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Discussion Starter · #1 ·
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.
 

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First of all, welcome to the forum.


Is the replacement head off a 1984?
 

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Is there any way you could have gotten the plug wires crossed?
 

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Discussion Starter · #5 ·
doesn't appear so, also, the system sends out a duplicate spark on the coils, so even if you had the timing off 180 degrees on one side, it is supposed to still run (stupid if you ask me as this would probably shorten coil life...or smart if you look at cost of coils)
But, will double check again.
 

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Timing Belt -

It may very well be that the timing belt on the left side is off a tooth but I'd check the timing belt drive gear/crank marks on both sides. The spark sounds like it's arriving with a valve open.

You also might check on the timing pulse generator on the back side of the 84 engine. They sometimes get moisture under the cover.

Good Luck, Michael
 

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Discussion Starter · #9 ·
still searching but...

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.
 

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Compression Test -

Hey Wings, Hopefully you have found your problem to be a series of air leaks. Don't forget to check for a float valve that has stuck open in one of the carburetors. Excessive fuel can cause some backfiring as well - but you should be able to smell the fumes if this was the case.

Before tearing in to the cylinder head, I'd run a quick compression test on each cylinder. Normally you should see around 125 psi or better for a healthy engine. Of course a compression test is normally performed after the engine has warmed up, oil has coated the cylinder walls, ignition disabled (handle bar RUN switch to - OFF), the throttle held wide open and using a fully charged battery.

In your case, what you'd be looking for in a cold engine would primarily be to check to see if all four cylinders had similar compression readings. I think the max difference between each cylinder should be less that 10%. If you had any bent or damaged valves - there would be a significant drop in pressure on one side.

Good Luck, Michael :)
 

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"Backfires, won't start" huh? Gee, sounds like me!:p

Once good spark is confirmed at both plugs in the replacement head, my first thought would be the timing, too. Any chance the timing mark on the replacement cam is supposed to line up with a different mark than what you're using? Seems unlikely, but...

It'll be easier to diagnose once all air leaks are sealed. Good luck!
 

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Final Diagnosis -

Hey Wingsfan, What did you determine to be the problem on your 84 Goldwing ? Was it a mechanical issue with the head installation, timing belts or an electrical problem (pulse generators/ignition unit/coils) ?

The result of troubleshooting this type of problem is good to know information for everyone on the site. :)

Michael
 
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