Thread: Tuning opinions here??
08-24-2007, 01:14 AM #1
- Join Date
- Aug 2006
Tuning opinions here??
I am having the most annoying time of tuning my carbs for my 785 recently!!
Here's my deal... I want some opinions.
'97 engine/carbs etc..
Last summer got done redoing the whole ski, '00 hull, everything new in the engine/carbs etc..
Got it going and running just top notch. When I was done, she'd pull 7800-7900 all day long without a hick-up.
This summer started off crappy. (Ski still ran 7800-7900 prior) Plugged my strainer, popped the head gasket. My damn trim quit working so I thought I'd fix that and go with O-ring head mod since the metal head gaskets blow donkey.
Decided, might as well get a ADA head instead of modding the stock head.
Got 23cc domes with the head, and had Ronnie open them up 2cc for 92 pump fuel.
Here's what I've tried so far....
First blended 111 Rocketbrand fuel, with 91 pump....came to like 102 octane blended or something. First tried that with the same jetting specs that I was tuned in at for stock. Ski seem like it ran great all around, but only pulled 7600 rpm's. Plugs looked scarry lean. So for that weekend I openend the lows up 1/4 and the highs up 1/2 just to be on the feel more compfortable.
And as one would guess, it started running like crap from these settings. Midrange seemed good, but bottem end was way rich and loaded up till it got on the pipes, then after about 3 seconds would clean out, rev good, and then fall off and hung at 7300 rpm
Have tried different blends with fuel with basically the same RPM results.
For now, I'm blending how I had intended 111race with 87pump to make 93 octane and internally I'm not seeing any sign of detonation, and from what I can tell, wash looks "safe", I'm just still stuck without RPM's.
I can't remember my jet sizes, but I'm back where I was last summer with Lows at 1 and Highs at 1/2.
Great bottom, strong midrange, and top just isnt there. 7500 rpm's top end at 58 MFD indicated. (Plugs still appear lean) Last year ran 78-7900 at 62-64 MFD indicated.
Here's the thing....This is new fuel to me, and I have no idea if plug readings will appear lean like what fuel I'm used to (VP c-12, c-14)
I have not tried closing my H's at all for one the plugs appearance, and two....why or when has heads ever required leaning a mixture (especially at WOT?)
When I open my H's an 1/8th turn, I drop from 7500 to 7300. Which tells me the fuel is taking my R's, but am not too anxious about closing them at all.
I have checked my exhaust hoses, and my exhaust manifold gaskets and I'm almost positive I am leak free.
My exhaust valve cable's are showing some signs of wear since last summer, but I have them adjusted and they are working properly.
Anything I might be overlooking that you guys can come up with???????
I'm stumped.....this ski took 5 gallons of gas and 45 minutes to dial in last summer!
08-24-2007, 01:17 AM #2
- Join Date
- Aug 2006
I wouldn't be at a impellor limit or something like that limiting my top RPM's would I with just a head change????
Impellors are somethign that I'm pretty new at yet and to me just wouldn't seem like that could be....but maybe worth askin.
Stock '97 impellor in pristine shape.
08-24-2007, 10:05 AM #3
Dont know much about the 785 motor, but I'd try a quick run after turning the highs in 1/8 and see if the rpm comes back. Generally, you can lean the jetting when running race fuel, as its more deto resistant and has a lower specific gravity. I lost RPM with my ski when I started running a race gas mix, until I leaned it out one jet size. Leaded racing fuel can also make reading the plugs a bit harder, as the lead deposits can make the plugs look lean. As long as you keep the WOT pulls short, you shouldnt have any burn down issues by leaning it slightly.
08-24-2007, 01:30 PM #4
pics of the piston wash and knowing your jetting would help the most..
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