[Shiny]

Better, but still not right, will have to make some changes to the carb I guess.

I cleaned and rebuilt the carb, replaced idle tubes, installed new Cliff parts, added an inline filter before the fuel pump.

I took the old gas out of the tank and put in a few gallons fresh. The stuff in the tank smelled bad and was dark, so that couldn't help.

I found my throttle cable wasn't allowing the throttle blades to fully close and thought that may have been the issue. Was excited about this until it turned out to not matter.

Unfortunately, after fixing the cable, I'm still not able to get it to idle without pulling some fuel through the primary nozzles. I'll mess with it tomorrow, but am starting to think the idle system needs more fuel.

If I close the needle valves, it obviously stumbles, but opening them way up doesn't increase idle rpm much. Is this an indicator of not enough fuel in the idle system? Seems maybe the limitation is upwind of the needles, right?

All ideas and opinions welcome:

New idle tubes are .034" as received.

Jets are currently 70, rods are 041 per my initial post.

I set timing at 9 degrees without vac advance.

Kenth was nice and responded to an IM asking for carb setup advice. He suggested I needed larger idle tubes, larger jets and different primary rods. This makes sense if my interpretation of symptoms is good:

.037" idle tubes
.052" down channels
main airbleeds .070"
73 jets
primary rods 43B
CK secondary rods with G-K hanger


And Chiphead, yes I've got a rusty tank. Here's what the filter caught.

The filter obviously kept a lot out of the carb. I didn't find any big chunks inside the carb, nor did I find the filter filled with the black hose particles so I'm not sure the junk explains my issues. I suspect not... I think it has more to do with not running off the idle system..

[Shiny]

Warning - longest post ever.

I'm very frustrated. May have to vent a little (and I'm not talking about my carb), looking for suggestions.

I pulled and opened the carb again, drilled out the idle tubes to 0.037 and the DCRs to 0.055. No dirt inside, nothing weird to my eye, gaskets all looked compressed, float is at 3/8" per original spec for the carb.

Fired right up, but still running rough and can still see fuel coming out the primary jets when it's idling at ~700. May be a little better, but still wrong.

I have to ship the car next week (will not have access to it again for about a year), so I'm out of time to deal with anything beyond trivial. It needs to be running well enough to drive it a block to the car carrier and right now, that's iffy, so I'm anxious.

I turn the idle mixture screws in and the engine stumbles, so there is gas coming through them. I can get a little response from the idle screws and I tried to set them to peak the rpm, but the idle isn't steady enough to see this well on my tach and the sensitivity is low.

When I tip in the choke, it runs better, which makes no sense to me after opening the idle tubes and DCR. I open a vac port, it runs worse.

I set base timing at 12, is steady. I have another 22 in the mechanical, but it doesn't start kicking in until about 1500 rpm (I added a stiffer spring on purpose), so not a factor. Vacuum is 18" below 1000 rpm.

I have an adjustable vac advance. It is adding another 30 which seems high so I cranked on the adjuster to try and reduce it, but it did nothing. Another source of frustration. I would have to pull it again to put in a hard stop. Seems the adjuster must be about rate and not about magnitude?? And how would I decide the right level of vac advance? 10 degrees seems a popular target.

I bypassed the TCS and did all my adjusting brake and tranny hoses removed in case I had a leak somewhere.

All I can figure is I missed something obvious in the carb that is causing it to act totally weird or my engine is otherwise in bad shape. I wish I had another known good carb to bolt on, but I don't.

The plugs are seriously dark, which I interpret as crazy rich, consistent with the flooding I thought I fixed. Temper the judgement with lack of operation above idle, and yes there could be some oil:



Would these be expected to clean up at idle if the carb was better? Would they actually mess up the idle? Car is not a driver but I need a better idle.

Any more easy diagnostics?

And no, I'm not sure the cam and valve adjustment are OK. The engine hasn't really run in years, but was better than this 10 years ago when I first rebuilt and installed the 4bbl and cam. That was at 5000 ft and I'm now at 0 if that matters.

