I was wondering if someone could be of assistance. I am finally at the stage where I am trying to get my 75 up and running and am having a hard time getting it right. So, let me give you some background. I pulled the engine and transmission for rebuild and decided to upgrade the motor while I had it out. Here is what I did:

Howards Cams Roller tapet conversion CL113215-10
217/225 at .50
duration 270/278
lobe sep angle 110
http://www.summitracing.com/parts/HRS-CL113215-10/

Dart SHP aluminum heads
64cc combustion chambers
http://www.summitracing.com/parts/DRT-127122/

Edelbrock 2101 intake
http://www.summitracing.com/parts/EDL-2101/


Upgraded alternator to 80amp, rebuilt tranny (th400) to stock. Installed CC dual exhaust, and removed the EGR. Oh, and I even had Lars rebuild my carb for me (thanks again Lars).

I followed Lars papers on distributor install and how to set initial and then vac advance timing. I tried to set initial timing at 8* btdc but the engine loped and stalled. I then moved it up to 12* then finally settled around 16* btdc. Seemed to be idling well but started to get a lot of spitting out of the tailpipes (too rich maybe?). I reset idle and then hooked vacuum back up to the dizzy (ported). Idle increased and timing was coming in around 36* btdc, hit the throttle linkage and timing came all in around 2500 rpm. All sounds ok.

Here is the problem. Once I adjust idle down and then engage the tranny, it dies. Hooked up a vacuum gauge and get readings between 7-15 in. Could a vacuum leak be causing this? If so, from where? I replaced all of the vacuum lines and have plugged all ports not being used. I only ask because my vac gauge is a little old and I'm not convinced of its accuracy.

If not vacuum, what else could it be? Any and all help/opinions are welcome. Or, if someone is in the Germantown Md area and wants to stop by to lend a hand, I'll buy the beer, or soda, whatever your preference.

Thanks in advance.

Bryan

 

What do you mean when you say "Hooked up a vacuum gauge and get readings between 7-15 Does the vacuum reading just kind of wander around, or is there a pattern to it? Does the needle flicker between 7 and 15? Here's a link to some good info on how to use a vacuum gauge:

http://www.secondchancegarage.com/public/186.cfm

In general, your post is difficult to understand. What do you mean when you say you "set the idle"? Why are you using ported vacuum for the vacuum advance? If you are following Lars's papers on timing, why are you trying to set initial timing?

Scott

 

What is your idle at rest before you put it in gear? I found that my warmed over L48 won't idle in Drive anywhere below 700rpm when warm with brake applied. If idle drops below 700rpm, it starts to search for a comfortable idle spot and often dies. That means my idle level in Park is 800-850rpm. This is not intolerable to me.

I don't sit in Drive with brake applied when it has just been started. Park and cold; no problem. It is cold-hearted but once even slightly warmed up, it will idle at 700rpm in Drive with no problem.

 

Scott,

I connected the hose on the vac gauge to a port (should be manifold) on the carb to get a vacuum reading at idle. The gauge reads at around 7 in at idle but will go up to 15 in if rpms increase. I should have made that more clear.

If my post is difficult, I apologize. I am trying to understand what is going wrong and I am admittedly getting somewhat confused. Here is what I did:
- removed #1 cylinder spark plug and bumped engine over until compression stroke (verified by big blast of air pushing my finger off of the spark plug hole)
- installed dizzy with reference mark made before removal to #1 cyl pointing towards #1.
- started immediately. with vacuum hose from dizzy removed and plugged, set timing to 16*btdc.
- adjusted idle to 900 rpm.
- with vacuum still disconnected, increased rpms at throttle linkage and got total timing at 36* btdc, so 16 initial and 20 centrifugal.
- reconnected vacuum to dizzy and got increased rpms. adjusted back down to 900.
- checked total timing with vac connected, comes all in at 51-52*.
- get in the car, push the brake, put in R, curse as engine dies.

Why am I using ported vacuum? Until recently I didn't understand the difference and just hooked it all back up the way it came off of the car. I will probably switch to manifold vacuum but from what I understand, which I admit could very likely be wrong, shouldn't be affecting me like this.

Hope that clarifies a bit.

Thanks,
Bryan

 

I set it at 900 in park. In gear it rapidly drops from 900 to 0.

 

Do you let it warm up first or do you put it in Drive when cold? If I am not letting the car warm up, I tend to give the gas a little blip once I put it in drive so that it does not die. And, I tend to keep my foot on gas (and left on brake) at a couple stop signs until it is showing signs of wanting to stay running in Drive at stop.

 

Ted,

Yeah, the car is fully warmed up when I try to put it in gear.

