what is the correct jet specs?

[mrkf250]

just wondering the correct specs for running todays fuel? I had 290 mains and 135 power jets and it melted down the pto side. Now i am running 330 mains and 140 on pto and 135 power jets on mag. I did this per the suggestion of a tech at a dealership. He said these were not to run on todays gas at factory specs. It starts without using choke and plugs are wet at idle. I have the air screws out a half turn. Do i need to turn them out more? I live in northern illinois...Just wondering where to go with this thing for good reliability.

[tyler440]

my sled is running 290 mains and 135 power jets, it runs fine... is all about having those carbs clean, that means more than spraying the outside with carb cleaner... a 290 jet turns into a 100 real fast when i starts getting plugged... then POP!... also if you were to fattan up the mains all the way to 330 you should also need to richen the pilots... i mean thats 4 sizes bigger(300,310,320,330)... what elevation are you at?

[Vmax540]

Temp, elevation, Octane at least 91(look inside your gas cap flange), porting, is your air box stock, condition of carb flanges/boots/crank seals are all factors.
http://www.vintagevmax.com/reliablitity.htm

[mrkf250]

I had the carbs apart soaked them and blew out all the passages. All the boots seals etc are in excellent condition. I checked the seals doing a leak down test. Its just odd how sometimes it runs great and other times it sounds like it only hits on one cylinder. Compression is at 150 psi each side. I am not sure what elevation i am at to be honest. The air box is still stock and it even still has the screen on the back of it. I am just trying to make it trouble free a little rich would not bother me. Plugs are cheaper than rebuilding it again. I have seen people running anywhere from 340 mains down to like the 280's. This is the first time i have ever been stumped on a 2 stroke. At wot my plugs and pistons look great...but getting there is another story. It is either gas and go or fight it taking it up slow.

[Vmax540]

"I have the air screws out a half turn. Do i need to turn them out more?" Remember this is a air screw (2 stroke). Possibly one of the Fuel pumps are weak ? Do a search.... many going to a one dual outlet fuel pump off of any 5-600cc twin cylinder and eliminating the Over engineered/complicated Yamaha dual pump set up.

[mrkf250]

I found my pto side vacume line came undone the other day. Now i am just waiting to find a set of pipes so i can run it again...My other ones kinda started to fall apart. I just dont know if i should switch the mains to a leaner ones or just leave it alone. When it melted down last time i was only going like 45 mph with 290 jets in it. And the carbs were spotless with new filters on each carb...It just sometimes seems to run erratically...Maybe because the pipes had so many cracks? Another issue i noticed is i almost empty the oil res. in one and a half tanks of fuel. I know to much oil will lean them out also. My manual does not really say how to adjust them. Unlike my polaris you lined the dots up on the cam arm..I run this on the chain o lakes here in illinois and i love the looks i get when i ride it. Gotta love the classics.. Justr wish it ran the way it was meant to.

[tyler440]

At wot my plugs and pistons look great...but getting there is another story. It is either gas and go or fight it taking it up slow.

your proplem is not in the main jet then... if it was the MAIN jet it wouldnt show good plugs at WOT which is when the main jet is used... the main jet does NOTHING for you at 1/2 throttle... it has to be above 3/4 throttle to get on the main jet

i think your issue is clutching... clean and inspect the clutches, i bet you something worn out

[mrkf250]

My primary is like new it engages at around 4200. My secondary on the other hand....I took it apart cleaned it the helix and cam slides are all good. But someone messed with the shims. So i took them out except for one and my belt still rides about 1/8 inch low. The spring is set to the factory setting. The sled only had 652 miles when i bought it. I think i have it on c 2 as a setting..
Another thing i noticed is that according to serial numbers i have a 84 motor in a 85 chassis...It looks like it was never touched..so im stumped.

[Bob Vehring]

Any fuel that flows threw the main jet, must also flow threw the needle jet, this is controled by the needle which has 5 clip posistions on the top. This is what governs the fuel in part throtle conditions. Often the hotest EGT happens at upper midrange. If the needles are set to low for the conditions, that will burn you down.

[tyler440]

i just noticed you said it hard clean AIR FILTERS... running without an airbox will make it lean, that could be an issue... and in that cause i wouldnt run the 290's.... maybe 310's but im just guessing

[mrkf250]

So if i am set to rich on the needles that will burn it down also? I was thinking of putting 300 mains in it or 320's. My dealer is out of 310's or should i leave the 330's and raise the needle half way? I read somewhere that if you run ethanol which all gas now a day is to jet up 1 size which would make it 300's. Have these always been this tempermental? I used to have an xc800 with pipes and it was not this difficult..LOL. I appreciate all the input i am getting.

[Bob Vehring]

The question becomes, how well do those filters flow? some restrict, some don't. That will matter.
I run 340 mains most of the time, my engine is ported but not very well due to some hack that owned it before me. I also removed the air box and got rid of the power jet system.

[mrkf250]

I might have miss spoke about the filters. It has a stock airbox but i put new inline fuel filters for each carb.

[tyler440]

oh ok good...

[mrkf250]

They flow fine i believe...There is never any air in the lines. Except when the vacume line came undone. What would be a safe bet for the needle? half way between rich and lean? still can not figure out why the plugs are so wet at an idle. I know like today it is 8 degrees out. by next week it will be 27. will i have to change the clip constantly? Or is there a happy medium?