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Discussion Starter #1
Hello, I just rebuilt the top end of my sled due to it over heating and seizing up. Now that it’s all back together I have pulled and pulled it trying to start it and I get nowhere. I have gas, spark and compression but it just will not start. The choke switch is broken so I cannot choke the engine while attempting to start. I have tried everything any advice would be greatly appreciated.
 

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I'm guessing you installed new spark plugs. If not, do so. If you cannot choke the machine it may not wanna start cold. You could pour a little mixed gas in each plug hole and she should pop to life. On the other hand it might be so flooded with gas it can't light it. Their are crankcase drains on those, they are low on the case, on the front of the motor and a 10mm. How is cranking compression? Is everything put together correctly? If your not building at least 90psi most engines won't start. What does the spark look like? Should be a big fat blue spark on the plug when ya check it. Do you have the coils hooked up correctly? If you have them out of order, your timing is so far off it won't fire. Hopefully this helps
 

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Discussion Starter #3
I'm guessing you installed new spark plugs. If not, do so. If you cannot choke the machine it may not wanna start cold. You could pour a little mixed gas in each plug hole and she should pop to life. On the other hand it might be so flooded with gas it can't light it. Their are crankcase drains on those, they are low on the case, on the front of the motor and a 10mm. How is cranking compression? Is everything put together correctly? If your not building at least 90psi most engines won't start. What does the spark look like? Should be a big fat blue spark on the plug when ya check it. Do you have the coils hooked up correctly? If you have them out of order, your timing is so far off it won't fire. Hopefully this helps
Yes, I replaced the plugs and I’ve tried putting 2 cycle mixed gas into the plug holes with no avail. I’ve drained the crank case multiple times also. As far as I know everything is put back together correctly and starting on the clutch side I have 125 psi, 149 psi, and 150 psi. There is blue spark coming from the plugs when I tested them. I don’t think I took anything do so with the coils apart, and I labeled the plug wires prior to taking the top end apart so everything is as it was when it was running. I’m to the point where it almost has to be a fuel problem being that after pulling and pulling and pulling the plugs are dry. I’ve replaced the fuel line up to the pump and I’m thinking I’m going to have to replace the rest. But I’ve checked and gas does squirt from the fuel lines when I pull it over. I’m at a loss and frustrated lol
 

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Yes, and I'm thinking on it. You said you put gas down the plug holes and nothing. Now that's interesting. Those compression numbers would definitely run. May be low on one side because she hasn't fired yet... When you drain the crankcase, does fuel come out? If fuel is coming out then she is flooding out and drowning the spark. Did you go through the carbs before you put them back together? Obviously she did run once upon a time, she seized up. I'm gonna think on this for a few minutes and get back to ya
 

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Does that machine have the 34 or 38mm carbs on it? Also sometimes it's hard to tell if a brand new plug has fuel on it, and how much. Just for fun try this, pull the crankcase drain s and the plugs. If you have an air compressor, blow air into the cylinders to clear a flood. Grab a set of used plugs if you have them, and drop them in. Try to start it. Don't choke it at first. See if she will pop. If not go ahead and give her some choke. Don't pull your arm out, we are trying to run this thing down. Pull the plugs and look at them. If they are totally soaked, then ya found the problem. If they are totally dry then we keep move forward.
 

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I'm thinking carb problem. Too much fuel can be an issue. If the floats are not shutting off, then she will just pump fuel right through the carbs and drown the engine in fuel. That being said, I have seen ignition units that would produce a good visual spark but wouldn't run a machine. Let's not go there yet.

When you had her all torn down for rebuild, did you completely drain the fuel tank dry? Snowmobile tanks like to collect water in their off season. This can cause a whole host of issues. If you haven't then definitely do that. While you are doing that, check the fuel line that is inside the fuel tank. Those like to get old and break off inside the tank.
 

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Discussion Starter #8 (Edited)
I'm thinking carb problem. Too much fuel can be an issue. If the floats are not shutting off, then she will just pump fuel right through the carbs and drown the engine in fuel. That being said, I have seen ignition units that would produce a good visual spark but wouldn't run a machine. Let's not go there yet.

When you had her all torn down for rebuild, did you completely drain the fuel tank dry? Snowmobile tanks like to collect water in their off season. This can cause a whole host of issues. If you haven't then definitely do that. While you are doing that, check the fuel line that is inside the fuel tank. Those like to get old and break off inside the tank.
Does that machine have the 34 or 38mm carbs on it? Also sometimes it's hard to tell if a brand new plug has fuel on it, and how much. Just for fun try this, pull the crankcase drain s and the plugs. If you have an air compressor, blow air into the cylinders to clear a flood. Grab a set of used plugs if you have them, and drop them in. Try to start it. Don't choke it at first. See if she will pop. If not go ahead and give her some choke. Don't pull your arm out, we are trying to run this thing down. Pull the plugs and look at them. If they are totally soaked, then ya found the problem. If they are totally dry then we keep move forward.
 