Bryan

 

Bryan,

Forgive me if this has been verified but what is the condition and routing of your vacuum hose systems that are fed off of your intake vacuum? I am asking as I had a very similar issue after I rebuilt my engine. I found upon investigation that I had a cracked 3-way vacuum fitting off the rear of the intake (near carb), the plastic power brake fitting where it connects the vac line to booster had a hairline crack, and I had multiple cracked hoses and plastic connectors. Faced with that situation, I bought all-new vacuum hose systems. This is not as difficult as it may sound. And, the kits are well documented with routing diagrams. The kits I bought are from a vendor that is not welcome to the forum anymore. His name has 'Dr.' as a prefix. I bought four systems: EGR, EFE, headlight and EVAP. Granted, you have removed your EGR but many of the hoses just need to be re-routed. I also removed all thermal switches from the intake/radiator hose housing, plugged the vacuum lines that feed the thermal actuators on my air cleaner and stubbed off a vacuum line off the back of the carburetor. The system works great and I removed all leaks.

You may not need as extensive surgery but it sure was nice to have all-new plastic connectors and hoses vs. the old brittle pieces I was finding and replacing one at a time. And, I didn't have to use the cheap car parts store hardware (hoses that dried and fittings that still cracked from use).

 

Ted,

I would like it to be that simple. I already replaced all vacuum lines. Maybe one is bad.

 

OKJ, that is much clearer, and it sounds like it is set up correctly. My first thought is that you should be getting a lot more manifold vacuum than 7". This may seem obvious, but you didn't mention it, so I have to ask: have you fiddled with the idle mixture screws? If not, then play around with them until you get the highest vacuum reading, then re-adjust the idle speed, if necessary. Then play with them some more, until you get highest vacuum reading. Either do this and let us know how it goes, or verify that you have already done this, please.

Scott

 

Scott,

I have not messed with the idle mixture screws yet. I will give it a try tomorrow and report back.

Thanks,
Bryan

 

So, is the advance can on the distributor hooked directly to manifold vacuum, or it is hooked up to "ported" vacuum from on of the carb ports? I believe that you need to have it connected to manifold vacuum. That could come directly off the intake manifold, from the carb base, or from a fitting on the carb that is "manifold" vacuum connected.

Ported vacuum will have "0" [or almost 0] vacuum at idle, so you would get no timing advance from that can, until the throttle is cracked. And that doesn't sound like the best arrangement for what you have.

 

At all? What, did you just bolt it on and expect it to work perfectly because Lars laid his hands on it? I wouldn't be surprised if an idle mixture screw adjustment, and a little more timing at idle by using manifold vacuum for vacuum advance, made a big difference in how your engine runs. Only one way to find out, give it a try, let us know how it works out.

Scott

 

Lars sets it up and tests it 'on-engine' to get good adjustment on mixture screws and idle speed. Mixture screws 'might' need a small tweak, but probably not necessary....unless the affected engine has some other vacuum leak or problem.

 

Really? And there isn't a big tuning variance from engine to engine? I didn't know that.

Scott

 

When I reinstalled the QJet I just upped the idle speed a little.
http://forums.corvetteforum.com/c3-t...et-photos.html

 

No, as a matter of fact, that is not what I expected. If I didn't anticipate the possibility that adjustments needed to be made or something else needed to be done, I wouldn't have come here for guidance.

 

I finally got around to adjusting the idle mixture screws. So, considering the fact that I was getting so much popping coming from the tailpipes, I thought I would start by making the mixture leaner. I started slowly turning the screws clockwise about 1/4 turn at a time. I managed to get the vacuum up to around 15" but it still wavers a bit, say between 12-15 on average. Also, when I increase rpm over 2k, vacuum will get up to about 20". Anyway, the effect of this was a dramatic reduction in the popping and a much smoother idle, although it drifts a bit between 900-1200 or so. Additionally, I moved the vacuum advance from ported to manifold vacuum.

So, having done all of that. I put the car in reverse. Stalled. I'm at a loss. Admittedly, I don't really know what I'm doing, but at a loss nonetheless. So could this still be a vacuum leak? Torque converter? Vacuum modulator on the trans? Any and all ideas accepted.

Thanks,
Bryan

 

Well, that's a real kick in the head, ain't it? In your first post, you mention that Lars rebuilt the carb for you, right? If I were you, I would send Lars an e-mail, and tell him about your problem. He's a wiz at this kind of stuff, I would bet a steak dinner that he could help you out.

Scott

 

It sounds like you might have a vacuum leak. Are you using good intake gaskets, new carb base gasket and how about the vacuum hose to the transmission, is that in good shape, top and bottom hook up locations? When you installed the new cam and lifters, how much preload did you put on the lifters, 1/2 turn, one turn? Have you double checked them all?