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Discussion Starter · #1 ·
Can a bad stator cause an intermittent sputtering and backfiring condition?
 

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I am unique
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Can a bad stator cause an intermittent sputtering and backfiring condition?
So can bad wiring. SparkPlug. Coil. Sparkplug cap. Defective park brake and reverse rev limiters switches. Bad gasoline ETC......
 

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Master of the Electron
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Bottom line, it's possible - but it's just as likely 5 or 10 other things. Troubleshooting is in order.
 

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Discussion Starter · #4 · (Edited)
Well here's the whole story:

This is a rebuild project I've just finished, put in a .20 over Wiseco piston and Hot Rods stock crank, the only internal mods. It has a full Yoshi RS3 exhaust, UM racing air box with Pro Design foam Filter and Outerwears cover, 155L, 160R, #25 Pilots, 2.5T L, 3T R on the screws.

Took it out for a test ride last Sunday, let it warm up a good five minutes or better as I got all my gear on, then took off down the gravel road. It hesitated off idle then pulled hard. It would backfire bad when I'd let off and coast downhill. When re-accelerating from a coast, it would bog slightly then pull hard.

I brought along a flexible screwdriver to try to adjust the pilots, had them at 2.5 turns out left and 3 turns out right. After a few runs up and down the gravel road, I stopped and checked the air box. It had some water in there, but no gas. I adjusted the pilots in about 1/8 turn, and tried again. Not much difference, still backfired like crazy when coasting down, and bogged before pulling hard on re-acceleration. Something else odd I noticed, when running along about mid 3rd gear, I would hear this popping or clanging noise every few seconds from the engine, sounded like spark knock.

I tried a few more runs on the gravel road, and adjusted in the pilots in a little each time, and the problem never really went away. So I tried a section of trail. As soon as I turned off the gravel road and got on the rough trail, it started the popping and sputtering. These are rough trails, so I'm working the throttle a lot more, and using a lot more "low end". I had to constantly pull the clutch and rev it up to "clear it out". It would pop and backfire something awful at the lower speeds on the trail. Down in the bottom where it's real wet and these paver block "doubles" are (1st gear) would mess it up every time. But as I would get going faster it would clear out and pulled hard.
 

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Master of the Electron
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1) you're turning the pilot screws the wrong way - you're exhibiting symptoms of being too lean on the pilot circuit (popping on decel, hesitation when coming on throttle) yet you are leaning them more by turning in - turn them OUT (CCW) instead.

2) what needles are you using? With your mods you need aftermarket (DJ or GYTR) needles and their more aggressive taper - stocks will be too lean between 1/4 and 3/4 throttle.

3) with your mods, I would have used 160L/165R Mikuni mains - you're close, and they may be okay, but every symptom you have described so far implies too lean.
 

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Well here's the whole story:

This is a rebuild project I've just finished, put in a .20 over Wiseco piston and Hot Rods stock crank, the only internal mods. It has a full Yoshi RS3 exhaust, UM racing air box with Pro Design foam Filter and Outerwears cover, 155L, 160R, #25 Pilots, 2.5T L, 3T R on the screws.

Took it out for a test ride last Sunday, let it warm up a good five minutes or better as I got all my gear on, then took off down the gravel road. It hesitated off idle then pulled hard. It would backfire bad when I'd let off and coast downhill. When re-accelerating from a coast, it would bog slightly then pull hard.

I brought along a flexible screwdriver to try to adjust the pilots, had them at 2.5 turns out left and 3 turns out right. After a few runs up and down the gravel road, I stopped and checked the air box. It had some water in there, but no gas. I adjusted the pilots in about 1/8 turn, and tried again. Not much difference, still backfired like crazy when coasting down, and bogged before pulling hard on re-acceleration. Something else odd I noticed, when running along about mid 3rd gear, I would hear this popping or clanging noise every few seconds from the engine, sounded like spark knock.

I tried a few more runs on the gravel road, and adjusted in the pilots in a little each time, and the problem never really went away. So I tried a section of trail. As soon as I turned off the gravel road and got on the rough trail, it started the popping and sputtering. These are rough trails, so I'm working the throttle a lot more, and using a lot more "low end". I had to constantly pull the clutch and rev it up to "clear it out". It would pop and backfire something awful at the lower speeds on the trail. Down in the bottom where it's real wet and these paver block "doubles" are (1st gear) would mess it up every time. But as I would get going faster it would clear out and pulled hard.
Why are you turning the fuel screws in, you need to turn them out for more fuel, are these the stock carbs.............
 

