Slow yamaha on incline
 

UPDATE !!!!! With all the great advice from all… I jacked up the cart .. removed skid plate .. removed spark arrestor .. took 20 minutes… results are wayyyy better acceleration … no bog on hills … top speed went from 21 to 23 mph .. arrestor was very clogged with carbon .. a black hands job … thanks to all !!

Issue … A 2017 Yamaha quiet tech.. runs great at 21 mph on flat but slows on incline .. going over bridge at Spanish Springs slows to 5 or 6 mph on steep incline .. is this normal or is my belt needing change etc ? thanks

Ever had any maintenance done on this vehicle like a belt change? If not, that may be your answer?

Does the engine seem to be running at a normal speed or bogging down when you go uphill? Does it sound as fast as when you are on the flat but just moves more slowly or does it sound like it's having a hard time?

If it sounds like it is running regular or fast but the cart is moving slowly then you could have a belt or clutch problem. If you haven't changed the belt in years then it couldn't hurt to try that. If you haven't lubricated the clutch in years then that could be an issue. And, eventually parts like the clutch just go bad.

If the engine is struggling to get up hills then it could be bad gas (unlikely), needs a tuneup, or it could be an issue with the clutches sticking in the high-speed position rather than moving to the high-torque position.

Sorry, no good answers but maybe some things to look at.

You need to remove the spark arrestor. A spark arrestor screen is a device designed to prevent fires by stopping sparks or flames from escaping. There are two common types:
Screen type: Uses a metallic mesh to prevent large particles from leaving the exhaust system. Commonly used on motorcycles, ATVs, golf carts and small engines.
Known to cause your issue.

We had exactly this problem. Clogged exhaust. Apparently they make these quiet by packing a lot of insulation in the muffler. It can work itself loose. Replace muffler.

Do not remove spark arrester. Can’t believe I had to say that.

Definitely could be the spark arrestor. In general, QT’s don’t have a lot of power relative to other carts since they have a smaller HP engine as part of the design to make them quiet. Also, the spring in the secondary clutch is designed for golf course use where the carts don’t go more than about 12-14 MPH. Yamaha adds high speed gears to their Personal Transportation Vehicles used in the Villages, but doesn’t modify the clutch spring. Adding the high speed gears increases top end speed but can compromise torque (start up speed and hill climbing power). An easy modification will solve the problem, which involves putting a stiffer spring in the secondary clutch and replacing the belt with a premium aftermarket drive belt. I did the modification to our QT using the green spring and premium belt available from powerequipmentman.com and there is a noticeable performance difference (not top end speed, just torque). The website also has an excellent YouTube video showing how to do the modification. It does require some basic mechanical knowledge, and two specific tools that most people don’t have, a clutch compressor and a snap ring tool. My neighbor up north loves to fix stuff and helped me fabricate the clutch compressor and let me borrow his snap ring tool. I’m very happy with the modification, but the cart definitely was a little jumpy for a couple days until the new belt broke in. I keep the old belt in my cart as an emergency backup and hope to be able to use it someday to help someone stranded with a broken belt.

Regardless of the problem, it’s a good idea to remove the spark arrestor next time you change the oil and you have easy access to it. You will be eliminated a potential future problem that is only there because of a stupid California requirement. The cart will run better and you will only notice a slight increase in noise when driving through tunnels or alongside a dividing wall.

Wrong.

No, that’s not normal.

Sounds like you need to take it to a repair shop unless you can do it yourself.

Totally agree. I had the same problem slowing excessively over the bridges. Had spark resister removed and problem solved. Many friends had same problem and same cure.

I took a large Phillips screwdriver and punched a hole in the spark arrestor and immediately noticed an increase in performance. I also suffered to failure of the secondary clutch, had this repaired, and they noticed I had the wrong drive belt, the replacement of both of these items made a big difference. I have never experienced a slow down on our 2017 like you are describing, so I am GUESSING a belt or clutch problem.

Had the same problem re incline speed. We did, as others have suggested, and removed the spark arrestor and problem solved for us.

Secondary clutch(the one in back)
 

Plugged spark arrestor affects performance at all speeds eventually. Our 2018 slowed to a crawl with a plugged arrestor. Punching a hole through it
fixed that issue. Put on a new secondary clutch purchased from powerequipment man and problem solved.

I had the same issue with my Yamaha Quiet Tech last year. I had a clogged spark arrester. Your cart will only get worse. I cleaned and drilled small holes in the arrester. The arrester is about three inches long and is located at the end of the tail pipe. There are YouTube videos on how to get to and remove it. I think you can get to it from underneath the cart but will need to jack it up. I got to it from the top after removing the seat and the muffler. It takes time but will save you money. If you are not mechanically inclined, pay someone to do it. My cart now runs normal.