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Help me with my timing, what am I doing wrong?

BIG*RED

BIG*RED

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My k5 has been backfireing through the carb and dieseling when I shut it off lately, so i went out to check and adjust my timing today.

I have a 350HO with an edelbrock 1904 (795cfm) carb, a accel billet distrub, and an msd6a box.

I let the truck warm up to operating temp, disconect and plug the vac line at the distrub advance, and make sure my idle was were it was susposed to be, and hooked up the timing light. and sure enough the timing was off. it was approx 18 degress atdc. and it should be at 10 degress btdc.

so i turn the distrub until the propper timing markes line up. and this in turn raised my idle rpms. so i adjust the idle screw until its idleing back down where its susposed to be.

recheck the timing and its off again, so i adjust it back to 10degrees btdc, and now my idle is off again, re set idle, now timming is off

its just a never ending circle, what am i doing wrong?
 
Really DUMB question. Are you tightening the dist holdown good after setting the timing? Maybe its not seating round the base of the dist like its supposed to and letting the dist turn.
 
yeah the distrib hold down is good and tight
 
Make sure your vaccum to the distributor has no vaccum at idle. If it has vaccum at idle you are plugged into the wrong port.
 
I've had them rotate on me while tightening it down so I loosen the clamp just enough to move the distributor, no more. Having it still snug helps prevent movement and it doesn't take a whole lot of rotation to throw the timing off. Maybe that's not the problem but it did the trick for me after doing the runaround. Good luck.
 
I'd like to chime in with a similar problem. My son just bought a 72 K5 Blazer with a 350/QuadraJet. We've rebuilt the carb and put on new points/rotor/cap, plugs, wires, etc.

We cannot seem to get the timing to lock in where it belongs. Rotating the distributor (with vacuum disconnected) just a tiny bit causes the timing to jump from around 0 to around 20. It seems to be impossible to get it set anywhere between.

Vacuum is also very low. Around 7-8 at idle.

Has anyone seen this behavior before?

Matt
 
I fyou have a vacuum leak somewhere, that might be your trouble. And you have low vacuum, so I'd start there.
I've also seen the cheapy timing lights do this.
 
We checked all the easy stuff. No vacuum leaks. As it happens the timing light is brand new and cost $50.

When the timing jumps the idle goes up significantly, 500 rpm or so.

We really have no idea how many miles are on the engine. What kind of symptoms would you get from weak valve springs? Sloppy timing chain?
 
U might want to check the pin holding the drive gear on the distributor ,and see if the gear is sloppy on the pin or shaft..also a pick up coil on HEI units,or the bushings in the distributor housing.and the base plate the points bolt to can cause timing to fluxuate or be erratic on a point style distributor..so can the timing chain, and cam gear being worn..many older motors and some newer had nylon teeth on the cam gear...eventually they break off and end up in the oil pump screen..sometimes IN the pump too..add a stretched timing chain too the picture,and timing can jump all over the place..causes surging usually..
 
How difficult is is to swap out the points style distributor for an HEI model on the 72 model?
 
Very easy..

Its just like putting the point style distributor in..have to make sure the rotor on both point at the same place when removing and installing them..if you can pull and put your old one in,an HEI is exactly the same procedure..

Only thing different on HEI is they require a new 10 or 12 ga wire from a 12V source hot only when the key is in the "ON"..and "Start" positions .. a suitable empty spot in the fuse box us usually available,check for power with the key on and while cranking with a test light..--
(dont crank the motor over without the distributor in it--it'll be hell to get it timed again!--pull the points distributor out, and drop the HEI in,with the rotor the exact same place as the points one was pointing too)-then play with the power wire!..

-make sure its got power only when the key is "ON",and during cranking on "START"..and not while its on "ACC"..don't want power going to the HEI if the motor isn't running,like if your parked and listening to the radio,etc..

You can't use the original 12V wire from the point style coil to power the HEI..its a resistance wire that won't pass a full 12V ,and the HEI needs FULL voltage..it would run with the old coil wire,but poorly..

I see many older tucks with HEI swapped in that run crappy,and foul plugs because someone used the old coil wire instead of running a new wire of proper gauge and hooking it to the right source!..one guy said he was about to junk his truck,it kept fouling plugs, and was cutting out under heavy pulls, like taking off quickly into traffic, climbing a hill,etc..!..and he bought a lot of stuff trying to fix it..someone had swapped in an HEI,but used the old wire to power it..:doah:

When I changed the BAT + wire to the HEI the right way,he actually squealed the tires as he pulled away from my shop!--said it would NEVER do anything but sputter and stumble when he goosed it before that!..and he spent a lot of dough on a new Edelbrock carb,headers,etc..and was very disgusted with it!..If I was dishonest,I could have bought it from him cheap,and had a nice truck for short money..but I'm not like that..:crazy:

not yet anyway...:wink1:
 
Mechanical advance

Does your mechanical advance work right? They can lock up from rust and gunk, or move too freely if incorrectly weighted or undersprung. I will never run anything other than an HEI distributor because they are so versatile. You can really fine tune their performance. Be sure you have mechanical advance and then see how vacuum changes your advance. You might be able to get an adjustable vacuum pot also. I get better performance with advanced timing but I live at 10000 feet. I use a vacuum gauge as a reference when playing with timing. Definitely make sure your distributor is installed correctly also.
 
I think a trip to the junkyard for a HEI is probably the best move. We did check the mechanical advance and it moves freely, very freely in fact. We bought a set of new weights and springs but it made no difference.

Is there any year consideration when looking for the HEI at the junkyard?

I'm a little concerned about it fitting too. There is so little clearance at the back between the distributor and the firewall.

We live at 8,600 feet. What do you think a good timing setting is for this altitude?
 
i vote for timing chain. My chevy does that and i ignore it because its close enough and its a used motor. Beat the f**k out of it in a mud pit long enough and mileage does not matter timing chain and valvetrain take a beating! Bad distributor was my problem on my last chevy and put a pick n pull used hei in there and it was all good after that. just a suggestion!
 
Well... we finally got it fixed.

Putting in the HEI distributor was a piece of cake. We also replaced the mechanical weights and springs just to be sure. It ran some better and at least we could adjust the timing again. But it still did not run right (no power) and still did not have any vacuum to speak of.

What finally fixed it was relashing the valves. Two of the cylinders had the valves WAY overtightened. The difference was immediately noticable after adjusting those two cylinders. That's where our vacuum leak was! The exhaust valves were not closing all the way.

So now... after a carb rebuild, upgraded distributor, timing and valve adjustment...it is running sweet!

Thanks everyone for the help.
 
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