1976 STX 340 no spark

A

Andy07

New member
Joined
Dec 12, 2008
Messages
4
Location
Canada
Hi,
I bought this sled during the summer hoping to fix it... As per previous owner it's been sitting in his garage for 19 years or so. It has only 1700 Miles and overall is in a good shape. I believe I had a spark on both plugs few months ago. Later when I've started working on it I could not get it to spark anymore. Maybe it's been something I've done? There were few places where mice made home around the engine, around the stator and inside the muffler. I have cleaned all that. When I could not get it to spark I've decided to disconnect kill switch and put a jumper across.... now I know that I should not have done it. I've started reading some forums on the net, tested coils with multimeter and determined that both coil and cups were bad. I bought and installed new coils with wires and cups now. I had a consistent spark on one of them and intermittent on the other. I've swapped the coils around and both coils gave spark. It looks like I had some voltage coming out from both wires from CDI. I have not removed the stator yet since I don't have the puller. I have tried to clean the contacts inside the stator with very fine sand paper and blow it out with a compressed air and now I don't have spark on both plugs or actually I have it on a first pull occasionally, but very inconsistent. I have bought Clymer Vintage Snowmobiles Vol II, but can't find a solution in there....
Any suggestion would be greatly appreciated.
 
I am not an expert by any means but any yamaha I have been around had normally open, Short to turn engine off, switches. If we had a problem we just unplug them. no jumper, seems to simple though with everything else you have tried
 
i had that problem once along time ago on a old johnson 440 i had ....i changed the points and ran like a dream ....not sure if yours has points tho
 
I bet the mice ater through the wiring somewhere. You have to pull the harness and go over it very carefully.
 
Got the spark now, but plugs stay dry

Thanks for all replies... I'm sorry I've been away from my pc and did not have time to check the forums. I have removed the CDI box and all cables that connect to the engine. I just looked it over and check the cables with multimeter again to make sure there are no open. I've put the CDI back on the sled but bolted only one of 4 screws, connected the cable and now I have consistent spark on both plugs. The bad part is I still don't get any gas going to the plugs. They stay dry despite me pulling the cord multiple times. I can see the gas going through the line to the carb and actually I've noticed a mist of gas coming out via the air intake every time I pull the cord. I've tried to adjust the choke so it should allow more gas with the choke on. Also I've tried to push the throttle to full open while I've pulled the cord and that has really scared me... I think it backfired. It was like a gun shot. I have removed and cleaned the carb before. Maybe there is still something plugged in there? I have removed the carb again and noticed that it was full of gas, but again it would not let any gas on to the spark plugs since they remained dry. I'm planning to take the carb apart again and try to soak and clean it. Everything looked ok when I had it apart last time. I have not replaced any parts on the carb (they all looked ok to me). Any suggestions would be appreciated.
 
Hi there again...
I have made some progress with my STX. I have been able to start it few days ago. That felt soooo good:)This thing has come back from dead. It would start at first pull at times. It has smoked like crazy since I've had a premix in the tank and I've found the oil injection to be working:) I have removed all premix gas from the tank and refilled it with regular gas. It has worked better after that, but still would die on me after wormed up. I have been able to ride it few times around the field. I'm new to this so this thing feels so fast. It looks like the carb air to gas mix needs to be adjusted. Also it might be caused by missing original air intake. I have installed a new belt and tried to adjust a tension on it. The only way I have found this to be possible is to loosen up 4 engine bolts and push the engine away with 2x2;) It has helped, but the belt is still bit too loose and the sled would only move if I rev the engine very high.
I wish there would be a good book available for my model. The only one I've been able to find is Claymer Vintage Snowmobiles Vol 2. I find it too general.
The biggest problem is I have lost the sparks again.... I've been able to start during the day and take it for a quick ride. When I've tried to start it tonight it would start. It would sort of start for a 2 sec and than not at all. I've been pulling and pulling, removed the plugs, checked for spark on both of them, nothing, tried different plugs, nothing, I've tried plugging and unplugging wires, bending them, disconnect all cables of ignition. Eventually I have got a spark on one plug, but not the other. I have had this before, but after removing CDI and cabling harness and putting it back I did get sparks on both plugs. What could this be? It's so frustrating... It came back to life to die on me again. Any suggestion on any of those issues?
1. Carb air to gas adjustment or would it be something else?
2. Belt tension adjustment?
3. Intermittent spark
Thanks again.
 
Andy, I pulled an 83 Vmax 540 out behind an garage a few years ago and went through many of your same Issues. After many hours of cleaning, adjustments ....... I had it running really good than it would just quit and not start. After pulling my hair out I changed the CDI box and she ran strong for two years intil I sold it. There are some real vintage experts on here and soon they will chime in! Good luck I am sure you will get her going!
Blue
 
Thanks for the reply....
Has anyone of you had a CDI ever rebuild? I was also told that I might need my stator rewired. The question is which one of the two is causing this?
 
You must log in or register to reply here.


Back
Top