Suzuki problem...

[Tiger]

 :) At present, I have a neighbours 1979 Suzuki GL750L sitting in my garage which needs fixing...The owner put it into a shop that told him he has low compression...(but its well within tolerance and shouldn't create the problem anyway). They are supposed to have checked the old girl out completely but the problem still remains...

Problem:

Bike starts o.k, however, within a few second's the #3 cylinder, (going from left to right), header pipe is cold/bike splutters/spark plug loads up with gas and obviously starts firing raw gas out of the exhaust :o ::)

The owner tells me that since the problem started, he has: rebuilt the carbs (twice)...float heights are all good and new needle valves, etc replaced with new. New spark plugs installed and #3 changed out with the other plugs as well as another new one. Plug wires/caps check out o.k....and all checked by the shop!!

This bike has two coils with two leads coming out of each one to feed the four plugs. I'm thinking coil problem maybe...coil works o.k. when cold but "opens" and creates a short when warm...but how do you check/eliminate it for sure. I don't have a spare part of any kind, let alone a coil, for this old girl in my garage and won't just go and buy something for the hell of it...

What do you guys think....... :-\ 

                         8).......TIGER....... 8)

[Paul Mc]

The coil for #3 will likely feed #2 also - if the problem isn't on #2 then it isn't the coil.
Since they're close enough together, swap the leads for 2 and 3 around - 4 cylinders have usual firing order 1, 2, 4, 3 (although not always true) so is most likely working on the spare spark principle so should still fire up at the right time with the leads swapped - and see if the problem shifts.
If it was me, regardless I'd change the HT lead on #3 = intermittent problems on spark are 90% HT leads in my experience. Many 4 cylinders have the coils shared 1,4 and 2,3...
I understand the idea of coils 'breaking down' when hot (resistances increasing) but usually takes longer than a minute (!) and again, should affect both cylinders.
The pick-ups and the CDi won't differentiate between cylinders, I think it's your HT lead.

I'm pretty sure that you already know the above.

You can also swap the coils over (or even just the supplys) to test your theory of the coil being the problem - usually the earths as they tend to share power (always on) and have switched earths via the CDi/TCi whatever...
But I'd still replace the lead myself.

Paul

[Rick G]

On some coils, with the HT leads moulded  in to the coil , I have used a dremel to cut away the coil and expose the wire, I remove all the insulation from the wire and solder a new wire to the 1/2 inch of exposed wire that is left. Next I apply a coat of J B weld, to seal up the new HT lead . It works well and is much more convenient and cheaper than replacement . Of course if you have coils with replaceable leads , you wont have to do this. I get HT lead from a lawn mower shop, it a wire with actual wire , not carbonized thread.

[fiat-doctor]

I'm with the others on checking the leads and it would work fine to switch 2 and 3 to see if the problem moves.

If it stays on 3, then I'd sure check the valve clearances.

Good luck,
               Steve

[Tiger]

 :) Thanks a lot guys. Hopefully I can get at her this week...

                      8).......TIGER....... 8)

[YellowJacket!]

Actually Tiger, you sum it all up in the posts title: "Suzuki Problem".  ;D

David

[jasonm.]

did you forget in 1979 the 2 valve head Suzuki has points ignition?!? Not electronic. So that is the first thing. Get a timing light and check along with the proper point gap setting  .012" to .016"(.3 - .4 mm). Then if all that is correct, spark plug wires and caps. Yes, same coil fires #2 and #3. But you can still have a bad output on just one side...but rare. Spark plugs should be B8ES ngk or similar.

[supervision]

 Make sure the plug gap is small. a split secondary like those have , is jumping both plugs at once, so the coil has to work hard and jump the combined gap of both plugs, each time it fires. 

[Tiger]

 :) O. K...Here is what I've done/found...

Before starting her.......

* I pulled all the spark plugs, cleaned and gapped them.

* Removed the spark plug caps and cut the wires back about 1/4" and reinstalled the caps to the opposite head leads.

* Point's gap's checked out fine.

* Replaced the gas/vacuum lines.

* With the gas tank removed, I noticed that #2, #3 & #4 carbs have a vacuum port...The petcock vacuum line goes to #3 carb...the other two have no lines or vacuum caps!!! This can't be right...

The gas tank sender unit also has a vacuum line type outlet...but again, no line or cap...

With the gas tank back in place, I fired up the bike...Within a few seconds there was white smoke billowing out of the right side exhaust, (#3 & #4 head), with a lesser amount coming from the left side!!!

#3 header pipe was just warm...you could grip it!!...the other three were, as you would suspect, all way hot.

