I broke the Yamaha completely apart this year due poor running and low compression. Turns out that despite that all the local dealers/mechanics will tell you that there aren't any compression relief mechanisms in the head of this engine,,,, there are(Thanks Glen Hawkins). You have to get the engine up past an idle to get an accurate compression reading. Once again the dealers are a big disappointment (they set it on fire doing warranty work on an oil seal leak in the head years ago!). I broke mine apart thinking I had a compression issue and was perplexed when all the tolerances passed a mic test with flying colors. I went ahead replaced the rings (they were brittle) and all the required gaskets. FYI: I Found lots of grease in the coolant chambers that get there when you’re pumping in grease and it’s not coming out (Be sure to keep the overflow grease tube free of old thick grease to prevent this). I had Mikes speed shop do a head overhaul just because I had it off and I didn’t want to do it myself when they would do it for $140. I’ve had the Carbs off twice and been all the way through them. I still have a hesitation between idle and WOT but overall it’s working fine for now. I plan on getting a carburetor synchronizer kit and trying to find out which carb or what the issue is later this winter. To be fair I’ve had pretty much every bolt off this motor and jet pump at least once. I rebuilt the Jet (replaced the main bearings just because) a few years ago.
So almost 11 years, a bazillion miles wide open, and she’s still going strong. These are very simple engines and super easy to work on. If you own one, and have decent mechanical skills, you can fix anything on it. It’s hard to imagine switching to a newer engine now.
Topic: 40/30 Yamahamer Jet (Read 4326 times)