Wont idle in gear

[78 C10]

I have been fighting this motor from the beginning. Its a 355 10:comp GM 486 heads with major work, Vic Jr intake, Comp cams 292 .501 hyd flat tappet, Factory HEI with moroso recurve kit. Initial timing set at 12* total 36* at 3000 RPM. It has a fatory vac advance but there isnt enough vacuume at idle to make it work. I bought a crane adjustable vac can last night and havent had a chance to put it on yet.

The truck runs good as long as it isnt at idle. I stop at a signal light or stop sign and it wants to die. If you dont give it any throttle and put it in neutral or park it will idle fine, after its warmed up and you take it out of gear while its idling sometimes it will rev up to 1200-1500 RPM on its own and will not idle back down. I dont know if I should be looking into the carb or the ignition system. Could my current factory style Vac advance be doing weird stuff with the timing?

I really would like to get this thing sorted out today because tomorrow is the big carshow and cruise night that I would like to attend.

[JES]

You need at least, a 3000 stall for that cam. If not you will never get it to work. John Eric.

[ytnova]

I am thinking when the idles drops, the timing drops and compounds the problem. I would like to see some more initial timing with the same total, if it will take it, try locking the timing out at 36. Also, what stall converter is in it? You need to have all the timing in (full advance) around the stall speed. Where are the float levels at? You can try lowering them a tad, but this also lowers the fuel in the main well which can cause a slight sag when it transitions to main metering.

[78 C10]

Im not sure what kind of converter is in the truck. It was in it when I bought it from my father in law and every time I ask him I get a different answer. It feels to me that it flashes right before 3000 RPM and I think that is causing some of the problem but not all of it. It sometimes acts like it has a vac leak and I can never find one. I think the machinest didnt mill the intake right and it may have an internal leak into the valley. I installed my Adjustable vac advance last night to full manifold vacuume and bumped up initial to 14*. With 14 initial and 8 from the vac advance I am getting 22 a idle and it seems to make a huge difference in the way the truck runs. It will idle in gear now on its own but I think it needs more converter. It was getting late and my neighbors probably were about to call the cops so I didnt adjust the carb other than the idle and i wanted to take it for a test run. I will see if adjusting the A/F ratio screws will do anything or not and put a vac guage on it and see if I picked up any vacuume tonight.

[JES]

Most 3000+ converters are 10 inch diamiter or less, you can pull the inspcetion cover to see. John Eric.

[78 C10]

I am making some changes to the motor now. I will be ordering the following parts in a week or two: New set of aluminum heads, intake manifold, and a 3,500-3800RPM stall converter. I crawled under the truck and with out measuring it I can tell its not a 10" converter. Besides that I have a gut feeling that my intake has a sealing issue at the head(s) due to the milling of the heads and decking off the block. I had the intake milled to match but I think the machinest didnt do it right.

[JES]

Sounds like your in for a lot of fun. Make sure you have a trans cooler. After you make a few heat cycles retorque the heads. John Eric.

[78 C10]

I have the trans cooler that is built into the radiator then on top of that I have two air coolers up in front of the radiator. I also have a trans temp gauge on the dash so I can keep an eye on things.

I have never owned a set of aluminum heads before do I need to know anything about them? I am also not sure if I need special gaskets due to the aluminium sitting on a iron block. I know the two metals have a different heating and expansion rate so I was wondering if that will give me a head gasket issue of some kind.

[wikd69]

I have the trans cooler that is built into the radiator then on top of that I have two air coolers up in front of the radiator. I also have a trans temp gauge on the dash so I can keep an eye on things.

I have never owned a set of aluminum heads before do I need to know anything about them? I am also not sure if I need special gaskets due to the aluminium sitting on a iron block. I know the two metals have a different heating and expansion rate so I was wondering if that will give me a head gasket issue of some kind.

I'm told you need to go through repeated heat cycles with new aluminum heads, re-torqueing them after each session in order to get them to settle in correctly.

[JES]

Use Fel-Pro 1003 gaskets, pay atention to the markings, for right side up. Use ARP head bolts that are longer than stock length, make sure the inner bevel on washer is to the bolt head, lube washer both sides with ARP moly lube and threads with ARP thread sealer. torque in three steps to final torque. Check for washer interference to valve spring/locator at center exhaust valves, if so get grade 8 washer(wich is thinner. may need to be 3/8 and enlarge) and bevel inside, like ARP washers. NOTE, when torqueing head bolts don't just pull to torque, sneek-up on it! Have fun! John Eric.