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I have an '83 Honda Shadow 500, and the specs I've been able to find for it say the torque should peak at 5000 RPMs. However, the only time I've been able to get it revved up that high in sixth gear is downhill with favorable wind. It pulls the hardest at about 3k, and at highway speed it stays at 40-45 tops at WOT. Any clues to what my problem is?

I'm pretty sure it's getting sufficient air and fuel, so the only things I can think of is faulty ignition timing (it's non-adjustable) or valve timing if a previous owner mokeyed with it and now it's a tooth off--is that possible without valve damage?

I would bet ignition timing or fuel related issues.

Need more info on the bike to give you a better idea (How long have you owned it, mileage, previous owners ... etc

The odometer says 13K, but the speedo drive gear was broken when I got it, so It's probably closer to 15-20. I bought it last spring from this woman who had it up on CarSoup, and the only thing I've done to the engine is two oil changes and a half-assed carb sync with a homemade manometer. No change in performance, maybe just slightly higher revs after the first oil change.

The bike is a beater, but it's been very reliable so far, despite the three times I put it down moving last year. It's my second season riding and I'm already familiar with three materials not conducive to good traction...

As far as I can tell the engine doesn't burn a drop of oil, so it can't possibly be worn enough for such a drop in performance. I'll look for directions on how to check the timing, and see if the fuel filter is clogged--if I can figure out where the damn thing is.

Turns out it's just poor compression

SausageCreature wrote:Turns out it's just poor compression

Try adjusting those valves to get the compression up.

CORSCO wrote:

SausageCreature wrote:Turns out it's just poor compression

Try adjusting those valves to get the compression up.

Shouldn't he do a leak-down test with oil in the cylinders to make sure it's not the rings?

ZooTech wrote:

CORSCO wrote:

SausageCreature wrote:Turns out it's just poor compression

Try adjusting those valves to get the compression up.

Shouldn't he do a leak-down test with oil in the cylinders to make sure it's not the rings?

You do not do a leak down test with oil in the cylinders, that is for a compression test. I figured your average home mech. does not have these tools. Also, he mentioned that his bike does not burn oil. The most common reason a bike has low compression that was running fine previously is tight valves.

Also, I have this engine in one of my bikes. The 83 VT500FT Ascot is the exact same engine, just different body. I have 33k miles on her and have only had problems with the cam chain tesioners. She even fired up when I neglected her for 10 years!!

CORSCO wrote:

ZooTech wrote:

CORSCO wrote:

SausageCreature wrote:Turns out it's just poor compression

Try adjusting those valves to get the compression up.

Shouldn't he do a leak-down test with oil in the cylinders to make sure it's not the rings?

You do not do a leak down test with oil in the cylinders, that is for a compression test. I figured your average home mech. does not have these tools. Also, he mentioned that his bike does not burn oil. The most common reason a bike has low compression that was running fine previously is tight valves.

I guess I could expand on this. My thinking is:
When you do a compression test and it is low, you put oil in the cylinders to see if is indeed the rings. Oil will seal the rings.
When you do a leak-down test, you are searching for the CAUSE of the leak by forcing air through the cylinder. You WANT it to leak to find the culprit. If leaking through the intake tract, it is tight or poor sealing intake valves. And the same for the exhaust pipe. If air is leaking through the oil fill cap or the crankcase breather, it is the rings leaking, letting air into the crankcase.
That is the way I go about it.

I think that you are not getting good fuel delivery to the carbs. If there is a filter any where on the line you might want to check it for foreign matter ( trash).

SausageCreature wrote:I have an '83 Honda Shadow 500, and the specs I've been able to find for it say the torque should peak at 5000 RPMs. However, the only time I've been able to get it revved up that high in sixth gear is downhill with favorable wind. It pulls the hardest at about 3k, and at highway speed it stays at 40-45 tops at WOT. Any clues to what my problem is?

I'm pretty sure it's getting sufficient air and fuel, so the only things I can think of is faulty ignition timing (it's non-adjustable) or valve timing if a previous owner mokeyed with it and now it's a tooth off--is that possible without valve damage?

Hey man, I own the same bike you do, though it's an '84. It's got almost 60k miles on it, all factory sealed engine except for the usual maintenance stuff nothing else was done to the engine. Last thing I did was adjusting the valves and change oil and filter. Chains are a bit noisy but still holding. Riding with front wind, some bags and even with my girl on the back, on 6th gear (OD) it tops at 55-60mph, about 5000-5500rpm. 'course if you want to go top speed, should do it in 5th gear, not overdrive. Though takes a while to get it up to 90mph, though. Oh, and it burns some oil on the front cylinder, worn piston rings. So far it delivered what it promised, considering the high mileage it has and that the engine was never rebuilt.
Have you fixed your problem yet? would be interesting to know.

Regards,
AdR.