GP760 Carb Problems (POP-OFF Pressure)

[steelroe]

Can anyone please confirm the correct colour carb spring and the correct pop-off pressure for a GP760. I have got several different answer to this query on other forums

I am having fueling probs with this ski, see thread here http://greenhulk.net/forums/showthre...98#post1019198

[torquenut]

Re: GP760 Carb Problems (POP-OFF Pressure)

Carbs should be stamp with;
Front Rear
64X00F 64X00R
(101) (102)
This will mean you have OEM carbs, if they are 65V that’s OK still a 760.
Valve seat for a 760 states it is 1.5, remeber this is mark on valve seat and to view it you have to take it out and turn it upside down use a magnify glass.
mach color of spring with value.
Gold 55 PSI
Dull Sliver 43 PSI
Green 38 PSI
Shiny Silver 32 PSI

Part numbers to order the spring from Yamaha are;
6R7-142253-00-00 Gold
63M-14253-00-00 Dull silver
64T-14253-00-00 Green/dark.


Stock speed screw settings are
Front Carb Rear Carb
Low 1 5/8+- 1/4 1 5/8+- 1/4
High 1/2+- 1/2 5/8 +- 1/4
Remember that you seat speed screws fully, clockwise, then back out set number of turns.
Remember to keep the pop off relatively the same, this is to say if you have a Front Gold spring that is not within specs but you have dull silver then replace both front and back with the dull green so that you have a constant pop of 43 on both carbs.
last all springs have a +- minus of about 5 psi so do it a couple of times to get an average and don’t forget to wet the seat with WD 40 do not do a pop off check dry.
Once you get it in the water adjust speed screws about 1/8 to 1/4 at any one time and check, big adjustments will get you mess up.

[steelroe]

Re: GP760 Carb Problems (POP-OFF Pressure)

Thank you for the reply. I have rebuilt the carbs including new needle and seat. As far as I am aware the ski is stock so I need to know what the pop off should be. I have received conflicting answers.

The springs fitted are silver with a measured pop-off of 43psi. I have been told by a members on another forum that the 760 should have a gold spring.
I tried gold but problem got worse.

re-fitted the original silver spring, which much improved the performance but still have a small prob.

see my post here http://greenhulk.net/forums/showthre...=gp760+pop-off

"Removed the gold springs and put the original silvers ones back. Checked pop-off, 43psi on both carbs. Back on water and it is much improved.

Starts up first time and if i floor the throttle it will run perfect right up to wot firsttime.. If I then leave off the throttle from wot allow it to slow, floor it again and it will choke at approx 3000rpm for a few seconds and then it will take off.
What I have noticed is if i alow it to idle for a few seconds after wot and floor it, it works fine.
I think the correct Pop-off is key here, can anyone please confirm the correct pop-off for this GP760.

any suggestions are welcome.
The prob is definetly something to do with the carbs.

I am really tearing my hair out here. ""

[torquenut]

Re: GP760 Carb Problems (POP-OFF Pressure)

i feel your pop off is ok.
You need to now look at low speed screw settings.
But before we go there, do the following checks.
With the boat out of the water the idle rpm should be at or around 1800 rpm.
In the water with a load it should idle at 1200 rpm.
if you need adjust the idle screw, this is the screw that pushes on the throttle for both carbs.
Next remove air covers so that you can look straight down the throats of both carbs.
start engine, look down into throats, do you have any dirps of fuel? If you do your flapper seal is bad.
this is the small seal that is held by one small screw and the kidney shape contraption on the diaphram end of the carb. The valve (kidney shape gizmo) is held onto by two #2 screws. The seal seat on the opposite end so you need to remove the valve flip it to get to the seal.
This seal prevents fuel into engine via high side speed screw at low rpm, after about half throotle fuel then overcomes this seal and goes engine thru high side jet/speed screw.

Since you are having low side problems I have looked at a to much fuel.
If all this is good then you need to adjust the low side speed screws.
PLEASE NOTE DO NOT ADJUST SCREWS WITHOUT FIRST DOING WHAT I HAD WRITTING.
I have wasted many hours and found this is the best way to adjust carbs.
Once carb is rebuilt, carbs pop is set,idle is set you know can adjust speed screws.
screw each speed screw 1/8 at a time and check. Clockwise closses fuel while counterclockwise allows more fuel into carb.
So turn speed screw and check engine, if it go better trun screw that same direction same amount into it gets worse, then back to setting is better.
The throotle should be crisp and quick.
Do not mess with high speed screw.
Once you have a good low speed screw you may have to decrease or increase idle screw so no worries if you find that you have to adjust it.

[steelroe]

Re: GP760 Carb Problems (POP-OFF Pressure)

Carbs heve been completely rebuilt with new parts including needle and seat (1.5).
The flap you refer to is the regulator check valve, and this is also new.
Pop-off is 43 psi and low and high speed screws have been set to factory settings.

So what else might be causing my problem

[torquenut]

Re: GP760 Carb Problems (POP-OFF Pressure)

Remove air covers so that you can look straight down the throats of both carbs.
start engine, look down into throats, do you have any dirps of fuel?

If yes go back into carbs check your rebuild you did soemthing wrong.
If fuel is not seen dripping into carb then adjust the low side speed screws.
Ski must idle about out of water 1800 Rpm in in water 1200 Rpm.
You will only adjust the low side speed screws.
Screw each speed screw 1/8 of a turn check throotle responce.
A Clockwise closses fuel while counterclockwise allows more fuel into carb.
turn screw until engine runs better or worse.
This will tell you wich way to go.
Once you know if it needs or or less fuel then you can make final adjustments.
The throotle should be crisp and quick with no bog.
Do not mess with high speed screw.
I am assuming that you rebuilt carbs correctly with new OEM (Mikuni) kit.
I dont monkey with any other brand.

[steelroe]

Re: GP760 Carb Problems (POP-OFF Pressure)

Can anyone please confirm if the gp760 should have a silver or gold spring and what the correct pop-off should bei.e 43 or 55 psi.