Thread: carb tuning, pop-off question
09-01-2009, 07:30 PM #1
carb tuning, pop-off question
i just did the carbs on my 01 gp1200r and jetted them to 125 mains, 110 pilots, 1.5 n/s, 95 g spring and flame arrestors. the ski has a milled head for 92+ octane, d plate, 13/19 prop, r&d grate and riva plate. i searched the forums and didn't see what i need. i set all of the pop-offs on the bench using wd-40 and they all poped @44. on the ski after adjusting the lows some i tried them on the ski and they are all popping @ 46. is this too high? i did fine tune them on the bench by slightly tweeking the n/s arm. i just saw that it should be flush. is there any harm in what i have for readings? are the bent arms going to affect anything? any help would be great before i take them off for nothing. also the issue i have is a low speed hesitation after idling for a couple of minutes or just starting off. the only time it doesn't hesitate is after a full speed run and it only idles for about 30 seconds or less i do have the fercho jet works mod done also. thanks again.
09-02-2009, 01:52 PM #2
- Join Date
- Jun 2008
- St Clair Shores, MI
I wouldn't be concerned about the difference between 44 and 46. I don't know how much you bent your arm, but I suppose it could be an issue. I can't recall off the top of my head how that part fits together with everything around it, so maybe someone else can answer the question as to whether that'll be a problem.
My understanding is that what you're describing off idle is "loading up" and not "hesitation". "loading up" is basically hesitation from being too rich, it loads the cylinder up with fuel and it sputters a bit as it burns off the extra, then goes. "hesitation" is hesitation from being too lean, it has to wait for enough gas to get to the carb. Too rich is just an annoyance, too lean blows shit up. If it's loading up, it shouldn't matter whether of not you just came off a high speed run, but it should matter how long you're idling. If you can come off idle and get it on plane and cleared out, then go back to idle again, and gun it with no hesitation, then what you're experiencing after a longer idle is "loading up". And that's what my ski does too, but i'm more concerned about getting the highs dialed in first.
09-02-2009, 03:55 PM #3
If you did not adjust the needle valve arm to be even with the carb body, they will open at different times. Remember the diaphragm is what opens them in use, It is pulled in with vacuum. That is why keeping them even is important. I don't understand how you tested them on the ski this one mystifies me.
09-02-2009, 04:38 PM #4
i just pulled the feed to each carb for my tester, used hose pinch off tools onj the returns and joining feed lines. made sure that they had fuel each time and pumped away. i decided to remove them again to adjust the arms even with the body since i understand that now. trimming the spring to get right @ 43. i will post back with results.
09-02-2009, 10:59 PM #5
If you get them all within 1-2 PSI of being the same you are fine. Some times I compress the springs fully with my fingers or strech them a bit depending on which way I need to go.
09-03-2009, 08:23 PM #6
took the ski out tonight. it started right up w/o using the choke. never started this well, even after running for a while. i had all of the lows set @ 7/8 of a turn out, highs 1.5 out. pop off's set @ 42 psi on all 3. ran ski for a few to warm up then did a good full throttle run around the lake. brought it in full throttle and killed it to get a reading on the plugs. all 3 looked good, maybe a little on the darker side. on the factory tach it is going 1 bar above 7k which it never did before. i know i need a tiny tach to do it accuratly but the highs seem fine. great throttle responce mid range on up. when putting along around 1800 - 2500 rpm's there is a little bit of a mis-firing, ran it like this for a few and came in to check the plugs, #2 had some unburnt fuel on it. so i put that low @ 3/4 of a turn out and that seemed to clean that up, has decent throttle responce off idle. the issue i have now and always seemed to is when you idle for a while and then accelerate it climbs up to 5000 rpm's and then sputters a bit then goes like a rocket. if you just sit for a few seconds and hit it all is fine. the p.v.'s cycle when the engine is shut down, i have ridden it w/o the seaty and a white zip tie around the p.v. shaft and they seem to open fine. the only odd thing i noticed is when the motor is shut down and after they do their self check cycle they p.v. motor will make that high pitch noise and the motor will "jump" around a bit, almost like they are trying to cycle again. i have tried another p.v. motor (used) and same thing. don't know if this is related? i did buy and install (used again) a pro tec p.v. controller and the valves didn't move at all. removed and they worked. it was hooked up correctly also. don't know if that did some damage?
09-04-2009, 12:36 AM #7
Sounds like you are well on your way.
09-08-2009, 08:13 PM #8
had ski out again just for a ride with my wife on the other ski. i notice now when just cruising around 4000 rpm's that there is a mis-fire, almost no load on engine. as soon as i give it more throttle, just a bit it clears up and come alive. it is around 1/2 throttle or so. not sure if it is the needle opening letting more fuel in when it clears up or if the main jet circuit is coming in which i have 125 mains in it. i am switching to 120's this week to try that. any other thought's? thanks in advance, especially you Bill.
09-12-2009, 08:19 PM #9
put the 120 main jets in and rode it today on a lake that a freind lives on. how nice it was to be able to have the tools i needed right on the dock and plenty of time and space to do so. still has some hesitation after idling and then hitting the throttle around 5-6k rpm's. well i removed the seat and rode it in the same manor and saw that when it would hesitate up in that rpm range the p.v.'s werent opening, as soon as they did it took off like a shot. so at least it know now that i have to deal with the p.v.'s before i can further tune the carbs. i mentioned in an other post that i thought it was having p.v. issues so now i know i am. also next thing i need is a good tach.
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