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GS450 = Huge Headache!

  • Thread starter Thread starter cobusb
  • Start date Start date
C

cobusb

Guest
I'm having the following problem with a GS450, I truly hope that someone can help me.

The bike ran perfectly for the last couple of years, later it started using oil and performance wasn?t what it used to be. It was the sent to a local repair shop for a major overhaul.

The following work where done:
1. Cylinders bored out with new pistons and rings (Genuine Suzuki oversized).
2. Top-end totally redone with new valves and seals.
3. Bottom-end inspected and new bearings.
4. New timing chain.
5. New filters, fuel hoses, points and condensers and spark plugs.
After the repairs the bike ran perfect.... only for some 600 kilometres.

Now the Problem:
When riding all seems OK if the revs are kept below 4000 RPM. When reaching 4500 RPM there?s NO power, it backfires through the exhausts and there?s a loud noise coming out of the carbs. If I pull the choke i'm able to get it past 4500 RPM eventually but the backfiring and carb noise still continues. In Neutral I can Rev the engine to the redline although it takes about 5 seconds.

I?m able to ride the bike if I keep the revs below 4500 RPM, torque is great, no noises, no backfiring not even a single miss.

I took it back to the repair shop; they told me that I over-revved the motor. They refused to help me; I even offered to pay them to repair it. I?m on my own now.

I?ve tried the following:
1. Carb Rebuilt.
2. Swapped the carbs with a running GS450.
3. Swapped the coils with a running GS450.
4. New Points and Condensers.
5. New Filters
6. New Gas.
7. New Spark Plugs.
8. Redone the wiring.
9. Checked Charging system.
10. Checked compression.
11. Set Ignition timing with a professional strobe.
12. Checked Ignition timing advance with a professional strobe.
13. Replaced the petcock.
The only other problem I can think of is valve timing.
My manual only covers the later GS models with electronic ignition so I may have screwed up here.

On the timing marks behind the points I found the following:
For the Right cylinder: T @ TDC, F @ approx 10deg BTDC, R @ approx 20deg BTDC and L @ approx 30deg BTDC.
For the Left cylinder: T @ TDC, L @ approx 15deg BTDC.

Manual says that I should line up the RT marks to set the timing, but there?s 20deg difference between R & T.

If I set timing with R: Cut-outs facing each other, mark 1 horizontal with head, mark 2 facing up and 18 links to intake mark 3. Valves hit piston when turning over by hand.

If I set timing with TDC: Cut-outs facing each other, mark 1 horizontal with head, mark 2 facing up and 18 links to intake mark 3. Engine Starts but still the same problem.

What Am I Missing???

Please help me....

Cobus
 
Have you inspected for leaks, exhaust and intake? Are you running the stock airbox? Is it properly sealed and the correct filter in place?

May not be much help, but those are pretty common issues.

BTW all 450's have the same style timing (carried over, I do believe, to the the new GS500) using the ATU unit.
 
Well...if the bike ran fine for 600 km after the rebuild, why do you think the valve timing could be off now?

The timing is correct with TDC, 1 on exhaust cam horizontal and 2 up, 18 pins to intake mark 3. Done

If I were you I'd check the compression again to make sure your experimental valve timing test, which lead to the valves hitting the pistons, did not damage anything - don't ask me how I know this. :(

Assuming you have compression, you can rule out the engine mechanical. I know you have checked the spark and fuel but something is still not right, obviously. I'd go after the spark since you have already tried two different sets of carbs. Do you get a nice fat blue spark when turning over the motor? Oh, and points on a 450? I thought they came with magnitic coils and ignitor (they did on the US anyway).

One last desprate thought is that maybe your exhaust is pluged. Could it be that the muffler is rusted and a chunk came loose inside blocking flow? Sorry, can't think of anything else.

Good luck.
 
Thank you for your reply BGMART450.

Air filters = K & N Performance. Worked previously with these filters on original jets.
Rubber boots between Carbs & Intake = No leaks.
Exhaust = Stock, no leaks there.

The engine runs perfectly on low Revs. Only thing i can think of is timing.
 
Thank you NESSISM.

I turned the engine over by hand when it hit the valves, It barely touched. I did check compression afterwards, 160 psi cold both cylinders.

Spark is just perfect, jumps about 1/4 inch big blue and nasty to the touch!!

Bike starts first time everytime, without choke.

No rattles in Exhaust, when it runs i can feel the wind rushing out the back in pulses, dont think its the pipe.

Bike is from South Africa, dunno why we got points and you guys got electronic?

The wires from the points go straight to the coils. ( Both Coils Have 4 Wires ) Another wire gets ignition power. Another gets connected to the condensor. And the last remaining on each coil goes to a small box next to the regulator. Could this box be a cdi? Is it posible that someone removed the Electronic pickups and replaced it with points?

The Valve chain tensioner sprang a leak 2 days before the trouble began, the shop either sealed or replaced it, just thought that the chain could have slipped then.
 
Last edited:
That box next to the regulator sounds like the ignitor. I don't think bikes with points have this? You might want to experiment by bypassing the factory wiring and running wires directly up from the points to the coils.

good luck.
 
Nessism

It certainly looks like an ignitor. Bike shop told me its for regulating advance on timing. Theres already a mechanical advance behind the points so maybe i should try to bypass the ignitor. Makes sense to try it...

Thanx
 
Just rewired the ignition system. Now only uses points, condensors and a straight ignition wire. Still the same problem.

Just for interrest sake: What would the symptoms be with cams running in advance, like 1 link too early? And retarded, 1 link too late? would it be noticeable?
 
My guess is that it would be noticable but not to the extent you have experienced.

Another thought, is the mechanical advance for the timing working properly? Points cam should have springs and weights which move outward when rev'ed.
 
The mechanical advance works great, i even lubed it up just for incase. I have a digital timing light, it show the advance steadily moving up when revved. Advance goes up to about 40deg BTDC @ 4000 - 5000 RPM. As the problem suddenly appeared while driving I figured it must be valve / cam related. Stupid Question: Can a valve spring do this? I havent opened up the "valve buckets" Maybe a spring collapsed or patially broke?
 
Anyone wanna buy a GS450??

Great condition.
Engine Rebuilt.
New Paint Job.
New Tyres.

WITH A FREE FITTED BUILT IN REV LIMITTER
 
cobusb said:
Anyone wanna buy a GS450??

Great condition.
Engine Rebuilt.
New Paint Job.
New Tyres.

WITH A FREE FITTED BUILT IN REV LIMITTER
Click to expand...



Awwww man, hang in there dude. I can bet you can get it sorted...
 
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