1983 Yamaha Maxim Xs400 won't rev?

[willem]

When you turn your throttle and look at your carbs on the right side of the bike, you see the throttle lever moving there. The position of minimum throttle is set by a screw with a spring on it, that's the idle screw. Turn it up a bit so you have a little bit more throttle as a base level, your idle revs should be slightly higher then. That usually helps against problems like bogging down and stalling while idling. If it doesn't fix anything, just put it back the way it was and look for problems elsewhere. My guess is that since there is some fluctuation in your revs, your bike is maybe running a bit lean. If you take a pic of your spark plugs we can see if that's the case (here's how to read spark plugs)

 

[chrisd1984]

Oh sorry yes I know where the idle screw is on the side, I meant the idle mixture screw. Where would that one be located and could that help rectify the idling issue? And if I turn it up, won't that cause the bike to move forward incrementally without applying any throttle? Just not sure why the mechanics didn't notice any of this and correct it or make suggestions...I even asked them and they said it wasn't an issue. I've looked at the spark plugs a few weeks back and they seemed to have carbon on them but I'll take a photo again and post it on here.

 

[willem]

ah the idle mixture screws. right. they're on each of your carbs, theyre the ones that are not the float bowl drain screws. Should be about 2 1/2 to 3 turns out, but you can play with them a little to make the bike run well. There's a lot of factors involved that make your mixture run leaner or richer, it's just trial and error most times.

Nope, it won't make your bike run away. Not while in neutral, anyways.

Another thing you could do is a carb sync. And preferably a valve clearance adjustment before that.

 

[chrisd1984]

Hey so I hit the carbs with a rubber mallet and it seemed to correct the fuel leak issue.

I took a photo of the spark plugs...what do you think?

Also attached a photo of the carbs from both sides with letters...can you help identify where the idle mixture screw is located? I know the drain screw is at the bottom and the idle screw with the spring but figured adding letters would help you describe where the mixture screw is.

And probably most importantly, I added a video of my rev problem to youtube. Is it safe to ride this way? Any idea why it doesn't rev? It's just in neutral and I try to rev but it almost stalls....the revs are behind the actual throttle movement (sound is bad on the vid)

 

[willem]

Spark plugs don't look that bad actually. Perhaps slightly lean, but nothing major.

The idle mixture screws are easier to find by process of elimination. You know it's not the idle screw, nor the float bowl drain screws. That leaves only the carb sync screw (of which there is only one, and it's located on the bracket between the two carbs) and the two idle mixture screws.

Your inline fuel filter is upside down. This way it's going to get clogged very soon, since the dirt builds up on the inside of the filter instead of on the outside. You also won't be able to see if it is clogged. If you only put it on yesterday, it's safe enough to just flip it around, but otherwise get a new one.

I've watched the vid twice, but I'm not completely sure what the problem is. Your idle is a bit high maybe, how's your choke when you shot the video? It looks and sounds like there is just something wrong with your carbs. Hate to say it, but I think you're gonna have to clean them again. It's either that or the timing, and you better hope it's not the timing cuz that's harder to fix than a little carb cleaning.

 

[chrisd1984]

yeah I did get a new filter and line but it's a bit awkward to put on, I feel that when it was on the carbs weren't getting enough fuel..it's larger so it just kind of dangles there.

The audio is hard to hear in the vid but teh revs are behind the hand movement....whereas I used to just rev the bike and the rpms would go up right away, now there is a lag and it takes a second or two for the rpms to respond to the revving of the throttle...

 

[Lou Ranger]

yeah I did get a new filter and line but it's a bit awkward to put on, I feel that when it was on the carbs weren't getting enough fuel ...

Well, if you had the backwards filter on for any length of time, and if there was any detritus. . in the tank, maybe your bike wasn't getting enough fuel.
Try that new line asap.

 

[chrisd1984]

yeah that was the PO who had that on there. Can I just add a fuel line without a filter for a quick ride to see if it changes anything?

 

[Lou Ranger]

yeah that was the PO who had that on there. Can I just add a fuel line without a filter for a quick ride to see if it changes anything?

I guess if you are confident that your tank is clean you can. The risk will be that if the tank is not clean, the detritus. .will not go straight into the carbs.

 

[chrisd1984]

Do you think the bike is safe to ride this way? I know it doesn't come across well in the audio, but when I first got the bike there was immediate response on the rpms when I revved the throttle. Now, I'll rev it in neutral and it will take a seocnd or two to register on the rpms or get any response at all...if shift into first and try riding this on the street, is the throttle going to do something crazy or should i expect problems?

 

[chrisd1984]

haha guess you're never in Toronto eh? just noticed you're in Guelph..

 

[chrisd1984]

yeah so cleaned out the carbs again and checked for leaks everywhere - couldn't find anything besides a slight leak in one of the exhaust manifolds (ordered a new gasket to cover this up). Re-tightened all connections and boots as well.

Everything is fine on the bike except the throttle issue - almost wiped out actually trying to ride it the way it is. It's very sensitive and even the slightest twitch of the throttle will send the rpms skyrocketing. Is there any way to fix this? It used to be I had steady rpms but now it's almost unrideable which sucks as it starts every time now. Would setting the idle screw in the carbs fix this at all?

The mechanic said it was the clutch plates but not sure how that could have a direct causality on the rev issue...

 

[Lou Ranger]

haha guess you're never in Toronto eh? just noticed you're in Guelph..

Well, near Guelph.
I'm in the BigSmoke every couple of weeks but never on my bike. I don't south of Mayfield unless it's well west of Brampton. Too many dangerous drivers talking on cell phones. In my Silverado, they are welcome to pay for a new paint job if they like.

 

[chrisd1984]

Yeah if you're ever down you should let me know, would love to get more knowledge about these bikes and general and hopefully figure my bike's issue one of these days

 

[iggyramone]

Hey man. Not sure if you're still having the problem or not, but my 82 Maxim has done the same thing to me twice as well. Poor start, nearly dying, throttle suffocated it. Other times the choke would catch and send the rpms cycling way too high. First time it fixed itself and I don't know why, second time was because I crashed her. Second time was when I went through and resized the main jets two sizes up (it's lean from the factory, PO put pods on her, and on top of that the mix screw was all the way in) and gave her a new set of spark plugs and suddenly she ran better than ever.

Did you have any luck using the choke lever to help warm the bike up?