Thread: GPR Carb Tuning HELP
05-30-2008, 09:46 PM #1
GPR Carb Tuning HELP
Looking for some carb tuning input guys. I've read all the info (searched) and have tuned carbs in the past but I'm a little "Stuck"..
Here's my setup:
premix at 36:1
stock carbs 115's at 1 turn and 135's at 1 turn popoff right above 40 with 1.5 and dull silver.
Riva flame arrestors
stock 1300 reeds
It runs perfect until I have to idle around a bit. Then it's loaded up pretty good and takes several seconds to clear up. While it's clearing up it smokes like a chimney!
If I only idle for a few seconds or not at all the ski runs perfect. It's only after idling around.
I figure I'm rich somewhere just not sure where.... or am I over oiling?
At first I thought I might be fat on my low screws, however it starts right up with only hitting the button.. Then I thought maybe my jetworks was not set right, double checked everything ok..
The ski pulls VERY strong. Pulled a 77 @ 7360 today running next to Tim (04RXP22) sitting upright on the seat still not pulling full throttle as I hit 7400 quick..still under propped but closer than it was earlier this week.
Thanks for the input guys!
05-30-2008, 10:48 PM #2
Raise your pop-off one spring up. this will bring it in a bit later. Are your returns drilled and are you using a restrictor jet in the return? accelerator removed? and yes I would go to 40:1 minimum on the premix.
05-30-2008, 10:59 PM #3
05-30-2008, 11:18 PM #4
To help balance out fuel pressure between the carbs you drill out the fuel pump return in the carb body to 1/8" and then use a 90 main jet in the return line as a system restrictor. I will post a pic up of where to drill later.
05-30-2008, 11:37 PM #5
So one hole in each of the 3 carb bodies and then just 1 main jet in the return? Or a main jet in each of the 3?
What's your take on the metering passages from one carb to another at the intake/base? Mine came back blocked.
Thanks for your help Bill.
05-30-2008, 11:48 PM #6
one for the whole system this balances all three the same. I block the cross over channels on mine.
05-30-2008, 11:56 PM #7
needles and seat
I would expect to find one or more needles and seats leaking. They can be tested by doing a pop off. They should hold pressure consitently until they reach the pop off pressure and the springs releases....
I bring the pressure up to about 2 psi before it pops and spray some WD40 and completely cover the needle and seat. If you have bubbling then you have a problem.....
05-31-2008, 12:04 AM #8
Here is a good link to read it has some info on the fuel system including a schematic on the return system.
Checking Pop-off should always be done wet. I fill the seat with wd-40 open it so it soaks into the seat, then bring the pressure up. Be sure the arm is set to proper height and do more than one test per carb. springs are rated in a range so pop-off does vary, but you can dial it in with a little effort, plus or minus 2 psi across the carbs is acceptable.
05-31-2008, 06:36 AM #9
Thanks for the help guys.
N&S are not leaking. I checked pop off as I got the carbs put back together and according to my gauge I was popping just over 40psi. The ski has only been out 2 times since the carb work. I've rebuilt several carbs and have been down that road of the results of not checking pop off before putting the ski back together...
I had posted over the winter showing pictures of my wash and it was pretty lean but ran awesome with no issues at all. I was really suprised to see the wash was that lean. I think it was 105/120 for jetting then at about 1.5 turns all the way around (per groupk). So, I took it up to 115/135 at 1 turn all over as I didn't like the look of the wash ...
Now it runs great until I have to idle it around for awhile then it's a smoker and bogs HARD... but ONLY after idling..
I'll pull the carbs again over the next week or so and go up a spring to the gold and do my homework on the restrictor...
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