Bike dies when stopping at light/stopsign

soriFern

soriFern

XS650 Enthusiast
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Location
Calgary Allberta , Canada
Hey all

Have only posted a few times and meant to put a pick of my bike up, but never got around to it. It's February here in Calgary Alberta Canada and I got my 77xs650 special out. I have been trying to figure out a problem for a while and don't really know where to start but I think its a carb issue. When my bike warms up after about 20-25 minutes of riding she will get to a light, sputter, and then stall....embarrassing stuff. I can get her going again if I give it some juice and hit the starter. However, I usually have to keep it at 1500 or above rpm to keep her on. I was messing around with the mixture screws and I noticed that I could maintain the bike on one cylinder from the left carb at about 1000rpm, but the right carb usually dies, or sits around 800-750 to dead on its own. Any ideas? Carb sync? I'm pretty new to bikes but love learning. Any idea would be great.

Fern:)
 
Check also that there are no leaks or cracks on the carb boots, and that the venturi nipples(if you have any) are either sealed off or connected to the petcock. Mine kept dying when one of my plugs popped off the nipple, and also once one of the carbs popped off just enogh to suck in more air than needed!
 
I was thinking a vacuum leak as well. I just pushed down the hoses going from the nipples to the petcocks, so they are alright. I was thinking about the carb boots as well. I heard WD40 works well for finding leaks?

Fern
 
soriFern said:
Hey all

Have only posted a few times and meant to put a pick of my bike up, but never got around to it. It's February here in Calgary Alberta Canada and I got my 77xs650 special out. I have been trying to figure out a problem for a while and don't really know where to start but I think its a carb issue. When my bike warms up after about 20-25 minutes of riding she will get to a light, sputter, and then stall....embarrassing stuff. I can get her going again if I give it some juice and hit the starter. However, I usually have to keep it at 1500 or above rpm to keep her on. I was messing around with the mixture screws and I noticed that I could maintain the bike on one cylinder from the left carb at about 1000rpm, but the right carb usually dies, or sits around 800-750 to dead on its own. Any ideas? Carb sync? I'm pretty new to bikes but love learning. Any idea would be great.

Fern:)
Click to expand...

Welcome fellow Calgarian:
A few questions to start. Does the bike have stock carbs,stock exhaust and stock air box/filters? If not, what have you got?

What is the history of the bike? How long have you owned it? When was the last time the carbs were taken apart for cleaning, etc.? Do you know if the carbs have the correct stock jets?

There's no point in messing with the mixture screws, unless you know for sure that the carbs are clean inside, float levels set correctly, and the correct pilot jets are being used.

Its also important to know what the battery voltage is when the engine is idling at 1200 rpm. (If you start using the starter motor, wait a few minutes before measuring).
 
They are stock carbs for sure, as for the exhaust I am unsure.Air filters are not stock, they are K and I have owned the bike for 2 years now, and i know the previous owner pretty well (Girlfriends uncle). I know absolutely zip about carbs, and I have really wanted to take them off but have been a bit freaked out. haha. From what I understand though they were rebuilt so there could be some variances in the internal components. And I am a kick starter kind of guy so I will give the battery a measure after a good kick start. I have been thinking its the carbs to be honest, but i just needed to get the courage up to take them off and tear them down. I am relatively mechanically inclined with cars, and have a manual for the bike. So you think I should do some investigating on the inside?

Fern
 
soriFern said:
They are stock carbs for sure, as for the exhaust I am unsure.Air filters are not stock, they are K and I have owned the bike for 2 years now, and i know the previous owner pretty well (Girlfriends uncle). I know absolutely zip about carbs, and I have really wanted to take them off but have been a bit freaked out. haha. From what I understand though they were rebuilt so there could be some variances in the internal components. And I am a kick starter kind of guy so I will give the battery a measure after a good kick start. I have been thinking its the carbs to be honest, but i just needed to get the courage up to take them off and tear them down. I am relatively mechanically inclined with cars, and have a manual for the bike. So you think I should do some investigating on the inside?

Fern
Click to expand...

First thing...............there is no 1977 Special. The 1977 is a Standard model. You should now post a few clear pictures of your bike so that we can see what type exhausts, carbs, and air filters you have.

When an old bike starts stalling, and won't idle well, and you don't know for sure the condition and jetting of the carbs, there's only one option. The carbs must come off, and taken to the bench for a full inspection. Otherwise you're just shooting in the dark, and going around in circles.
 
I agree with check your battery.. Not sure what ignition system your running sounds like it's possible a coil is dropping out due to a weak battery.. My bike died on me Sunday.. Would crank then die.. Replaced battery runs fine again..
 
retiredgentleman said:
First thing...............there is no 1977 Special. The 1977 is a Standard model. You should now post a few clear pictures of your bike so that we can see what type exhausts, carbs, and air filters you have.

When an old bike starts stalling, and won't idle well, and you don't know for sure the condition and jetting of the carbs, there's only one option. The carbs must come off, and taken to the bench for a full inspection. Otherwise you're just shooting in the dark, and going around in circles.
Click to expand...

Alright, hold on, will go snap a few picks. I guess the battery covers say special, so i figured it wouldnt lie to me :p. Rookie mistake.

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theres ma gal.
 

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Looks good! Give us the VIN? leave off a couple numbers for privacy. It's got standard spoke wheels, shocks look like they are at the "standard" style steep angle, gauges head pipes might be standard, seat, tank, sidecovers, look like Special. Might be special parts on a standard frame, but it makes little difference. Read up on head stud retorque, then do it!
 
gggGary said:
Looks good! Give us the VIN? leave off a couple numbers for privacy. It's got standard spoke wheels, shocks look like they are at the "standard" style steep angle, gauges head pipes might be standard, seat, tank, sidecovers, look like Special. Might be special parts on a standard frame, but it makes little difference. Read up on head stud retorque, then do it!
Click to expand...

Will post the vin tomorrow as there are no lights in my shack of a garage. Haha. She's actually not in bad shape considering I only paid 500 for it ;). I really love this bike. The pipes do need to be replaced, she sounds like a monster! It scares the children. I'm hoping after I graduate from university to do some more work on her and maybe put a few modern twists on it. I will read the retorque posts, I was thinking that the cylinder head gasket was actually shot, but maybe they aren't. I am gonna try to make some time to take off the carbs as well and inspect and clean them. PS, why does everyone put pamco ignitions on these bad boys....and what do they do. Lol

Fern
 
I agree with Gary.......................definitely its a Standard frame and wheels. The tank, seat,side covers and taillight appear to be from 78/79 Special.

If you get around to removing the carbs, that is when the carbs can be identified. Carb identity is important because the jetting is quite different between the 76/77 carbs and the 78/79 carbs.
 
I will get them off either this week or next week. Unfortunately I am a bit bogged down with school work. I'm a science student 4th year. Its terrible. So it seems like its a bit of a frankenbike? Haha, I actually didnt know that there were so many mods. I remember looking up 77 special and coming up with nothing so it's good to know it's just a 77. Great bike, love it soon much. Will keep you guys posted on what I find and VIN tomorrow, I do know it starts with 77...wait I'm an idiot, its on my registration. Here's the first5 digits. 447723.
 
That seat looks comfy! Could be someone got it off a Special and then had to put Special side covers on to fit right. Just shows how versatile these Lego block bikes are.
 

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