Hello. Bone stock 97 that I picked up cheap. A little rough in some areas, engine ran good with just the slightest stumble around. 1/8 to 1/4 throttle. Then my 21yr old went for a ride, seen a boy in blue, got worried came home in a rush…. Bike had oil over the top of the engine(vent hose from case wasn’t attached to the air box) . Since that day the engine doesn’t seem to be the same. Revs slower. Almost like it’s air is restricted. doesn’t build power the same. nothing in the air box, not even a filter. The plugs are good. Choke has to be on to start. Very cold blooded. Does build rpm’s just slower. Doesn’t smoke up the garage when running. Compression tester coming soon. Any ideas?
New member from NWPA
- Thread starter Frick314
- Start date
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Yes.
Replace the filter with an OEM.
Reconnect the crankcase breather hose to the airbox.
I suspect your pilot jets are plugged, partially or totally, some or all. That's going to require a carb disassembly, removing the jet blocks, removing the pilot jet and the other, ensuring they are open and not partially-obstructed, same for the carb passages.
Check the float levels. Adjust if needed.
Numbers above correspond to this link.
https://www.ronayers.com/oemparts/a/yam/50045c0ef8700209bc7942f3/carburetor
https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf
Replace the filter with an OEM.
Reconnect the crankcase breather hose to the airbox.
I suspect your pilot jets are plugged, partially or totally, some or all. That's going to require a carb disassembly, removing the jet blocks, removing the pilot jet and the other, ensuring they are open and not partially-obstructed, same for the carb passages.
Check the float levels. Adjust if needed.
Numbers above correspond to this link.
https://www.ronayers.com/oemparts/a/yam/50045c0ef8700209bc7942f3/carburetor
https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf
Attachments
Be sure to take plenty of pics to guide you in proper reassembly.
I usually split the throttle cables at the white nylon box. Be careful with that, as it's now an obsolete part not available from Yamaha. It's easy to lose the tiny screws that hold-on its top-lid, or to strip the holes out for them by trying to tighten the screws excessively. Snug-tight is good-enough, not tight-tight. Just seat the screw head so the nylon box lid is not loose.
It will help you greatly, if you immediately reassemble the pairs of cable into the box, after disassembling. Remember, pictures! If you build some muscle-memory about the proper reassembly, it will help speed things up when you go to reassemble the white nylon box.
Assuming that the slack in the cables at the twist-throttle is proper for the amount of free-play before you undertake disassembly of the nylon box, I usually find that upon disassembly/reassembly you don't need to readjust the cable slack after checking for sufficient free-play to ensure smooth twist-throttle operation (no binding in the throttle cables). Be aware that the proper cable routing plays a big part in whether or not you have binding in the cables upon operation of the twist-throttle. The service manual, in the back, has a chart with diagrams showing proper cable routing. See chapter 8 starting at p.24
https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf
When you go to remove the float bowls, have the carburetors separated into two pairs. Left and right..
Inside, to remove the jet blocks, after removing the two phillips screws, if you're careful with removing the jet blocks, you may prevent the jet block gaskets from tearing if you carefully pry-up the jet block. Be aware the jet block gasket will usually cause the jet block to stay on the 'roof' of the float bowl chamber after the screws are out. If you have a small L-shaped pick, you may be able to carefully lift one end of the jet block, and use the pick to separate the jet block gasket from either the body of the carburetor, or the jet block itself, depending upon how the gasket separates. I suggest having four of those K & L rebuild kits on-hand, before you tear-into the carburetors. There is less of a chance of making errors if you perform the disassembly, cleaning, and reassembly all at the same time.
I recommend using ultrasonic cleaning if you have access to a tank. If not, a strong carb cleaner and compressed air will usually suffice. Be aware you need to get the pilot jets clean and unobstructed, they block-up easily and you may need to use some sort of a wire or tiny drill bit by hand, not in a drill to poke-clear the opening. You need to be able to see light through the pilot jet hole and the others too.
DO NOT USE the cheap rebuild kits you see on ebay! They aren't going to work well! many members here can attest to their poor machining and fitment.
Many members like to replace the screws with phillips heads with allen screws, if you do that, I suggest SS.
I usually split the throttle cables at the white nylon box. Be careful with that, as it's now an obsolete part not available from Yamaha. It's easy to lose the tiny screws that hold-on its top-lid, or to strip the holes out for them by trying to tighten the screws excessively. Snug-tight is good-enough, not tight-tight. Just seat the screw head so the nylon box lid is not loose.
It will help you greatly, if you immediately reassemble the pairs of cable into the box, after disassembling. Remember, pictures! If you build some muscle-memory about the proper reassembly, it will help speed things up when you go to reassemble the white nylon box.
Assuming that the slack in the cables at the twist-throttle is proper for the amount of free-play before you undertake disassembly of the nylon box, I usually find that upon disassembly/reassembly you don't need to readjust the cable slack after checking for sufficient free-play to ensure smooth twist-throttle operation (no binding in the throttle cables). Be aware that the proper cable routing plays a big part in whether or not you have binding in the cables upon operation of the twist-throttle. The service manual, in the back, has a chart with diagrams showing proper cable routing. See chapter 8 starting at p.24
https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf
When you go to remove the float bowls, have the carburetors separated into two pairs. Left and right..
Inside, to remove the jet blocks, after removing the two phillips screws, if you're careful with removing the jet blocks, you may prevent the jet block gaskets from tearing if you carefully pry-up the jet block. Be aware the jet block gasket will usually cause the jet block to stay on the 'roof' of the float bowl chamber after the screws are out. If you have a small L-shaped pick, you may be able to carefully lift one end of the jet block, and use the pick to separate the jet block gasket from either the body of the carburetor, or the jet block itself, depending upon how the gasket separates. I suggest having four of those K & L rebuild kits on-hand, before you tear-into the carburetors. There is less of a chance of making errors if you perform the disassembly, cleaning, and reassembly all at the same time.
I recommend using ultrasonic cleaning if you have access to a tank. If not, a strong carb cleaner and compressed air will usually suffice. Be aware you need to get the pilot jets clean and unobstructed, they block-up easily and you may need to use some sort of a wire or tiny drill bit by hand, not in a drill to poke-clear the opening. You need to be able to see light through the pilot jet hole and the others too.
DO NOT USE the cheap rebuild kits you see on ebay! They aren't going to work well! many members here can attest to their poor machining and fitment.
Many members like to replace the screws with phillips heads with allen screws, if you do that, I suggest SS.
If you get your bike running there's a vmax gathering in somerset pa june 22nd thru 26th staying at the days inn ..Feel free to join us
