Taming Suzuki’s TM400 Vintage Motocross

18 May 2015 | Author: | Comments Off on Taming Suzuki’s TM400 Vintage Motocross
Suzuki AN 400 S

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Taming Suzuki’s TM400

Came across this 1972 test in a DIRT BIKE magazine to tame the 71 – 72 TM400 Cyclone motors, I have heard of other solutions using the TS400 ignition systems but I have not found any written tests on that yet. Not sure if the 74 model needed the same treatment as the 75 TM400 was said to be ok but by then the RM series were out and that was the end of the TM’s.

A BOLT-ON SOLUTION for TM400 sweaty palms?

Some people have this healthy fear of snakes. Others cringe inwardly when they find themselves alone in a dark room. Yet others can’t stand being up high, or even worse-flying in an airplane.

All of these fears pale by comparison to the fear-inducing potential of a stock 400 Suzuki MXer. This is one of the truly Frightening Machines Of All Time.

What makes it increase your pueker power? Part of the problem lies with the frame. another part with the suspension—but the bulk of the guilt lies with the power band of the engine.

There is no such thing as “just a little more” from the twist grip on the TM 400. Nosirree. You either get a giant handful or the engine stalls. This phenomenon is, of course. caused by the lack of flywheel weight.

A logical cure, then, would be to bolt on some weight to slow the rev buildup down to a more usable level. Remember, power that does not get to the ground is wasted power. And slower building revs mean that the bike will be easier to ride.

At least in theory.

And that’s why DIRT BIKE decided to test S0me of the bolt-on flywheels currently on the market. Woodland Hills SportCycle supplied the bikes and the equipment for our controlled testing. Along with our intended test of the 400, a flywheel was also bolted on the 250 MX.

Even though this model doesn`t have the jolly gruesome of the larger machine, Woodland Hills SportCycle claimed that it makes the 250 into an easy to-ride trailbike.

The bikes were ridden in standard trim first, to get the feel of the stockers. If you read the test in the October “72 DIRT BIKE, you’ll remember that we were favorably impressed with the power band of the 250, so we really couldn’t see why SportCycle offered heavier wheels for this bike. Their reasoning was that some people might want to take the 250 trail riding or something of that nature.

They claimed that the addition ol their flywheels would allow the rider to bog the engine down to very low r’s. Would we test the 250 also? Sure. Why not?

Our other machine was a brand-new, totally stock 400 Cyclone MX. For this machine, we had two separate flywheels to try. A 2-pounder and a 4·pounder. We chose the heavier item.

Off to the trails went the DIRT BIKE Wrecking Crew, with two Suzukis in tow. Both, as previously stated, were first ridden stock. The 250 was as we remembered it—decent power and very rideable. It could be ridden at very low revs for a racing machine low gear would let the machine move forward at a walking pace with the clutch out, just above idle.

Any slower than this and it was necessary to slip the clutch to keep the engine from stalling.

A 2-pound flywheel was then bolted on the 250 (after a trip back to the shop). The 250 will not accept the 4-pounder—2 is the maximum.

An immediate difference was felt in the engine performance characteristics. Not all of it desirable. While the engine would lug down lower and smoother, engine response was sluggish. Not only did it take too long for the revs to build, but it also took a great deal of time for the engine to return to idle when the throttle was shut off.

Much like a trials machine.

One additional factor made itself felt: The rear brake was less effective and had difficulty slowing the bike down. This will always be the case where heavy flywheels are working against brake shoe efficiency. In the case of the 250 Suzuki, however, it never had a giant reserve of brakes for starters, so this cannot come under the category of a Good Thing. No way.

A rider who installs a heavier flywheel on the 250 will find his lap times on the motocross course getting slower. For trail riding? Even though we feel it makes the engine more tractable, the undesirable side effect on the rear brake makes us hesitate to recommend its use on the 250.

Unless the rider modifies the rear brake to be more efficient.

Our attention turned to the 400. First a ride on the bike in standard trim. Culp. The merest tweak on the throttle produced a spinning rear wheel. Or if there was a modicum of traction available, the front end would leap for the nearest cloud.

If contact was made with a series of harsh bumps, the machine would slither and hop sideways in an instant. Coming out of a corner under heavy power was a true adventure, indeed.

Back to the shop and zip-bam-boom—there we were with a heavy wheel bolted on. This one a 4 pounder. Back to the riding area, and a pleasant surprise. That 4—pound slab of steel did astounding things for the 400 racer. No kidding.

Without taking a single iota away from the top end of the Cyclone, it made the power band almost pleasant. Additionally, much of thc tendency for the rear wheel to lock up under braking was eliminated. Unlike the 250, the 400 had an overly sensitive rear brake.

This is the best thing, the single best thing a rider could possibly do to a stock 400 Suzuki. In Fact, there really ought to he a law requiring the installation of the 4-pound wheel before the bike can be sold.

Much of the sideways hop disappears and the machine is infinitely more tractable. The bad handling is still there, but even this is helped considerably because of the more predictable throttle reaction. One can almost trail ride the bike—but not quite.

We would recommend that the rider go for the 4-pound flywheel rather than the 2 on the 400.

Woodland Hills SportCycle offers these wheels either mail order or at their high-rolling shop. The address is 22726 Ventura Boulevard, Woodland Hills, California 9136-1. Phone number (213) 340-2191.

Tab for the items is $19.95 For the 2-pound wheels and $23.95 for the 4-pounders. They pop for the postage if prepaid and you get burned For the tab on COD stuff. If you stop by the shop, they’ll install the wheel For Free.

Providing, of course, you bought it there. Don’t expect much more than a nice smile if you bought yours in Wilmington, Delaware. Oh yes.

They have all manner of trick items for the Suzuki line of dirt hikes and will send you a free brochure if you want to gamble a stamp. It’s your stamp.


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