I just got a 95 spx ski i checked compression its 145 in ea cylinder i changed out all the gas lines and cleaned everything and rebuilt the carbs, the problem i have is it will not run good from idle up to mid range but then from mid to top end it runs perfect runs clean ! so i think fuel delivery is good i can not tune the low end needles to make it run correctly, when i pull the choke out just a little it runs perfect thru the whole range so its not getting enough fuel at low end ,any ideas ? i think my pop off is 50 psi at the lever needle assembly is this to high ?. thanks
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tuning spx
- Thread starter grgfraz
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Yes, Too high. 1995 SPX 657X 270500262 270500261 BN-38I (SB) MAIN-135 PILOT-72.5 Ndl=2.0 270500264 (D) pop-off = 22 - 37 LOW- 1-1/8 HIGH- 0 Set at 30 psi and within 1 psi of each other. Then fine tune LS adjuster 1/16rg turn at a time, to get the plug Mocha.
Dr Honda
Well-Known Member
With what you are describing... it can only be a couple things (assumming the jet is clear, and the low needle is set)....
1) In the carb body... there are 3 or 4 "Transition Ports." They are right were the butterfly is opening. I bet one, or more are clogged up. (they are very small, and a single backfire can carbon them over)
2) the check valve on the high jet is leaking, and you are drawing air past it at low RPM's.
1) In the carb body... there are 3 or 4 "Transition Ports." They are right were the butterfly is opening. I bet one, or more are clogged up. (they are very small, and a single backfire can carbon them over)
2) the check valve on the high jet is leaking, and you are drawing air past it at low RPM's.
thanks for the info how can you clean these ports and where is the check valve ?
Dr Honda
Well-Known Member
The check valve is the little clear part, behind the main jet block.
To clear the transition ports... switch back and forth between compressed air, and carb cleaner. When doing this... look into the throat of the carb, and make sure you see carb cleaner spraying out of all the holes. (Spray it into the the pilot jet)
ok i finally got to test the ski it runs a lot better but still has some hesitation on low to med throttle if i pull the choke out some it runs perfect. i had 50 pop off i changed it to 28 and checked the ports filters ect whats next i was thinking lower pop off to 22 ?? or bigger pilot jet pulling the choke is just making richer on low end also i have adjusted the low speed needles in and out but not much difference is in richer or leaner seems to run better as i run them in
You have to have the Flame Arrester installed. On the bottom of the seats is marked its size. Someone may have changed, or you still have some petroleum "tar" in the orifaces of the carb. I use tolulol (tolueen) $17 a gallon at paint stores or hwr stores. I use it also on electric in-tank fuel pumps one part T to 4 parts gas, and circulate, to bring those back from the dead. LOL.
That petroleum mineral tar particles gets aluminum oxide (from the moisture permiation) from the carb(s) & fuel selector switch and turns to a JB WELD type of hard crud that is VERY HARD to just flush. Ever cleaned a fuel selector switch? you have to run a drill bit in the three tubes to get the coagulation out! Did you notice in Mikuni's instructions to paint the carbs? this is because of the A-Oxide permiation. We also advise to go a little further and fully grease the outside of rebuilt carb(s) & selectors. I also put a clear glass marine fuel filter after the carbs to catch any rust from the internal carb screws or Oxide in the re-circulatory line back into the fuel bafel. Ever seen the bottom fuel screen of the fuel bafel ? It will be full of the petroleum mineral "tar" clumpings that are present in all refined gasoline. Hope this helps! Thanks Dr Honda! You nailed it!
The flame arrestor creates the correct vacumn to draw the fuel out into the venturi.
The reason for the "spread" of the pop-off calulations, is to veri the PO for each individule engine condition in accordance with the jetting size specified, as engine breathes will vary with an engine's heat and compression.
That petroleum mineral tar particles gets aluminum oxide (from the moisture permiation) from the carb(s) & fuel selector switch and turns to a JB WELD type of hard crud that is VERY HARD to just flush. Ever cleaned a fuel selector switch? you have to run a drill bit in the three tubes to get the coagulation out! Did you notice in Mikuni's instructions to paint the carbs? this is because of the A-Oxide permiation. We also advise to go a little further and fully grease the outside of rebuilt carb(s) & selectors. I also put a clear glass marine fuel filter after the carbs to catch any rust from the internal carb screws or Oxide in the re-circulatory line back into the fuel bafel. Ever seen the bottom fuel screen of the fuel bafel ? It will be full of the petroleum mineral "tar" clumpings that are present in all refined gasoline. Hope this helps! Thanks Dr Honda! You nailed it!
The flame arrestor creates the correct vacumn to draw the fuel out into the venturi.
The reason for the "spread" of the pop-off calulations, is to veri the PO for each individule engine condition in accordance with the jetting size specified, as engine breathes will vary with an engine's heat and compression.
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