Tomorrow I may try new plugs, verify firing order, and try opening the mixture screws a lot. I guess I could also disable the vac advance and look for a sweet spot beyond base timing by rotating the distributor?? This might tell me if the 30 degree vac advance is part of the problem, but I doubt it..

Raises a question: should I be adjusting the idle with vac advance or not? I'll try it without the vac advance tomorrow.

If you've read this far, thanks... give me some ideas on simple things to try.

[Cliff R]

What size are the upper and lower idle airbleeds? That engine shouldn't need much idle fuel beyond what a stock 7029240 carb would deliver. The 2800 cam in a 350 is pretty much like a stock cam, smooth idle, high vacuum, etc.

Idling rough and not responding to increased idle fuel and throwing timing at it makes me think that you either missed something with the carb set-up, vacuum leak, or something fundamentally wrong with the engine.......Cliff

[Shiny]

Thanks Cliff

I posted specs on your forum, you thought they were OK.

I'm coming to the same conclusion - I missed something in the carb or I've got bigger issues. I expect the engine is well worn, but the rough idle seems inconsistent with that.

Here's the carb:

69 Buick Quadrajet 29240MD

Measured:

Idle Tubes 0.037
Down Channel 0.055
Upper Air Bleed 0.053
Lower Air Bleed 0.079
Bypass 0.089
Mixture Holes 0.090
Primary Jets 70
Primary Rods 44B
Secondary Rods CH
Secondary Hanger O
Power pump spring Blue
Float 3/8

How do I find a vacuum leak? Spray carb cleaner around it?

I'm going to replace plugs, verify firing order. I may check compression after that. This engine had coolant leak into the oil through a hole in the timing cover, so maybe that hurt something. I am also capable of messing up the lifter adjust, so I may pull the valve covers if the compression is uneven.

History of carb is also questionable. It was given to me 10 years ago and maybe there's a reason! Could be a commercial rebuild gone bad or Frankenstein castings I failed to notice, I suppose.

If the compression checks out, it may be time for a new carb.

[Cliff R]

If the IDLE airbleeds are .079" lowers and .053" uppers you should have plenty of idle fuel for engine combo with .037" idle tubes and .055" DCR's......Cliff

["QUICK-SILVER"]

Definitely need new spark plugs.

If you still have a points distributor...have you checked the dwell?

You may not have a carburetor problem at all if the ignition system is in trouble. Weak spark and fouled plugs is going to make a rough stinky idle that no amount of carb work will cure.

Clay

[Shiny]

Thanks Quick Silver. Yes, dwell was 30, steady. My first task was to buy new plugs and rent a compression tester.

I worked most of the day on it, concluded I had a stuck float, but cannot explain why.

I checked the compression, were no bad surprises - all within 125 to 130. This was a relief.

While I was cranking for the compression test, the gas smell was strong, so I guessed the carb was flooding just cranking.

Carb came off again, gasket was saturated, intake was wet.

I ran to O'Reilly's and bought a MightyVac. Pumped on the inlet fitting, was wide open. Swear words were uttered, as this is a brand new needle and seat from Cliff, so I was flabbergasted. I now have two filters ahead of the carb after my first adventure, so unlikely to be dirt. I tipped the carb upside down, pumped again... was WIDE OPEN... so I either had a stuck float, high pressure, or a leak somewhere. I measured the fuel pressure at the carb, pulsed 4 to 7, so call it 5 or 6 average... maybe higher than I expected? What should it be off a mechanical pump?

Air horn came off, could see nothing obvious. I filled the bowl with carb cleaner, there were no leaks.

My conclusion is I had a stuck float, but could not find a reason. Needle and seat were clean, no debris.

I widened the legs on the float to make sure it would not bind:



I verified it would seat with the MityVac, checked the float height, put it back together. Shook it around, verified seating again both right side up and upside down.

Installed new plugs, got the carb back on, started it up.

Runs waaaayyyyyy better!

I conclude the float was stuck, but really have no idea why - nothing was obvious. The needle doesn't have much clearance in the seat, so maybe I had it jambed ???

