1987 Polaris Indy 488 fan with 34m Mikuni Carbs - Snowmobile Forum: Your #1 Snowmobile Forum

Yankeenh · 12-25-2012, 05:14 PM

Hi all I have a 1987 polaris indy 488 fan with the 34m mikuni carbs. I am having problems keeping it running. it will start, Idle high then after about 30-45 seconds it will stall. I have cleaned the carbs including the pilot jet and have the pilot jet fully seated, pilot air screw 1.5 turns out and idle screw 2 turns out. What I have a question about is how far the throttle cable adjustment on top of the carb caps should be turned in or out or if this even makes a difference. Any help is very appreciated. thanks guys!

meburdick · 12-25-2012, 09:23 PM

Idle screw 2 turns out? Sounds like it would be idling at 5000RPM... Do you mean 2 turns in?

Also, what is the exact model of your sled? Based on being a 488 Fan motor with 34mm carbs, I believe it's an Indy Trail. With that in mind, your air screws should be one turn out.

When you pulled the carbs to clean them, did you check the movement of the floats to be sure it was smooth? Did you check the float arm to make sure it was adjusted correctly (you have to stand the carb "on its head" and ensure the float arm is level)? In addition to the pilot jet, there are some passages through the carb for the idle circuit that need to be cleaned out very well. Choke plungers must be adjusted correctly to ensure that a) you get the fuel enrichment when you are cold-starting and b) you do NOT get any additional fuel when the choke is off.

You should also check the fuel pump to be sure that it's delivering adequate fuel to fill the bowls and keep it running.

joshkidner · 12-25-2012, 10:43 PM

second what he said. i believe idle on those old fanners was 2000-2100. fanners run higher than lc sleds. check your fuel pump/pulse line first. then make sure you have no leaks.

dhridenh · 12-25-2012, 10:49 PM

yea idk on idle cus my 96 488 runs about 1500 but maybe i should bring that up and 3x on what these guys are saying about the air passages and the idle screws

meburdick · 12-26-2012, 06:12 AM

1600-1800 on idle is fine for all sleds, liquid or air cooled. Some are higher than others, some are lower. Either way, you don't want them idling too high because it makes the motor unnecessarily warm.

Yankeenh · 12-26-2012, 11:02 AM

I'll check all that out, but I'm not sure if my question got across right. How or where should the throttle cable adjustments on the carb caps be at. and how do I adjust the choke plungers correctly? Factory specs for this are idle=1900rpm, throttle cutaway=3.0(I have no idea what this means) and pilot air screw 1 turn also pilot jet is 35. thanks for the great info guys will put it to use!

meburdick · 12-26-2012, 11:15 AM

Your question came through [to me] clearly, but it isn't "useful" to try and answer exactly what you asked. Here's some info that will likely give you what you need, but is not necessarily in response to your actual question...

Adjustment of the the carb slides is achieved as follows: Pin the throttle wide open and look into the inlet side of the carb. At that point, the leading edge of the main slide should be *just* higher than that of the carb opening. Once you've adjusted the cable for the slide to be in this position at WOT, the slides are adjusted correctly. From there, the slides will be in the same position all the way down to idle.

It's important to be sure that the cables are connected to the slides correctly - so, double-check this inside of the carb body before you start.

Adjustment of the choke plungers may or may not be necessary. Here's an easy test to do:

Use a thin gauge solid wire and bend it at ninety degrees about 1" from the end. Put the choke on full and insert the tip of the wire into the opening that goes from the carb body toward the plunger. Once the wire is fully inserted, flip the choke handle to "off." At this point, you should not be able to easily pull the wire out of the opening because the plunger would be resting on it.

Apply pressure to the choke lever as if you were going to apply the choke. You should be able to apply some pressure to move the cable a slight amount and the wire should then easily slip out of the opening.

Repeat this check for all plungers / carbs. If your results are different from what I described, adjust the plungers until you get the results you need.

Adjusting the plungers is as follows:

There's a jamb nut on the top of the plunger section. Loosen it. If the plunger is in "too far" (doesn't lift out as soon as it should), unscrew the plunger. If it doesn't seat correctly (you can slip the wire out with the choke off), screw it in. Once you have the plunger adjusted to yield the results of testing above, tighten the jamb nut.

Idle anywhere from 1500 to 2000 is fine, and many sleds seem to fall in the 1600-1800 area. 1900-2000 for yours is fine.

I *believe* the cutaway number is a measurement of how much "play" there should be in the throttle control itself before it begins to move the slides.

Yankeenh · 12-26-2012, 02:09 PM

EXACTLY what I wanted to know! Thank you meburdick for going into detail about the slide and choke adjustments. you rock! Oh for the cutaway(play in the throttle) I'm guessing 3.0 is referring to 3 millimeters?

meburdick · 12-26-2012, 02:11 PM

lol...

Tell me that the info was great AFTER you've got yours running well.