08-22-2009, 09:50 PM #1
SL750 low end issues--going to retweak
I have a SL750 normal upgrades (fuel lines, triple, premix, etc)
add: .5 over on all pistons due to rebuild
I am going to redo the carb setup from the beginning tomorrow morning.
The ski runs ok
I am a big guy 6'2 230 so I am not expecting race results
but is seems to cavitate a lot on take off. takes a bit to plane and then it takes off to 48MPH on DOM at 5800-5850 RPM (I think I am rich at bottom and top end, but wash does not say that) (just barely have thumbnails in all cylinders)
Close all screws
open all lows to 5/8
tweak low's to best 50' starts
WHAT DO I LOOK FOR ON WASH/PLUGS ON THE LOW SPEED CIRCUIT SETUP (IF ANYTHING?)
based on current screw settings (will note in the am)
then tune to fastest top speed.
I believe that this will be lean and plan on 1/8 turn past prime on all high speed screws to go a little rich
IF I TAKE THE FLAME ARRESTOR OFF TO TUNE, DOES THAT NOT CHANGE THE AIR/FUEL DYNAMIC
HOW DO I COMPENSATE FOR THAT
IS THERE A STANDARD
CURRENTLY HAVE STANDARD BLUE PLASTIC TOPPED FA WITH METAL PLATE INSERT
IS THERE ANY OTHER ISSUES THAT WOULD CAUSE THE LOW END HESITATION OTHER THAN PURE ENGINE POWER THAT I AM MISSING
STOCK PUMP, SEALED WELL, STOCK PLATE, STOCK GRATE
08-23-2009, 12:53 AM #2
- Join Date
- Oct 2006
- Cleveland OH
F/A missing isn't going to make that much difference, esp. if you have a free flowing F/A like a 780 to begin with. It will make it more convenient for carb tuning on the fly though.
Take a quick peak in the water intake area of the hull. Is there any exhaust soot present? If so, you have a bad pump to hull seal. That will cause a low end hesitation.
08-23-2009, 12:14 PM #3
ok, so heres how it went
go the lows set, that was pretty easy. found a sweet spot that gave me good acceleration
set the highs to 1 1/4 m 1c,1p
and she took off like a bat out of hell. 6350 on the tach and 54.8 on the dream o meter.
ran for about 2 minutes WOT and did a plug chop. Plugs had gone from dark black to almost white
added a 1/4 turn to all, repeat, repeat, etc. Finally got it to where all teh plugs looked good and my top speed runs were 6100 RPM and 50.1-51.0 MPH
Figured I was a little rich, but that would be good for what I would use it for.
Put the flame arrestor back on and RPMs dropped to 5700 and top speed of 46MPH.
How much should I back out to account for the FA?
Got home and was doing my post ride clean up and decided to check wash again and check compression.
PTO--Great wash, 135PSI
Cen--Great wash pattern, 135 PSI
Mag--slight wash at ports, 90 PSI
Pulled the head and no noticeable damage to the piston, rings, cylinder walls. But did see finger nail wash pattern developing
SO: Can I just hone and get a bigger rings, or do I need to bore again?
Last edited by seaobin; 08-23-2009 at 12:16 PM. Reason: spelling
08-23-2009, 12:43 PM #4
- Join Date
- Oct 2006
- Cleveland OH
Tenjuna was finding similar RPM issues with the F/A cover on. I guess that old plastic cover is very restrictive????
I suppose you need to adjust the screws with the cover on now, I'm sorry. OR get a free flowing F/A instead. Much better idea IMO.
You cab just hone and re-ring as long as the piston clearance is still within specs.
08-26-2009, 09:21 AM #5
I suggest tuning with the FA put together, using a tool like this:
I ended up getting something similar at Harbor Freight and spent another grueling 14 hours fine tuning the carbs on my 650, then found I could not get the engine to run right with the rubber snorkel attached.
try leaving that rubber snorkel off and run it and see what happens...I am pretty sure it just make the air intake way too restrictive for some reason.
I intend to upgrade the air intake to one similar used on the 780.
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