1983 Yamaha Maxim Xs400 won't rev?

[chrisd1984]

hah so it was running good for a couple of days and now it seems the bike has low revs again and stalls when I shift into first. Could a dirty carb really cause this? Could it be something like how the jets were set? (even though they haven't been tampered with). I swear I went through that entire carb and didn't see a speck of dirt anywhere....and the fuel filter doesn't seem to obstruct any fuel as I can see it going through the line. is this a common problem for a dirty carb?

 

[willem]

Yes, carbs can cause this when they're dirty. I've had my fair share of dirty carbs, and I was very reluctant to clean them at first. But it's just something that has to be done thoroughly and many times, until they are absolutely clean. After that, the fuel filter will hopefully keep them that way. It sounds to me like there's still a speck of dirt in a passage somewhere. Make sure you probe through all your jets again, use guitar string or very fine wire.

How's your air filter doing? Have you cleaned that one out yet? If there's a hole in it, dirt could come into your carbs there as well. If it's dirty and restricting air flow, you could be running too rich altogether. Have a look at your plugs again and see what they tell you.

Your jetting could be a problem, but it's not likely if your exhaust and air filters are stock.

That all being said, sometimes you just need to beat the dust out the bike. As in, it'll get better over time, especially if the bike has been sitting for a long time. My XS started out with piles of sh*t in the carbs, and after I cleaned them again and again it would run fine but sometimes misfire. It wouldn't really stall, but just not run 100% smooth. It took about 3 weeks of riding for that to disappear.

 

[chrisd1984]

I'll check the air filter again, it looks pretty clean though. Could dirty gas also really be an issue for this? It's sort of a blend of older gas and newer gas in the tank right now. But I know when I checked the carbs, I cleaned almost everything. That being said, I didn't unsrew the main jet (the bronze thing?) Should I take that out and clean any dirt in there? I know I could see through the tiny hole though.

Could that choke switch have anything to do with it? Or the float height? Or idles screws?

I checked the plugs and there doesn't seem to be too much gas on the ends (except from me trying to turn over the engine). So I don't know if it's how the jets are set.

 

[Lou Ranger]

How old was the old gas? Was it ethanol-free (like SHELL or ESSO 91) or an ethanol blend? And did it have stabilizer in it?
If it's from last season drain ALL of it out and dilute it in your car's tank. If it also had ethanol or no stabilizer mixed in, then for sure you need to clean the ethanol gum out.

 

[chrisd1984]

Hmm not sure about that one. It was the PO's so definitely at least 9 months old now. I did add stabilizer to the tank before storing it in Winter though. There wasn't much of his gas left though when I added the newer stuff but I'm sure 15% of it is still from what he had. Could something like that really cause the bike to stall when shifting into 1st though?

 

[HoughMade]

Do you have an external fuel filter? A bike that runs well for a while after a good carb cleaning, then goes bad is a classic "ick from the tank" situation that only an external filter will solve.

 

[Lou Ranger]

I don't know. I have been fortunate not to experience any ethanol woes but I have read stories in other sources about how it can separate from the gas and turn into gunk. If you believe all the eye-witness testimony on this Forum, the tiniest bit of gunk (from any number of sources, including old gas) can mess the carbs. Again, people on here have found tiny passage ways on the the third cleaning that they didn't know were there on the first 2. So, I would say carbs would be the easiest and safest place to start.

But don't unscrew anything inside until and unless you have read that it is the correct procedure on here - e.g., I simply don't know if that big brass thingy is something you should unscrew or touch. If you can't find it written down by Drewpy, Houghmade or BentWrench (and a few others) DON'T do it.

 

[chrisd1984]

Hmm never considered an external fuel filter but was thinking of replacing the inline anyway so this could be an option.

As for the brass thingy, I believe it was the main jet in a carb cleaning video. I may try to unscrew it and check for any particles. Anyone on here have any luck with ultrasonics? Or cleaning with diesel?

 

[chrisd1984]

Could this issue perhaps be from something else?

1. Maybe I need to set the idle screw?

2. Could it be a clutch cable or clutch adjustment related since it stalls when shifting into 1st?

3. Do these bikes have sensors do detect when a kickstand is down?

4. What does the red light on the top of the instrument panel mean? This comes on soemtimes (silly question I know)

5. Could the float bowls have anything to do with this stall?

 

[willem]

Ultrasonic is nice, but it still doesn't rule out clogged passages.

