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Fresh Slant Build, Can't Get It To Idle.
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Author:  72polara [ Mon Nov 08, 2010 3:40 pm ]
Post subject:  Fresh Slant Build, Can't Get It To Idle.
Hello All,

After buying a house, getting laid off and finding a new job, I'm finally back to playing with the slant build I've been working on. :)

Previous threads I've started on it are here (just for reference):
Super Six + Dutra Duals
Carb ID

So the setup is as follows:
-1973 Dodge Dart Custom
-fresh 225 ( + .030" bore) Hydraulic cam motor - valve stem heights within a couple .001", custom length pushrods to offset head milling.
-compression ratio at 9.2:1.
-Comp 252H cam, 106 degree intake centerline, installed at 103.5 degrees
-Super Six + dutra duals, 2" out into a single 2 1/4" pipe.
-Head is stock valves, but mildly ported & gasket matched w/ manifolds
-904 transmission & 2.90 SG 8 1/4" rear
-rebuilt Carter BBD, electric choke
-MSD Ignition
-Aussie intake/exhaust gasket, manifold set milled to be true.

Ignition timing is set to 10 degrees BTDC, total advance is about 31 degrees at 1800 rpm.

I've completed the cam break in, and taken it for a drive to seat the rings. Running Rotella 30w for the breakin, will be changing to 10w30 upon oil change (very soon).

Oil pressure at 50psi at 2k rpm. 18 inches of vacuum at around 900 rpm. Manifold set torqued to 10 ft/lbs with a torque wrench. Plugs consistently read a very pleasant light brownish color. Did a compression check and am seeing 160psi, +- 4psi on all cylinders.

So the issue I am having is that I just can't get it to idle. 900 is the lowest I can go, and it's still not stable. I have to turn the idle screw in until I'm on the main circuit to get it to keep running. I've disconnected everything (vacuum advance, choke pulloff pot, pcv) to eliminate those (potential) sources of vacuum leaks. Manual brakes, so no brake booster to leak. Dashpots are disconnected. Sprayed ether and wd40 like crazy to check for vacuum leaks (throttle shafts, all 6 intake runners, blocked off egr port, carb base gasket), no luck there.

If I can get it in gear and get going, it pulls very well through all the gears, I'm actually very pleased with how it's running. Just won't idle...

The vacuum reading seems a little low, but not sure if I should be concerned about it with that cam. It is pretty stable, doesn't jump all over the place.

I only have 2 guesses on this, and they are a vacuum leak I've somehow missed, or I've screwed up my carb rebuild and have something wrong in the idle circuit. Unfortunately, I have no known good carb. I picked the most original looking one I had (still had the ID tag) and rebuilt it, under the hope that it would be un-modified from stock. I'm usually pretty darn good with carbs, but most of my experience is with holley's and webers. This is my first carter rebuild.

Any suggestions on where I should go hunting? This one is starting to really drive me nuts, I've never had this much trouble getting a rebuild going.
Author:  Doc [ Mon Nov 08, 2010 4:21 pm ]
Post subject: 
One test is to slowly close the choke flap while it's running "ragged" to see if the idle smooths-out. If it does smooth-out with a partially closed choke flap, you have a vacuum leak or a lean / plugged idle circuit.

Another test is to see if the hydraulic lifters have their plungers set corrrectly. The best way is to use some rocker shaft shims to see if the extra clearance improves the choppy idle.
DD
Author:  72polara [ Mon Nov 08, 2010 7:44 pm ]
Post subject: 
Thanks for the input, Doug.

I think I'll start with the easiest and go for the more time consuming - 1) dissasemble the carb again and pay special attention to the idle circuit, 2) vacuum leaks, 3) checking the valves as you suggested.

When I set up the motor, I put the head, gasket, block together, and measured with an adjustable pushrod such that the lifters would be compressed the specified amount (have to dig up my documentation, I think it was .015"?), so I kinda doubt it's the valves, but I'll give it it a try for sure. I do have a set of the rocker shaft shims, so it won't be too tough.

Any suggestions on where else to hunt for vacuum leaks? :(
Author:  olafla [ Mon Nov 08, 2010 9:32 pm ]
Post subject: 
Hi 72polara, it seems you have thought of most things, but have you confirmed that the zero degrees mark on the damper is actually at the top of the stroke, so the ignition is not way off at idle?

