Rick Hodgkins

Newbie old guy on home confinement from the rubber room
Never in my life have I run across such a frustrating run of nonsense.
Anyway, I posted this on another member's older post because the symptoms were identical.

So this is a very straight forward build on a 400 that refuses to idle.
I've shamelessly posted this so other builders could maybe discover any error I may have made.
The motor is basically a stock build running a mild Comp 308-4.
The original carb has been done and gone through twice and came off a running 350 that was in the car when purchased. .
The second I close up the choke a bit the engine straightens out and vacuum climbs to 16 from 12 and stable.
Valves are adjusted by firing order on bottom side of opposing valve at 1/2 turn of -0-
Timing is at 12 btdc and motor needs 950 to stay running.
The minute I put it in gear it starts to hunt like a pro stock engine near stall.
There is a B&M 1800 stall converter installed with new stock manifolds
All vacuum ports have been plugged, propane leak detection done.
A Mr Gasket intake set is in use with Loctite high temp sealer on the block cross overs.
The front of the motor has been taken down to check the cam gear alignment and its spot on.
A builder friend of mine said these are known for cracks on the bottom of the runners on the crankcase side, not sure how accurate that is.
I just am trying to avoid taking this down if something else is wrong.
Any help would be appreciated.
r

olds 307 and 403

That cam isn't super mild, not huge but still has 224/224 duration. What year of a 350 did you pull that Qjet off? The mid to late 70's carbs are super lean in the idle circuits. I bet it needs the idle circuits enlarged to idle properly. Closing the choke and better running means it needs more idle fuel and probably more through the whole rpm range. Good luck.

Rick Hodgkins

The carb is the numbers matching original off the 400.
It ran great on the 350, not sure what year it was.
The original 400 was apart when I bought the car last fall.
Without proper vacuum, no carburetor is going to function.
I am suspecting this problem is across all RPM as there is a flat spot when accelerating for a split second then it goes like hell.
Planning on taking the intake off tonight.

Vintage Chief

Post the Model No. of the Q-Jet - that will provide more insight. I'd hate to see you take it down again - maybe a simple carb swap? Modified electric choke or OEM mechanical (coil)?

matt69olds

Check the weights on the centrifugal advance. Maybe something is screwy with them.

Vintage Chief

Matt - I was thinking along similar lines. Those carburetors were matched to engines (not numbers matching), and the distributors were matched to engines. Removing a 350 carb to a 400 engine (of select model year) does present a modest challenge in consideration(s) of distributor &/or centrifugal advance.

Vintage Chief

The one item which has not been addressed which will definitely effect idle is the high idle cam adjustment. Rick, you stated from the get-go it refuses to idle. You stated the carb has been gone over twice - what that means we can only guess. I'd double-check the high idle cam adjustment.

Rick Hodgkins

Getting 36 degrees full advance, 12 with vacuum to distributor disconnected.

Rick Hodgkins

Choke stove on intake

7029251

Rick Hodgkins

The choke closes, the high idle cam kicks down once the engine is warm and throttle tapped.
I am very well versed in Qjets being in the marine business, overhauled hundreds in my time over the decades.
I've done a metering well drip test on my stand to eliminate well plug overfueling.
When I first took it down, the wrong spring was under the accelerator pump and the primary metering plunger had the wrong spring under it.
The feed passages to the primary and secondary wells are wide open.
It has a copper float that is clear of fuel and set properly.
Again this came off a running engine with no idle issues what so ever.
I can build a carb to test with if needed.

Vintage Chief

Thanks. At any rate, the 7029251 was used on the 400/455 engines of the 1969 model year, while the 7029250 was employed on the 350 engines of the 1969 model year. I don't suspect that (came off a 350) in & of itself would demonstrate any significant differences since it is most likely a better match for the current 400 in which it is installed (assuming a previous owner did nothing to change the jetting).

Barely idling w/ 12" Hg (speaks to high idle cam) @ idle but when choke opens it straightens out to 16" Hg. Still sounds like high idle cam adjustment. The fact it came off a 350 & mounted on a 400 could well indicate there was a prior adjustment to the high idle cam while it was on the 350. Additionally, if I recall correctly, you won't get a good high idle cam adjustment unless the high idle cam is adjusted during the engine timing, I believe.

Vintage Chief

Rick - Our posts passed one another. You actually have more knowledge & years of experience than me on Q-Jets. You never know the background of the individual on the other end of a post - just trying to assist.

Rick Hodgkins

If you go to the last post on this thread there is a video of this beast in action with a vacuum gauge connected.

Vintage Chief

I don't do FB. Quit when their security went South; albeit, can't view.

Vintage Chief

You most likely have read something by Lars Grimsrud over the years. I've rebuilt a fair number of Q-Jets, but I have always found this one article (posted by another member) very useful when reviewing Q-Jet basics while trying to resolve issues with them. Of course, I know you're not 100% convinced it's even the carburetor, but I review this article when I have issues.

Quadrajet Info by Lars

Rick Hodgkins

Here is a video of the problem

https://vimeo.com/540280049

Rick Hodgkins

While on the subject of issues refusing to be solved....
Anybody know the solution to losing the fuel prime on the lines, pump and carb where its crank crank crank and finally it fires after sitting more than a day?
New pump, new rubber lines, new basket filter with spring in the carb.

1970-W30

Can you explain how, in your stock rebuild, how you managed to adjust the valves a "1/2 turn down after zero"?. Do you have adjustable pushrods or aftermarket rocker assemblies?
Stock Olds rocker assembly hold down bolts are tightened all the way down, locking the assembly in place, not adjusted like a Chevy unless you have gone to aftermarket rollers.

Rick Hodgkins

Yes, the engine had roller tip rockers and stud/guide kits installed.

Vintage Chief

I suspect you can't post that URL because you are on your account MANAGE page. You need the URL from the public page where you posted the video.

Rick Hodgkins

Correct url, sorry.
First part of this video the motor is up on cold high idle.
Second half is warm when the hunting begins.

Fun71

Is an 1800 RPM converter loose enough for a 308º duration camshaft? Just wondering if that may be part of the problem, but I don't know the answer, so hopefully others will be able to clarify that.

Rick Hodgkins

Once we get this leak squared away, we will know for sure....
Update: We have a leak at #5 that didn't respond to propane. This port location is really a stretch to the nearest intake bolt. The torque is 15 Ft pounds and a 3/8 16 bolt is for sure capable of 30 in iron which is was, yet still we are breathing.
But wow it liked the ether so much it would run right for 30 seconds. This gasket was hard as stone and as brittle as a potato ship with very low run time.
I couldn't lift the intake off alone, but clearly we have venting.
It may well be the port flange angle, tomorrow will tell. But that said, would you use the turkey tray once piece or the bikini 2 piece gasket at this stage of failure wanting to prevent a repeat?

Vintage Chief

The iron intake manifold is heavy, maybe 45 lbs-50 lbs. I use the turkey tray - reduces oil slop. Be aware on some of the turkey trays the boss indents (at the corners) were manufactured a little sloppy & didn't fit perfectly. I had to use a little persuasion to get the boss indents to seat properly, but I had no issues. I'm pulling a constant & steady 17.5" Hg on a 350 cid.

Vintage Chief

You're rock solid certain you used the correct carburetor base plate gasket? They make several.

Rick Hodgkins

Carb base gasket is a Felbpro copper core heat shield by the numbers.
For sure we had a leak on the #5 intake port.
I will know first thing if the port flange is off