Timing issues

[SpeedyTurtle86]

So I have an 86 half ton 4x4 GMC high sierra. I gotta it from the original owners. About 12 years ago they put a Goodwrench crate 350 in it replacing the 305 that came in it from factory.The OO drove it about 5 years, put 9000 miles on it then had his left knee replaced and couldn't push the clutch any more so it got parked until I came across it about a year ago. I have replaced: mechanical fuel pump, valve cover gaskets, pcv valve and grommet, plugs and cables, rebuilt the carb and pretty much replaced everything I can on the distributor without pulling it and putting a new one in. I CANNOT get it timed it runs fine for about ten to fifteen minutes then dies and acts like it's vapor locked and won't start back up until it's cooled back down. I tried the clothes pin trick, didn't work, that's when I rebuilt the carb and got the same issue. That being said the OO used the carb from the 305 motor when the 350 was installed. I'm thinking they reused the harmonic balancer and distributor as well. Are the timing marks different on the 305 harmonic balancer? Should I pull both the balancer and distributor and replace with parts I know are correct? I'm dying here I traded a $4000 motorcycle for this rig and haven't even been able to run it for fear of damaging the motor!

 

[dvdswan]

I had a similar issue on mine of starving for fuel. I blew out the fuel line from the pump back to the tanks. (actually to the top of the tanks and got a lot of crap out of the lines) Never had an issue after that.

 

[QBuff02]

when you say that you can't get it timed, what exactly are you meaning? As in you time it but then it jumps around? or you think it might not be right and don't know where to set the timing? If the distributor weights and pins are wore out (under the rotor) it will time above a certain rpm but if the rpm drops off it will cause it to retard itself (due to the weights over centering) so much it will literally kill the engine. I had one do this awhile back and I fortunately had a timing light on it and caught it when it happened. idling along just fine, buddy dropped it into gear and as soon as the rpm started to decrease in gear I watched the timing fall from 8 before to the mark on the balancer disappearing and as it did the engine struggled, sputtered and died. had to bump the distributor back around to get it fired back up. pulled it completely apart to investigate and found the weights, pins and bushing pretty much gone under the rotor and some excess play in the shaft. needless to say it got a brand new distributor the next day.

 

[SpeedyTurtle86]

With the distributor in the engine and cylinder one in the front right corner on the cap my timing marks on the balancer are on the left. I have to turn the distributor about 45° clockwise to bring the mark around to the indicator on the block.

 

[QBuff02]

If your 45 degrees is actually where it is, you have an oddball 305 balancer installed on the engine. And a way to tell is the balancer would measure roughly 7" across. An 8" balancer is generally the norm for a 350 engine. There's a couple variations of balancer/timing tab locations for sbc engines. But the most common are timing tabs at 12 o'clock (early)and the most common (late) at about 2 o'clock. If you're ever needing another way to find tdc on a Chevy engine here's a little tip- pull the harmonic balancer bolt. the keyway machined into the crank snout lines up with tdc on the #1 cylinder. +/- possibly by a few degrees.

 

[Snoots]

Does it have one of those damn exhaust outlet valves on the passenger side manifold?

If so, that may be rusted shut.

 

[Frankenchevy]

In this case, I’d find true tdc of #1, find a good viewable reference point on the block, then paint a mark on the balancer.

If you don’t have an advance timing light, but just a regular timing light; figure out what base timing you want to set it at.

Then use this equation (example based on 8” diameter balancer at 10 degrees):

8” x 3.1415=25.132” circumference

25.132/360 x 10(degrees adv)=.698”

So .7” from your TDC is 10 degrees

.56” would be 8 degrees and so on...

Obviously most fabric tapes don’t have inches in decimals, but micrometers do or you could do the conversion. If you have a micrometer, stick a piece of masking tape on your counter, mark zero, then mark .7” or whatever you need. At that point you can transfer it to your balancer.

If, however, your balancer is spinning on its hub, no timing marks will help and you’ll need a new balancer.

 

[SpeedyTurtle86]

I forgot to mention that in order for it to run after I rotated the distributor I had to cram the throttle screw in as far as it would go and it's still idling a little low

 

[Frankenchevy]

I forgot to mention that in order for it to run after I rotated the distributor I had to cram the throttle screw in as far as it would go and it's still idling a little low

What is your adjustment for idle/air mixture screws on the QJ carb? I don’t know QJs at all, but most carbs I’ve ever worked with are 1.5-2 turns out from lightly seated. If you feel your idle/air is properly adjusted, you may have another fuel supply issue with the pump, filter, something in the jets, an orifice, bad float adjustment...tough to say.

Have you verified fuel flow from the new pump?

 

[bucket]

So you rotated the distributor and now it doesn't want to run...

My simple mind says that's your problem. How are you determining where the #1 terminal is on the distributor? If you are going by what a repair manual says, don't. When dropping a distributor into an old Chevy, you can basically set it up with the #1 wherever you want. The position of the #1 plug wire is what determines where the rotor needs to point while in the neighborhood of TDC.

Also, the outer ring could have slipped on the balancer, or the engine could have the wrong timing tab installed.

 

[SpeedyTurtle86]

With the distributor rotated 45° it brings the timing mark to the tab at 2 o'clock. I can start it, warm it up and shut it off and it will fire right back up but the throttle position screw is bottomed out on the spring, not the idle air screws. Before I rotated it, the timing mark on the balancer was at about 10 o'clock. I could fire up the truck warm it up and it would die after about 15 to 30 minutes, or if I shut it off it would not start again until the truck cooled

 

[Frankenchevy]

I understand you were talking about throttle screw, but what about idle/air screw?

I’d go back to my previous post about finding true TDC, marking the balancer and timing it from there. Anything else is guess work. If you have a buddy with a timing light, this costs $0.00. With it properly timed, at least you won’t be in fear of detonation or other timing related problems. Remember to pull the vac advance tube and plug it to set base timing.

 

[SpeedyTurtle86]

I have a timing light with advancing capabilities

 

[Frankenchevy]

I have a timing light with advancing capabilities

Perfect, then you don’t need the math, just find your actual TDC on #1, mark the damper to any viewable reference on the block and dial the light.

If you reference seems to walk after it’s said and done, you may have a bad damper.

 

[Rick Dobbins]

So I have an 86 half ton 4x4 GMC high sierra. I gotta it from the original owners. About 12 years ago they put a Goodwrench crate 350 in it replacing the 305 that came in it from factory.The OO drove it about 5 years, put 9000 miles on it then had his left knee replaced and couldn't push the clutch any more so it got parked until I came across it about a year ago. I have replaced: mechanical fuel pump, valve cover gaskets, pcv valve and grommet, plugs and cables, rebuilt the carb and pretty much replaced everything I can on the distributor without pulling it and putting a new one in. I CANNOT get it timed it runs fine for about ten to fifteen minutes then dies and acts like it's vapor locked and won't start back up until it's cooled back down. I tried the clothes pin trick, didn't work, that's when I rebuilt the carb and got the same issue. That being said the OO used the carb from the 305 motor when the 350 was installed. I'm thinking they reused the harmonic balancer and distributor as well. Are the timing marks different on the 305 harmonic balancer? Should I pull both the balancer and distributor and replace with parts I know are correct? I'm dying here I traded a $4000 motorcycle for this rig and haven't even been able to run it for fear of damaging the motor!

Before it dies, does it run rich? Black smoke, rotten egg smell?

The timing just won't change on it's own. Sounds to me like it's loading up and dying from too much fuel.