Pilot Jets
- Thread starter townsend1
- Start date
x2ryder
New member
I rode last season with my 780 bigbore with a stock 42.5 pilot with no problem.
40 pilots in a ported srx are hard to make them run properly, you will be more then 2 turns out on the fuel screws and this indicates you need to go to the next step up in a pilot jet. I always use 42.5 pilots in trail ports and 45 pilots in lake race type engines. The 40's are awfull lean and when you step up the power and work the engine harder with good clutching it needs more fuel.
Yamablue
Member
Any idea where to start with a 38mm rack of a viper or srx that has been ported?
x2ryder
New member
any idea who ported the cylinders?
valin
Active member
With my 38's I ran 45 pilots. If your 38's are from a Mach Z, they come with 50's, but that's a bit much. I ran 45's on both my ported motor, and the big bore.
and for the mains a hex jet is what the 38mm carbs use and the equivalant to say a 160-165 round main just as a STARTING point would be a 330-340 main jet. You will need to read plugs and piston wash from here for your paticular sled.
Yamablue
Member
Bo Whiteman ported the cylinders. I have 45s in there right now with 390 or 410 mains. The rack is a XCR800 w/tps. I go much below 380s and the EGTs go into the 1350+ area. The needle setup in it has a lean spot around 3/4 throttle. Stock needles for the carbs set on 3.5.
vipertripplexxx
New member
If you have hooded needle jets you can run about 8 sizes lower on the mains.
true about the hooded needle jets, because the increased vacum signal they give off pulls more fuel. I cant comment on the 8 size drop have never scaled that to see how many it is.
Are your carbs vented to the bellypan or the airbox?
Do yourself a favor and take black tape and place it over the egt's, then go out and jet the sled using plug readings and piston wash to determine your settings, then take off the tape, you might be surprised to what your egt's will read!! A egt is just a tool to help you minitor your settings AFTER YOU ESTABLISH A BASELINE SETTING!!! and yes you do this the old fashioned way of plug reading and piston wash.
If you have wicked lean spot you may wanna look into a richer needle/nozzle set up and adjust from there down to where you need to be instead of trying to go up, the mid range is the most often section where a engine lives or dies.
Are your carbs vented to the bellypan or the airbox?
Do yourself a favor and take black tape and place it over the egt's, then go out and jet the sled using plug readings and piston wash to determine your settings, then take off the tape, you might be surprised to what your egt's will read!! A egt is just a tool to help you minitor your settings AFTER YOU ESTABLISH A BASELINE SETTING!!! and yes you do this the old fashioned way of plug reading and piston wash.
If you have wicked lean spot you may wanna look into a richer needle/nozzle set up and adjust from there down to where you need to be instead of trying to go up, the mid range is the most often section where a engine lives or dies.
vipertripplexxx
New member
If your running 390-410 mains you have hooded needles in those 38's. no hoods, and your gonna be up around the 480's.
Pull your needles up one notch, and try running a smaller pilot.
x2ryder
New member
Mr Viper is totally correct. I had 1004 t cat a couple of years ago. I had egts on it they would run real hot like 1400 or more if I remember right. If you looked at piston wash or the plugs they were just fine. You could even put your hands on the cylinders and not have to pull them away. 1250 was supposed to always be the burn down number. I was told many a time all that is, is just a number. Every motor is different. Hell I would race on a lake and have numbers and red lights flashing at me the old 1004 t-cat would just keep on trucking. I miss that sled.
Yamablue
Member
If I run it on the 4th clip it has a low-midrange burble. I suppose I could try some 42 needles, but I'm already 2 turns out on the pilots. As far as the needle jet, it is fixed, so I can't do to much about that. I have looked into different needles, but I need a chart that lists the diameters to determine if it is going to be to lean or rich.
I do not have an airbox, just uni filters, so the carbs are vented to the bellypan. I may try putting the airbox back in there to see what happens, but first I need to really spend some time and get the carbs synched in better. I just did them with a drill bit, but I am going to try it with a manometer.
I do not have an airbox, just uni filters, so the carbs are vented to the bellypan. I may try putting the airbox back in there to see what happens, but first I need to really spend some time and get the carbs synched in better. I just did them with a drill bit, but I am going to try it with a manometer.
the pod filters explain the large jets. I would revert to a airbox if it were mine for winter riding, it might cure your midrange lean out spot as well, it will slightly richen the whole fuel curve and make it less finiky to temp changes, all you can do is try it
Yamablue
Member
Thanks, I think I will give it a whirl. Should I vent to the bellypan still or to the airbox?
bellypan
Yamablue
Member
As far as the airbox is concerned, should I leave the shelf out or just put it in and modify it?
well.... I am old and I dont like all the noise without em, so I run them and just drill 3 1.25" holes in them to supply some more air, and it still cuts down on the intake noise when trail riding. Drill the holes so they are in between the factory tube plate, this is for the topshelf plate I am refferring to drilling holes.