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Discussion Starter #9 (Edited)
I don’t have the old plugs but I will try the air compressor thing and get back to you. Thank you for your insight so far! I have checked the fuel line inside the tank and it’s all good there. I put fresh fuel into it when I started this whole thing also. It back fires once and a while when I’m pulling it over and over again but no start. It did pop last night and the headlight came on for half a second when I put some mixed fuel into the plug holes but that’s all I’ve gotten it to do.
 

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blow air into the gas tank to force the fuel into the bowls. You said the choke lever broke, can you use pair of pliers or vise-grips to pull it out?
 

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Discussion Starter #11
blow air into the gas tank to force the fuel into the bowls. You said the choke lever broke, can you use pair of pliers or vise-grips to pull it out?
I have tried pressurizing the tank a little, I was afraid to mess something up but I will try again. And I’ve used the pliers technique so much that there is nothing to grab onto anymore... could the old fuel lines have possibly partially rotted out creating a check valve inside the line therefore not letting the full amount of fuel into the carb?
 

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Discussion Starter #12
blow air into the gas tank to force the fuel into the bowls. You said the choke lever broke, can you use pair of pliers or vise-grips to pull it out?
I have tried pressurizing the tank a little, I was afraid to mess something up but I will try again. And I’ve used the pliers technique so much that there is nothing to grab onto anymore... could the old fuel lines have possibly partially rotted out creating a check valve inside the line therefore not letting the full amount of fuel into the carb?
 

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You have fuel getting to the carbs. I don't know how old the fuel is but it should kick when you put fuel down the spark plug holes. Is fuel draining out of the crankcase when you open the drains? Are the plugs soaking wet?
 

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Discussion Starter #14
You have fuel getting to the carbs. I don't know how old the fuel is but it should kick when you put fuel down the spark plug holes. Is fuel draining out of the crankcase when you open the drains? Are the plugs soaking wet?
The fuel is new, there is some fuel coming out of the crank case when I pull the plugs but as far as I can tell the plugs are dry
 

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Well you are getting fuel to the engine then, the big question is why isn't it making it from the crankcase to the combustion chamber. When the pistons fall, fuel and air should pass through the transfer ports and enter the combustion area. Even if the pistons were installed backwards you should be drawing fuel in. How about a massive air leak, say like a melted crank seal. Do you see fuel coming out of the engine anywhere? At the rate your going it would be a lot of fuel.
 

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Discussion Starter #16
Well you are getting fuel to the engine then, the big question is why isn't it making it from the crankcase to the combustion chamber. When the pistons fall, fuel and air should pass through the transfer ports and enter the combustion area. Even if the pistons were installed backwards you should be drawing fuel in. How about a massive air leak, say like a melted crank seal. Do you see fuel coming out of the engine anywhere? At the rate your going it would be a lot of fuel.
I haven’t noticed any amount of fuel coming from the engine...
 

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Well, it sounds like you have been over the fuel system. It's getting enough fuel to fire, and enough compression to light. Let's explore ignition. Did you remove the engine from the sled to rebuild it? Maybe we are dealing with a timing or ignition problem. If your getting enough fuel in the engine that you have to drain it, she should at least try and pop a little. You said you labeled everything. Is it somehow possible that the coils are not firing the correct cylinders at the correct time? Did you remove the stator? If so is the timing correct? If your not sure, like 107% positive, then verify this. People often forget that you must have spark at the correct TIME, for an engine to run. Sometimes CDI systems can fail or brake down causing timing to wonder off towards the fence @ right field.
 

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Discussion Starter #18
Well, it sounds like you have been over the fuel system. It's getting enough fuel to fire, and enough compression to light. Let's explore ignition. Did you remove the engine from the sled to rebuild it? Maybe we are dealing with a timing or ignition problem. If your getting enough fuel in the engine that you have to drain it, she should at least try and pop a little. You said you labeled everything. Is it somehow possible that the coils are not firing the correct cylinders at the correct time? Did you remove the stator? If so is the timing correct? If your not sure, like 107% positive, then verify this. People often forget that you must have spark at the correct TIME, for an engine to run. Sometimes CDI systems can fail or brake down causing timing to wonder off towards the fence @ right field.
I didn’t remove the engine, I rebuilt the top end inside the sled. And I over labeled everything lol. I put the exact same choke caps, carbs and plugs back to their exact locations. This is why I’m at so much of a loss. We just got 8” of snow in Michigan and this sled doesn’t want to fire up.
 

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Discussion Starter #19
I just pulled the crank case plugs and plugs themselves and shot some compressed air through the plug holes and got some gas to squirt out. Then I put some gas into the plug holes and I did get it to pop. But that’s about it. Being that the plugs are new it is hard to tell if their wet or not.
 

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You really need to get a new choke cable and install it. Not being able to choke it when starting is hurting you.
 
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