Warm Weather/Warm Sled Issues

[Sup3r22]

Hello All. I am gonna get right to business. I have a 93 Indy 440lc. In warmer weather I lose all bottom end with lots of bogging with load or without, cold weather the sled runs great. My clutches are set up perfectly, no cracks in carb boots for too much air. Between myself and 3 other mechanics it comes down to carb problem but all 3 dont know much about them. This is what i have done to the carbs so far. They are very very clean, the throttle needle/clip has been adjusted properly, and air screw is set to .75 (3/4) of a turn. Possiblities for issues are needle and seat wear? 10thousand miles with no change yet. This machine just started doing this for the past 2 winters. It only happens in warmer weather. -10 and above. Any suggestions or help or thoughts would be great. if you need any more info on the sled please feel free to ask. thank you from Ontario

 

[Modman]

Hello All. I am gonna get right to business. I have a 93 Indy 440lc. In warmer weather I lose all bottom end with lots of bogging with load or without, cold weather the sled runs great. My clutches are set up perfectly, no cracks in carb boots for too much air. Between myself and 3 other mechanics it comes down to carb problem but all 3 dont know much about them. This is what i have done to the carbs so far. They are very very clean, the throttle needle/clip has been adjusted properly, and air screw is set to .75 (3/4) of a turn. Possiblities for issues are needle and seat wear? 10thousand miles with no change yet. This machine just started doing this for the past 2 winters. It only happens in warmer weather. -10 and above. Any suggestions or help or thoughts would be great. if you need any more info on the sled please feel free to ask. thank you from Ontario

Do a compression test.

 

[Sup3r22]

Helo modman, thanks for the suggestion. left and right both get 100 to 103. any other thoughts?

 

[Sup3r22]

118 views but no help? Thoughts? or fixes? please?

 

[Modman]

Sorry man, missed this thread on my list.

When you did the compression test, was that with a hot motor or a cold motor?

normal compression should be about 120-130 psi or so, 100 is getting pretty low. I think you might need new pistons and rings unfortunately (my internet diagnosis).

If its harder to start when its warm than when its cold, or it runs better when its cold, that is usually a strong sign that the rings are gone.

 

[Sup3r22]

well it was plus 15c outside and compression was done on cold start and warm motor with the same results, i will put new rings on and see if it helps but still not sure if this is the issue..thanks for the suggestions any more?

 

[takethebounce]

Going back to your carb problems, do you have a carb heater on that sled? I honestly can't remember as its been awhile since I have seen one of the 440LC's.


Most people believe carb heaters are for when its extremely cold. What also is true is the greatest chance of the carb icing is just above freezing or slightly below when there is still unfrozen moisture in the air.

That moist air is sucked into the carb, speeds up the airflow, cooling it down and then freezes.

Its a far fetched idea, but could contribute to your problems.

But yeah 100-103 is pretty low for compression. Are you holding the throttle WOT when pulling the sled over for the compression test?

Last I would try is the coil/cdi pack. When its getting warm its faulting. Used to see this happen on the older Cats.

 

[Sup3r22]

no carb heaters.
wot when compression test was done
no faults with cdi. tried 2 others same results

thanks for the ideas anymore out there?

 

[Modman]

no carb heaters.
wot when compression test was done
no faults with cdi. tried 2 others same results

thanks for the ideas anymore out there?

definitely sounds like rings even more now.

 

[Sup3r22]

but only on low rpms? once the sled has engaged and moving fairly quick no more problems. thats why we were thinking carb/gas/air problem..

would i not get more compression when the sled is running on a warm day since everything will be hotter and expanding...

also put some oil down the jugs and tested with the same results.

 

[Modman]

but only on low rpms? once the sled has engaged and moving fairly quick no more problems. thats why we were thinking carb/gas/air problem..

thoughts?

Its super hard to say without riding it unfortunately. I'm guessing (and guessing here with only what you've told/described to me) that once it gets spinning a little bit, there is enough flow to change how its running and that's why it gets better as the RPM increase. Besides that, you might think it has a lot of power, but once you get it fixed it will be like night and day.

Regardless of the what the actual issue is, you need new rings IMO at 100 lbs compression, at least that's my opinion. Once any 2 stroke I own starts into the 110's, I replace pistons and rings. If it was me, I would do the rings and hone the cylinders, and if that doesn't fix the problem, you've taken out one variable that could be a potential problem.

You seem to have throughly checked over every other peice of the machine (carbs tuned right, no eletrical issues, etc), only thing left is to suspect something in the motor. Low compression leads me to the rings. Did you check the reeds (does it have reeds)? Make sure none are chipped or broken.

Did you change anything in the carb 2 winters ago that would have brought this on?
Did you check the pilot jet and make sure it was clean?
Did you blow out all carb passages with air, take out the needle and seat? Did you check the fuel pump?
Did you check the choke cable and make sure that it was not sticking open slightly (could be a possibility)?
Did you look at the plugs to see if they were plugged up or nice and clean (this will determine your running condition at idle - rich/lean)?
Any change in where you bought fuel?
Any change in clutching? track?
Did you overheat the sled at all?
Is there a mouse nest in the exhaust pipe?
Did you take the exhaust pipe off and look into the cylinder to see if there are any scratches on the cylinder walls or if a ring is chipped or broken?

These are all things I am assuming you did, if not, you should have a look at them first. Things like the choke cable are easy to check and I assumed you have already done this.

 

[Sup3r22]

modman that is a great check list that i have gone over 5 times now thanks

I will change the rings and the choke cable has been adjusted and the carbs have been ripped apart and cleaned very very well. once i change the rings i will let you know if the issue has been fixed....thank you very much and i will post once i get to test it out.

 

[Ancient Sledder]

I had a similar problem on an old Honda dirtbike with a lot off hours on it. I did the rebore and piston, but it did not run right. The problem was the needle and tube that the needle rides inside. Vibration over the years had worn the needle thinner and the tube was larger which upset the mixture.

 

[Sup3r22]

mr sledder. thank you for the reply. i think that is the direction i was looking for and hoping someone had a similar problem i will put some new carb parts in the next few weeks and then look into getting some new rings (thanks ancient sledder and modman) will keep posted on how the sled runs.