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Discussion Starter · #7 ·
Yes they are the stock carbs. From what I've been reading on here, I agree I'm way lean. I think a jet kit is in order, likely a Vito's kit.
 

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Yes they are the stock carbs. From what I've been reading on here, I agree I'm way lean. I think a jet kit is in order, likely a Vito's kit.
You can get needles from AlbaNate on this forum............
 

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Discussion Starter · #9 ·
Thanks, I just ordered a Vito's kit from VPracing on EBay.

This quad originally had the Vito's kit, and the needles and needle jets were worn, and one of the pilot screws was galled on the tip. I had replaced all of this with the parts from a Shindy rebuild kit off Ebay. Keeping the larger Mikuni mains and pilots that were in there and using the new needles, needle jets and pilot screws to replace the worn Vito's parts. The new needles were a thicker profile, and this has leaned it out more.
 

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Master of the Electron
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Thanks, I just ordered a Vito's kit from VPracing on EBay.

This quad originally had the Vito's kit, and the needles and needle jets were worn, and one of the pilot screws was galled on the tip. I had replaced all of this with the parts from a Shindy rebuild kit off Ebay. Keeping the larger Mikuni mains and pilots that were in there and using the new needles, needle jets and pilot screws to replace the worn Vito's parts. The new needles were a thicker profile, and this has leaned it out more.

Yep, this explains it - the Vitos kit should fix your problems.
 

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Discussion Starter · #11 ·
Update

Tonight I pulled the carbs in anticipation of my jet kit arriving. Still suspicious of this being electrical, I got to checking the resistances of the pickup coil and stator windings. The pickup coil and direction coil checked fine, but sure enough one leg of the stator was open. This would cause a low charge output and a high ripple current. Could this possibly confuse the CDI and mess up the ignition?
 

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Tonight I pulled the carbs in anticipation of my jet kit arriving. Still suspicious of this being electrical, I got to checking the resistances of the pickup coil and stator windings. The pickup coil and direction coil checked fine, but sure enough one leg of the stator was open. This would cause a low charge output and a high ripple current. Could this possibly confuse the CDI and mess up the ignition?
I doubt it. You don't need the charging system to run the engine. But then again, anything is possible...........
 

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Master of the Electron
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leave the regulator unplugged if you're concerned... but it shouldn't be an issue.
 

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Discussion Starter · #14 ·
Since I need a stator, should I trust a used stock one, or go aftermarket? Any certain brand?

I'm still re-jetting, but the open stator cant be helping things.
 

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Master of the Electron
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OEM - aftermarkets seem to have infant mortality issues.

The open stator should not be affecting the engine's performance. I would be very surprised if there was a connection.
 

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Discussion Starter · #16 ·
Just ordered up a new stator! Between that and the jet kit gonna have a busy weekend...
 

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Discussion Starter · #18 ·
It came with one. Hopefully between these two things I can solve the problem. Jetting is still the primary issue.
 

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Discussion Starter · #19 ·
Did some more investigating this evening. Pulled the plug and definitely had been running lean, the plug was slightly gray from where it had previously been run rich, but the insulator was now pearly white on one side, and barely gray on the other. Looked like a textbook picture of a hot lean plug.

Next I checked the valve clearance. They still had play, but had tightened up below minimum spec. The spec is .010 - .015 for the intake, I had them set at .012, now they were less than .010, didn't measure to see just how tight they were. I re-set then to .012 and tightened the locknuts. The exhaust valves were harder to get to with the engine installed, I'll need to get a slanted feeler gauge set with a smaller tip to properly check those. They still had play, but I'd say it's a safe bet they've tightened up too. I ran out of daylight, and needed a better feeler gauge, so I put it up for the night.

(Now tell me I've burned the valves and need head work....)
 

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Did some more investigating this evening. Pulled the plug and definitely had been running lean, the plug was slightly gray from where it had previously been run rich, but the insulator was now pearly white on one side, and barely gray on the other. Looked like a textbook picture of a hot lean plug.

Next I checked the valve clearance. They still had play, but had tightened up below minimum spec. The spec is .010 - .015 for the intake, I had them set at .012, now they were less than .010, didn't measure to see just how tight they were. I re-set then to .012 and tightened the locknuts. The exhaust valves were harder to get to with the engine installed, I'll need to get a slanted feeler gauge set with a smaller tip to properly check those. They still had play, but I'd say it's a safe bet they've tightened up too. I ran out of daylight, and needed a better feeler gauge, so I put it up for the night.

(Now tell me I've burned the valves and need head work....)
If you burned valves, it wouldn't start......
 
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