Thread: Need some tuning help
04-20-2009, 09:53 AM #1
Need some tuning help
I've decided that I need to finally take care of this hesitation problem I have with my Pro when nailing the throttle from idle or from 1/8 throttle. It becomes very annoying when I can't get any sort of hole shot because the ski almost dies every time. I can sort of feather the throttle from idle and get it to take off and I sometimes have to do the same to get it to start.
As a background, I bought this ski with some goodies on it as you can see in my sig. I've done some plug chops to verify the high speed settings and all 3 plugs yield a light brown/tan color on the insulator. So check on the plug chops. I'm turning between 7700-7800 RPM on the water. So check on the RPM. I still need to either get a bore light and check the wash or pull the heads but I don't want to have to get a new gasket.
The ONLY problem I have is this low speed hesitation. I've consulted Randy's "tuning tips for girls" that has been posted up before. I still have some questions though. See my questions in RED in the following paragraph.
My other question really is how do you tune each carb when you have three of them? Are all the low speed screws going to be turned the same? Do you tune each one independently until you find the best setting and then go to the next carb and tune that one? My '98 owners supplement shows that the high speed screw is set 0 turns out and the high speed is one turn out. Is this correct? I think I am correct in thinking that my high speed settings won't be effected by the tuning of the low speeds since that circuit isn't really feeding much fuel at WOT.
Start with the screws set at 1 turn out, and tune with the tachometer for peak Rpm, then stop there and count the number of turns on the high speed screws. Write this down on a piece of paper.. Then turn the high speed screws in all the way and open them to 1/4 turn open. (Now you will be testing starts only, so no more big high rpm trips around the course). You are only turning in the high speeds to allow you to easily tune the low speeds. OKAY, SO MY HIGHS ARE PRETTY GOOD CONSIDERING PLUG CHOPS AND RPM. HOWEVER, PLEASE SEE MY PREVIOUS QUESTION ABOUT TUNING ALL THREE CARBS AT THE SAME TIME. FOR MY INFORMATION, WOULD YOU TUNE EACH CARB BY ITSELF UNTIL YOU SEE THE MAX RPM, THEN MOVE TO THE NEXT?
Now check the low speed screws and set them at 1 turn and do a practice start; To test the low speed setting pretend that you just jumped the start and you have to start with no holder. Hold the ski by yourself and hold as many Rpm as you can (don't blow it out first for testing) and then nail the throttle hard.... NO FARTHER THAN 50 FEET, as you are only testing the start response.
If it blubbers like a schoolgirl trying to guzzle a quart of beer, then it's too rich on the low speed screws..
If it falls flat on the line (like someone punched you in the stomach).. It's too lean on the low speed screws.
COULD YOU PLEASE EXPLAIN THE DIFFERENCE BETWEEN BLUBBERING AND FALLING FLAT. MAYBE I'M THINKING ABOUT IT TOO MUCH, BUT IT SEEMS LIKE THERE SHOULD BE A DISTINCT DIFFERENCE BETWEEN THE TWO. WHEN I OPEN THE THROTTLE FROM IDLE, THE RPM WILL DROP A LITTLE, AND THE SKI WILL TAKE A SECOND OR TWO AND THEN TAKE OFF AND PULL HARD FOR THE REST OF THE RPM BAND. I'M NOT SURE IF THAT IS FALLING FLAT OR BLUBBERING. ALSO, I'M CONFUSED ABOUT WHAT IS CONSIDERED A "FLAT SPOT." WHAT WOULD THIS FEEL LIKE...WOULD IT BE LIKE AN RPM RANGE THAT HAD NO POWER, BUT THEN WOULD SUDDENLY GET MORE POWER ONCE IT GETS OUT OF THAT RANGE??
When you like the acceleration off the line, stop there and count the number of turns on the low speed screws. Write this down on a piece of paper.. Then re-set your high speed screw where they show the best peak Rpm earlier and try both a start and a peak Rpm run...
It will probably "blubber" a little off the line... DO NOT turn in the low speed screws... Instead, go back out on the course and fine tune for peak Rpm again.. The blubbering off the line is caused by having too much fuel in the high speed circuit... Write down your new high speed setting on the piece of paper along with the best low speed setting that you found earlier, this will be your base-line carburetor settings.
If the high or low speed screws are open more than 1-1/4 turns, then you need to swap to the next bigger jet.
If the high or low speed screws are closed all the way, then you need to change to the next size smaller jet.
*** If no matter what you try, it still wonít leave the line without falling on its face "lean bog"... Then try the next size lower pop-off spring in the carbs... Don't be afraid to try #95 or even #80 gram springs..
04-20-2009, 11:56 AM #2
It may help to hear it...this video was from last summer but you can hear the motor bog down when I nail it off idle in the very beginning and then it takes off.
04-20-2009, 01:10 PM #3
The hesitation is also called a bog,same thing.
The blubbering will be like a minor missfire( if you go real rich,you will feel it)
My understanding is that the jets are kinda like a ladder,starts and idles on the lows,then adds the highs to the lows ( as the rpm's climb ), a combination of lows and highs work at high speed.
Sounds like you are lean on the lows.
Turning out the low screws will add some gas to your high speed
04-20-2009, 01:54 PM #4
The more I think about it, it seems like it is bogging instead of blubbering, but I'm still not 100% sure. I briefly talked to Randy (Watcon) last Friday and he said it does sound like it is lean on the low speed screws. I think I need to start from scratch on the low speed screws and try it at one turn out and go from there and then double check the high speed with plug chops after I get rid of the bog.
Do you usually see the low speeds tuned the same on all three carbs or they independent like the high speed?
04-20-2009, 02:03 PM #5
Lows are typically the same setting. Don't rely on plug chops. Get an $8 flex light to check the wash.
04-20-2009, 04:07 PM #6
04-20-2009, 05:02 PM #7
04-20-2009, 07:31 PM #8
04-20-2009, 07:45 PM #9
Do you usually see the low speeds tuned the same on all three carbs or they independent like the high speed?[/quote]
Good question. I feel your pain as I have thought the same thing screwing around (literally) w/my 780. no answer; I usually try to make them all the same.
04-20-2009, 07:50 PM #10
Thanks for the help guys. Here is a short video of the hesitation on the take off...a little better than the one posted before. Do you still think this is a lean bog as opposed to a rich blubber?
Users Browsing this Thread
There are currently 1 users browsing this thread. (0 members and 1 guests)
By ArmyRXP in forum Open DiscussionReplies: 0Last Post: 02-13-2007, 05:42 AM
By somefun in forum 4-Tec PerformanceReplies: 3Last Post: 11-20-2006, 05:01 AM
By big83bronco in forum Yamaha PWC Performance (2-stroke)Replies: 10Last Post: 06-19-2006, 09:56 PM
By somefun in forum 4-Tec PerformanceReplies: 10Last Post: 05-14-2006, 07:08 PM
By Jrsrxp in forum 4-Tec PerformanceReplies: 3Last Post: 04-04-2006, 01:25 PM