85 mph speed restriction in early '80's bikes?

[robinjo]

As of yesterday I have a 1982 GS750T in my workshop who needs it headgasket replaced, this is an US import with the 85 mph speedo. Now the owner tells me that it is restricted to that speed also and can't go faster! 8O Since the bike is now in pieces I can't try this for myself. Also when I rode Karen's 81 or 82 550L (papers say it's a 82T but the bike is an L and the frameplate says 81) I took it on the Highway and it ran very well upto about the speed mentioned above and then cut out, sortof felt like fuel starvation, weird... It is also an American import with the 85 mph speedometer.

Anybody know any more about this phenomenon?

How does it work? The slides on the 750T can be fully opened, I checked that.

Or is it bull

[Anonymous]

Wrong!!! The bikes with the 85 speedo go just as fast as the others, the 85 mph speedo was found to be very dangerous, cause the rider didn't have a clue how fast they were going when above 85, especially dangerous in curves. The law was removed in 1983, and all went back to reasonable speedos. Speedo had no affect on how fast the bike would go

[earlfor]

Its only the speedo that is limited to reading up to 85 robinjo. Nothing else on the bike is different.

Earl

[WesV]

The law was put in place in the late 70s (read fuel crunch) to try and prevent people from going real fast, IE: using a great deal of fuel. This theory worked for cages with 4bbl carburators, but really didn't mean much for bikes. This was also the reason 55 was required to be highlighted on the speedo, because the government wanted everyone to stay below the double nickle. I have the 85mph speedo on my '81 450L and I know I have done better then 85 on it because it was just bouncing off the peg and a friend tailing me said we were above 90. Hope that helps clear some of that up.

[robinjo]

Found this bit of info on www.suzukicycles.org

"The GS750T was a budget model aimed for the North American market, available in the beginning of the 1980's. It had the 16-valve 750cc engine but its power output was restricted for maximum speed of about 80 mph (130 km/h) making more simple brakes adequate for the model (seemingly borrowed from the GR650, along with other details like the alloy wheels). At front, the GS750T had a single disc and the rear brake was a mechanical drum brake. The color scheme was similar to the GR650 and the larger 8-valve inline-four shafties GS850G, GS1000G and GS1100G."

http://www.suzukicycles.org/visitors-bikes/visitors_GS750T_page1.shtml

The one I have here now is Ard Bisschop's bike.

[Hap Call]

I believe Tim (HiSPL) had one at some time in the past...check with him...I find it hard to believe that they would limit it to 80 mph.

Hap

[chuckycheese]

80 MPH

I'm not an expert mechanic but it seems to me that the only way to limit the speed (other than gearing and horsepower) would be to put a rev limiter on it. If it had one of those, the gifted mechanics in our group would know about it and point it out...so it seems like a myth. :?

[robinjo]

Re: 80 MPH

I'm not an expert mechanic but it seems to me that the only way to limit the speed (other than gearing and horsepower) would be to put a rev limiter on it. If it had one of those, the gifted mechanics in our group would know about it and point it out...so it seems like a myth. :?

I have PM'd both Tim (HiSPL) and (Mark) Shaftzuki about this, I hope I get a reply. I knew I shouldn't have taken the bike apart right away :roll: Would the owner be pleased if the top speed of his bike have been increased with 40 mph? :twisted:

[robinjo]

Robin - the bike will well exceed 85 mph - before I tore mine apart, I rode mine "hard" a few times - well past the mark. As far as I can tell - there is nothing different from the T model motor and the standard E model motor. My carbs are the same, the ignition is the same - I haven't actually measured valves, etc. - but I don't think there is a difference.

I have noticed, however, that things like gasket sets, manuals and other stock items are under different part numbers.

I have a spare 81 750e model motor - I need to make some comparison measurements between the two.

Let me know if I can help - I don't have a manual for the bike (yet) but I can probably put my hands on what ever you need!!

Very quick reply by Mark here

The plot thickens...

[focus frenzy]

I believe Tim (HiSPL) had one at some time in the past...check with him...I find it hard to believe that they would limit it to 80 mph.

Hap

why would Suzuki produce a 750 that was slower than it's little brother, the 250??
I know the 81 GS 250 I had would pull past 85mph (135kph) to a top speed in the low 90's given enough room and tucked in good.

[HiSPL]

My 82 GS750T was NOT speed restricted in any way. It also had a 140 mph speedo on it. That however could have been put there by its first owner who was a Suzuki mechanic. It was then sold to my brother, then sold to me. It was run over in a parking lot in the summer of 1996. I still have most of the parts in boxes in my garage.

My T model actually seemed to have mored power than my current 81 GS750E. I know for a fact that the cam followers are different in the T. The cam is probably different too.

There has been some discussion about T models being speed restricted somehow. This has come up before and I answered lots of questions about it in the past, however I can't find the thread now. It must have been before Frank changed domains and it was lost.

If this bike truely is governed somehow, it shouldn't be too hard to reverse engineer the problem to provide a free running engine.

Good luck with your search.

[duaneage]

cams

I think the answer lies in cam timing, especially if the valve train parts are different.
The camshaft is known as the brain of the engine since it's profiles determine airflow at given speeds through the head.

The carb is a torque limiting device. It will provide progessively more fuel for a given airflow, carbs are seldom a limiting factor on engines like this. However a camshaft with close overlap on the intake and exhaust durations will purposely limit the amount of scavaging and charging that takes place at higher rpms. Reducing the intake duration will lower peak combustion pressures and prevent higher rpms.

Detroit did this in the early seventies to their muscle cars to lower combustion pressures ( and reduce NO emissions) before they stroked the engines and redesigned the combustion chambers.

my .02

[Anonymous]

My first GS bikes were two GS850GZ's, 1982 models. Both came with that silly 85 mph speedometer. Predictably, I took both of them past that 85 mark more than once.

No harm to either bike or to either speedometer.

Nick

[pano]

My 82 GS1100E came with an 85 mph speedometer. I put the 140 mph unit in that came stock on the 83 GS1100E model. I can assure you the needle does not stop at 85. I think the top speed spec according to the magazines at the time was about 142 mph.

[Jethro]

Also, my 81 1100e had the 85mph speedo. In top gear the speedo would hit 85 at about 6000 rpm, but the tach would keep climbing! I passed my buddy on his Harley once, he said he was maxed out at 110.