so I think its short on gas. I disconnected the lines from the petcock and tested it with a vacuum tester, and it works. It drips a little after the vacuum is released, but the diaphragm still opens when it should. I'm not sure whats wrong here.

Side note, after cranking the engine for a while, oil began pouring out from around the filter cover, and I believe one of those nuts is free spinning as well (like the bowl screws). This should probably have its own thread, but how can I fix this as well? No point in having a running bike when it can dump its entire oil capacity in 5 minutes.

[CrazyCloud]

On the carbs, you need to find out if the screws are stripped out, or their mating threads in the carb bodies. It is easy to replace screws, but re-tapping threads is a little more advanced. Did you try wrapping some gas proof teflon plumbers tape around your tee joints? Some people swear by that as a good fix.
As to your oil filter cover not sealing, it is pretty easy to pinch/move the o-ring while installing; causing a bad seal. Try holding it in place with grease during install. It is also not uncommon for the little studs the acorn nuts fit on to be stripped and need replacing. If they are only stripped in a small area, you might get away with putting a small washer under the nut to move the nut to better threads.

[JRHemmen]

On the carbs, you need to find out if the screws are stripped out, or their mating threads in the carb bodies. It is easy to replace screws, but re-tapping threads is a little more advanced. Did you try wrapping some gas proof teflon plumbers tape around your tee joints? Some people swear by that as a good fix.
As to your oil filter cover not sealing, it is pretty easy to pinch/move the o-ring while installing; causing a bad seal. Try holding it in place with grease during install. It is also not uncommon for the little studs the acorn nuts fit on to be stripped and need replacing. If they are only stripped in a small area, you might get away with putting a small washer under the nut to move the nut to better threads.

Thanks for the info. The screws are brand new from MikesXS, so I'd assume that it's stripped in the carb body. Do I just drill and tap for bigger screws?
How hard is it to take those studs out and replace for the oil filter?

[CrazyCloud]

I would try re-tapping the holes to their original size first, no drilling, sometimes that will clean them up enough to grab. Pay attention to when the tap bottoms out and STOP. If you keep putting pressure on after you hit the bottom of the hole you could crack the carb body. If that doesn't do it, you could find some threaded inserts to fit, something like this article http://www.motorcycleproject.com/text/carb_thread_repair.html.
Getting a stud out is easy. Find two nuts that fit it and thread them on. Put a wrench on the bottom one and turn counter-clockwise; it jams against the top nut and gives you leverage. If they are stuck, you need to soak them with penetrating oil, wd-40, etc, and apply some heat with a propane torch. Several cycles of that should break them free.

[John Park]

I would try re-tapping the holes to their original size first, no drilling, sometimes that will clean them up enough to grab. Pay attention to when the tap bottoms out and STOP. If you keep putting pressure on after you hit the bottom of the hole you could crack the carb body. If that doesn't do it, you could find some threaded inserts to fit, something like this article http://www.motorcycleproject.com/text/carb_thread_repair.html.
Getting a stud out is easy. Find two nuts that fit it and thread them on. Put a wrench on the bottom one and turn counter-clockwise; it jams against the top nut and gives you leverage. If they are stuck, you need to soak them with penetrating oil, wd-40, etc, and apply some heat with a propane torch. Several cycles of that should break them free.

You can also use a bolt maybe 10mm longer than the stud protrusion as a stop gap repair. They used studs for alignment purposes but two will do. Also to preclude wear or stripping of the holes in the block, so be careful.

[JRHemmen]

I tapped and replaced all the bowl screws with m5 screws. No more leak, but the bike still isn't starting. This is so frustrating.

[JRHemmen]

Enclosed are some pictures and a video of the bike. Theres something on the spark plugs that I can't figure out what it is. Oil? Gas? It doesn't really smell like anything. when I cranked with the plug out, something sprayed out of the hole once, so I guess it has gotten some gas.

Side note, I can't figure out what that yellow connection is below the carb.









Video of attempted start:

https://flic.kr/p/DpUC6T

[jdvorchak]

First thing lets do a sanity check. Pull all the spark plugs out and plug them back into the plug wires. Lay them on cylinder head so the threaded portion touches the head. Then hit the starter and make sure you have all 4 plugs sparking with a good strong spark. If you have spark then lets make sure your firing order is correct. The out side plugs (1 and 4) should plug into the left side coil and the inside two (2 and 3) should plug into the right side coil.

The video to me sounded like you don't have great compression. Did you run a compression test on it? If so were the numbers at least 120 or higher?

If you have spark and you have compression then all that's missing is gas or too much gas. Spinning the engine with the plugs removed, to check spark, will also dry out your cylinders if they are flooded. If flooded also note that checking for spark could ignite the fuel as the gas comes out of the spark plug hole. Won't hurt anything but it will scare the hell out of you.

[jdvorchak]

Forgot to comment on the wire under the carbs. It looks big enough to be a ground wire from the battery but the engine is spinning over with it un attached. You'll have to trace it back to it's origin to see.

That plug looks gas washed to me. Like the bike was flooded prior to you removing it or someone put some anti-seize on it last time it was installed.

[JRHemmen]

Thanks for all the info. I haven't tested compression with a meter, but when I put my thumb over the spark plug hole it pulled pretty hard. I'll see if I can get my hands on a meter to test it. It's a two cylinder, so there are only two plugs, but they both spark. I forgot to attach the picture showing where the yellow wire is coming from, it's grounded to one of the screws holding what I believe to the the starter solenoid to the electrics tray. I'm thinking maybe it could be a timing issue. I know the cams are in time with each other, but I don't see any markings on the pickups to see that they're in time with the crankshaft. I'll attach a picture when I get home.

[JRHemmen]

Got a compression tester, sure enough its low. The left cylinder put out 70PSI, and the right put out a lousy 40. Also, the right plug didn't have any of that gray stuff on it, it looked brand new. I swapped the valves from my old head into the new one, could that be the cause of my issue? I'm sure timing being off could cause a loss in compression too, but I am still unable to see any markings on the pickups to confirm my timing. I ordered a new oil filter gasket since mine was definitely crushed, and I'm going to try to replace the studs on it as well. I think the entire oil capacity of the bike leaked out overnight, my cut off milk jug is just about full.

*EDIT*

I created a new thread under the 2 cylinder engine section as I figured that was more appropriate now that the carb leak has been ruled out as the reason for the engine not starting.

[jdvorchak]

When you did the compression check did you have to hold the throttle wide open, fresh charge on the battery and spin the engine until the compression tester stops rising. Is that what you did? 70 and 40 are the lowest numbers I can remember ever seeing. Next in order is a "leak down test". See if you can borrow a leak down tester from a local auto parts store and watch some youtube videos on how to do a leak down test. That is the preferred way to determine where the low compression numbers are coming from.

[Grimly]

If that is the engine ground, it would be better to fasten it to an engine casing bolt to complete the grounding from engine to battery / frame, else the starting current might start finding novel ways back to the battery, including things you don't want fried. At the moment it's depending on the engine bolts to the frame, but they're not certain to provide an easy electrical pathway.

[JRHemmen]

Sorry for taking a bit to get back, I've posted mostly in my new thread on the 2 cylinder sub forum. I lapped the valves and my compression went through the roof, the bike started right up. I'm now backfiring through the carb, and I'm unsure if it's due to too lean a mixture, or if my ignition could be faulty due to the less than ideal condition of my spark plug boots.