View Full Version : Won't rev above 4000-4500
12-10-2006, 12:42 PM
Working on my vintage YDS-3. When out on the road, it won't rev above 4500 RPMs. It runs strong up until that point, then just sits there like it has a rev limiter or something. I've replaced and gapped the points, and also replaced the condensors. The coils are original, but the plugs are new. Could this be the old coils starting to break down?
12-10-2006, 03:08 PM
Upon further inspection, it would appear that both head gaskets are leaking. I don't know if the bolts have just come loose, or if the gaskets themselves are bad. I need to buy a torque wrench and see what I'm actually torquing these things to!
I'm also going to try synching up the carbs a little better, as well as rechecking the point gap. I'm still afraid the coils might be contributing...
12-10-2006, 09:57 PM
Could be the coils.I wonder if a set off a R5 or one of the RD series would be the same. If they are then they won't be hard to find. I would check the exaust pipes also for some blockage. If it can't breathe it can't rev.Then again you said about the head gaskets leaking a little bit that might be it.
12-10-2006, 10:11 PM
Exhaust pipes are very open... ;) The baffles are still there... technically. But there's not a whole helluva lot left to 'em. But yes, the air is flowing freely.
I'd love to find a source for some new coils, but I'm guessing they don't make too many of the 6v oil-filled coils anymore :(
12-10-2006, 10:29 PM
This is what the coils look like. (http://cgi.ebay.com/YAMAHA-YDS3-YDS2-YDS3C-COIL-CAP-LEAD-HANGER-ASSEMBLY_W0QQitemZ130056408077QQihZ003QQcategoryZ1 0490QQssPageNameZWDVWQQrdZ1QQcmdZViewItem#ebayphot ohosting)
12-11-2006, 07:41 AM
It sounds like the air is moving out pretty well, how is it on the way in? Does that have reed valves? That used to give me trouble on my AT3. How are the carbs?
12-23-2006, 04:43 PM
Okay, well... one issue here was that the carbs were NOT synched up... the right side carb wasn't opening at all... the cable must've shifted (nothing is really hooked up the way it should be). Once I got the carbs both opening at the same time, lo and behold, it takes off like a rocket now. All the way up to ~6k RPM where I let off, since I can't shift yet.
In second gear it really sounds nice, and once the revs hit 3k or so it really takes off. I can tell this bike is going to be a screamer when I'm done with it!
I still haven't checked the head bolt torque, so that's next on the to do list. Then, I really need to take the gas tank back off, and route all the cables and things where they're SUPPOSED to go.
12-24-2006, 05:02 AM
Cool. I know the old R5 Yamaha circa 1973 vintage I had would scream. I had a Yamaha Banshee ATV, basically a liquid cooled RD 350 motor or an RZ 350 motor minus the powervalves however you wanted to look at it, and that thing sounded neater than hell. Those old 2 stroke multi cylinder engines would wail.
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