*With #3 spark plug removed and grounded, she has good spark when you turn her over...

I also did a compression test:
* #1 = 120
* #2 = 112
* #3 = 108
* #4 = 118

Your thoughts ladies and gentlemen...

                      8).......TIGER....... 8)

[Kevin]

I think you need to look at the carbs again.

[kwells]

carbs

[Rick G]

That's one reason I hate  4 cylinder bikes so much. The carbs are such a PITA . I agree that there probably the problem.

[Paul Mc]

With the gas tank removed, I noticed that #2, #3 & #4 carbs have a vacuum port...The petcock vacuum line goes to #3 carb...the other two have no lines or vacuum caps!!! This can't be right...
That isn't right, they should be capped/connected together (at this stage, either will do, I'd cap them). They'd run rough in this condition, and possibly hot too.

The gas tank sender unit also has a vacuum line type outlet...but again, no line or cap...

With the gas tank back in place, I fired up the bike...Within a few seconds there was white smoke billowing out of the right side exhaust, (#3 & #4 head), with a lesser amount coming from the left side!!! Isn't white smoke sign of a head gasket gone (normally) although some old fuel can give the same effect. I'd check the water for signs of oil, just in case. But I think the compresion values don't show a head gasket, I'd expect lower values.

#3 header pipe was just warm...you could grip it!!...the other three were, as you would suspect, all way hot.

*With #3 spark plug removed and grounded, she has good spark when you turn her over...

I also did a compression test:
* #1 = 120
* #2 = 112
* #3 = 108
* #4 = 118
Centre two cylinders, most likely position of a compression problem with a warped head and therefore leaking head gasket.
Compression values don't look to bad 'though, and you're running on #3 albeit not quite right.
Could try torquing down the centre bolts (NOT advised) but I'd check the valve clearances on these cylinders anyhow, but not as a priority.

Your thoughts ladies and gentlemen...

Could be that the float needle in #3 isn't set quite right, the fuel level low and not quite enough getting to the primary jet in the carb and fed through into the cylinder. Could also be that the primary jet is a little gunked up with old crud.If it was me, I'd take off the carb top #3, remove the vacuum piston and spring (assuming it's CV carbs) and with WD-40 and a straw spray the jets from about as best as possible. Can also use a 12V tyre compressor to do the same thing (will splash fuel about a bit so take care) before reassembling the carb.
Normally the problem is dirt blocking the float needle and flooding the bike - probably still want to determine if you have enough fuel in the #3 cylinder compared with the other two.
Simplest way, assuming you can access them, is to undo the drain bolts and measure the amount of fuel in each carb with the bike on centre stand - I have a long screwdriver jsut for this job on 4 cylinder machines. That'll give you an idea if enough fuel is reaching the pilot jet in the first instance to run the #3 cylinder.
I'd cap the vacuum measurement take-offs first, as the other 3 cylinders may be getting too hot too fast by running lean (what colour are the plugs?) - make one change at a time (cap first, try to run etc) in case you fix it, as the cure can diagnose the cause - and the cause may have longer term issues built-in.

Sorry, rambled and a bit dis-jointed there, am rushing in my tea break to write this!

[Rick G]

I suspect Paul is in the UK! Tea breaks are popular there!! ;) ;) ;) ;) He also knows the correct spelling of "colour" and "centre"

[The Prophet of Doom]

I suspect Paul is in the UK! Tea breaks are popular there!! ;) ;) ;) ;) He also knows the correct spelling of "colour" and "centre"

As do we in the more civilised colonies  ;D

[Superfly]

Older Suzuki Gs's have a charging system that makes the Visions charging system look good. 
Have you tried: http://www.thegsresources.com/
I had an older GS once, and this place was a good place to start.

[The Prophet of Doom]

Older Suzuki Gs's have a charging system that makes the Visions charging system look good. 

I had two of those, and a couple of GTs.  They were ultra reliable, but when I moved to the XZ in 84 I was blown away by the performance and handling difference.  Even the odd time I was pushing the XZ home I was glad I made the move to Yamahaville

[Tiger]

 :) Thanks everyone...great site Superfly 8)

               8).......TIGER....... 8)

[Rick G]

Roro , I apologise for omitting the the southern hemisphere colonies ;D
When I went to school colour was the spelling, but tyre was optional.

[Tiger]

 :-\ I swapped # 2 & #3 plug wires around.......No change!! #3 header stone cold...

The two open ports between carbs 1 & 2...3 & 4 turned out to be vents, so I put new hoses on them.

So, plugs, wires, caps, coils, points all check out...Carbs are next on the list ::)

                   8).......TIGER....... 8)