Carbs, Clutches, and Oil... all from a 535 Vmax of course.

[Donnie]

Hello to everyone. Finally the snow found western PA near the Laurel Ridges. My brother ('86 Vmax), my Dad ('96 Polaris Indy Trail) and I ('83 Vmax) had the chance to go ride, but we didn't make it very far.

My brothers '86 began to bog badly about 10 miles into the trip. I changed out a spark plug, but that didn't help. I pulled the fuel line and there was fuel being pumped. When I unhooked the fuel line (left carb) the engine picked up speed again, so I quickly attached the fuel line and took it for a really quick stab of the throttle. I screamed like it should. About 2 miles away, bogged out again, had to pull the fuel line again. Could hear it fire again in that cylinder and away I went. It wouldn't bog as long as I stayed above 6000 rpm at a little over 1/4 throttle and 40 mph. Get under that, and it would bog again. The AAEN exhaust temp gage was showing about 400 degrees in the left pipe and 1000 degrees in the right pipe. Obviously the left cylinder was running cold. Here's the thing though... I don't know why!!! I pulled the carb when we got home and it was spotless inside. I have a theory, but I want to see what you all say first. Please keep in mind that the carbs are not from a Vmax, they are from an '87 Exciter, mains are #310's, no power valve.

Now onto my '83 running conditions. Please see the next post.

Thanks

Donnie

[8R9SRX]

sounds to me the carb is flooding over....

[Donnie]

That's what I thought, and I figured that when I took the carb apart, I would find a float broken or stuck or even heavy. I didn't have any of that. I think I will replace the floats anyway to be safe. I hope the local YAMAHA dealer has a set laying around.

Donnie

[Vmax540]

Donnie, sounds like you're on the right track..... I check the needle and seat by turning the carb upside down so, just the weight of the float is on the needle and hook a line on and see if I can blow past the seat by mouth ?

[Donnie]

I did try that. The needle and seat are closing off, which is why I thought that the float must not be pushing up against it while it was running. I even started to think that the float somehow wasn't moving freely up the shafts to close off the needle. How do I get those little plastic tabs off the top of those shafts so I can put the floats in some water to see if they bubble? I can't budge them.

Donnie

[8R9SRX]

they pull off really hard...

[tfin]

Because each cylinder has its own fuel pump and pickup and pulse line, I'm wondering if the fuel pump is leaking fuel into the crankcase while you are running. Whem you disconnect the fuel from the carb, only the fuel pump may be leaking enough gas to run. When the carb is connected, you may be getting double fuel.

[Donnie]

I see what you are saying about the fuel pump possibly leaking in from the pulse line. And since the pulse line is in a vacuum, it could pull the fuel in there. How would you go about checking such a condition? I do have a vacuum pump if you think that will help my to do a test.

Thanks

Don

[Donnie]

The floats are out and in the sink under a glass submerged to see if they sink. I am not seeing any air bubbles coming from them, so they might be OK. I did notice that one of them seemed to stick a little as I was sliding it on the shaft in the float bowl. If only one float came up, I can see how that would definitely cause a problem. I am going to monitor them for a few hours to see if they take on any water. If so, I will replace them for sure, but I still might go to the dealer just to have a set of spares in case. Those little white stoppers are a pain to get off. I thought I was going to slice my finger open even through the leather gloves I was using. Keep the ideas coming.

Thanks

Don

[standupjetski_com]

I would just suck on the line. You could possibly damage the diphragm if you use a vacuum pump. If you suck gas, its obviously bad. Good Luck

[Donnie]

Awwww man... I gave up sucking gas a few years ago after the doctors found out I had Dain Bramage. That doesn't sound like a pleasant way to go. But if I have to, I guess I could take one for the team... or I might just hook up a nice clear long hose and have a bend in it so the gas only goes into the bottom. COOL!!!

[Donnie]

After being in water for over an hour, the floats did not sink or take in any water. I shook them to hear any water inside and there was none. I guess we are to just two possibilities so far unless someone comes up with something else.

Those are
1. Float was stuck and not closing the needle
2. Fuel pump is leaking fuel into the crankcase through the purge tube.

Anything else?

Donnie

[opsled]

Hi Donnie, I think you are getting alot of good advice from everyone and that you are on the right track. I have a few tips for you that might be of help. (First) on the fuel pump leaking through the pulse line. It is not common but can happen and if it does there will usually be signs of fuel in the pulse line when you take it off (they are normally dry). (Second) to test a float you should always submerge it in the type of liquid it is run in. Water and gas have different surface tension properties and a fuel float leak may not show up when submerged in water. Gas will flow through a much smaller hole than water will at the same pressure. (Third) Getting the little plastic retainers off the float pins is easy. Finding the one I have dropped is hard. I use a medium sized side cutters that is about the same thickness as the distance from the float bowl edge to the bottom of the retainer. Put the cutter edges under the retainer and use the side of the bowl as a fulcrum and push down on the cutters and they will pop right off. Keep a thumb on the top of the retainer or it will disappear. A 1in square piece of masking tape stuck to the top of the reatainer before you put your thumb on it will help in keeping it located. To put them back on put the retainer upside down on a hard surface (still stuck to the tape is best), slide your float on and hold it with one finger while you turn the bowl upside down and push the float pin down onto the retainer. This method works best for me as I don't have to try and hold onto the retainer because it is to small to get a hold of. (Fourth) check the pins in the float end of your needle valves. They should be spring loaded and push in and out freely. The spring acts like a cushion to help keep the the needle valve from bouncing because of vibration and bumpy trails. If they are stuck the valve may not seat properly while the engine is running but will seem to work fine when you have the carb on the bench. (Fifth) Check your in tank fuel filter. I have had them break apart and and get small pieces stuck in the needle valve and hold it open. It is not that common and only seems to happen with sleds that have been sitting without fuel in the tank for many years. They must dry out and when the machine is put back into service they start to come apart. The 540 Vmax has a dual line filter that was still available from Yamaha the last time I checked for about $8. I had this problem on an SRV and must have cleaned the carb 10 times before I found the problem. It would be running perfect for days and the just start flooding out. I would pull the carb and clean it without ever really finding anything and it would run perfect again but when you are out on the trail and it is cold you don't spend alot of time really looking close you just want get it running. It finally happened close enough to home that I got it in my shop and this time there was a large enough piece stuck in there to get it figured out. Sometimes the piece that was causing the problem can get lost while you are taking the carb apart.
Good Luck, Phil (opsled)