I'll mess with adjustments later but feeling much better about it. I haven't checked the primary nozzles for drip yet, but hopeful the float is now working and grateful both the engine and carb are not obviously damaged.

[Shiny]

Defeated!

I'm giving up for now, time to accept I didn't have the skill to figure out what was wrong in the time I had.

After opening up the idle tubes and DCR, I still can't get the engine to idle without gas coming out the primary nozzles and the idle is still rough. Maybe there's a vacuum leak I didn't spot or the crap in the fuel is getting by the filters?

Doesn't matter now, as I ran out of time. I'm moving and had to ship the car. It idled well enough to move under its own power and get that done, which was the immediate goal, but it wasn't graceful. Let's just say the transporter was a patient and tolerant man!

So I now have lots of time to ponder the next steps. I'm inclined to declare this carb a mystery and buy a known good one. I think my energy would be better spent doing stuff I can accomplish. Like replacing the gas tank and all of the rust inside! Maybe I'll just send the carb off to have it repaired by a pro, but my guess is I'd be better off buying a replacement.

I really don't like giving up.... but have to balance banging my head on this carb against the lunacy of already spending over half the cost of a replacement on gaskets, parts, and tail-chasing with no success.

[Shiny]

Take a look at this and tell me if the pulsation and peak pressures are typical while cranking:

Link to Cranking Pressure Video

The peak pressures make me wonder if my fuel pump may be contributing to flooding.

I don't have access to the car now so can't ID the pump, but reading other threads made me curious if the peak pressures over 7 psi might overcome the float. I don't have a reading while the engine is running, so maybe the "average" is what matters?

[Formulas]

Do you have another float to try ?
And exactly how are you checking float level?
And where are you taking the measurement?
To simulate the top being on the carb holding the float pin down i use an old distributor weight over the float pin with a 3/16 screw in the front center screw hole for the top
Doing this makes it easier for me to get a real life reading on the float level
Also how far open are the butterflys?
And your positive no vacum leaks?

[Shiny]

Hi Formulas, thanks for the suggestions.

If you can stand to read through the thread, it was clear the float was stuck after I cleaned it out and installed new parts, but I'm still not sure why. I'm not sure it ever controlled correctly which was why I'm asking about the fuel pressure. When I took it apart again to deal with the stuck float, I'm confident the float was set to the factory spec of 3/8" and verified it sealed OK by turning carb upside down and pulling a vacuum on the inlet.

No, I'm not confident I don't have a vacuum leak, but didn't spot one. How would I know? All the gaskets appeared to be compressed and sealing. I sprayed carb cleaner around the carb, did not increase rpm. When the idle was trying to be decent, I could read 18" on the manifold.

I don't have access to the carb now, as I just moved the car.

The main issue remains inability to stay off the primary nozzles during idle, and I did not get this fixed by increasing the idle tube and DCR diameters.

When the butterflies are closed, I still had some of the transition slot exposed. I'm not sure this is correct or indicates the plates are binding. Might be encouraging if this is wrong and can be easily corrected. Here's a pic of the butterflies fully closed. Should the slots be fully covered or is this normal?

[Formulas]

Without the base being attached to the center i cannot tell what position the primary blades are in during runing
Your idle air bypass holes in the base plate look small perhaps during running you have to open butterflys to get enough air then that creates enough flow past the venturies to pull fuel

[Shiny]

Understood, but I definitely had to open it up to keep it running.

I had written down the bypass holes being 0.089, but I suppose I might have made a mistake. They look about the same as the mixture screw holes in the picture, which are 0.090, so I think that's right.

For now, I still want to know if there's anything obvious with the butterflies not closing enough or if the pump pressure is pulsing too high. If not, I may just get another core and try again.

[Formulas]

Your fuel pressure is fine..
If i was you i would try a different float
Also 125 -130 compression sounds low tho its good that its even what heads?
Did you degree your cam or at least double verify dot to dot
Reason i bring up compression is i have ran the 2800 350 with 1969 #47 ,heads believe about 80cc heads and if i remember correctly i was in 155-160 psi range

[Shiny]

Thank you for verifying the fuel pressure.