And yes, some of those could have a relation to the problem. But it's very unlikely. Most likely are still your carbs, and judging from your gas story, it's almost definitely your carbs. Clean them and put the inline filter in asap.

 

[chrisd1984]

ok. Would float bowls really have an effect on the this stall though? and any idea what that red light indicates?

 

[Lou Ranger]

ok... any idea what that red light indicates?

I think that would be the oil pressure light.

 

[willem]

Yes, the oil pressure light. It should go on when you turn the ignition, but switch off when the bike's running. When it stalls it'll probably turn on again.

let me go through your questions:

1. If your idle screw wasn't set right, it wouldn't idle well in neutral either, so that's fine.

2. Yes, but if it was you would feel the bike try to take off and stall. I'm guessing this is not the case. But if you want to be sure, try walking with the bike when it's not running. In first gear you should have a hard time, but with the clutch in you should be ok.

3. No, they don't.

4. as Lou says

5. The float bowls are part of your carbs. So yes, they have something to do with it, meaning you need to go in them to clean. There could be gunk in there, and it's likely there is.

It might seem like it has something to do with the gearbox since it stalls when you put it in 1st. But I had this as well, and the carbs were the problem. When you put the bike in 1st, it always shakes a bit. This little shake is enough to make the bike stall, if it's nearly stalling already. So yea, basically what we're saying is, clean your carbs.

Ultrasonic is nice, if you don't mind paying for it. You'll still need to probe through the passages with fine wire, but it'll reduce the chance of them getting clogged again. Just cleaning the carbs yourself with some carb cleaner, boiling them in vinegar or lemon juice, works as well.

 

[Lou Ranger]

... 3. No, they don't ...

Mine does.
Could be a North American safety reg that didn't apply to some of the European models or years.
The bike will start with the side stand down if the bike is in neutral.
It will not start and run if it's in gear with the stand down.
If the bike is running in neutral and the side stand is down, the engine will shut off if you put it in gear before lifting the side stand up.

 

[willem]

ah. another thing learned. I knew mine didn't, and I checked the wiring diagram to make sure it wasn't just taken off. But then it's apparently on some models and definitely in the US.

So chris, it might be a good idea to have a look around your side stand to see if you have a sensor there. It might be corroded, and that could be the root cause of your issues. Let us know how it pans out

 

[chrisd1984]

sure I can take a look for that...would it just be right by the stand? also could the clutch switch near the left handlebar have any effect on this? (whether it's turned on or off)

Big question too...if it does have something to do with the plates or springs in the gearbox, how could I text this? Could I walk it and test somehow? Just want to be sure it's the carbs and not the gear linkage

 

[chrisd1984]

Another big question....took off the carbs and am cleaning them now. However, I noticed one one of the floats has about 1 centimeter of free-play over the other one. Is this a big deal? I know I can adjust it with the small metal piece but can I leave this for now?

 

[Lou Ranger]

... also could the clutch switch near the left handlebar have any effect on this? (whether it's turned on or off) ...

The little switch on the left handlebar is a safety switch which prevents the bike from turning over if the bike is in gear and the clutch is NOT pulled in.
If the switch itself becomes disengaged from its housing (as mine did recently) then the spring in the switch completes the circuit. I suppose the reasoning is that it is preferable if the bike can always be started (even if not as "safely"), than if a broken safety switch totally disabled the bike.

 

[willem]

Another big question....took off the carbs and am cleaning them now. However, I noticed one one of the floats has about 1 centimeter of free-play over the other one. Is this a big deal? I know I can adjust it with the small metal piece but can I leave this for now?

Leave it for now, deal with one thing at a time. It's probably fine, and if you try adjusting it right now you might have clean carbs but create another problem with this. If after you're 100% sure its not your carbs or your sidestand sensor which are causing problems, you can check the fuel level inside your float bowls later. That'll tell you if the floats are doing their jobs.

 

[chrisd1984]

yeah when I cleaned them the first time I move the metal clip a bit on one and now it sits just a bit lower than the other one.

Is there a way to make sure it's not something with the plates or gears that's causing the stall?