Backfires, won't start


Information and questions on GL1200 Goldwings (1984-1987)
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wingsfan98
Posts: 8
Joined: Thu Mar 15, 2012 6:19 pm
Location: Pontiac, Michigan
Motorcycle: 1984 gl1200a

Backfires, won't start

Postby wingsfan98 » Sun Nov 25, 2012 9:27 am



So here is the background to this post. I have a 1984 gl1200a. When I first picked it up, it needed a starter switch (the key switch on handle bars) and a timing belt (left side as if sitting on bike facing forward). Replaced both and everything started as it should. Had fairings and body pieces off to repaint. finished painting and put all together. Was idling in drive and ramping up and down. at 4600 rpm's, it shattered a valve in the number 2 cylinder (front left). Destroyed cylinder head and piston. Took engine out of frame and replaced piston, cylinder head (replacement came with valves, springs and all the internals) and gaskets. Put everything back into frame, set the timing and hooked everything up.
First thing to happen was the starter relay (switch between battery and starter) stopped working and had to bypass with a dead switch. Tried to start engine and all it does is Backfire, alternating between exhaust and carbs as to where it is back firing. Sounds like it is the left side only doing it. But will not start. Took apart front timing covers and reset timing from scratch, reassembled and still same problem.
So, what is the most like cause of this? I keep reading several different things on this forum, but where do I start to trouble shoot? What is most likely to least likely? I am dumbfounded as I can see nothing obvious that is causing this. Like I said, it ran fine before the valve went.



rdraidr
Posts: 75
Joined: Fri Aug 19, 2011 7:02 am
Location: Roswell, New Mexico
Motorcycle: 1987 GL1200A

Re: Backfires, won't start

Postby rdraidr » Sun Nov 25, 2012 10:09 am

Fuel, Fire and Compression. Those are the basic blocking and tackling of proper ignition. From what you've stated, I'm asking about your compression in the Left side cylinders? If timing is off or a valve is bent, even slightly, you won't have compression.

Remove all four plugs. Place your compression tester on one of the LH side cylinders and go to each of the others until you have all four numbers. List them here and we can chime back in then.

wingsfan98
Posts: 8
Joined: Thu Mar 15, 2012 6:19 pm
Location: Pontiac, Michigan
Motorcycle: 1984 gl1200a

Re: Backfires, won't start

Postby wingsfan98 » Sun Nov 25, 2012 10:20 am

will have to get a compression gauge...don't own one and said to say, my first thought was either a scorched valve or broken inside spring in replacement head (was told there are actually two to each valve and the inside one is hard to see...this sucks as this is the second head...first one was a different supplier and was wrong model. This one looked liked they pulled and shipped with no clean up at all. Arrived filthy but looked fine.

rdraidr
Posts: 75
Joined: Fri Aug 19, 2011 7:02 am
Location: Roswell, New Mexico
Motorcycle: 1987 GL1200A

Re: Backfires, won't start

Postby rdraidr » Sun Nov 25, 2012 10:30 am

You can buy a fair one at Harbor Freight or similar. I mess with all sorts of vehicles, so I bought a nice one and use it all the time.

There are two springs on each valve. I'm not an expert, others on this board I'm sure are, but if you can't get it to fire and it's back firing to begin with, I'm suspecting a poor seat (fit) of the valve to the head.

wingsfan98
Posts: 8
Joined: Thu Mar 15, 2012 6:19 pm
Location: Pontiac, Michigan
Motorcycle: 1984 gl1200a

Re: Backfires, won't start

Postby wingsfan98 » Sun Nov 25, 2012 10:38 am

Yeah, was my worry as well. I am going out today and the first things on the list are
1, check that the seals for the intakes are all seated and good, not pinched or out of place
2, idiot check...spark plug wires...did you screw up order?
3, remove head cover and inspect springs...
4, triple check for pinched or shorting wires and vacuum hoses

Thanks

wingsfan98
Posts: 8
Joined: Thu Mar 15, 2012 6:19 pm
Location: Pontiac, Michigan
Motorcycle: 1984 gl1200a

Re: Backfires, won't start

Postby wingsfan98 » Sun Nov 25, 2012 5:41 pm

Well...spark plug wires correct, cams and gears correct. So far, found two gaskets on intake ports that were questionable...replaced both and a secondary air supply line going into the first cylinder with a crack in it, replaced it. Continued searching and found the PC Port vacuum line broken (how that got by me I don't know). Just getting ready to put back together and see what happens. If not, next step is taking off heads and inspecting valve and springs for anything...broken inner spring or not seating valves right/sticking open...hope the vacuum line and seals is it, though...will know shortly.

rdraidr
Posts: 75
Joined: Fri Aug 19, 2011 7:02 am
Location: Roswell, New Mexico
Motorcycle: 1987 GL1200A

Re: Backfires, won't start

Postby rdraidr » Sun Nov 25, 2012 5:53 pm

You can check this site for more information, but I recall the LH (when facing the front of the bike) coil feeds the two rear plugs and the RH side feeds the two fronts.

And, before I pulled the heads, I'd get that pressure gauge and do my checks. It'll be worth the money...




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