Timing? Issues

[MrSteve]

Hey everyone! I have an 82 GMC Sierra 2500 with a rebuilt 350. I have had a driveability issue that goes like this: I can set the timing according to spec with the advance plugged. The engine idles perfectly but when I put it in drive I move ok as long as I gently touch the throttle but If I try to drive normally it boggs and tries to die on me. I have checked all the vacuum lines and they are routed correctly with no leaks. The vacuum advance works and does move the plate in the distributor. Is it possible that the distributor is set/installed wrong? If I wanted to verify the TDC and position of the distributor and #1 how would you guide me and what steps should I proceed in? Assuming you don't have other ideas as to what could be the problem.

Steve

[fiyaweed06]

to verify TDC on the compression stroke put your finger over the #1 plug hole until air pushes your finger from the hole,when this happens get your marks set to 0 on the balancer or i stick a screw driver in the hole until it reaches its top most point and stab the dizzy that should get you close enough to get it started.

[James McClure]

Steve, everything you have done is correct. The problem isn't ignition or timeing, but carburation. The accelerator pump isn't spraying a good healthy squirt of fuel when you snap the throttle open from an idle. With the eng OFF, look down the throttle bore and open the throttle qiuckly. What you want to see is at least 2 good streams of gas into the primary bores. Once thats' corrected you should be fine. jim

[MrSteve]

I'm going to check that but what I have done is moved the timing way off from spec by feel (driving and moving it till it ran better). This has allowed the truck to run fine. The problem is that I have to smog the truck and when I set the timing to spec it is barely driveable and does what I described above. Thanks for guiding me!

Steve

[MrSteve]

Ok... I'm at TDC (to check distributor alignement) and timed at 6 degrees according to spec. I have checked the secondaries and they are squirting fuel just fine. Starts and idles perfectly but no accerleration without feathering the throttle, and forget about flooring it... it backfires and stmbles bad. Next?

Steve

[MrSteve]

I just discovered I have full vacuum to the distributor. The vacuum routing is correct according to the diagram but I don't know how to test the check or temp valves.

Steve

[Hottrucks]

back fire though carb or tail pipe?? carb means to much advance tail pipe means to far after TDC

[MrSteve]

Back firing through the Carb! But I think the advance is screwy! I have full vacuum at the distributor at idle, which means I have full advance at idle... correct? I have checked the vacuum routing and all is accurate. But there must be a check valve or temp check valve that's not working. I don't know how to check the valves. One of them is located right in line with the advance and when I try to pull a vacuum on it, it is open in both directions... meaning I can't pull a vacuum either direction. Isn't that check valve a delay? How is it supposed to work and how do I check it? Thank you for your help

Steve

[Hottrucks]

I usually pull vacum from the carb on the advance port...looking at the carb it will be the small one on the left next to the adjustmnet screw...it only pulls vacum when you stab it

[MrSteve]

Well I have it routed as per the diagram and it is acuurate. I plugged the line a through a light on it. The motor had already been set at TDC. When I put the light on it the mark on the damper was retarded way past the degree marker by about 2-3 inches. I tried to move it back to 6 degrees and the truck died. had to totate the distributor back to where I had it to start it. Is the distributor installed wrong?

[MrSteve]

K-O! The factory damper timing mark is off. I located another mark evidently made by the previuos owner and cleaned and remarked it. I was able to set the timing to 6 degrees according to spec. I then plugged the vacuum advance line onto the dist and it advanced and raised the RPMs. Evidently the vacuum delay check valve is no good. I'll pick one up tomorrow. I guess I can acquire one at the usual parts stores? Also I noticed that the automatic choke was not doing it's thing so I'll adjust it tomorrow morning. I'm keeping my fingers crossed that WE have found the timing issue. I'll report back tomorrow.

Thank You everyone!

Steve

[Hottrucks]

Kool!!!!!!!!!

[MrSteve]

Hey Guys! As previuosly mentioned... the vacuum delay valve to the distributor is broken. I know I can route the dist to a ported source but if I am taking the truck for smog, shouldn't it be hooked up according to the official emissions diagram? Won't I run into trouble if I don't repair it to factory specs? I'm having a hard time locating the proper valve. I guess I can grab a couple from the wrecking yard. New ones are $30 and have to be ordered.

Thanks!

Steve

[Oilbrnr]

I battled something similar, and it turned out to be my fault. The HB has a notch AND a bead. I was using the notch, and did not notice the bead until one day I had the truck up on my lift and just happened to see it! Doh!!!

[MrSteve]

Yep! That's exactly what I have! I set the timing to 6 degrees as instructed on the sticker. But I am having a hard time understanding how the advance for the distributor works. When I finished the timing I pushed the advance line onto the distributor and the idle went up. Obviously the vacuum was getting through the delay check valve. The vacuum source is the left base at the rear of the carb... which is how the emissions diagram shows it. So we have manifold vacuum with a valve that (as far as I can reason) blocks the vacuum at idle but is opened as the vacuum increases with throttle movement. Am I correct in my thinking here? So if this senario is correct, that means the delay valve is not working. I'm guessing that, all things being correctly routed, I need to replace this delay valve. Am I correct in my reasoning about how this valve actually works? Can anybody confirm this for me? I need to smog the truck in Cal. I believe the timing and everything else is set correctly now. Just need the advance working to OEM specs.

Steve

[fiyaweed06]

steve any more info on this issue!