Boatmad.com


Reply
 
Thread Tools Display Modes
 
Old 06-02-2013, 10:42 PM   #1
Registered User
 

Join Date: Mar 2010
Posts: 18
yamaha 90

Hi Guys
I'm running a 90 yam on a 5m humber rib and don't think its pulling as well as it could as it will only pull a 17 inch prop (standard ally yamaha prop.. New)
It reaches 5500 rpm on the tacho and sounds ok and pulls like a robbers dog.
I also tried both an 18'' and 19'' standard stainless prop but it won't pull full revs.
I measured the compressions cold and they were only 90psi, but equal on all three cylinders. I will however check with another gauge before getting the spanners out as I've had that one for about twenty years .
Anybody know what the compression pressure should be ? and if it is low as I suspect can I just have it rebored and fit new pistons etc ? or is it nickasil or anything tricky ?
I have been a car mechanic/garage proprietor all my working life so am fairly happy that I can rebuild it. I was thinking to give the ports a bit of a tidy up and fit some new reeds at the same time too ?
Once run in can I just do a flat out run and a plug chop to check the mixture and then main jet accordingly ? (like we used to with tuned cars in the old days !) I'd be grateful for any advice .
__________________

ribrunner is offline   Reply With Quote
Old 06-02-2013, 11:52 PM   #2
Registered User
 
driver510's Avatar
 
Country: UK
Location: Portsmouth
Occupation: Marine Engineer
Interests: everything fast
Boat make: Phantom 28/Ring 16
Engines: 2x Mercury 3.0 250 EFI/Evinrude 70
Cruising area: Solent

Join Date: Nov 2005
Location: Portsmouth
Posts: 1,255
Compression should be around
130psi+ the bores are steel so you can re bore if you need any info on the yam call me on 07702 958175 hope this helps rich
__________________

__________________
www.rsoutboards.co.uk
driver510 is offline   Reply With Quote
Old 08-02-2013, 07:11 PM   #3
Registered User
 

Join Date: Mar 2010
Posts: 18
Good Thanks
I'll try it with a new compression gauge and if it then needs a strip down I'll ring you first.
Best regards
ribrunner is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Powered by vBadvanced CMPS v3.2.3

All times are GMT +1. The time now is 09:12 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2019, vBulletin Solutions, Inc.