Do you have the correct flange gasket under the BBD? There is a difference between gasket for 318 and 225 BBD's, using the incorrect gasket may block some vacuum signals. Read from page 26 and check the photos at page 28 in the Carter BBD operation and repair manual.

You may also confirm the carb number on the tag by browsing the manuals in this thread Carter carb manuals with jet and metering rod sizes.

Olaf.
Author:  72polara [ Mon Nov 08, 2010 10:21 pm ]
Post subject: 
Olaf,

I have confirmed that the zero mark actually is zero - my damper actually hasn't shifted, amazingly. I've checked it a couple times, thinking that had to be it. :b

I do have the correct flange gasket, I verified it on that exact document. :) I have that printed out, along with a few other of the manuals linked on the site. Awesome set of resources!!! After reading the service manuals and going through the BBD, I really like the carter design. It's beautifully simple.

Thanks for the carb number, I didn't put that one together. Looks like it is what Charlie described, 1978 passenger car. It is too bad those PDF's aren't text searchable, though.

I went back through the carb again tonight, inspecting all passage ways and blowing with compressed air. I didn't see anything that made me go "ah-HAH!", but we'll see what happens when I run it. Reset all adjustment to service specs (again). Too late to do it now, neighbors have school age children, but I'll try tomorrow evening.

And just for laughs, I did take some pics of the engine in the car. :) (yes, I realize the PCV hose is disconected in the first two photos, took these after tonights carb re-check). Heater is disconected till I get the engine running right, and this is an A/C car. Planning to get a Sanden bracket from Charlie and going that route.

Image

Image

Image
Author:  72polara [ Wed Nov 10, 2010 1:01 pm ]
Post subject:  It was the carb
Alright, after a slight delay, the engine it now purring like a kitten!

When I went through the carb, there was a little piece of lint in the idle circuit passage ways. Didn't think much of it, and visually inspected & blew with compressed air everything to confirm it was open. Put the carb back on and started up the next day at lunch, and... rock solid idle at 650 in gear! :) Pulls 18 inches of vacuum while there, too. So clearly that little bit of lint (it was from the clean rag I had been wiping the carb with) was enough to foul up my idle circuit.

So the car now idles, runs, and drives real nice! Next step it the alignment shop, and the car will be ready to return to it's former daily driver glory! ;)

Thanks for all the help and suggestions.
Author:  olafla [ Wed Nov 10, 2010 5:22 pm ]
Post subject: 
Hi 72polara, thank you for the feedback, glad it turned out OK.

BTW: You should take a lok in the FAQ again and do the 'Fuel Line mod'.

(how do you guys manage to keep your engines so clean...) 8)

Olaf.
Author:  Joshie225 [ Wed Nov 10, 2010 6:14 pm ]
Post subject: 
Glad to know you got it whipped into shape. The idle circuits on my '74 Satellite's BBD packed it up one day. Rather than mess around I took the opportunity to install the AFB and Performer intake I had for the car. Along with removing the AC compressor it took 99 lbs off the nose of the car. I miss that car a little. The single 3" exhaust and welded Dynomax Ultraflow muffler sounded very nice.
Author:  72polara [ Tue Nov 16, 2010 8:39 pm ]
Post subject: 
olaf: I did the fuel line mod yesterday. I had intended to do it, but I had used stuff I had just laying around because I was in a hurry. I paid for it when crap in the lines stuck the needle valve open and caused an epic flood of gas in the intake. My theory is that when I formed the lines to fit, it broke loose some dirt (I had rinsed the lines prior to bending). After taking apart the carb AGAIN to clean it, and doing the fuel line mode with fresh parts, I think the corner has truly been turned.

The car made the 60 mile round trip to work today in Atlanta traffic without so much as a hiccup. Stop and go traffic all the way to 80mph on the freeway. :) I'm pleased.

I had mentioned that this is my first time with a carter... after having taken it apart and put it together no less than 4 times now, I'd say I'm getting to know it pretty well!!

One thing that is surprising me with this build, is that it seems to pull pretty hard from 2500-5000. I was kinda expecting it to really run out of breath at around 4500. Anybody know what I should consider redline for this engine? 5k is about as fast as I wanted to spin it so far.
Author:  olafla [ Fri Nov 19, 2010 9:03 pm ]
Post subject: 
You already found what most people think is the natural rev limit, there is no point in revving the old slant past 5k, even if it can take it.

Dirty fuel in carb: take a look at the pics in my little adventure!

Olaf
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