Thread: Pro 785 tuning
08-30-2013, 06:04 PM #1
Pro 785 tuning
I decided to go back to stock 98+ jetting on my carbs to get this ski running good. I did reduce the high speed jets by 5 points to 150 mag / 145 cen / 150 pto because I was not getting the rpm with the high speed screws turned in. I also kept the low speeds at 105 and have the stock 2.0 needle and seats and 80 gram springs to give me exactly 18 psi pop off on all carbs.
The compression is ~140 for all cylinders and I have ensured the phase is not out of spec.
1. I seem to get a hesitation off idle that I can't seem to clear with the screws. If I sort of open and close the throttle a few times it will then take off great.
2. I'm only getting 7550 rpm with the screws all the way in and the rpm drops with as I open the high speeds.
3. The mid range is freaking awesome with the high speeds all the way in but it just isn't pulling the tach.
08-30-2013, 07:26 PM #2
Just made a huge improvement on the off idle hesitation. My gas valves were blowing open due to the weak spring. Put in some other stiffer ones I had in the 1010 and wow. Tomorrow I will be putting in the ones Jay got for me to use. Also I got the rpm up to ~7610 with some more high speed adjustment.
08-31-2013, 11:51 AM #3
Finally got back in the water and the low end is awesome now. Unfortunately the springs are a little too stiff and aren't letting the valves open.
The piston wash also points towards being rich still.
08-31-2013, 01:24 PM #4
Put in some lighter springs from my 1010...orange/white springs and they are definitely the right ones. Takes off hard and I can feel when they start to open up.
Still running rich...I let off the throttle slightly and the rpms go to 7700 so I'm still rich on my high speed jets. I find this hard to believe considering I'm already 5 points down from stock.
Only thing I can think of is maybe it is so hot and humid here in Houston that it is just too much fuel? I have a 55 jet as the return restrictor. Is this the correct one for a stock 785?
08-31-2013, 07:32 PM #5
did you ever read Randy's tuning tips for girls?
did you ever see the handmade drawing for the pipes and restrictors?
what carbs are you running?
on my 97 stocker I had followed those instructions to the T and I was getting a solid 8000 rpm and 62.1 mph on the gps, It was so hard to get rid of the slight hesitation for a band start,
it was like on Saturday, it would be perfect then next day out it would hesitate,
check out this old post
08-31-2013, 07:47 PM #6
Hey Ronnie, I have been using Randy's tips and now the low end is perfect. I can pin the throttle and no hesitation. I ended up with about 1.5 turns out and the highs are turned all the way in.
My piston wash shows just barely some nicks for wash but I'm still only getting 7700 rpm with the throttle slightly let off.
I think my jetting and valve springing is good, I might need to look into water flow as suggested by others.
09-01-2013, 08:31 PM #7
Got a little better today. I pulled the exhaust springs out completely and did some runs. Couldn't get on a plane at first so I opened my seat and pushed the mag valve closed and she took off. Ended up pulling ~7700 without the springs so they might be not opening the entire way.
Checked the wash with all highs at about 1/16 turn and they are still showing about a pinky sized nail wash size. Might have to order some 145/140/145 main jegs and some slightly shorter springs for the valves.
09-03-2013, 09:55 AM #8
So all in all I think I made some good advancements on getting my Pro running a lot better than it has ever before. I had absolutely no idea that the exhaust valve springs would make such a huge difference in the performance of this boat especially when I thought I had the correct ones in there.
After running all day yesterday and getting some good high speed runs, I think I might need to look elsewhere on why I can't quite get my RPMs up all the way.
1. I removed the exhaust valve springs and got 7700 RPM. I now know they are opening all the way up now so I backed out the adjustment caps as much as I could and I was able to get the 7700 RPMs with the springs in. So I need to get some springs that are about as stiff as the orange/white but maybe a little shorter. I also might get some longer but lighter springs so I can get the caps turned in some but still allow the valves to open all the way. The holeshot and midrange of this boat is spot on. I can nail the throttle after iding and there is no sign of hesitation or blubbering. I ended up with about 1.5 turns on the low speed adjusters and the idle right at 1300 RPM.
2. My piston wash shows I don't have too much more room to play with the pulling fuel with the high speed jets. I am getting about half a pinky nail of wash on all pistons. I think I might be a tiny bit too rich as when I nail the throttle, the RPM will jump up to 7650 and slowly start climbing up until peaking at 7700. If I take a decent right hand turn, they then jump to 7750 so that shows I'm a little rich. I might try dropping the high speeds another 5 points as all my high speed adjusters are turned to only 1/16 turn out.
3. I noticed there was a bit of sludge coming out of the side of the head pipe to main pipe coupler on one of my pipes. I think I need to check all the pipes to be sure I am not getting any exhaust leakage anywhere. I wonder if that one pipe might have a bad o-ring that might be leaking some. This would definitely kill some RPMs. I will pressure test all my pipes to be sure there aren't any issues.
4. I need to double check my water orifice sizing to be sure I'm not oversaturating the stingers. I am using the stock orifices in line of each stinger feed after my Jetworks valve. I tested the popoff pressure of the Jetworks and it starts flowing water at about 3000 RPM.
09-03-2013, 01:15 PM #9
- Join Date
- Dec 2009
Sorry, thought you had electronic valves...didnt see you had gas valves.
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