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330 carb tuning
Quote from: Powerstroken;55511 Ok messed with it this afternoon and got the main down to a 175. It is to the point where it's not breaking up on the role during any more but seems like it still might be rich. I have the idle screw all the way in and air screw out 1.75-2 turns. It idles pretty good and not much hesitation when stabbing the throttle from an idle. The only thing is that it's still taking maybe 5-6 kicks to start even when hot. Not sure if it is just from such high compression or if I can still adjust something? What should I look at to help starting it With the idle screw all the way in, the slide is probably open 1/8" or more. The air velocity over the pilot jet transition holes is too low to draw adequate fuel from the pilot jet, especially when the air screw is at two turns and the slide has 1/8" or more of opening. Increasing the number of turns on the air screw decreases the suction on the pilot jet, resulting in less fuel being delivered to the pilot jet transition discharge holes. The choke is actually a separate enrichening circuit (a little carburetor inside the existing carburetor) where air must take another path and over a discharge hole that is connected to a very rich jet. If the slide is open 1/8" or more the choke will not work very well because the air flowing through the carburetor takes the path of least resistance. Adequate air flow will not go through the choke circuit to pick up the proper amount of fuel when the engine is cold and the throttle is open 1/8" or more. Your pilot jet is too rich and or the fuel flow area between the needle and needle jet at close throttle is too large requiring the idle stop screw to be all the way in to make it idle once you get it started. I would recommend that you set your side to be open about 1/16" open and reduce the pilot jet size a couple of sizes, set the air screw at 1 1/2 turns and see if idles at a reasonable RPM. You may need to optimize the airscrew and idle stop screw to get the best idle. The needles last letter in the 3 number sequence on the needle, designates the diameter of the needle from closed to about 1/2 throttle opening. On most new Keihin PWK, PWM or PJ carbs we use on the 250s or 250s with big bore cylinders, the diameter designator is usually an "H" xxH or "J" xxJ. As the carburetor needle jet wares with mileage, this straight or constant diameter portion of the needle must be increased to keep the mixture (fuel flow area between the needle and needle jet) optimized. If you end up needing to using a needle diameter designators that is a K, L, M, or N that is usually an indication the carb has appreciable ware in the needle jet. I have bore gages that can measure the needle jet holes and they usually ware into an oval shape with the largest diameter parallel to the air flow through the carb. The main jet size depends primarily on the type of air filter and the back pressure in the exhaust system. The back pressure is controlled by the stinger and muffler inside diameter, number of degrees of bend in the stinger and the inside diameter, the number of degrees of bend of a turn down if it exists. June 26, 2015, 09:27:55 PM |
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Re: Tx 4 racing
Ajbuilder250r, I’m in Ohio. I was on many R FB pages (too many that I have since deleted myself from most of them….still on a few select ones). Joe April 28, 2022, 05:39:09 PM |
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Re: Tx 4 racing
Croat, are you in Texas? on any of the "R" Fb pages? What were the other components that were tested with my cylinder...pipe, head, carb, reed, ignition curve, intake ?? I have built a lot of different engine packages for the Pro-x 310 and ESR 310 cylinders. I have seen peak power range from low 40s to low 60s with a zillion different shape power curves because many cylinders may have one or more components in the package that is wrong. April 29, 2022, 09:36:50 PM |
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DMR
Looks like Mr. Dave Moore and Modquad are staying busy. Joe May 02, 2022, 09:23:43 AM |
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Re: Tx 4 racing
I put the unported stock cylinder in it for the race with the new DMR coolhead and made it more mild for the woods, great setup for XC woods Congratulations on getting first place Joe May 31, 2022, 12:37:29 PM |
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Re: Little Sahara Oklahoma 2022
^^^ very nice ajbuilder250r Joe October 03, 2022, 11:14:53 AM |
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Re: Padla Brats being produced again ???
I spoke with the guy at Oregon motorsports a month ago and he said that he is able to get them. They are in Clackamas Oregon. Loren October 03, 2022, 04:19:24 PM |
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Re: Tx 4 racing
Finally got another first and got my points lead back. I started in second and it was a close pack until 45 minutes ish I finally found a way past first and got myself a little space from the group. 5 trx250r and a banshee. Not sure how many raced but there were 10+ atcs (200x, 350xs, 250rs, and a tri z). Maybe a 250sx Shocks from sf racing worked fantastic, running the zeel from Dave Moore along with a few billet parts, and Drw zeel mount and skids. October 29, 2022, 07:34:42 PM |
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