Thread: Compression Problems Gp1200
10-25-2007, 07:03 PM #1
Compression Problems Gp1200
I have a 98 65u motor that has been heavily modified then switched over to run 93 pump gas. I have a riva girdled head with 34cc domes. I just put in new wiseco pistons and tested the compression (Thanks to wonderful forums on "the right way to test compression" SBT). My results were 120-125-130 3-2-1. Why is the compression reading so low? I was thinking that the everything needs time to seat.
I am also going to change all the waterlines on my triple pipes. Would it be ok to change them all to the same diameter? Factory said that there is 3/8 lines and 1/4 inch lines and i should keep that way. Thats seems too small to me. need the help. THANKS!
Factory Pipe-Triple Exhaust
Riva big bore kit
12 Vane “D-75” Magnum Pump custom 14.20 pitch swirl prop
Riva - Billet Girdled Head
Riva - Flywheel
Riva - 34cc Domes
Riva - Porting & Polishing
Buckshot 46mm Carbs
Wiseco - Pistons
Riva-High flow Flame Arrestors
Riva-High flow intake
Boyesen - Pro Series Reeds
Riva-Quick-turn steering nozzle
Skat Trak-pump cone
Riva-Triple intake fuel pick up
Triple fuel lines and fuel filter routed directly to carbs
Tiny Tach-External digital tach
R & D–Re programmed Ignition
R & D–Ride Plate
R & D–Aqua Vein Intake
Riva-Dual Cooling System
Riva-Speed Shop Work (welded crank, polished ports, etc.)
Hydro Turf - Competition Mats
Riva- Billet trim tabs
10-25-2007, 08:11 PM #2
What brand of compression guage are you using? They will vary quit a bit between a cheaper one and a Snap-On.
10-25-2007, 08:14 PM #3
Snap-on world headquarters is 4 blocks from my house! My neighbor works there. Thats all we use around here. Even that would only make a small psi difference. I thought i would be sitting around 150 to 160lbs at least! I used the 1/2" adapter, Thats what yamaha said to use. 3/4" will give you wrong read. Thats what they said!
Last edited by krispaintballz; 10-25-2007 at 08:16 PM. Reason: added some info
10-25-2007, 08:18 PM #4
You got a nice deal on that ski on Ebay . I have that same set-up and I have 41cc domes on that riva head. I think you might have the wrong domes?
10-25-2007, 08:30 PM #5
Ive seen 8-10 psi difference in guages before.
10-25-2007, 08:32 PM #6
10-25-2007, 08:35 PM #7
10-25-2007, 10:05 PM #8
Whats the compression supposed to be,150-160?.Excuse me Kris...WELCOME to the forum...
10-25-2007, 10:24 PM #9
I don't know! I just got it and found that the compression was a little low with 34cc domes i thought. With the 34s i would have thought 150 -160. Come on 120-130 psi after all the mods, doesnt that seem a little low. I am guessing someone ported the s***t out of it. what do you think?
Oh thanks for the warm welcome, finnally somewhere i can work out my problems without paying the dealers big money and find out the guy that worked on it knows less than you (meaning us, the public) do! Sorry it is the truth sometimes.
Last edited by krispaintballz; 10-25-2007 at 10:26 PM.
10-25-2007, 10:27 PM #10
how big of a bore?
my ported 65U is 85mm and with 37cc domes i get 150psi. If your battery is low, you comp will be low, and if the exhaust port is super high it will lower it as well.
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