carbs and small engines

[swynx]

i dont have a ton of knowledge about carburetors. i tore one apart, cleaned it up, and installed it on a 22r, and the truck ran better. that being said.

bought a yamaha big bear 250 4 wheeler, from a buddy. its got an brand new amazon carburetor on it. at the top end of every gear it starts sputtering, higher the gear the worse it gets, especially if your on a long stretch going up hill.

would this be a jetting issue?

 

[Bird76Mojo]

Depends on the size of the carb. It could be too small of a carb to begin with, not allowing enough air. It could also be a jetting issue, and it's leaning out at higher rpm.

 

[adsm08]

I'm told not to trust those cheap carbs you get on Amazon and Ebay. I've used them on lawn mowers before, but those have a bit more stable RPM range.

 

[RonD]

Don't over look fuel flow, it is a gravity feed system so lines/hoses must be clear or you "run out of gas" at higher RPMs.

Drain the tank, remove fittings from tank, check tank and hoses, just to take that off the table

Then you can move on to carb issues

Do you know why your buddy put on a new carb?


You can get inline fuel filters if there isn't one for $5, and GOOD to use on off road vehicles

 

[91stranger]

I have a 2001 bear tracker and its a fun quad. I've taken it in some deep mud too and never got stuck where big heavy 4wd's were getting stuck. These only weight 400 pounds so they are light enough to not get stuck as much. Be sure to shut the fuel petcock off when you are not riding it. I haven't rode mine lately but I start it up for 15-20 minutes and shut the petcock off and then wait for the engine to run itself out of gas. I will say these are some of the easier quads to work on since they don't cover every inch of the motor with plastic crap. I will probably run that quad till it blows up or breaks in half just because I like it so much. Very easy to ride, kids love it, the ol' lady can drive it too. OH YEAH ONE MORE THING. I learned you can pop wheelies on it if you shift all the way down into neutral and instead of shifting into first, hold up on the shift lever and rev the engine and then drop the shift lever and it will pop right up. Once you get it up and running you will like it unless you are looking for a racing quad. This is far from a racing quad but just a good general purpose atv that didn't break the bank like a side by side. Got any plans for it?

 

[swynx]

the carb that was on it was the oem one from i believe 1987, and needed a rebuild. the amazon carb was cheaper than the rebuild kit. i cant remember what issues it was having before. i know it ran great for a long time and then i believe it did not want to idle. tore the carb apart, and turns out his brother put/left ethanol fuel in it.

put this carb on there, and it would idle fine, but needed quite a bit of adjustment to run properly.

the stumbling issues is hardly there in 1-2-3, but in 4th on a long stretch it gets pretty bad going up hill. which i why i figured it was probably a jetting issue.

what is the recomended upsize? like 2 jet sizes?

 

[fastpakr]

What happens if you coast for a few seconds, then hit the throttle again? I'm inclined to agree with Ron and question fuel flow to the carb. On a long open throttle period, you may be draining the flat bowl.

 

[Bird76Mojo]

http://all-offroad.com/main/2014/03/overview-jetting-101/

http://www.iwt.com.au/mikunicarb.htm

https://www.motosport.com/blog/a-simple-guide-to-jetting-your-carb

https://www.thoughtco.com/how-to-diagnose-carburetor-problems-743503

 

[alwaysFlOoReD]

3rd on fuel flow issue. It sounds exactly like clogged filter or partially clogged line. The carb has enough gas in the float bowl to idle and drive at medium speed but once you crank on it the fuel doesn't flow into the float bowl fast enough to keep up with demand.

 

[swynx]

if im coasting whether it be at high speed or low speed and then mash the throttle its fine till i get passed about 3/4. i know that it has a brand new filter on it, im not sure about the line tho. ill have to take a look at it.

 

[Bird76Mojo]

From one of the articles I posted earlier:


"4) Main Jet – This circuit affects the mixture from 1/2 throttle to full throttle. This is your full blast top end circuit. This circuit is most accurately tuned by checking the plug for the correct color, sort of mocha brown.

5) Float/Float valve/Float level – Your owner’s manual has the correct level and procedure for calibrating your bike. Here are some symptoms that would indicate the need for float adjustment.

A) If float level is too high, the float bowl overflows out the drain hoses, and fuel often blocks the air passages that allow the carb to de-pressurize. This causes a bog, or hiccup over large hits.

B) If float level is too low, the engine starves for fuel off idle, causing a “boooooowang” sound very similar to a pilot jet or air screw set too lean."

 

[swynx]

From one of the articles I posted earlier:


"4) Main Jet – This circuit affects the mixture from 1/2 throttle to full throttle. This is your full blast top end circuit. This circuit is most accurately tuned by checking the plug for the correct color, sort of mocha brown.

5) Float/Float valve/Float level – Your owner’s manual has the correct level and procedure for calibrating your bike. Here are some symptoms that would indicate the need for float adjustment.

A) If float level is too high, the float bowl overflows out the drain hoses, and fuel often blocks the air passages that allow the carb to de-pressurize. This causes a bog, or hiccup over large hits.

B) If float level is too low, the engine starves for fuel off idle, causing a “boooooowang” sound very similar to a pilot jet or air screw set too lean."

i did read those, thank you for them. gave me some options to mess with. going to start with the simplest thing first

 

[rusty ol ranger]

It doesnt have a vaccuum pulse fuel pump does it? My polaris 500 would do the same shit till i realized the pump was unhooked