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flextx500

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Reply with quote  #1 
I picked up a project '07 Predator last fall and am just finally finishing up the motor rebuild.  I had the cylinder replated because it was very worn out.  I've got a new JE 12.5:1 stock bore piston, complete head rebuild, new timing chain and tensioner.  The carb was completely disassembled, cleaned, and rebuilt.  The valves were shimmed properly and within spec.

The only way I can get the engine to start is by holding the throttle wide open.  It will then run and idle fine.  It's just getting it started that doesn't seem right to me.  It doesn't matter if it's cold or hot.

Any ideas?

Thanks in advance.
05pred500

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Reply with quote  #2 
What are you doing with the choke while starting? Full choke?
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2005 predator 558 - falicon supercrank w/ knife rod, ss valves, 12.5:1 wiseco, hpd 558, HMF full system, uni, CFM oil tank, pro design tether, suspension work by Monster Performance, HID light kit, ODI Rouge, Kalis Racing riser, Flexx bars, razr/razr2
flextx500

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Reply with quote  #3 
I've tried full choke and no choke, there's no difference.
flextx500

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Reply with quote  #4 
I tried it tonight.  I pulled the choke all the way out and tried starting it.  Nothing.  Then no choke and tried starting it.  Nothing.  If I give it throttle without choke, it'll fire right up.  If I pull the choke as soon as it starts to help it warm up, it'll quit.
LEOGM5150

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Reply with quote  #5 
If it'll start and run with the thumb throttle cracked open your thumb throttle safety switch may be shutting it off when you let off the throttle. If your throttle cable is be too tight it tell the cdi the throttle is stuck open and kills spark. The throttle cable needs at least an eighth of an inch to a quarter inch of slack so that the safety connections do not make contact and shut the bike down.
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FROM: POWELL WYOMING USA

MY GREATEST FEAR IS THAT WHEN I DIE MY WIFE WILL SELL MY TOYS FOR WHAT I TOLD HER I HAVE INTO THEM...

2014 POLARIS RZR 4 900 EPS
2012 POLARIS RZR 4 900 XP
2008 POLARIS RZR 800
2008 POLARIS OUTLAW 525S LE
2007 POLARIS OUTLAW 525 IRS
2000 400 RCR TWO STROKE SCRAMBLER
2001 400 TWO STROKE SCRAMBLER
2005 SKI DOO 1000 TWO STROKE SAND SLED
flextx500

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Reply with quote  #6 
I've already checked that also.  Once it starts, it will idle just fine.  It's just getting it started that has me stumped.
LEOGM5150

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Reply with quote  #7 
Could be the valve clearances are too tight.
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FROM: POWELL WYOMING USA

MY GREATEST FEAR IS THAT WHEN I DIE MY WIFE WILL SELL MY TOYS FOR WHAT I TOLD HER I HAVE INTO THEM...

2014 POLARIS RZR 4 900 EPS
2012 POLARIS RZR 4 900 XP
2008 POLARIS RZR 800
2008 POLARIS OUTLAW 525S LE
2007 POLARIS OUTLAW 525 IRS
2000 400 RCR TWO STROKE SCRAMBLER
2001 400 TWO STROKE SCRAMBLER
2005 SKI DOO 1000 TWO STROKE SAND SLED
ORION

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Reply with quote  #8 
Holding it wide open to get it to start, is a symptom of too much fuel. Are you sure the carb rebuild went correctly? Do you have another carb you can put on it to test the theory? Another possibility, is not enough fuel which is being remedied by the accelerator pump when you crack it wide open. If that were the case, the choke should make a difference. Anyway, it sounds like some sort of fuel issue, which is most easily tested with another carb.
flextx500

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Reply with quote  #9 
Unfortunately I don't have another carb to try.  [frown]

Just to verify valve clearances, the Intake valves should be 0.21-0.25mm (0.004"-0.008"), and the Exhaust valves should be 0.33-0.37mm (0.009"-0.013").

I will quadruple verify the clearances tonight, and then check the carb again.
flextx500

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Reply with quote  #10 
Ok, Re-checked valve clearances again.  Both intakes are at 0.006".  One exhaust valve is at 0.010", the other is at 0.012".

I pulled the carb, set the float height, checked everything again.  Now I can't get it to start at all.
cobra131

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Reply with quote  #11 
This is going to be a shot in the dark but I had a problem with my 03 my key way was sheared
flextx500

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Reply with quote  #12 
I think the problem is a weak battery.  I put the charger on it all night.  I went out this morning, hit the choke, gave it a little throttle and it fired right up.  Got home from work tonight, same thing, choke on with a little throttle and it fires right up.  [smile]

Guess it's time for a new battery with the high compression piston.  Besides the piston, it is bone stock, including the bore.  Any other suggestions with the high compression piston as far as jetting or anything else?
05pred500

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Reply with quote  #13 
Maybe try playing with different size pilot jets if you still need some throttle to get it started. Also, what is your idle set at? Maybe that is set too low.
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2005 predator 558 - falicon supercrank w/ knife rod, ss valves, 12.5:1 wiseco, hpd 558, HMF full system, uni, CFM oil tank, pro design tether, suspension work by Monster Performance, HID light kit, ODI Rouge, Kalis Racing riser, Flexx bars, razr/razr2
flextx500

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Reply with quote  #14 
I opened the air screw another half turn, now it fires up and idles perfect without having to touch the throttle!!!  [happy0045]
flextx500

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Reply with quote  #15 
Now when it's warm it won't restart unless I pull the cover off of the air box.  If I put the air box cover on while it's running it starts to bog down at idle, if I open the cover it comes back to normal idle.  Is there something different that I need to do/adjust because of the 12.5:1 compression piston?  I'm running the stock air box with new Polaris filters.  I've got a 150 main jet and a 42.5 pilot and the air screw at 3 turns out.
ORION

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Reply with quote  #16 
Have you tried returning the carb to stock OEM parts/settings? It is often overlooked how important the carb settings are, and how much they can effect the engine. If all you have is a carb problem, and you return the carb to OEM, then it will run predictably and reliably. All engine components and there to support the ideal combustion conditions, and the carb is the first stage of the process. Bad carb, and everything after that wont work at its optimum level. 


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flextx500

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Reply with quote  #17 
I believe all of the jets are the stock pieces that came with the wheeler.  I tried everything at the stock settings according to the manual, 3rd clip on the needle and 2 1/2 turns on the air screw.  It wouldn't start and run until I opened the air screw to 3 turns.  It will work good until I put the cover on the air box, then it acts as if I'm snuffing it out.
flextx500

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Reply with quote  #18 
I really haven't been able to take it out and drive it since the rebuild.  Well, today I was able to drive it and run it under load for a little while.  It actually ran well, starts  and re-starts good even when warm.  I guess sometimes they just need to be taken out and flogged a bit.  Keeping my fingers crossed!!!
ORION

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Reply with quote  #19 
Are you sure the intake boot is not cracked? Best way to check is to spray starting fluid around the area between the carb and the head. If it revs up while spraying, there is a leak. Make sure its not getting sucked into the carb though during this test. A leaky boot can cause all kinds of problems and symptoms. Its also fairly common. 
flextx500

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Reply with quote  #20 
That was one of the first things that I tried with no change in rpm.    I will try it again now that I have a little more run time on it.  I've got many other items that need cleaning and replacing yet, so for now I'll leave the plastics off and run it around the yard a bunch of times before wrapping everything up and calling it finished.
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