I recently posted a concern about my Bruin 350 4x4 running poorly after getting wet. A yamaha dealer said that the steam coming off the engine when it gets wet is being sucked into the intake causing the mixture to become affected which caused the poor running for a couple minutes. He recommended me to re-route the intake hose up and away from where it originally is. Well I did that with pvc and fittings. I basically extended the pipe straight up and cut a hole in the plastic that goes over the gas tank. The end of the new intake pipe comes out near the fuel cap.. When I went to test the quad it wasnt running right. low and middle throttle was ok but when upper range throttle was used it didnt want to really accelerate anymore and it was almost like the choke was on. The mod I did had to definately add more air to the mixture. What would be the best way to fix this problem?? Has anybody done something similiar to this on their Bruin 350 4x4?? Thanks for your help and opinions.

 

Let me take back "low and middle throttle was ok but when upper range throttle was used it didnt want to really accelerate anymore and it was almost like the choke was on" All I know was I took it for a two minute ride and I applied full and it just didnt want to really accelerate. It felt flat and didnt rev like it used to. That seems like a more accurate experience I was having. Sorry for the confusion.

 

What you did created more resistance to air flow, which means less air will enter the motor than before you extended your snorkel. That will cause it to run rich, and is most likely why you lost power. The solution to this would be to get your carb rejetted with a smaller main jet. Using a larger diameter piece of pvc could also minimize the restriction. What size pvc did you use, and about how long is it?

 

Im not sure I understand how you think I decreased my air flow. No additional bends were used and only about 8 inches of straight pvc pipe was used (2" dia.) The opening is now out in the open with no obstructions where as the original design is down underneath the seat and gas tank area.

 

If the only thing you changed before it started bogging down was the snorkel then that almost has to be the cause of the problem. Did you change anything else or did you just extend the snorkel? Try taking the pvc back off and see if it runs right. I can't come up with any ideas other than that snorkel restricting airflow. I guess it is also possible that you increased the airflow and now it's running lean. It's hard to tell for me since I don't know exactly what the bruin's intake system looks like.

 

I agree, the tubing causes a distrubance and a reduction in air flow. Youll need to jet leaner, to get some of the performance back, or go to bigger diameter pipe. Its complicated as to how air or fluid flows in a pipe, and it doesnt take much to upset or restrict the breathing. But from the desriptions you give...its too rich.

 

Well is there a way I can test the new system currently to see whether it is rich or lean?

 

The easiest test for you to do is to read the spark plug. You need to buy a new spark plug, and install it. Then you need to make a wide open throttle run through the gears, and hit the kill switch before you release the throttle and stop. Remove the spark plug and check the color of it. If it's black then you're running rich, if it's a grayish-white you're lean, if it's a tan color then you're on target with your jetting. This needs to be done with a brand new spark plug. Let us know what the results are.

 

You could also prop the air box lid open, about 1/2 inch, this will lean it alot.
Or try pulling on the choke when the motor is stumbling. If it runs worse, then its already too rich. If it runs better, its too lean.