Thread: GP1200R Carb tuning help
03-07-2010, 10:51 PM #1
GP1200R Carb tuning help
Put on a set of Tau Ceti FAs w/ socks.
Rejetted to 125/110/1.5N&S/95g Dull Silver spring.
1 1/2 turns on the Highs and 1 turn on the Lows.
Ski already had a freeflow exhaust prior to my mods.
Note: This was the prescribed formulae for a 1200R with FA/s and chokes removed, and runs ok even while rich.
Riva Free Flow Exhaust
TauCeti Flame Arrestors
R&D Power Valves
The ski seems to be running rich.
Smokes heavy, oil is in the water (premix) when ran off the trailer and max rpm has dropped from 7100 to 6600.
Full throttle out of the hole the ski hesitates but does not bog, no sputtering, just sluggish and then gets out and goes.
On deceleration, seems to be some burbling from the exhaust.
Loss of top end RPM from 7100 to 6600.
Lots of smoke on the trailer.
I would like to open up the airflow to the engine. Only one inlet is open on the right hand side of the ski, engine may not be breathing right.
I am thinking to ditch the socks, and at the same time, go from 1 1/2 turns on the Highs to 1 1/4 and 7/8 on the lows. Try to lean out the mixture a bit.
My big dilemma is, with the stock battery box, do I have to take my tools to the water and remove the stinger every time to adjust the highs and lows? I'll attempt to cut a hole in the stinger mounting bracket for access to the #3 cyl high speed adjuster.
Looking for a solution to get back my top end RPM.
03-08-2010, 12:20 PM #2
- Join Date
- Jul 2009
if you are rich taking the socks off will help with that..also try opening up your seat and see if that helps your peak rpms then you know if airflow would help..im shure oside bill or someone smart will chip in and hit the nail on the head but im only going buy what ive read since i havent had mine on the water yet
03-08-2010, 05:28 PM #3
Those are both great points. I took the stinger out today and wow, looks like the amsoil turned to crude in there. I took the socks off, and will mod the stinger bracket so I can get to the high speed handles with a long shank screwdriver. The lows, however, wow, I guess everything has to come out for those. Sadly, no test rides until next saturday
03-08-2010, 05:59 PM #4
125's are too rich for an unported 1200. But they should not have caused a 400 rpm loss. Look elsewhere for your problem.
03-08-2010, 06:37 PM #5
- Join Date
- Jul 2008
- cape cod
you realy need to talk to oside bill he is the carb god, listen to what he says
03-08-2010, 06:44 PM #6
I have a set of 120s for the main jets, but thought that the formula for chokes removed on a ski with Flame Arrestors as 125/110/1.5NS/95g Spring.
I have removed the socks from the FAs, and intend to ride the ski again on the weekend to see whats up. I'll also take my tools with me to tune on the fly to see if that helps. If it does, hooray, if it doesnt, then i'll swap in the 120s.
Any tips on reaching the low speed adjuster t-handles with the carbs on the ski?
03-09-2010, 12:37 AM #7
- Join Date
- Jan 2006
- Texas City, Texas
I really do not think that socks at this point are the big issue... leave them on for now.
To put things in perspective, many people with ported 1200's and about 140-150 psig of compression run 120 mains and 110 pilots. Typical adjustments for these are about 1 on the highs and about 7/8's turn out on lows.
You are unported, running with bigger highs. I think that you are a tad rich. Start thinking about approaching that 1 out on highs and 7/8 out on the lows. This could account for about 200-250rpms
But I'm with FullBoggie on this one. Running rich does not accout for a 500 rpm loss. Which makes me ask this question... what kind of tach are you using? The numbers that you are using to describe engine rpms are too rounded.... 6600 and 7100???? How often does that happen?
If you do not have a good reliable tach, then you are spinning your wheels when it comes to tuning.
About the low speed adjusters... you should be able to reach #3 and #2 fairly easily with your hand, even with the pipe on. Number 1 is a different story. I use a clothes hanger bent in a "J" shape with a little "flag" at the end of the curved part, a flash light, and a mirrow. It is not easy, and not fun, but it is better than removing the pipe. You can generally open (or close) the pilots by as much as 3/8ths turn fairly easily. I would suggest you go a little bit closed first heading for that 7/8th's target in 1/8 increments. This should help wake up the bottom a tad.
Then do the same thing in 1/8 increments with the highs until you get the love you think you should get.
03-09-2010, 09:34 AM #8
Damn...I'm using the stock RPM meter. Which before read all kinds of different numbers at WOT.
I'll invest in getting a tiny tach, which should help out with tuning.
What about the jetting specs though? I have 120 Mains that I could swap in, and also have the stock jetting, which I could return to. Just looking for guidance going forward.
Thanks for the tip on getting to the lows, but my arms are short and I think that I will have to take out the pipe to get it right. I just hope I dont have to put the stock jets back in the machine...
03-09-2010, 09:12 PM #9
- Join Date
- Jan 2006
- Texas City, Texas
You should get by with the 125 mains. There have been others that use them. You just may have to close them off a bit more than you expect... but that is why you need a tach to find the sweet spot.
If you are using the OEM tach, you are at a severe disadvantage. You MUST get a good tach.... PET or TINY tach are the ones of choice... do your research and check your wallet.
Honestly, you are probably not more than 250 rpms off the mark, but those last 250 rpms on a GPR mean the difference between a slug and a really loose, free running ski.
Don't short change your self on the bottom adjustments. Having short arms are not the issue, it is having big arms that work against you. Give it a try and find the adjustment screws. Number 3 is easy, and #2 is no where near difficult. It's #1 that will have you talking to yourself.
On the top end you will probably get away with closing the highs 1/4 turn (if you are really 1 & 1/2 turn out). After that, you really need a good tach to move forward.
03-09-2010, 10:09 PM #10
I pull the battery box out and can reach #3 and #2 no problem #1 I can just get a finger on enough to adjust it. If it hits hard off the line without a stutter you are fine on the lows. Sounds like just the highs need adjustment.
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