Need help with Stihl 066 Magnum

Jason280

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I've been running a couple Husqvarna 372 & 575XPs for a few years, but have been looking for something with more displacement to run a 32" bar. I recently ran into a deal on a Stihl 066 Magnum that I couldn't pass up, so I added it to the saw pile. Well, its been an absolute PITA from day one.

When I first got the saw, it would crank easily, pull well through the RPM range to WOT, but simply wouldn't idle. The saw would promptly die without feathering the throttle. I attempted to adjust the LA screw, but there wasn't enough adjustment to get the saw to idle. Assuming the H & L screws were out of whack, I went to tweaking them with an RPM gauge to try and get the saw set up perfectly. This turned out to be a failure. I started with both jets 1 turn out from stop, and was able to get the saw to idle fairly well around 2800 RPM with a handheld tach. Problem is, it had sluggish acceleration, an intermittent idle surge to 4k+, and would intermittently be very slow to idle back down once the throttle was released from max throttle. I could adjust the L jet to get the throttle response issues and surging idle corrected, but it returned right back to the saw not wanting to idle. I've confirmed that the idle screw is making positive contact with the throttle arm on the carb.

So, I went back to step one. Here's what I've done so far:
-Tore down & completely cleaned carb (removed jets, etc)
-Rebuilt carb with Stihl rebuild kit (new gaskets, fuel metering lever, etc)
-Changed plug to correct NGK, gapped 0.020 (previous was Champion CJ8, not the correct plug)
-New fuel filter, fuel line in tank, and impulse hose
-Flywheel cleaned, ignition module gapped to 0.008"
-Checked compression, 150 psi

Now, with the saw back together, I have hit a brick wall. Saw now will not crank. Period. Won't crank on fuel from the tank, won't fire with starter fluid sprayed in the carb, and won't fire with starter fluid sprayed in the cylinder head. I am getting fuel to the carb, and I have a good/blue spark with the plug grounded out on the cylinder head. Isn't enough, as the saw will not run. Won't even run rough, cough or sputter, nothing. Now, every once and a while when the carb is reattached, I will get a quick "pop" on the first pull or two. Its just enough to reset the decomp valve, but absolutely nothing more.

It has to be something simple that I am not seeing, but I have no idea what it is. What makes no sense is the saw would crank and run before I did all the work to it, but won't even sputter for a little while now. I guess I need to start back from square one, but wanted to get a little more insight from others who know more about this stuff.

Any suggestions?
 

DefinitiveDave

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sounds like an air leak, did you give it a pressure/vacuum test?
intake boot
Dave
 

thomas1

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I'd second the air leak suggestion.

Also, what did you set the coil gap with? .008" is on the narrow side, you might try opening that up. I normally just use a business card as a gauge.
 

PogoInTheWoods

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Make sure the flywheel isn't out of alignment with the keyway due to a sheered (or missing) key. Gotta agree on the vac/pressure test as a must to determine system sealing integrity.
 

machinisttx

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I'd second the air leak suggestion.

Also, what did you set the coil gap with? .008" is on the narrow side, you might try opening that up. I normally just use a business card as a gauge.

I just checked the thickness of a business card. .010". I set everything at .008" with a brass feeler gauge.
 

pioneerguy600

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The saw would run ok set at .008 just to get started. Check the flywheel as Poge has stated, if the engine is getting fire at the wrong time it won`t run, the fire has to happen when the piston is nearly at top dead center, actually around 20 - 18 degrees before TDC when the piston is compressing the fuel and air mixture.
 

Jason280

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I understand that timing could be an issue, but I don't understand how it could have changed or gotten "out of time" considering all I've done is rebuild the carb and change out a couple fuel components. The saw was running prior to the rebuild, albeit not perfectly, but it would run and rev (just wouldn't idle well).

As far as the coil gap is concerned, it was set with a feeler gauge...what is the Stihl spec?
 

