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Discussion Starter #1
I’m new here to Yamaha but have been around engines some for years. I just picked up a Yamaha Grizzly that’s been sitting for a few months. Sellers story seemed legit so I took a chance on buying a non-running atv with 400 hours and in great shape. Checked compression while I had the carb off to replace it and it’s at 120 PSI which I’ve read is slightly low for these and should be about 160psi. Could the decompression cam be causing the slightly low numbers or did I probably end up with a lemon?
 

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Hey...Subzero..Welcome to GC from Wisconsin.

The FSM indicates 188psi at 850rpms. Did you get it spinning fast enough?
 

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Discussion Starter #3
I doubt it was spinning at 850 rpms- I was just using the electric starter. Without a tachometer it’d be hard to tell. Is there any spec for just pull starter compression? Thanks for the information.
 

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I am assuming you have a 660.
With spinning to slowly the compression release will hold a valve open a little for easier starting giving a low PSI.
Never heard of any spec on using the pull rope.
You could squirt a little (teaspoon) of 30w oil in the cylinder to see if/how much the PSI goes up.

Might hear from some other member.
 

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Welcome from Colorado.
With the age, the valve(s) could be tight.
I'm impress you got 120 p.s.i. on the pull start.
I would spray a shot of starting fluid down the intake to see if she'll fire.
 

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First questions for me....do you have it back together? And does it run and how so? If the answers are yes, yes, and great....then I wouldn't sweat it. Ride on. If it's not running or running poorly, then I'd look more carefully at these numbers.

Had an old TRX250 utility we revived a few months ago. Sat for 10 years. But was told it was running before it was parked. Didn't use a compression gage but thing had hardly any discernable compression while moving the kickstarter by hand. We put some 2 cycle oil in through the spark plug hole, dispersed it by kicking it over, gave it a couple weeks, and still almost no compression. Finally rebuilt the carb, then tried starting it. Took a few good turns, but she fired to life. After running good and getting warmed up we shut it down. Voila, has great compression. Temporarily stuck ring perhaps? Not too concerned cause it runs like the day it came off the production line.
 

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Discussion Starter #7
I haven’t gotten it running yet, still waiting on my new aftermarket carb in the mail. I figure I’d rebuild the original one later on. The bike I’ve been told was sitting for about three months and ran perfect before. BTW has anyone had any luck with these Chinese clone carbs? I ordered mine from Caltric.
 

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I believe a number of members have had good luck with the Caltric carbs. I think Dezz has used them. He should be stopping by.
 

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Caltric parts are hit and miss. Some are good, and some are not. I will not buy their electrical parts anymore, because in my experience they have been either cheaply made or are not made correctly (their coolant switches are made backwards to what the OEM parts do).
I have no experience with a Caltric carb yet, but I have experience with a few Chinese carbs....and like many other people, have found them hit or miss. Some have great luck (and have posted on here stating that), while others never can get them working right.

With your engine, I wouldn't worry about the compression until you get it running again. If you getting 120 psi now after sitting for months, that's not bad.
It's a good chance your valves are leaking and will need a lapping. The 2002-2004 660's were known as oil burners, and it was mainly due to the piston rings. Yamaha used different rings in the 2005-2008 models that cured this issue.
If you feel you need to open the engine up after getting running first, then I would do a new piston, rings, valve seals and lap the the valves. You'll have very reliable, excellent performing platform that will last for years.

Btw, believe it not not, OEM will be your cheapest route in the engine. Yamaha engine parts are surprisingly cheap compared to how they price their accessories.
 

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Discussion Starter #10
Thanks for the replies, I installed the carb tonight, read online these carbs run slightly lean because of emissions and have a brass insert over top the mixture screw so I removed it and turned the mixture up a very slight amount just to be safe. I think it has a 153 jet installed out of the box but came with a 150 and 155. I’m at sea level here so I don’t think swapping jets is necessary. Still waiting on a new fuel petcock in the mail to have a complete machine and then it’s time to see if it will run.
 

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Thanks for the replies, I installed the carb tonight, read online these carbs run slightly lean because of emissions and have a brass insert over top the mixture screw so I removed it and turned the mixture up a very slight amount just to be safe. I think it has a 153 jet installed out of the box but came with a 150 and 155. I’m at sea level here so I don’t think swapping jets is necessary. Still waiting on a new fuel petcock in the mail to have a complete machine and then it’s time to see if it will run.
Interested to hear how that carb works out for you, keep us posted.

My guess is that after only sitting 3 months, your stock carb won't be all that horrible inside. Quick disassembly and cleaning and that one will be good to go again.
 

