'88 Exciter runs OK, then bogs down

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rkhanso

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I am new to snowmobiles. Just purchased a used '88 Exciter 570.

It starts fine, runs good for quite a while, but at some point, it'll lose power and not rev over 3-4000 and not have enough oomph to get the drive going. I think it happens after I've let it idle for a while.

After shutting the engine off and checking the sparkplugs, they are really wet. They're pretty new plugs and aren't very colored yet - still mostly white.

The guy I got it from (he didn't ride it, just found it for me and fixed it up a bit) lubed up the choke cable since it was stuck (I broke the lever), but the choke lever/system seems to be working OK now. Prior to me initially picking it up from him, he cleaned the carbs and did some other minor fix-ups.

When it runs good, it really moves. It's got a lot of power and runs great....until it won't get the RPMs up enough to take off. It starts really good, too.

Before I got the snowmobile, I think it sat for a couple years.

No, I haven't replaced the plugs yet, but will get some today and see if that makes a difference....but it's raining today here in central MN and I may not get it out again to test the new plugs for a number of days.

Anything else I should check?
 
Have u checked the fuel filter in tank....they get dirty and dont provide sufficient flow ....could be the problem, wet plugs tells me it isn't that , may be the ignition getting week spark once hot...thats not at all uncommon . My sled was just recently doing the same and it was the filter, it looked good but nothing above 4000rpm, it would bog down and if i held it there it would go to one cylinder and backfire a bit....put in new filter and perfect.....worth checking, easy and cheap.
 
forgot to mention...it has BR8 plugs in it. I saw that BR9 is the factory recommended plug. Again, not that I know anything about snowmobile engines, but it seemed to me that if I'd switch to BR9 (a colder plug, I think) the problem may be worse? I haven't purchased new plugs for it yet. Recommendations appreciated.

I don't see any leaking fuel under the hood anywhere. When the choke cable was gummed up and not moving, you could start the cold engine up without using the choke at all. I just tried it and can still start it w/o using the choke...but it's about 35 degrees in the shop where it's sitting.

Regarding the filter and gas: the guy I bought it from (an auto mechanic and Yamaha snowmobile fanatic) drained and cleaned the tank. Not sure if he replaced the filter....but I'd also suspect that's not the problem since I'm getting too much gas. Is there a way to check for quality and consistency of spark?
 
what about needle and seats. that will cause that issue for sure if they are getting old, they will do that. I can alsmost garantee its not the plugs number. those numbers will both work, yes the b9's are colder but also the right plug for that machine.when ignition works good cold and then not good once engine is totally warmed up that usually is a sign of a week or bad stator coil in any sled. cheers good luck...happy new Year!!
 
I replaced the plugs and it appears that the problem is still there. I'm wondering if the idle mixture is way off. It still starts from a cold engine in 10 degree weather without using the choke. The plugs are still wet looking at them after it's been shut off.

I'd like to adjust the carb according to pages 2-68 and 2-69 of the manual (Low Speed Tuning section) and see if that helps with this problem. There's not much room near the idle mixture screw. How in the world am I supposed to get a screwdriver in there to adjust it? Is there a special tool for adjusting the idle mixture screw?
 
Your wasting your time, try the above suggestion, those fine adjustments your attempting wont fix your problem, If its boging down, it either has way too much fuel or not enough..... Fine tunning your carb is not going too change that. It might idle a little smoother , but thats it...don't touch them...Are u sure the choke plungers in carb are not sticking out after u take the choke off.....cause that is a known problem for these sleds.... If it wont move after its warm when its not needing all that fuel it uses when the engine is cold...then I would guess its getting way too much fuel. No fine tunning is going to help u here.Again....stuck choke or needle and seats . Keep it simple.....why would the carbs be so out of wack tunning wise that it wouldn't run properly. Something happened to this sled and they sold it, now you must fiqure out why its not running right....it wont be carb tunning...I can almost garantee.
 
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I just lived with this problem the rest of last riding season, but am going to tackle it again before it snows.

A little more info, to maybe help out.....

Last year, it only made about 40-60 miles per tank. Doesn't that seem to be going through a lot of gas? Related to the boggy/misfire problem after idling or ridden slowly?

Someone I talked to thought it may be a hole in the fuel pump diaphram causing gas to get into the engine. I'm not sure how that all works, but I did get a rebuild kit for the fuel pump and will put it in this week.

I think the problem of no power, after the symptoms started - it was running on only one cylinder due to the wet spark plug.

If I drive it 1/2 to full throttle, it will go all day with no problems.

Since the airbox is out now, I'll also look closer at the carbs/choke. I do remember that last year, I could start the engine in the cold weather without using the choke. Maybe that's an indication of one or both of them not releasing all the way?
 
i would check the chokes,make sure there is some slack in the cable and there down all the way.then i would unscrew and carefully lift them out and set them aside,pull the choke lever and see if they move ok,then look in the hole and make sure thats clean.every time i had junk in the needle and seats gas flowed out my overflow vents like crazy.my exciter will never start without the choke on when cold,i remember around 90 miles to a tank for mileage,hope this helps and dont lose any parts,the chokes are spring loaded
 
Chokes like dsc557 said. Cable routing is also critical. I've seen them (chokes) get pulled up a little when the bars are turned on many different Yammies. The manual has a routing diagram for everything.

