what is the correct jet specs?

[Bob Vehring]

What are you refering to as a vac. line? the lines from the lower case to the bottom of the fuel pumps?

If the needle circut is to rich, you will loose power, if to lean it could burn it down.

Have you checked that ALL jets are the right numbers. The specs are listed on the ft page here.

Most all sleds from the factory come jetted rich to protect them in any weather conditions. Many riders are happy with that jetting set up and never change. If you want the engine to be crisp and clean you have to jet it down, as you get close to the edge, yes you do have to change as the weather changes. I have my SRV and Cat to where I only need to raise or lower the needle for anything between 30 and 0. My VM someone else worked on before I bought it, its a mess. I'm working on a different engine for it but haven't got it done yet so am not happy with it yet.

Where in Northern Il. I'm in Wacunda most weekends at the Snow x races on 12 and 120

[mrkf250]

I found the vacume lines for the fuel pump had came undone...I just bought egt gauges so now i hope that will help with tuning...Just not sure what temps it should be at..And what the max temp should be. I live in Antioch IL. I run the chain all the time so i dont want to burn it down...

[Vmax540]

~1250-1300 but...... Different engines have different max readings, depending on fuel, engine tune, exhaust and probe placement ect. so, it is best to note your piston wash and plug readings and Correlate all three that way you know where you want to be and not go over that temp readings.

[Bob Vehring]

The factory puts it out with their jets they feel will be safe in most situations. That will work for most people. If you don;t like changing jets or moving needles stay on the safe side of the factory recomendations. That should be safe unless you very cold.
Other things do come into play. Stock jetting is often rich for the temp of the day, some people jet to get back that power, but you have to stay on top of it. Another circomstance is worn rings and / or low compression, the engines does not draw fuel as well if its worn. A sealed up engine simply sucks harder through the carb and draws in more fuel. Have you checked that all the right parts are in your carb?

[mrkf250]

I put 300 mains in and 135 power jets. My compression is excellent. But it seems to backfire through the pto carb when i get on it hard. Would that be the needle is to rich still? I have them set in the middle position. I also noticed that the pto side seems to run a bit hotter like 100 degrees or so. If it gets to much fuel does it run hot also? I also wonder with the oil consumption of this thing if that is part of the running issue. It uses like the whole res. in a tank of fuel and the cable is adjusted the way the manual says to.

[chrisrider63]

why dont you set it up stock with an airbox it would eliminate a lot of tunning and they run awesome stock, i dont know why you guys take one of the most reliable liquids ever made and f)*&(&k with it. You will go fast by keeping this sled stock and making minor adjustments to clutching.

[mrkf250]

It is completely stock airbox and all. But when i first got it it blew the pto side piston due to to low of a jet. It runs great with the exception of the popping through the carb. The person that owned it before me had his hands into everything except engine internals. So all i am trying to do is make it reliable and quick..Not to worried of being the fastest having kids took that out of me. Just want good reliability.

[mrkf250]

Also i just looked and found out i have 6dh7 needles...Can that be a problem?

[Bob Vehring]

Theres a chart of the jetting specs in the referance section, if you not looking to really tune it up, start with what ever is listed OEM. Sorry off hand I don't know what was stock.
I have to disagree on Yamis choice on the carbs here. For two reasons. One with the stock PJ carbs, unlike a regular 38 where the main points down and sits inside the little well of fuel in the brass plug, these carbs have the main pointing up. Tha almost an inch higher in the float bowl. If your bowl runs low, if the fuel sloshes to one side during cornering, being that high, it could suck air much easier. Sounds like an EZ burn down to me. IMO theres not much use for the PJ, at anything other then WOT, the needle is in the tube to some degree and controling jetting. If i need to change things in the mid range I can do it with the needle and the tube. At WOT things are controled of the main, again if I need to I can change that, why have the extra circuit? I understand the principle of atomizing the A/F better, but if it was such a great idea, I would thing many performance sleds would have came with a PJ carb, few did.

Speaking of potential problems, I never understood the thinking on the oil inj. on these, The oil is put in way back by the pumps ( why are their two pumps? My 617 Rotax makes 145 hp on the same single pump as everyone else uses). I know the story was to prevent the slides from sticking, they don't stick in any of my other sleds. What worries me is, if your cruising around at a slow speed, the oil pump is puting out minimal oil based on throttle position. Now you pin it, you have a very lean oil mix both in the bowls and the entire lenght of the lines, and you 8600 at WOT. You blast all the way across the lake and back down to cruise, now the reverse is true. Your bowls and lines are filled with overly rich ( for part throttle) driving, somehow, if this makes sence, I'm missing it. I change to regular float bowls, plugged the PJ's off, and premix.

BTW Chris, the reason I play with all my sleds is, when someone pulls up next to me, with a sled just like mine, I want to win

[tyler440]

bob, here is something to think about with that oil injection issue... tho i dont totally disagree with you, where does it ever say that the amount of oil pumped is more or less or a ratio at WOT than it is at idle?

i dont believe there is anywhere that says the oil is mixed at a certian ratio at idle and a differant ratio at WOT... maybe there is but i dont know.
so my defense for the oil injection is that possibly the oil is always being injected at say 40:1 no matter what the throttle position. in this case it wouldnt matter how long the fuel lines are or how you run it. correct me if im wrong your certiainly more of a engineer than i am

[mrkf250]

All i know is when i dump the fuel out of my carbs after idle or WOT it is dark as smurf piss..And the cable is set to spec. But it loves to drink the heck out of that oil. Last night i put 6f4 needles in her and it is sounding better. I am running about 880 egt temps on both sides at about mid throttle. I have not taken her to the lake yet but hopefully i can before the warm up coming. Does anyone know the equivalent of the stock 6dh1-4 needle? my dealer said that was brand specific. I also found out the lower the number the leaner the needle. So i am getting really close now. Thanks for all the help by the way it has been greatly appreciated.

[Bob Vehring]

Ty, Regan has the engineering schooling.............I quit in the 10th grade to go drag racing
Your ight, I have never seen a chart from a factory giving the oil break down, But, if it wasnt, continuoaly variable, why do we have a cable from the lever going down to the oil pump to change its settings?

KF, go to, http://www.sudco.com/ and download their catalog. You will find pages of break downs of every carb part and there all sorted by rich to lean. I printed copies and keep them on the carb bench and in my notebook that goes with the sleds .

The needle you choose will be related to the tubes (needle Jet) you use. Tubes have more of an effect then the needle, but the needle is used for dayly adjustments.

I wish I had more go info on my VM, I wasn't happy with it last year because of the work done to it before I got it, I thought I would have the new engine done and in by now, but other stuff keeps getting in the way