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Discussion Starter #12
Today I got the new fuel petcock and installed everything else. Put some fresh gas in the tank and the bike fired right up and runs great. It is smoking some from the exhaust but it cleared up after riding it and allowing it to warm up. The bike runs pretty good even with the Chinese carb. I did have to adjust the idle up some. The smoke looked black/white. Still had good power and the smoke did clear once it was warmed up. Any thoughts on the possible cause and how long I can expect the bike to be reliable? The bike has just over 450 hours which seemed low to me for an engine to have worn rings, especially one that looks to of been taken care of. It is an atv the places I will take it won’t be the best to break down in...
 

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I wouldn't be surprised to see some smoke on first start of a machine that has been sitting for a long time. Who knows how long it will last. It all depends on whether there was condensation build up in the engine while it was sitting for a while. Just run the heck out of it and enjoy it. With that many hours on it, there likely could be some ring wear. Don't worry about it and just fix it when you have a problem. Congrats on getting a good deal on a Griz.
 

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Discussion Starter #14 (Edited)
Started the bike up today and it’s running a little more rough than yesterday, seems to be misfiring and has a slight popping noise from the exhaust. Revs up fine and still drives fine but at idle it makes the noise. Almost like just after reving up when you release the throttle. Can’t seem to figure out what it could be. New carb, spark plug was just changed. Only thing I did between yesterday and today was a new fuel line as the other one was leaking and an oil change. I linked a video of the bike running


 

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Started the bike up today and it’s running a little more rough than yesterday, seems to be misfiring and has a slight popping noise from the exhaust. Revs up fine and still drives fine but at idle it makes the noise. Almost like just after reving up when you release the throttle. Can’t seem to figure out what it could be. New carb, spark plug was just changed. Only thing I did between yesterday and today was a new fuel line as the other one was leaking and an oil change. I linked a video of the bike running


https://youtu.be/iTalFRnNxIY


Rebuild the Yamaha carb and put it back on .... I tried eBay carb on my 04 in a pinch . Never got it to run right . Rebuilt the old carb and she runs like a top ...


I should be out riding instead of on here
 

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Discussion Starter #16
Checked compression again today, right on spec at 188 psi and the starter was able to turn the engine fast enough to overcome the decompression mech. The bike runs better just after cutting the gas off on the petcock for a few seconds and the spark plug is black after only a short time running. I think you are right and it is the Chinese carb that is causing it to run badly. Strange it ran well the first hour of running but now doesn’t do good. I have no idea how to rebuild a carb properly and I’d rather just not mess something up more as I need the bike ASAP. I see a brand new one is around $390 from Yamaha. What would a shop charge to rebuild the carb off the bike?
 

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Checked compression again today, right on spec at 188 psi and the starter was able to turn the engine fast enough to overcome the decompression mech. The bike runs better just after cutting the gas off on the petcock for a few seconds and the spark plug is black after only a short time running. I think you are right and it is the Chinese carb that is causing it to run badly. Strange it ran well the first hour of running but now doesn’t do good. I have no idea how to rebuild a carb properly and I’d rather just not mess something up more as I need the bike ASAP. I see a brand new one is around $390 from Yamaha. What would a shop charge to rebuild the carb off the bike?
Just rebuild your carb. Don't blow 400$ on something your perfectly capable of doing in 30 min yourself!
 
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Checked compression again today, right on spec at 188 psi and the starter was able to turn the engine fast enough to overcome the decompression mech. The bike runs better just after cutting the gas off on the petcock for a few seconds and the spark plug is black after only a short time running. I think you are right and it is the Chinese carb that is causing it to run badly. Strange it ran well the first hour of running but now doesn’t do good. I have no idea how to rebuild a carb properly and I’d rather just not mess something up more as I need the bike ASAP. I see a brand new one is around $390 from Yamaha. What would a shop charge to rebuild the carb off the bike?
Why didn't you just say from the beginning you've never rebuilt a carb before? There's no shame in that. That explains why you just bought the Chinese carb right away. But here's the thing... You had the skill to get to and remove and install the other carb. So I'm confident in your ability to to clean and install the parts from a carb rebuild kit in your OEM carb. And if the thing only sat for 3 months, it might only need a good cleaning and not even need a full rebuild kit.

Plus, tons of videos on YouTube to guide you. AND you have us here to coach you along. Youcandoit.

Just rebuild your carb. Don't blow 400$ on something your perfectly capable of doing in 30 min yourself!
AGREED
 

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Discussion Starter #19
I’d like to replace the diaphragm too when rebuilding. I used some intake/carb cleaner without removing it earlier on when I first got the bike and it deformed it. Which rebuild kit is good to buy?
 

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I’d like to replace the diaphragm too when rebuilding. I used some intake/carb cleaner without removing it earlier on when I first got the bike and it deformed it. Which rebuild kit is good to buy?
Sorry for the inactivity...

I would just see what Rocky Mountain ATV, Dennis Kirk, or Motosport.com has available.

But if you're not in a hurry, just pull the carb apart before you buy anything and see what it needs. Might just need a float bowl gasket, and can just get that from local dealer.
 
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