Valve clearance help (Grizzly 660) - Yamaha Grizzly ATV Forum
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post #1 of 12 Old 12-16-2012, 09:50 AM Thread Starter
 
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Valve clearance help (Grizzly 660)

Hey all,
My grizz was backfiring through the carb at low rpm, so I took it to my uncle who`s a mechanic, he checked the valve clearance, intake was in spec (0.10mm), but exhaust he said they were too loose, so he tightened them to 0.10mm too, but in the service manual it says 0.15-0.20 mm, I told him that but he insisted that 0.10 is better, should I be worried? I dont want to get the valves damaged! Any advice?
Thanks

Grizzly 660 '02. Almost stock.
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post #2 of 12 Old 12-16-2012, 10:56 PM
 
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Originally Posted by erichamk View Post
Hey all,
My grizz was backfiring through the carb at low rpm, so I took it to my uncle who`s a mechanic, he checked the valve clearance, intake was in spec (0.10mm), but exhaust he said they were too loose, so he tightened them to 0.10mm too, but in the service manual it says 0.15-0.20 mm, I told him that but he insisted that 0.10 is better, should I be worried? I dont want to get the valves damaged! Any advice?
Thanks

...Have you ran it with the tighter lash and if so has the backfiring stopped?...

...As a general rule the reason certain lash #'s are given is depending on the cam profile (Lobe angles , and ramp rates etc) having too tight of lash will cause a few things like decreased piston to valve clearance at higher rpms , poor lowend performance and adding premature stress on the cam lobes when they come off the base circle and the rocker meets the lobe part...
.... Having said that , too loose a lash will do the same thing with regards to beating up the lobe by taking more of a run at it if you will and you will also be hurting the power in the higher rpms ....

....If the backfiring has stopped with the tighter lash but comes back to haunt you again relatively soon I would say the cam may be going flat on the exhaust lobes...
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post #3 of 12 Old 12-16-2012, 11:15 PM
 
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Part of the reason for the valve clearance is to allow room for heat expantion. The valves expand as they get hot. The exaust valves get a lot hotter than the intake, so they need more room to expand. I'd do what the manual says. I set mine to upper range prescribed by the manual to allow for my increased compression, and I have no problems at all with my valve clearance.

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MUDIFY-verb. To modify for the purpose of increasing mud performance.
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post #4 of 12 Old 12-17-2012, 07:33 AM
 
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I would go off the engineered specs than the experienced specs in this instance

2011 700 Grizzly, Viper winch, Ricochet skids, Yamaha Bumper, RDC Rad Relocate

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post #5 of 12 Old 12-17-2012, 08:47 AM
 
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You gotta loosen up that exhaust valve clearance. tight clearance makes these things hard to cold start the engine.

2015 Grizzly 700
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2006 Grizzly 660 (SOLD)

Coop45 Machined Primary
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post #6 of 12 Old 12-17-2012, 09:10 AM Thread Starter
 
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Quote:
Originally Posted by Patch700 View Post
...Have you ran it with the tighter lash and if so has the backfiring stopped?...

...As a general rule the reason certain lash #'s are given is depending on the cam profile (Lobe angles , and ramp rates etc) having too tight of lash will cause a few things like decreased piston to valve clearance at higher rpms , poor lowend performance and adding premature stress on the cam lobes when they come off the base circle and the rocker meets the lobe part...
.... Having said that , too loose a lash will do the same thing with regards to beating up the lobe by taking more of a run at it if you will and you will also be hurting the power in the higher rpms ....

....If the backfiring has stopped with the tighter lash but comes back to haunt you again relatively soon I would say the cam may be going flat on the exhaust lobes...
I have tested it and its the same thing really, atleast in warm weather.
What i wanted to fix was that it was almost impossible to start in cold weather, it would backfire too much and i had to play with the throttle with precision trying to keep it running until warmed up, then it could finally move. Choke didnt help much. And when the engine is already warmed up, what it still does is backfire continuously when i touch the throttle just a little bit above idle to move very slowly, but at every other range it has no problem, i can go full throttle with no problem, but no wheelies. The only thing that changed now is that it can be idling without it to die cuz of a sudden backfire, i think thats just because he gave the idle screw 4,5 turns out for more fuel. Maybe its easier to start too, but cant really tell. He said it was running too lean, but all my spark plugs have always a dark color.

Any other ideas for a solution? My plan was to make it run fine with valves in spec and the idle screw in 2,5-3 turns out, like a new machine.

