Carb jetting question. Indy 650 BB ported and piped.
Hello. I bought a 86 Indy 600 decent shape, blown center piston. I bought a new jug, new piston and had the top rebuilt by Irondog's in Clio. The Engine has the 650 big bore kit, The heads have been ported to the max, it has SLP pipes, comet clutch, The carbs have been bored out and the jets are as follows: L 320 C 320 R(mag) 370.
Heres the question, what determines the jetting? Why is it straggered? Are these numbers sounding good? I ride in Lower Michigan incase you are wondering for altitude.
Thanks for the help!
Also I just picked up a 1" paddle track with 1 1/4 woodys carbide studs. I think this should be a great track on the sled.
Last edited by VanDamage007 : 11-18-2009 at 08:15 PM.
Reason: Add track info
When we speak of engines, we use P for PTO, C for Center, and M for Mag. Nothing wrong with how you did it, we just have a standardized approach.
Jetting is staggered for different reasons. Sometimes the cooling routing causes a cylinder to run a little hotter or colder than the rest, and they jet it accordingly. Other times, the tuned pipes are slightly different volumes (to make the bends under the hood) and it warrants different (staggered) jetting. There are other reasons, ones that aren't as good, that could cause the jetting to be staggered: The PTO crank seal could be leaking and they richened that cylinder up to account for it - OR - someone messed up on the porting.
Jetting is determined by the engine; you want a perfect 14.7:1 (14.7 parts oxygen to 1 part gasoline) ratio. A larger CC cylinder has more oxygen in it and therefore requires more fuel, and that's where jetting comes in. Jetting is both complicated and simple. The whole point of jetting and adjusting carbs is to achieve a 14.7:1 ratio over the entire operating RPM of the engine. The problem is that not a single portion of your carb can cover the entire throttle range, and the different jets/needles/mixture screws cover different parts and they overlap.
Here is a ton of information on a basic venturi style carb, probably the kind that's on your sled ;)
Kick butt. Ill read up. I really want to learn more about jetting. I guess you must tell if you have the 14.7:1 by exhaust tempatures? I have SLP pipes but a Aaen EGT gauge, but no probes. I guess I better get the probes. Thanks for all the info. Do the numbers seem high to you? Should I start there. I forgot to mention I bought new carbs that are not bored. I intend to switch the jets into the new carbs, and use them. The bored ones are three different carbs! I dunno if the original engine builder used them on purpouse but it seems odd. Id rather have the matching carbs unbored but jetted. Will that make a difference in jetting? Thanks again!
Good Posts IBS. EGT's are the extreme option you have, but even the EGT's aren't an exact science. The best way to check jetting is to go run a full throttle quickly shut it down, pull the plugs and see if they are the correct color and that the piston wash looks good too.
For plugs white is bad, this means you need more fuel or a bigger jet. Cardboard brown is perfect jetting.
Black is too much fuel and you need a smaller jet.
Piston wash is a small area of the piston that the fuel takes the carbon off the piston by the inlet port. It should be about as big as a thumb nail. Bigger means too much fuel. Smaller than a thumb nail is lean and you need more fuel.
Ok piston wash is a new one for me. Where do I look to see this? Do I need to remove the carbs to see it? I got the plug thing down. Ive never re jetted anything. The motor when I got it had the middle piston all jacked up. It looked like it got kind of side ways in there because the front and back were jarred along with the ring. The top of the piston looked a lil rough in the middle. No holes tho. I will inspect the plugs when I get home. I hope to start putting the motor in tonight.
Should I use RTV around the joint in the pipes to seal them? I never have had a piped sled. I cant wait, the neighbors are gonna love this one... HAHAHA!
Oh yeah Ibreakstuff, WHERES THE DAMN SNOW!!! Dont worry. I think Gods holding it off for me till I get this sled done. Ill get on it asap!
Hey the part about the jets compensating for bad lower seals scares me a lil. I had the top half redone. We were assuming the lower is good, but how would I know if I had a problem?
Im sure they would have check it it out at the shop. I think they took off the fly wheel for something. Does this motor have timing? They said something about all the coils and plugs fire at the same time. Hows that work? Dont the pistons need to fire at seperate times? Weird. All the coils are run from the same two wires. Any info on that?
Piston wash is seen with the plug out and you look down into the cylinder with a flashlight or a tool with a light and a optical swivel I guess I'd call it.
To check the lower end seals you can run the motor at idle and observe the RPM. Then take some ether and spray it right on the seals. If either is leaking you'll see a slight increase in the RPM when the ether gets past the seal.
It is called "wasted spark", the cdi triggers for each piston as it nears the BTDC point that it is set to fire at. All two/three plugs fire at the same time. It's actually easier than setting points for each cylinder.
My answer? Spend $12 and get new crank seals while it's apart. I have my engine apart right now, with less than 1000 miles on it, and I'm changing mine. Cheap insurance and it's a royal pain to do after the sled is together.
__________________ You don't have to flinch for me to know that you're scared.
I agree there if apart do it now... Case in point I rebuilt a 440 few years ago, took it apart, new bearings, pistons, rings, checked everything else looked good reassembled, half a day run time seals failed... It was a yamaha..., but still good to replace if apart, lot less headaches!!!
Yeah I just spent enough on it already. Honestly this is my first liquid cooled sled. Im a fan of fan cooled. I dident want to get into the lower half of the engine unless I had too. If they are bad I will deal with it then I guess. I trust the guys who did the work on the engine. It was Irondog, they have been doing it for over 30 years. What kind of power are we talking when porting a 650 big bore with slp pipes? Any clue on HP or 0-60, or top end? Am I gonna be able to ride this out on the back roads and ditches and stuff?
A 600 bored to a 650. Now Im looking at the track clearance with the front heat exchanger. I think I am going to have a problem with the 1 1/4 studs. Anyone ever move or remove one of these? Could I remove it and install a radiator somewhere? Wouldent it run cooler with a radiator? I will post that in the tech section.
Well not exactly. The 600 heads were bored over to 650. Its the big bore kit. The heads have been ported and the carbs were bored however they were three different carbs for some reason. I am going to revert to stock bore carbs and change the jets.
Oh and it is a 1" lug track. Paddle track. The track only has clips and windows on every third opening. Other than that it is a 121 by 15 track. Aggressive for sure. The studs are at lease 1 1/4" Im sure it will hook up well. I hope I dont flip this bee-otch over.
Great, thank you. Whats the top speed, and horsepower any idea? I bet these things get up and go huh? Do you trail ride yours? Im wondering if the big port job is gonna be ok to rip around back roads. Do these mods make them run hotter? I assume so. I may have just enough room under there after all. If not I may get a new heat exchanger and try to shave it down some. IM really leaning towards putting a radiator in. I dont want to overheat and burn the motor up. If all else fails I will get a 440 fan motor for this thing.