08-19-2008, 12:34 AM #1
Fuel Pump, Compression, and stuff
I hope I'm finally getting this beast in the ballpark. A HUGE THANKS TO 785LUGS FOR LOANING ME HIS ALIGNMENT TOOL That was a big help getting the ski back together in time for my vacation!!!!!!
Tonight I installed a new set of diaphragms and gaskets in the fuel pump. I did not test it before disassembly, but I did find fuel between the diaphragm and the pulse nipple. I didn't find any rips or cracks in the diaphragms, but the edges of the "bowl" on the pulse side were very rough. So, I took a fine stone and smoothed out all the rough areas. Both diaphragms were very warped, but hey, there's 435 hours on the ski and I didn't see any signs of this pump ever having been opened so that's not too bad I guess. I've suspected for a while that excess fuel is getting to the PTO through the pulse line. Hopefully this new kit will get that fuel situation lined out.
While I was wrenching on the ski I ran a compression test. I was in such a hurry when I put the ski back together a few weeks ago I didn't do this done to have a fresh ZERO hour value . Anyway, tonight on my gauge they were:
MAG = 110PSI
CEN = 115PSI
PTO = 110PSI
This was on a cold engine with all three plugs removed. OOPS, I just realized I didn't have the throttle WOT for the test, so maybe my values are slightly higher than those above? I guess these aren't too bad for SBT pistons and rings . I need to borrow my buddy's gauge and see what kind of reading I get with his. I know for certain mine is a bit of a cheapy so I doubt it's very precise. While the plugs were out I checked the gaps on the plugs. Hmmm, these were pre-gapped plugs and they were all about 0.030". I set them all to about 0.026".
Finally, I've found that I frequently get bit of water in the hull while playing in the waves. I have known for a long time my front compartment seal was bad due to the previous owner always leaving a rope tied to the front hole and closing it under the hood . I replaced that tonight as well, so hopefully the majority of my water instrusion is history.
08-24-2008, 10:13 PM #2
Well Nate (my oldest son) and I had a chance to take the ski out this afternoon.
For the longest time this ski has blubbered and loaded up at idle. That was the reason for the rebuild of the fuel pump. Well, for the most part that problem is gone. It still blubbers a little, but I think some tuning of the jets will get rid of the problem.
From mid range to WOT the ski pulled harder than it ever has. That tells me the old pump diaphragm couldn't provide enough fuel under high demand. My WOT RPM increased to about 6450. It was previously 6300.
I've used a pen light to look at piston wash, but I hope to soon pull the domes and get a first hand look and post pictures here. I'll post those as soon as I get the snapshots.
So far so good on the ski. I might just keep it after all.
Users Browsing this Thread
There are currently 1 users browsing this thread. (0 members and 1 guests)
By the_natrix in forum Yamaha Old School SkisReplies: 30Last Post: 01-20-2014, 09:21 PM
By elwesso in forum 2-Stroke PerformanceReplies: 5Last Post: 10-05-2011, 08:46 PM
By GPRFrank in forum Yamaha ClassifiedsReplies: 2Last Post: 05-12-2010, 12:59 AM
By the_natrix in forum Yamaha PWC Performance (2-stroke)Replies: 27Last Post: 06-20-2009, 12:58 AM
By SpongeyBrain in forum 4-Tec PerformanceReplies: 4Last Post: 05-14-2008, 06:41 AM