Author Topic: Weak Spark please help  (Read 11713 times)

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Offline Silentstrike

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Re: Weak Spark please help
« Reply #60 on: February 26, 2009, 12:53:50 PM »
(raises hand) oooh oooh pick me

all joking aside

We varied the timing till it wants to kick but it just won't it's turning over strong,  The carb said it was pretuned from the factory it was marked as direct replacement for my exact engine,  My dad didn't wanna mess with it too much,  I personally still feel it is the carb or something with it because gas doesn't seem to be getting into the cylindars well.
« Last Edit: February 26, 2009, 12:56:36 PM by Silentstrike »

Offline Rick

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Re: Weak Spark please help
« Reply #61 on: February 26, 2009, 01:06:46 PM »
At this point, it should pretty well fire up as long as the carb is putting *any* fuel into the engine.  At the risk of asking a really stupid question, you don't have it flooded, do you?  If you think it might be, you can block the throttle plates open and blow air down the carb into the engine until the gas smell abates a little.  A flooded engine can be very difficult to start.

Offline stimpy

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Re: Weak Spark please help
« Reply #62 on: February 26, 2009, 02:13:56 PM »
may I ask how many miles are on the motor ???  and when it died did it make a popping noise ? and was the motor running sluggish at low speed but the performance was good at hiway speed ?( 45-60 )

Offline Silentstrike

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Re: Weak Spark please help
« Reply #63 on: February 26, 2009, 02:47:27 PM »
I pulled the plugs to make sure they weren't wet and I haven't seen any sign of flooding,  There is 178K on my motor but it made no popping noise and ran fine beforehand

Offline Joker (§ir£Ğragon)

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Re: Weak Spark please help
« Reply #64 on: February 26, 2009, 02:58:23 PM »
Well, fine and sluggish are relative terms. Especially when talking about a little 305 that's traveled 3/4 of the way to the moon. ;)  I know where Stimp's going with this. Has any work been done on the engine? It's possible it didn't pop, but that the timing chain skipped a tooth the last time you shut the engine off.
Larry


Offline Rick

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Re: Weak Spark please help
« Reply #65 on: February 26, 2009, 04:46:05 PM »
Yeah, it's starting to sound like maybe it's timing-chain related.  If it's not flooded bad, then it's timing related.  You have gas in the engine, and you have spark, so what's left is timing in these circumstances.

The distributor is driven by the camshaft.  The camshaft is driven by the crank via a chain (i.e., the timing chain).  The crank gear is all metal and pretty durable.  The chain stretches over time, but overall it's pretty durable also.  The "weak link" in the design is the cam gear.  Stock GM cam gears have nylon teeth on them -- that's to make the engine run quieter.  Those are only good for about 100,000 miles.  With age, mileage, and heat from the engine the factory nylon teeth begin cracking and some can even fall off.  As it wears, the timing chain gets looser and looser, and finally the timing chain can slip a few teeth.  When that happens all the King's horses and all the King's men can't get the engine started again.  Why?  Because the timing of the valves opening and closing and the distributor firing is all out of kilter.  That stuff all has to happen in a sequence that's dictated by the crank position, and if the timing chain slips it's all screwed up.

It doesn't take much to make that chain slip, either.  It can happen just starting the car up.  I've had it happen to me just setting at a stoplight, not touching the gas.

If that's the case, then what you need to do is to replace the timing chain.  You get a new cam gear, a new timing chain, and a new crank gear -- replace them all as a set.  You follow the procedure in the service manual and go from there.

It's not hard to do at all, and it's not very expensive.  If your engine has 178K on it and it's either never been opened before then it needs replacement.  Even if it was replaced once about 1/2 way through that interval, it's time anyway.

I'd start looking in that direction rather than fooling around with the carb, since the carb is new.  Just satisfy yourself that you've done all you can do with the timing/distributor and make sure it's not just flooded badly first.

Offline ta78w72

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Re: Weak Spark please help
« Reply #66 on: February 26, 2009, 05:35:40 PM »
Before you pull the timing chain cover (I agree with everyone that it could be the timing chain.....that's exactly what I was thinking) I would measure the voltage at the BAT terminal of the distributor with the engine cranking.  Just make sure you have at least 7 volts there.  If you do, you've got enough current to give you enough spark.  It's a five minute test that will eliminate the ignition switch or bad bulkhead connector from the mix.

If you pull the timing chain cover, you can at that time check your distributor position with the gears at twelve o'clock.

Offline Silentstrike

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Re: Weak Spark please help
« Reply #67 on: February 26, 2009, 08:11:16 PM »
My father is still stuck on this bad gas thing because it doesn't smell 100% correct do you guys know anyway to check for that?  I would check the timeing chain myself but I don't like to get into anything big without my dad backing me up he said we'll do it if we can prove the gas isn't bad

Offline fireman_033

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Re: Weak Spark please help
« Reply #68 on: February 26, 2009, 08:17:07 PM »
    Pour a little on the ground and see if it lights easily.. I stress little and be careful.  Scott

Offline Silentstrike

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Re: Weak Spark please help
« Reply #69 on: February 26, 2009, 08:31:34 PM »
I can light it with a grill lighter but it burns with more smoke and doesn't seem as hot as regular gas

Offline fireman_033

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Re: Weak Spark please help
« Reply #70 on: February 26, 2009, 08:56:32 PM »
   Does it light instantly or hard to light. Smoke........... You dont think you put diesel in by accident do you....Scott

Offline stimpy

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Re: Weak Spark please help
« Reply #71 on: February 26, 2009, 08:57:14 PM »
to check the timing chain theres a simple proceedure  bring the balancer to the tdc mark on the crank timer , then remove the cap and rotate the crank backwards while watching the rotor and when it starts turning stop!  then look at the timer tabs and see how far it moved before the rotro moved if its over 5 degrees its bad .  

Offline 78ta

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Re: Weak Spark please help
« Reply #72 on: February 26, 2009, 10:03:42 PM »
To eliminate the gas a a problem, Get your lawn mower gas can and a length of fuel line long enough to go from the gas can to the fuel pump and use that as your source. This ofcoarse assumes the gas in the can is good. Just go put some fresh gas in the can to be sure.
Randy

Offline Amtrak

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Re: Weak Spark please help
« Reply #73 on: February 27, 2009, 01:16:20 AM »
If you pour a quarter cup of gas in the carb and the engine won't start the timing is OFF!!!!!!!!!!!!!!!
it doesnt matter is the carb is good or not the engine should crank and run about 5 seconds

Offline ta78w72

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Re: Weak Spark please help
« Reply #74 on: February 27, 2009, 11:31:50 AM »
Not necessarily.  Remember this thread starting with a complaint of weak spark.  I still believe it prudent to check the voltage at the bat terminal just to make sure he doesn't have a bad ignition switch.

I've had my car sit in the garage for two years in between starts and the gas was still "good".

But, I tend to agree that the timing chain is suspect.  If it were my car, I would pull the timing chain cover just to visually check it.  The engine has a lot of miles on it.