GS450 1981 won't redline, missing 20hp

[Thefidel]

I just bought a gs450 from '81.
I've done the service with oil, plugs and checked clearances. It starts and runs well with no strange sounds. However it feels like it lacks 20hp and after 7500rpm it feels like it won't go any higher up. I've watched some YouTube videos and my machine aren't near the acceleration times on those videos.

Engine is prepped with k&n pods (and the correct jets) I tried with a somewhat larger jet but it ran worse with that. Plugs are brown and looks replay nice.

One time I started it the timing chain tensioner was "spinning" as I've read some other has encountered. But it has not happened again. What would be your next step in finding the issue?

 

[tom203]

"One time I started it the timing chain tensioner was "spinning" as I've read some other has encountered. But it has not happened again. What would be your next step in finding the issue?"

this is a big red flag for me. Best to remove cam cover and check camshaft to crankshaft timing, cuz maybe it skipped abit. Probably now is also time to remove camchain tensioner to check that it's working correctly and has been installed correctly.

have a look here..

http://www.bwringer.com/gs/camchaintens.html

 

[Thefidel]

I checked timing, counted the pins aswell on the chain and got it to 18. This should be accurate according to the service manual. Thank you for this tip!

Starts to look like ignition issue to me.

 

[Thefidel]

Actually, I might have found it. One of the pins on the advance weights are broken of. So advance only works on 1 cylinder. Would this affect be as big as 15-20 hp on high end?

 

[roeme]

Actually, I might have found it. One of the pins on the advance weights are broken of. So advance only works on 1 cylinder. Would this affect be as big as 15-20 hp on high end?

Easily.

(Think a minute what happens if the advance doesn't do it's job. Wikipedia also explains it well).

 

[JJ]

Twenty horses on a 450 is a huge loss!

 

[Thefidel]

The bike makes it to 120km/h so there's not a lot of power. This is of course an estimation of the potential loss.

 

[Gorminrider]

Actually, I might have found it. One of the pins on the advance weights are broken of. So advance only works on 1 cylinder. Would this affect be as big as 15-20 hp on high end?

huh? "advance" works for both cylinders or not at all....but maybe you mean one weight is not working somehow...so I'd suppose there's not enough advance at high speed....or maybe you mean the pickup coils?

Yes, I know, you've put pods on and rejetted, but I thought I'd mention it anyways: You are aware these 400s were "detuned" when sold in Germany? , as they often show up online with specs stating a low hp...

 

[Thefidel]

You are correct, it is one of the weight where the hook has broken off. This would mean that advance isn't what it should be. The bike is registered as 31kw/42hp so there really should be a lot more punch than what I get from my mower

 

[Guest]

My 82 450 got dyno'd at 32HP... it was too rich on the main at the time but that won't have made a lot of difference, and that was when it was all stock... so -20HP is huge!

It definitely has more get up and go now with GS500 carbs and camshafts, but never been back on a dyno. My jetting "feels" better with the butt dyno but it's not perfect.

Missing one half of your advance weight will have a big impact as it probably won't be fully advancing... redline is at 9500 but real power doesn't come in until 5500 - 6000. In the twisties I'm regularly at 6000 - 8000 where it's fun, once you hit 9000+ she doesn't have any more to give and that's definitely shifting time.

 

[Thefidel]

I've ordered a used spare parts with both weights intact. I'm hoping this will be a big difference for how it feels. As it is now there's nothing more to give after 7500 rpm. I'll go through the carbs again and clean them properly.

 

[Thefidel]

Unfortunately the new weight didn't do any difference. I tore the carbs down and blew them clean with compressed air.
i took the time to sync the carbs aswell and it runs better at idle speed now.

However it still lacks power. I got a friend to take it for a test drive and we are unanimous about that there should be a lot more power. What else should I be looking at?

 

[Guest]

Few things I guess... have you checked compression? How about valve clearances, are they in spec? Remember if they need adjusting you will need to sync the carbs again. Have you checked the timing with a timing light? Bad coils will limit power also.

Probably a stupid question... is it definitely a 450? The capacity should be stamped on the cylinder block... 448cc from memory.

 

[520eek]

What about fuel supply from tank? It's not partially blocked or any thing is it?

 

[Thefidel]

There a nice flow of fuel from the tank. There's no bogging or misfiring. It runs really nice but just lacks the power and the abibilty to rev through the meter.

Im fairly certain this is a ignition issue by now. As the previous post indicates I need to check the timing with a lamp. It bothers me that the issue eludes me this way. I noticed that there was some wear on the timing advance distributor. So I suspect that this affect timing somehow, not sure how the pickups have been affected by this so I should order a new set of that plate aswell.

 

[Gorminrider]

I know that It's not very helpful to say, but Maybe the 35 year-old tachometer is tired....they use magnetized steel to move the needle and this can lose its charge over time...so From this reader's perspective, "not redlining" is not much of a symptom .

But "lack of power" seems to be the kernel.

The bike makes it to 120km/h

Is that the limit? Yes that's truly gutless . I expect that's what the de-powered (german) bikes would do....I'd look up what they did de-powering (as to jets?) and doublecheck your own against it. It might be a clue as to how to improve yours.
add: or maybe someone replaced the original carbs ...

Given the weights are working, and your strobelight test looks decent, but you have pods, carburetion still seems to be a possibility too. Might just be the air filters on the pods themselves....

 

[Thefidel]

I haven't ruled out carburetors. Pods are k&n with 135 main jet. I tried a 145 jet but that only made it worse. This made me think that it ran rich but since there's no black smoke and plugs look good I let it go. Since the lack of power is through the whole register my suspicions point towards ignition.

I also have a GSX400f from '82 and that one runs amazingly well compared to the GS. (Same bhp)

 

[Thefidel]

This thread can be put to solved!

Tacho was as someone stated not working properly, after 6800~ it wasn't following the engine speed the same anymore. Recleaned carbs again and checked compression. Everything was fine!
I got annoyed by not finding the issue so I looked up another gs wich was for sale, I contacted the owner and got a test ride. They ran exactly the same. So I guess I was expecting too much from the old sack

Thanks for all the input in the thread!

 

[Guest]

You could get some US spec camshafts. They are cheap, easy to install, and as far as I know that's the only difference. You would [probably] have to go bigger on the main jet.

I don't think that year is a critical factor, but you'd probably be safer with cams made in the 80 - 84 period; I think everything from '77 to '94 fits, but there may be slight differences in endplay, etc. to contend with.

 

[Gorminrider]

yes, it's very common the old tachs get tired...