Genius

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I understand that timing could be an issue, but I don't understand how it could have changed or gotten "out of time" considering all I've done is rebuild the carb and change out a couple fuel components. The saw was running prior to the rebuild, albeit not perfectly, but it would run and rev (just wouldn't idle well).

As far as the coil gap is concerned, it was set with a feeler gauge...what is the Stihl spec?

I gap my stuff at .010. (I like the business card idea, now I don't need to unfold my feeler gauge set)

I think spec is .008-.012
 

Jason280

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I checked the gap on my 026, and its pretty much the same at 0.008".

When I first couldn't get the saw to crank after the carb rebuild and line changes, I initially suspected the kill switch wasn't assembled correctly. I pulled the carb bracket cover, and found that the switch was wired correctly. I tested it with my multimeter, and found that I was getting continuity between the two wires from the ignition module (one is black, the other is green with a yellow stripe) regardless of the switch position. It didn't matter if the switch was "ON" or "OFF", I still got continuity. I assumed the wires had frayed or maybe even become damaged, and I moved them enough swapping out the impulse hose to cause contact. I traced them back to the ignition module, and found the wires were fine....but I still got continuity across the module connectors. Looking at the pic below, I'm referring to the two areas outlined in red:




I've tested resistance with the ignition module installed, and get 0.7-1.3 ohms from the spade terminal on the module to ground and 12.88-12.91k ohms from the same ground to the spark plug boot terminal.

At first, I thought maybe the ignition module had gone bad, given the continuity across the terminals. My understanding of the kill switch was that it grounded out the coil to kill the spark to the plug. I checked the same wires on my MS210, and there was no continuity unless, as expected, the switch was "OFF" (which forced the two wires in contact). I figured this would explain my problem with the 066, except I also tested my 026....it gave me continuity across the terminals.

Which, brings me right back to square #1. I just cannot figure out how the saw would run before, but not even crank or sputter now after a simple cab rebuild and line change. I honestly believe I am losing fire in the cylinder, which would explain why it won't fire on starter fluid. But, I get a good spark with the plug out of the head, so I have no idea how to proceed.
 

PogoInTheWoods

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....so I have no idea how to proceed.

I would begin by avoiding the use of "starter fluid" in favor of proper mix as a direct prime.

It still sounds like a timing issue or a significant air leak. Have you checked the flywheel keyway alignment as suggested? BTW, some early 066's used a dual keyway flywheel, so don't be confused by that if yours has one...unless, of course, there's no key and the alignment is off.

Also, I checked the coil on my 066 and it yields the same basic results as you describe yours providing.

As for the possibility of an air leak occurring out of nowhere as a result of a simple carb rebuild and line replacement, double check the intake boot for a secure/tight fit -- particularly at the intake port clamp. I had an 036 project give me fits in a similar manner. Wouldn't pop on a direct prime even with a new plug. Discovered the intake boot still had another turn or two left in the clamp screw. Snugging it down did the trick. Had great spark and was getting plenty of fuel, (flooding, actually), but would't pop for anything.

Is the plug wet after trying to start it normally? Is the choke functioning properly? Maybe you're experiencing a similar problem. Hope so..it's an easy fix!

And double check your metering level height to ensure it's correct for the carb and not just immediately flooding the saw.

Good luck with it.
 
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angelo c

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start with the simple stuff...pressure test to eliminate air leaks, visual check timing through flywheel
try the "old" plug
check decomp button. known to leak
ask for a known running carb from one of us guys to check your existing one out.or send your carb to a member to run on a known runner. ?
same for coil.

where are you located.
 

Jason280

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Sorry for the lack of response, but I have taken a little break from the 066. I picked up a cheap MS250 over the weekend, and have been playing with it a little. Couldn't justify having 7 different saws, so I ended up selling an MS210 I've had for a few years.

Anyway, I should be able to start back working on the 066 later today....fingers crossed!
 

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