Need carb help for an old sled

[kunar]

Alright, so i got a 1978 Polaris Apollo 340 in partial trade for some old junk i had. He said it didnt run, had been sitting a couple years. I pulled the cord, it feels like it had decent compression. Started looking at fuel lines, and that's where (at least part of) the problem was. The fuel tank is goofed up and the line from the tank to the pump was bad. The pump is a round diaphragm style mounted on the crank case of the engine. It's got two outlet ports to go to the two carbs. So i grab a gallon can and temporarily run some fuel line to the inlet port on the pump. pull the cord a couple times and can see it moving fuel through the line. Couple more pulls and it eventually started to spit and sputter. Playing with the throttle, i could get it to run. It was running really rich, to the point that fuel was pouring from the muffler, but at least it ran. So i pulled the carbs off, they're the old zinc style mikuni slide carbs. Not sure what size as the body is stamped 34m but the carb is 26mm id. Anyways, i pulled the bowls off, and one had the float arm obviously adjusted different than the other. got them both in spec for a vm26 carb, put a couple new bowl gaskets on, set the needles to factory spec, button it all back up with new carb boots and everything. Fire it up and its running just as rich and rough as it was before. Now before i throw any more money at it, does it sound like needle valves and seats should be next? I probably should have done it in the first place, but they *look* okay (i know, hard to tell just by looking at them) and im on a pretty tight budget so i dont wanna spend money that i dont have to. BTW, they look great inside, very clean, i poke a wire through the passages with no trouble, blew it all out before i put it together.

this is the first time ive ever gotten into these slide style carbs, or 2 stroke engines for that matter. i might be overlooking something simple, i dont know. any help would be appreciated, i can take pics as well if that would help.

 

[martin]

Long time since I worked on anything like that and also not sure about the carb model however on many of the slide type carbs the slides will stick if they have not been used for a while, sometimes up, sometimes down. I remember lubricating them with wd40 initially and after running for a while they used to sort themselves out. If that's not the problem then needle and seat would be the next thing to go for.

 

[kunar]

Thanks for the reply. Ive had the slides out more than once. they seem to move as they should, nice and clean, no noticeable damage. Anybody know where to get the needles and seats for a reasonable price? Looks like its gonna be $50 or so for two sets.

 

[RonD]

Found this How-to for the carbs, with pictures : http://kawtriple.com/mraxl/carb/carbadj.htm

Assuming air cleaners are off so no restrictions there, i.e. you are not sucking in gas to replace air .
Slider should go down enough to almost cut fuel completely from mains.
And I might adjust the floats lower so overflow can be ruled out.

 

[Mark_88]

I would check the floats again also and reset them lower in the bowl.

Something else that is hard to determine unless you know the parts is the idle adjustment screws (if present) can be damaged by turning them too tight...and they have such fine points on them usually that you can't tell just by looking at them without some magnification.

As with truck or car carbs, there should be (may be) tags on them somewhere that identifies them and you need that to buy anything for them such as rebuild kits. Not sure if they would include new idle adjustment screws thought as they may be sold separately.

This may be helpful, but it does cost less than $10 according to the website...it's a service manual download...

http://www.thefind.com/sports/browse-1978-polaris-snowmobile#page=8&local=0

 

[kunar]

im pretty confident that i have the floats set properly, though the symptoms do lead me to believe they arent seating properly. maybe ill adjust them another 1-2 mm from where theyre at just to be sure. i won't really get a chance to work on it till tomorrow evening though.

there's a few markings stamped into the carb, no tags at all. ill grab pics next time ive got em off, but the markings don't coincide with the actual measurements of the carb, so i dont really know...

no air filters on the sled at all, never was even from the factory as far as i know. two reasons ive heard for this. one is that there's really no dust in the winter, because of all the snow and moisture. the other is that snow can get trapped on the filter and clog it up. either sound plausible, maybe a combination of the two? im still temped to put some universal filters on the carbs though, it just seems so wrong to me!

all the needles are adjusted to factory spec. one holds the slides from bottoming out, so it basically adjusts the idle speed. the other one is called an air screw if i remember right. sounds like these 2 stroke carbs are 100% opposite of a 4 stroke carb, backing out the screw lets in more air (not fuel) so it leans the mix. im still trying to wrap my head around it haha