1986 ATC 350X

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This ATC has the biggest engine ever put into a mass produced 3-wheeler. Most reviews from the mid-80's say that not much gets in the way of a 4-stroke 350x, IF and WHEN you get it started. I understand that this is a common problem with big-bore 4-strokes. My right leg is about twice as strong as my left due to the many minutes of kicking this machine when I kill it at the bottoms of hills. Sometimes, it starts right up, other times, it takes several minutes of exhausting kicking. Oh well, the price we pay sometimes for our fun...

Anyway, I just can't leave anything stock. It's just too much fun to tinker with something to get it to be different from everyone else's stuff. Some of the mods done to this ATC were done by the first owner, and some were done by me in 1991, when I bought it for $800. That was definitely the best $800 I ever spent!
I ride exclusively in the sand, so some of these mods may not be appropriate for your riding conditions.
38 mm Mikuni carburetor (part number and jetting unknown)
Supertrapp exhaust (part number unknown)
Valvoline synthetic oil
K&N air filter
Airbox vents
Lowered from 13 inches of ground clearance to 6 inches by:
Relocating rear shock mount
Removing small fork spring
Reclamping forks 2 inches up
Remove front fender for better cooling
Add 21x12x8 Sand Tires Unlimited Sand Skate I rear tires
Remove engine and swingarm skid plates for weight reduction
Tether kill switch
Aftermarket "D" handlebars
Scott handlegrips

With the mods done on this machine, I can keep up with and occasionally pass my riding buddies on their ATC 250R's and Fourtrax 250R's. A lot of the time, when we are racing around, they will miss a downshift, and get out of their 2-stroke's powerband. The 350x 4-stroke powerband is much wider, so I don't have to downshift as much, and I go right around them. Flat out, 250R's are faster, but just playing around, we are much more closely matched. When it comes to reliability, though, the 350x is much better.  All I've had to do in the 9 years I've owned it is change the oil regularly and adjust the valves once.

Relocated Shock Mount

Here is the relocated shock mount.  As you can see, the Honda forging is gone, and the shock has been attached to the lower of the two swingarm bolts.  Since the lower bolt flanges are spot-welded to the swing arm, there must be a method to transfer the load from the lower bolt to the top bolt.  I found two pieces of 1/2 inch steel and made the first hole at the top the same diameter as the upper bolt.  Then, I bolted the Honda forging to the steel pieces and used the Honda forging pattern to drill the lower holes in the steel pieces.  Since the lower shock mount is larger in diameter than the lower bolt, I made a bushing out of some tubing to make the fit tighter.

Carb Swap

A couple of people have asked me technical questions about the 38mm Mikuni swap.  It's not a straight swap for the stock carb, so here are some tips.

Throttle Cable: The cable tip of the carb end for the Mikuni is different than that used on the stock Keihin.  The Mikuni uses a small cylinder acting directly on the slide, whereas the Keihin uses a large puck on a linkage.  The best way to find the right throttle cable is to take the old throttle cable and the new carb into a local motorcycle shop for them to find you one.  They may have to even order it, but mine was an off-the shelf unit.

Air Supply: The next problem is getting the stock air inlet hose to fit over the Mikuni.  It doesn't.  The throat of the Mikuni is considerably larger than that of the Keihin, so an adapter is in order.  Take the Mikuni to a full line auto parts store like NAPA and get some fuel filler hose and worm clamps to fit the throat.  Then, go to a hardware store and get a piece of ABS coupler that fits inside the hose.  Cut off the small end of the Honda hose right about where it comes to the crankcase vent.  Grind off the ribs on the Honda hose to make it so it will expand, and use a blow drier/heat gun to expand it to fit the ABS coupler.  Then, put the gas filler hose in there as a splice using worm style hose clamps from the full-line auto parts store.  As you can see in this photo, the stock Honda hose fits so tightly onto the ABS coupler that no clamp is needed.  I don't even think I could get it off if I wanted to!

Now, if only I could get the darn thing started....

NOTE: I received the carb and exhaust as part of the purchase of the 350x.  I do not know the part number of the carburetor or exhaust, nor do I know the jetting in the carb.  If you are trying to do a swap, my jetting will not work for your machine anyhow, since we don't ride in exactly the same place in the same manner.  You MUST figure the jetting out on your own, as every machine, riding terrain, altitude, engine condition, and a host of other factors are different, and will change the jetting requirements.  In other words, don't ask me about jetting!

200x and 350x


Flying at Pismo!

This is my older brother, Fred, at Pismo a few years ago.  In the photo above, he landed on another blow sand hill above the one he just left, and motored right on up.  This manuever is very difficult!

This is the large hill in the back of Pismo Dunes.  It was a windy day, during the week, and we were the only brave souls out there.

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