Grizzly 660 '02. Almost stock.
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post #7 of 12 Old 12-17-2012, 08:29 PM
 
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Sounds like the pilot jet is leane. But, the idle is set too rich to compinsate. Try going up 1 or 2 sizes on the pilot, then turn the screw back in to see what happens.

TO BOLDLY THROW MUD NO MAN HAS THROWN BEFORE!
660 SS member
MUDIFY-verb. To modify for the purpose of increasing mud performance.
OL' SCRAPPY
2004 660Red now
MUDIFICATIONS
Bored to 686
Uni Air Filter
Mudbuster Cam
JE 10.75:1 Piston
Mild Head Port
DynoJet Needle and Spring
4 450 Wieghts
1.5mm Shim
EPI Purple Spring
500 RPM Stall Springs
Monster Mayhems/HD2s
Custom-
-3" Snorkels
-Exhaust with Snorkel
-Radiator Relocate
-Bumpers and Skids
-1" Lift
Warn 2500lb. winch
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post #8 of 12 Old 12-18-2012, 08:37 AM Thread Starter
 
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Quote:
Originally Posted by spaceman78 View Post
Sounds like the pilot jet is leane. But, the idle is set too rich to compinsate. Try going up 1 or 2 sizes on the pilot, then turn the screw back in to see what happens.
That makes sense. So where do you buy pilot jets? Do they come in kits?
And the screw works at the same range with the pilot jet, right?

Grizzly 660 '02. Almost stock.

Last edited by erichamk; 12-18-2012 at 09:31 AM.
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post #9 of 12 Old 12-19-2012, 12:02 AM
 
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I'm a little new to jetting too. I'm trying to get mine straight after snorkling. From what I've read, the pilot and screw cover some of the same range, but the screw has most of the idle control and the pilot has most of the control just above idle to 1/4 throttle. Stock pilot size is 40. A 42.5 or maybe a 45 may help. Then set your screw somewhere around 2.5 turns, give or take a 1/2 turn or so.

You could try raising the needle, but that mostly controls 1/4 to 3/4 throttle. It could help if it opened sooner, but that's kind of a slim chance.

I get my jets from my dealer. You can get them on line at sites like jetsrus.com. I don't think you can get pilots in a kit, but I'm not sure.

On the other hand, it may just need to be cleaned good. I'd try that first.

TO BOLDLY THROW MUD NO MAN HAS THROWN BEFORE!
660 SS member
MUDIFY-verb. To modify for the purpose of increasing mud performance.
OL' SCRAPPY
2004 660Red now
MUDIFICATIONS
Bored to 686
Uni Air Filter
Mudbuster Cam
JE 10.75:1 Piston
Mild Head Port
DynoJet Needle and Spring
4 450 Wieghts
1.5mm Shim
EPI Purple Spring
500 RPM Stall Springs
Monster Mayhems/HD2s
Custom-
-3" Snorkels
-Exhaust with Snorkel
-Radiator Relocate
-Bumpers and Skids
-1" Lift
Warn 2500lb. winch

Last edited by spaceman78; 12-19-2012 at 12:05 AM.
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post #10 of 12 Old 12-19-2012, 07:50 AM
 
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Yeah, it your Grizz is 100% stock then I'd start with cleaning and rebuilding the carb if you think its a carb issue.

2015 Grizzly 700
2000 Warn winch

25" Bighorn 2.0

2006 Grizzly 660 (SOLD)

Coop45 Machined Primary
500 rpm wet clutch springs
Carb spring mod
Uni clamp-on air filter mod(mud_dogg450)
WPS heated grips
2500 Warn/Yamaha winch


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post #11 of 12 Old 12-20-2012, 08:28 AM Thread Starter
 
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Quote:
Originally Posted by Cutlass View Post
Yeah, it your Grizz is 100% stock then I'd start with cleaning and rebuilding the carb if you think its a carb issue.
I bought a new carb some months ago, so it's almost brand new. So I think the last option is to try with the bigger jets, hopefully i'll be getting them in january for my next ride, since i dont live in the usa and shippings are like 3-4 weeks to where i live, too late for my new year ride.
Thanks everybody for the help!

Grizzly 660 '02. Almost stock.
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post #12 of 12 Old 12-20-2012, 09:00 AM
 
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You might have a vacuum leak? With everything hooked up like normal you can spray some carb cleaner or starter fluid around the boot going from the carb to the motor. If the engine noise changes then you might of found it. You could also try covering some of your intake to see of that runs better. Let us know if any of this works.

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