Idle Troubles

[Yankeelights]

OK, I'm stumped. I installed the ol' 406 as planned but I can't get the thing to idle correctly. I can start it up and while it isn't in gear the engine races; then loads up and shuts down. If I start it and immediately put it in gear it seams to idle fine. When I tromp down on the throttle, there is a slight hesitation then the ol' 406 lights up the tires and sends me down the road sideways. On the highway crusing at 60 mph, I can feel the engine hesitate a little before going uphill.

• Vacuum leak(s)? I hooked up no emissions; just the pcv, vacuum advance, brake booster and vacuum modulator line with all new line. Everything else is plugged.
• I converted to electric choke. Could the vacuum port built into the choke housing be causing me problems?
• What's an effective way to check for vacuum leaks around the manifold?

I'd like to rule a few things out before I look at the carb. Any insight is appreciated!

~ Dave

[Jerry Jones]

I use a can of carb cleaner around all gaskets and vacuum fittings, if the idle smoothes out or rises you found a leak.

[Yankeelights]

OK, I'll try the carb cleaner trick ... thanx!

[swb85]

An unlit propane torch is how I prefer to find leaks.....carb cleaner is rough on painted surfaces.

[Yankeelights]

OK, no vacuum leaks to speak of using the carb cleaner method. Fortunately there are no pretty painted surfaces to be concerned about. This was an emergency engine swap and the 406 was just sitting around. The propane torch is a great idea!

I bumped up the timing to 10 BTDC and the cam seamed to like that much better than 6, but it's still surging sometimes. No more hesitation when tromping down on the hammer though ... just break-neck accelleration.

I also plugged the vacuum port for the old choke, just in case.

I suppose I'll fiddle with the primary jets next.

~ Dave

[82c10]

it does sound like the carb to me, but you didn't say which carb you were running

[Yankeelights]

It's a Ram Air Quadrajet.

[swb85]

Since you mentioned a cam, what are the specs? If it's much more than very mild, it'll want more than 10 degrees advance at idle.

[Yankeelights]

266 dur; 440 lift; 108 deg separation running Rhoads lifters.

[82c10]

Originally Posted by Yankeelights

266 dur; 440 lift; 108 deg separation running Rhoads lifters.

with that small of lift why are you running roads lifters? with that can they won't help that much, if any

[Yankeelights]

because they smothed out the choppy idle

[Captkaos]

Did you add the Rhoads later after you found the "choppy idle".

I am guessing 266 is advertised lift not actual. With those specs you have a light towing cam that shouldn't have a choppy idle unless the timing was set low. In a 406, it should be really smooth due to more displacement.

What kind of vacuum is the engine pulling at idle?

[Yankeelights]

It's at 19 inches of vacuum. I ran the engine from 1989 through 1994 in a bracket car; the idle was choppy in drive ... maybe lopey is a better term. In any case one could easily tell that the cam was not stock. I recently freshened up the engine and added the rhoads lifters and they're working perfectly. I noticed that the top gasket on the carb is wet with gasoline which indicates a warped horn; probably from someone over tightening the carb in the past. In most cases the carb cannot be economically saved. I have another Qjet that I'm going pop on this weekend to try out.

[Captkaos]

Is it this cam: http://cranecams.com/?show=browsePar...tType=camshaft

Let us know what the new Q-jet does.

[Yankeelights]

No, it's a Huggins cam.

[Yankeelights]

So I'm driving home from about 25 miles away Friday night and on the first up-hill (about 16% grade for about a mile) the ol' 406 starts sputtering & pinging and top speed is now 15 mph; I have 20 more miles and three more steep grades to get home. I barely made it. I pulled the plugs and 6 were fuel fouled. Did a vacuum check and it read 9 inches .... WTF!!!

So, Saturday morning off with the intake & carb; double check the adjustment on the Rhoads lifters, still OK; re-install the intake ol' s'kool style using hi-tack to avoid vacuum leaks; installed 8 new plugs. Installed the alternative Quadrajet; started er' up and sputter sputter *POP!* #COUGH# with 9 inches of vacuum.

Re-installed the Ram Air Quadrajet and same thing; rough running and 9 inches of vacuum. Now I'm pizzed!

With only one more rabbit to pull out of the hat I wait for night fall tonight and take a run up the road a few miles (sputtering all the way); pull back in the driveway; leave the truck running (barely); hop out of the cab and sure enough, there it was .... the cherry red glow of a glogged cat illuminating my gravel driveway.

Next stop; local auto parts to cob up a bypass until payday. Payday weekend will consist of installing a double hump cross member, long headers; duals and NO DAMNED CATS!

[jermasaurus]

Clogged cats can be a little difficult to diagnose. Good think it started glowing.

I have seen one you could mistake for trans problem and another that had similar symptoms of a bad fuel pump.

[Yankeelights]

Originally Posted by Captkaos

Did you add the Rhoads later after you found the "choppy idle".

I am guessing 266 is advertised lift not actual. With those specs you have a light towing cam that shouldn't have a choppy idle unless the timing was set low. In a 406, it should be really smooth due to more displacement.

What kind of vacuum is the engine pulling at idle?

Originally Posted by 82c10

with that small of lift why are you running roads lifters? with that can they won't help that much, if any

Originally Posted by Yankeelights

because they smothed out the choppy idle

Correction: The Rhoads Lifters did NOT smooth out the idle no matter how high I set the timing. I believe that it's duration and overlap that makes the lopey idle; not the lift. Perhaps there's a cam grinder that can chime in. It sounds awesome and now that the clogged cat has been exterpated the vacuum is at 22!

Thanks to all for the input!

~ Dave

[Yankeelights]

Originally Posted by jermasaurus

Clogged cats can be a little difficult to diagnose. Good think it started glowing.

I'll agree to that!

~ Dave