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Fourth exhaust pipe won't get hot?

  • Thread starter Thread starter 82 GS550L Basket Case
  • Start date Start date
8

82 GS550L Basket Case

Guest
Hey guys, I rebuilt a 1982 GS550L and ended up getting it running and it looks sharp. It is a 4 cylinder engine, for some reason pipe number four (Farthest to the right when riding the bike) will not get hot, no matter how high the RPMs are. We checked the spark plugs, there is a spark but a small one. However, when removing the rubber boot connector between the Coil wire and the actual spark plug the spark increases greatly in size. I believe this is part of the problem that I've been having with my power. The bike has trouble maintaining 65 miles per hour comfortably. Does anyone have any ideas as to how I can fix this problem? Please let me know.
 
First swap the # 1&4 plug wires, also make sure you have 12V on the coil. IF you still have cold #4 pipe I would suspect a carb problem
 
try replacing the plug boots on the end of the wires, or swap the boot between 1 and 4 and see if the problem moves over. if it does then its a faulty boot.
snip 1/4" off the end off the plug wires before fitting the new boots.
 
SqDancerLynn1 said:
First swap the # 1&4 plug wires, also make sure you have 12V on the coil. IF you still have cold #4 pipe I would suspect a carb problem
Click to expand...

You're talking about the input side of the coil for 12V, right?

It really shouldn't be the carbs - Josh TCK rebuilt them, and the K&N filter seemed to make it run a bit lean so we swapped in some new jets.

We've been very, very careful to get the boots on both sides of the carbs fully seated every time we've removed the carbs.

I wonder - if #4 isn't actually burning the fuel that the carbs are sending it, would that generate smoke from the exhaust (especially on in-neutral revs and under acceleration)? It's black smoke, and it doesn't really smell like burning oil.
 
Thank you guys for the great suggestions! I'm going to go try these! Crossing my fingers that it isn't a carb problem! Too many times have I taken those carbs apart! :P I will let you guys know what I find out! Thanks again!
 
A few things to check:

- coil voltage: should be at least 11 volts

- compression: make sure to adjust the valves otherwise they will burn and damage the engine

- pilot jet in the carbs: very small orifice in play here

- carb vacuum sync

Good luck
 
82 GS550L Basket Case said:
It really shouldn't be the carbs - Josh TCK rebuilt them, ...
Click to expand...
Not going to say that he doesn't do good work (who knows, I might have even helped him on that set of carbs), but it does not take much to plug up some of those small holes AFTER installing them back on the bike.

I have rebuilt a set of carbs, had one cold cylinder like you. Pulled the carbs, opened up that one carb and blew out the jets and passages. Put it back together, that cylinder started working, but another one failed. Pulled the carbs again, cleaned out the latest problem and re-installed the carbs. This time, everything went well and all four got hot.

Usually, if it's a carb problem, it's just the pilot jet that gets plugged, and you will notice that the bike comes alive above 1/4 throttle or more. Since you are evidently having problems through all ranges, I would suspect electrical issues, but would not totally rule out the carbs.

.
 
Low compression ...

Low compression ...

Thanks for all the advice, y'all!

Tanner's mechanic/mentor helped him do some troubleshooting, and they wound up putting a new boot on one of the spark plug wires. (I'm not sure why they didn't simply swap out all four - I tend to replace things in sets, personally).

The performance and pipe heat didn't markedly improve.

We put a compression tester on it, and it's clear to me there's a problem. Here are the results:

#1: 75
#2: 90
#3: 105
#4: 45

Now, this is the first time I've ever done a compression test (shiny new gauge! New toys! yay!) but the process seems simple enough, and it looked like it was working like the instructions described.

So T is going to take it into the shop and find out whether Frank (the shop owner who was his mentor for the project/rebuild) will work with him on doing the rings and valves.

Neither Tanner nor I is terribly confident that we'd get it put back together correctly, if we dig into the motor.

That said, are we looking at pulling the motor back out to do the pistons/rings and valves? Or is that something that can be done while the motor is still in the frame?
 
Did you adjust the valves?

Was the compression test performed with the engine hot and throttle held open?

Has the engine seen some mileage recently, or has the bike sat in storage for a long time?

The valves loose clearance with mileage and failure to adjust the valves damages them. You can not perform a compression test unless the valves are adjusted first otherwise you will get false readings.

Also, the compression will increase with mileage if the bike sat for a long time. GS bikes like to run.
 
OK, so stupid newby mistakes run rampant.

The engine was hot (got that right, anyway.)
We didn't hold the throttle open.
We haven't adjusted the valves. That just became Job #1, maybe even for tonight.
Tanner has put a couple hundred miles on it since he put it back together.

Valves. First.
 
Some spark plug caps have a resistance built into them, their purpose is to keep the hum off radios. Some folks here remove that resistor (which is a small piece of metal) and put a piece of copper or other conductive metal in it's place. This makes the spark hotter. If you have those you can look inside the cap and see if it's slotted for a screwdriver, unscrew it and replace the metal, also you can unscrew the lead wire from the cap, cut about 1/4 inch off the end and screw it back on. All connections need to be tight.
Or you could change over the leads as previously suggested, the timing is the same for cylinders 1 & 4 and see if the problem follows.
If it doesn't your problem is likely elsewhere.
 
The questions up top:
How freaked out should we be that two of the valves were so tight we couldn?t get any feelers to fit?

Is it ?normal? for the shims to range from 2.5mm to 2.8mm?

I heard a rumor that the cams on the 550s can ?twist? if the engine is abused. Is there a more scientific way to check that #1 and #4 hit TDC at the same time than putting screwdrivers down the spark plug holes and watching them go up and down?

Took the valve cover off and ran through the valve measurements over the weekend. Thanks (and a HUGE shout-out) to BikeCliff?s wonderful site full of tutorials (again!) Thanks, too, to Steve for his Valve Shim Spreadsheet!
http://members.dslextreme.com/users/bikecliff/

These were the measurements we came up with. Note that the exhaust for #4 and the intake for #1 were so tight we couldn't even get the 0.02mm flimsy feeler (the smallest in our set) between the lobe and the shim. We tried removing and re-seating the shims on those two cylinders, and even tried sliding the feeler in while we slowly rotated the engine, with no joy.

The intake for #1 was the only other one that was out of specs.

We did put a 2.70 into the #4 exhaust and got the 0.09 to slide in, so it looks like a 2.75 should work.

We didn't experiment with the #1 exhaust in the same way, because of time constraints.

Cylinder 1 2 3 4
Previous clearance - - - - - - - -
Ex. cl. (mm) 0.02 0.06 0.07 XXXX
Mid-point (mm) 0.055 0.055 0.055 0.055
Difference (mm) -0.035 0.005 0.015
Present shim (mm) 2.70 2.75 2.75 2.80
Needed shim (mm) 2.65 2.75 2.75 2.75

Previous clearance - - - - - - - -
In. cl. (mm) XXXX 0.06 0.04 0.06
Mid-point (mm) 0.055 0.055 0.055 0.055
Difference (mm) 0.005 -0.015 0.005
Present shim (mm) 2.60 2.65 2.80 2.65
Needed shim (mm) ??? 2.65 2.80 2.65

Any thoughts, comments, or suggestions?
 
A LOT of GS bikes get scrapped because idiot owners never perform valve adjustment maintenance. The clearance reduces with mileage until the valves never close and then burn. If your engine has no valve clearance there is a chance there is damage already, but GS engines are really tough so it's unlikely.

No way for cams to twist. Check cam timing using the procedure in the factory Suzuki service manual. The procedure is very easy and clear once you look in the manual.

good luck
 
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