Go through everything and make sure it's right in accordance to the book.

Worked on every stock Yammie I have messed with.

opsled
 
yes check the chokes but the way it sounds you have other issues check the crank seals by spraying a little carbs spray around the clutch and in by the recoil and se if things change but when you have the carbs apart check the needle and seats if they are the all metal genuine yamaha ones they are most likely junk and can cuae the problems you speak of put a set of genuine mikuni 1.5 viton tip needle and seat in it if you put the over priced yamaha ones back in you will have the same problem in about a year ..............i could go about 90-110 miles on a tank of fuel on my 88 570 and that was with givin her

Nutz
 
I have one of the carbs out so far (I think the on the side that had the trouble - but not 100% sure).
After taking the bowl off, I see that one of the floats is pretty sticky. I tried to pull on the pin that holds it in, but don't see how to remove it to clean. The other side float moves freely.

IMG_20110929_135558.jpg


Not sure if this is a real problem since one side is working OK, but I'm guessing it could be. How do I take this out to fix the stickiness? I don't want to break/bend anything that shouldn't be. I also noticed that the arms (seen to the right of the bottom/bowl of the carb- where the floats touch to shut off the fuel) - is kinda sticky, too.

Also, would it be a good idea to just put a kit in each carb (assuming they make carb kits for these)? That gasket looks pretty nasty.
 
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the caps on the ends of the pins snap on and off.just pull and twist,fill the bowls with water,hold the floats down and check for air bubbles,
 
no holes in the floats.

Maybe with fuel in the carb, it lubes everything up so it moves more freely?

Since I'm taking the carbs out, I'd like to make sure that I do everything needed to them...so I don't have to take them out again soon.

Is it a good idea to get a kit? Replace the gaskets? Unnecessary?
 
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pull the float out,theres a metal liner that slides on that post,clean it all up,it should move freely.gaskets are fine,take out that needle an seat while youre in there,
 
dsc577 said:
pull the float out,theres a metal liner that slides on that post,clean it all up,it should move freely.gaskets are fine,take out that needle an seat while youre in there,
Click to expand...
When you say float, you mean the 2 separate black floats? I did get them off and cleaned the shaft. They slide easier.
The other part I saw sticky were the arms that the floats go up to touch....that push the needle up into the seat. That's sticky on the horizontal shaft it pivots on. Does that pin get pushed out to take that apart? And, it looks like I need to remove that piece to get to the needle/seat, right?

BTW, thanks for the help.
 
yea,floats are those two black things,that shaft does need to be moved to get at needle and seat and that plate should swing freely,no resistance at all,need to slide shaft over,see which way its been moved before and with a small punch or nail pop it loose,be carefull not to bust the whole post off it slides threw,then remove spring holding needle in seat and then put a socket on seat and remove it,
 
OK. got the float/needle arm moving freely. The needle and seat look good to me, but it is the solid metal only type. Should this be replaced with the other mentioned above?

Or, if that's all that needs to be done, I can put it back together and start to clean up the other carb?

I'll search the web for how to adjust the float level before putting it back together. I'll also check to make sure there's free play on the choke cable/assembly after putting it back together, and that the choke moves freely.

IMG_20110929_184318.jpg
 
yea thats what i would try after you remove and clean the main jet,nozzle and pilot jet,after you remove the main jet pull the part it screwed into out the top,crud can get in there to,pilots clog easily also,write down all the numbers for future reference such as 166-p6 nozzle,320 main,42.5 pilot
 
I noticed on one of the carbs, there was a washer under the main jet (I think that's the main jet, anyway), but not one on the other. I'd guess this would cause a difference between the 2 cylinders.

Is it important to find something to put in there? It appears to be part# 35A on the Mikuni exploded diagrams for the VM carb.

[##EDIT##] - Going to the local hardware store, I found a washer that is 'close' to the right size in diameter, but too thin. If I put 2 of them together, it's just a hair bigger than the washer in the other carb. [/##EDIT##]


IMG_20110930_135322.jpg
 
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I put everything a back together (with 2 washers under that main jet?) and it runs. It doesn't run very well, but it does run.

It appears that the choke cables have about 1mm or a little more play when it's fully released. When you put the choke on and release it again, one side seems to be a little sticky....maybe. I may need to make some more slack in the choke cable.

Do I have to do the special coolant bleeding process (I suppose just at the head bleeder bolt) after replacing the carbs? The coolant level went down, but I don't know if it's enough to have to bleed the system.

So, what I did:
Put in a fuel pump kit
clean the carbs and blew it out
adjust the carb float level to about 17mm
replaced the exhaust manifold gaskets
put it all back together
started it up

It seems like it may be mis-firing, it doesn't idle well, it won't rev up easily.

One thing I know I messed up on...when putting the airbox back in, the throttle valve/bore thing (that the throttle cable is connected to) long needle thing got bent about 1" from the end. I straightened it the best I could. It appears pretty straight, but I'm not sure if that would cause any trouble.

Turning the choke on when it's running kills the engine, which is good.

I'm not sure that adjusting these carbs will be something I can do. I may end up taking it in.
 
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