Cam was installed dot to dot on stock 70 350 with #11 heads.

The heads are 90cc per thread below, which says others see 125 to 135 psi on the same engine. I measured mine cold, which I understand will read lower than hot.

Link to Thread Discussing #11 Heads

Is what it is for now... will pick up the battle again next year after I move to the car. For now, I'll probably look for a more original and unmolested carb and rebuild it to keep busy.

[Half-Inch Stud]

tank full of bad gasoline?

Assume you have an HEI and not points.

[Shiny]

Hi HIS

Still has original points disty but sparks were jumping gaps, molecules were ionized.

Yes, had a tank full of neanderthal bad gas with a healthy dose of rust and sluffed rubber particles as you can see earlier in the thread. That was definitely a contributor when I first fired it up.

"Sure it's got gas... I put it in there myself just a few eons ago"...



I drained the caca as best I could and put in 2 gallons while I cleaned the carb up and increased the idle tube diameter. I tossed an inline filter in front of the new carb filter to get it running, but maybe those were not totally up to the task? Even with the diluted bad gas, it wasn't idling right.

A new tank is on the list next year, fuel line condition is also suspect! Half the trouble could still be related to old gas, I suppose.

I am lucky and happy the car ran well enough to drive itself out of the garage, roll on and off the transport trailer, and into the new garage. This was the first time I'd driven it in 9 years... felt good!

I'm looking forward to having more time to go after it next year. Maybe those #11 heads need to go away too!

Note to self: don't let gas sit in the car for 9 years.

[Shiny]

I am finally picking up where I left off in 2018 and NEED help again.

I suggest you read through the thread for context.

........

In this episode I decided to deal with all the known and "possible" issues that may have kept me from getting the car running in the past.

I have now replaced the gas tank, bought a new fuel pump, installed a new balancer, and have a new radiator.

I opened the carb once again to check for dirt and verify the inlet seat. While open, I revisited the carb tuning and to my shame, concluded I have the wrong baseplate.

Doh!

There are multiple concerns/implications but what I know now is there are holes for bypass air in the idle circuit that should not be there. You can see them in post 31 but I had no idea they didn't belong and nobody else caught it. I have not yet confirmed they are actually providing air.

Thanks to Kenth for confirming the holes don't belong!

Here's my post on Cliff's forum that led to my unpleasant discovery:

Link to Frankencarb on Cliff's Forum

I am going to pressurize the inlet next before I separate the baseplate from the body and then find out if the holes are connected to a vent.

So...

If the holes are indeed adding extra air, I think it might explain some of the nozzle drip issues I had. I think having too much air at idle might have ended up causing me to open the throttle blades too much, ending in nozzle drip. Does this sound possible/likely?

Questions:

1. What else could go wrong with a mismatched baseplate and carb body? The baseplate does have the APT provision which helped me feel good about it at the time... What else should I look for on the baseplate?

2. If I conclude the holes are providing bypass air and that's the only concern, how do I fill them? I read somewhere that rebuilders use lead shot.

3. If I conclude the baseplate needs to be replaced, where would I find the correct one? As posted on Cliff's site, here is the only marking I could find on the baseplate:



The only reference I found in the Delco listing that says 7036596 is the correct assembly number for my carb. Do I interpret my Frankenplate number 38752 as 7038752?


Mike

[Shiny]

Originally Posted by Cliff R

What size are the upper and lower idle airbleeds? That engine shouldn't need much idle fuel beyond what a stock 7029240 carb would deliver. The 2800 cam in a 350 is pretty much like a stock cam, smooth idle, high vacuum, etc.

Idling rough and not responding to increased idle fuel and throwing timing at it makes me think that you either missed something with the carb set-up, vacuum leak, or something fundamentally wrong with the engine.......Cliff

Ummm.... yup!!

Pay attention, Mike....

[rohrt]

Welcome back to your post after 5 years

I'm curious what vacuum your pulling.

That amount of nozzle drip in your first video is amazing. Have you messed with trying to close the primary throttle blades and increase the idle screws.