1ME Carb/ 77 Inline 250

[bob77]

I'm replacing my carb today. I can't find any specifications on a torque for installing the carb. Any suggestions or just tighten it to what feels right?

[bob77]

Question:
What would the difference be between a "Fed" carburetor and a "Heavy Duty Cycle Emissions" carburetor. There are monojets with both of these descriptions. The "Fed" carburetor is also described as a High Altitude carburetor on one website. As I am barely above sea level, I didn't opt for this carburetor. But now I am second guessing my choice. I haven't seen my replacement yet. I am to pick it up this afternoon. I will never have to pass any emissions testing, so will the "Heavy Duty Cycle Emissions" carb work? I hope I didn't jump the gun when I made my purchase.

[VileZambonie]

You want Federal emissions.

[bob77]

As far as I can tell, the difference is in the vacuum line connections, EGR valve. Essentially, the EGR valve is bypassed on the NON-Federal carburetor. Aside from the obvious excess emissions and pollution, what would be the performance/driveability positives and negatives to the Heavy Duty Cycle Emissions setup?

[cb7501]

Bob,

My '84 GM shop manual suggests torquing each mounting nut to 37 in. lbs., then retorquing to 16 ft. lbs. for the 1ME. That should be in the ball park at least. My guess is that you are right about the 'heavy duty' carb lacking some vacuum lines,etc. I doubt that it is jetted any differenly.

If your crankshaft is not drilled and tapped (some 250's aren't) putting the new balancer on can be a little hairy. I carefully 'press fit' mine because a GM dealer told me to 'just hammer it on with a pipe', but I didn't fell good about it. Better to have it drilled and tapped and use an installer tool.

Jason

[bob77]

Just picked up the new carb. Surprisingly, the vacuum fittings are about the same. Close enought that if I put a "T" on one, I could hook the thing up exactly as it was before, including the EGR. (I'm going to experiment a bit without it). There is actually even an "Extra" one compared to the current carb. All fittings have tight caps on them. It appears to me that Holley has kind of generalized some of these carbs for multiple applications. Leaving options for different setups.  I was a little put off that the bracket that holds the throttle return spring to the carb was tweaked, but the fella at the auto parts store gave me a pair of pliers and let me straighten it before I signed for it. I could swap it for the old one if I felt like it.

[bob77]

Replaced the carb. Still had to back the idle mixture screw out about 3 turns to get the truck to idle somewhat smooth. It has this odd little rough spot in the idle, but as soon as you get to about 1200 or 1400 rpm's it goes away. I put new plugs, wires, cap, and rotor, and adjusted the timing. I'm wondering if I don't have another issue with the distributor. And I had to stay in the throttle this morning to keep it running until it got warmed up. I need to tinker with the choke.

[bob77]

I am also going to trace and check all vacuum lines....again. Does anyone know where I might find a complete engine schematic/parts breakdown for the 250. I would like to crawl over it front to back and see if anything is missing or out of place.

[Lt.Del]

vacuum schematics should be displayed on a label on your radiator support or other place on the truck itself. It should be a silver-like color decal.

[bob77]

Yeah. I got the vacuum schematics. I'm stumped. I have to have the idle mixture screw almost 4 turns out to make the thing run decently. It seems to me that I MUST be getting air sucked in from somewhere. When I rev the thing, it smooths out and runs well. But I can't make the thing idle at all without having that idle mixture screw pulled way out. And it idles a bit rough at that. I had to pull the idle stop solenoid off of the old carb and install it on the new one as it didn't come with one. Is it possible that I need to drive that thing in further? I couldn't find any decent information on where to set the idle stop when comissioning a new carb.

[bob77]

Ok. I have one other bit of info that I probably should have shared earlier/ payed closer attention to. When I picked this truck up, the throttle linkage had been replaced. And by replaced, I mean that there is a bent piece of a wire coat hanger or something in place of the throttle linkage. The chances of this linkage being the exact right length I'm sure are slim to none. So, I believe that I need to set the idle and such before even connecting the throttle cable. Maybe the throttle linkage being too short is holding the throttle plate open slightly and allowing more air to the carb at idle, thus causing the need to have the idle mixture screw set out further than what it should have to be.
Once again, I could be completely off base on my assumption.
So... If I were to disconnect the throttle linkage (coat hanger), what would be a good point at which to start with the idle stop? Just barely touching the throttle? Slightly pushing in on the throttle?

 I appreciate everyone's help and continued advice.

[VileZambonie]

What happens if you cup your hand over the carburetor with it running?

[bob77]

She will stall out.

I do get a pretty good whistle from the carb when it is idling.

[bob77]

I just happened on some information that could be dead wrong, but I will throw it out here. Almost everything I have read and been told is that the idle mixture screw should never need to be more than 1 1/2 to 2 1/2 turns out. I just read one bit of information (on some website that I found through an AutoZone link I think) that mentioned that 4 full turns out is a good starting point on a monojet. That's right about where it was at it's running best. I gathered that this meant I definitely had some issue so I have been trying to make it run well without having the idle mixture screw out more than 2 - 2 1/2 turns. How far out will that thing actually go?
I apologize for the constant asking of maybe silly questions, but I am just a bit frustrated on why I can seem to get the truck to run smooth. Good compression, good spark, timing set, can't find a vacuum leak (doesn't mean there isn't one), remanufactured carb from Holley, yet it has a rough spot in the idle and It seems I need to have the idle mixture screw out too far to make it run...... Oh the frustration... 

[VileZambonie]

You can set the idle mixture screw all day long but if you have vacuum leaks it will do you no good. Use propane around the intake, in the crankcase, around the carb etc to see if it has any effect.