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78 Eldo Hesitation/Sag on Cold Drive-away

Started by Jakes, May 21, 2015, 05:16:55 PM

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Jakes

Hi Gentlemen... Since getting the car last Oct. it's always been a little fussy on a cold drive-away even after letting it fast idle for a full minute and then letting it idle again for a full minute after unloading the choke.  I'd back it out into the street, put in gear, gently press the pedal, it would start to go, then "sag", but not stall.  I'd ease up on the pedal and apply it again gently, a little less sag, and then she'd take off.  This action would continue at lights/stop signs for a while until the engine fully warmed up and she'd be fine with smooth and strong acceleration from a stop.

I've put about 1400 mi. on the car since getting it by exercising it regularly over a 30 mile local/highway route and fill up with hi-test at a Hess station.  Lately, however, the cold response has gotten worse.  Now I have to pump the pedal somewhat to overcome what has become a kind of "bucking" as she tries to move out.  But when the engine fully warms, no problems whatsoever.

I pulled the air cleaner to look at the carburetor (4 bbl quadrajet M4ME).  First thing I checked was the choke setting which was set right (2 notches rich).  The throttle and vacuum break linkages and the choke plates looked fine and I tested their movement, along with the fast idle cam, which was fine.  I removed the front vacuum break and it tested fine (push in the rod, hold a finger over the vacuum port, watch for no movement in the rod, although there was a little, but no evidence of a leak).  I replaced the loose-fitting short rubber tube with a fresh one.  Then I re-torqued the carburetor bolts to 8 ft-lbs front and 12 ft-lbs rear.

Today in testing her out on my street, she was as fussy as ever.  This time I tried pressing the pedal more fully as she sagged (rather than "jiggling" the pedal up and down) and the engine stalled.  But she started back up OK.  To get her on her way I had to "baby" the gas pedal as before until she warmed up, as described above.  But it's gotten to be a nuisance because with a cold engine I have to ensure there's no traffic for a long distance when I get to the first intersection where I have to make a turn.

The car now has about 15,200 mi on it and when I got it it had 13,800 mi on a 36 year old car.  So, my guess is that the carburetor is probably gummed up in that part of the system where it needs to run under rich mixture condition while the engine warms to operating temperature.  Before taking her out today I bought a carb cleaner -- SeaFoam Motor Treatment, which was highly praised by users on Amazon.  The car was down to a quarter tank, so I dumped it in at the station before filling up.  Since the engine was hot I have no way of knowing if this stuff is effective until I start her up from cold the next time.  In the meantime, I'd appreciate your advice, suggestions and recommendations on this problem that I'm sure you've all encountered with a carbureted engine at some time in the past.  In particular, is SeaFoam a good choice for carb cleaner or is there something more effective such as: Red Line SI-1... Chevron/Techron concentrate... Royal Purple Max-Clean... Berryman Chemtool... Lucas Fuel Treatment... BG44K fuel sys. cleaner... Gumout carb cleaner... or our old standby, Marvel Mystery Oil?

If none of this stuff solves the problem, it's time to pull the carb and get it cleaned out and rebuilt, right?  As always, looking forward to your comments.  Many thanks for your help.
Paul
'78 Eldo. Custom Biarritz Classic

35-709

#1
Check the accelerator pump, probably weak and gradually getting worse.  Look in the carb while manually operating the throttle (engine off  ;D) you should see a healthy squirt of gas.

If it is the accelerator pump, "mechanic in a can" isn't going to help.  Might get away with just replacing the acc. pump if that is the only problem.
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

Jakes

Thanks "35-709"  for advice.  I was surprised that yours was the only response; maybe folks preparing for the Mem. Day weekend.  So, I'm resubmitting in the hopes that others will also provide some wisdom.

I did work the throttle with the engine cold, but with this huge engine bay it's hard to see if gas was spritzing into the throat.  I have a feeling the accel. pump IS the culprit though, because I heard little or no sound of "spray" while working the throttle and there was no flooding.  Also, when the engine is fully warm, the acceleration from a stop sometimes is slightly jerky which, again, tells me the pump's going bad.  More input will be greatly appreciated.  Many thanks.
Paul
'78 Eldo. Custom Biarritz Classic

bcroe

If you have the original (plastic teeth) timing chain set, it might be on the way out.  These
all need replacement with all steel, you pick the time or the car will pick it for you.  Bruce Roe

Joe V

This's too nice of car to have it run that way. 

With that big carb, the pump should sound like a faucet.  If it is not pumping it's either warn as noted in previous post, fuel is restricted, or carb is gummed up and vacuum bound so it can pump.  I'd rule out the carb accelerator pump first as you suspect.  Also, can't discount the impact of ethanol fuel and how it can gum up the carb.  Especially if the car sits.  No amount of fuel treatment will clean the carb out if it is really gummed up.  Sometimes the investment in a carb rebuild in these situations is best as you are considering.

I'd replace all fuel filters next.  After running for a while the flow of fuel sometimes dislodges sediment in filters enough to get the gas flowing at a reasonable volume but the volume can sometimes be restricted when first started and sediment is settled. 


Jakes

Thanks for your input, gentlemen.  Today I learned something disturbing.  I called a well-known carburetor specialist, Larry Isgro in Wantagh NY, who has advertised in Hemmings for years and attends the fall Hershey show, to get his diagnosis about the bog/sag when the engine's cold with a view toward bringing him the carb for rebuild.  Many of you may know him.  I couldn't believe what he told me:  The 1978 M4ME Quadrajet is one of the few carbs that he no longer works on.  He considers this model in the 1978 Cadillac....and he specifically cited the 78 model year..... to be poorly engineered because the ones he rebuilt he could not get to work properly (presumably due to customer feedback).  He wouldn't even just replace the accelerator pump.  He was very definite in his opinion of this carb and will not touch it!

Please understand that his comments should not in any way reflect on his solid reputation as a carburetor specialist for classic and vintage cars.  When I researched the car before I bought it last October, and in discussions with my local AACA club members, there was never a hint that the M4ME Quadrajet was the Achilles heel of the 78 Cadillac.  So, my purpose in posting this message is to solicit any views and opinions as to whether rebuilding this model carburetor opens up a Pandora's Box of problems that result in poor performance and reliability in the 78 Cadillac.

I still have more "testing" to do before I conclude that the cold drive-away bogging problem is indeed in the carb.  In the meantine there's a good number of carb specialists listed in the Services section of Hemmings some of whom highlight the Quadrajet.  Any recommendations?... or perhaps there's someone in CLC I can turn to who doesn't have to spend money advertising his carb rebuild/testing skills.

Again, many thanks for your help.   
Paul
'78 Eldo. Custom Biarritz Classic

TJ Hopland

Interesting that he would say that.   I'm by no means a carb expert.   I have cleaned and thrown kits at a few dozen Q jets including a couple 78 Cadillac's including one that was mine and a semi daily driver for a couple years and I don't remember anything that seemed that unusual about the 78 and I know I didn't have any sort of sag issue other than initially when I got the car the distributor weights were sized and the carb that was filthy and leaky to start with kept clogging up.   Turned out that it was sucking charcoal bits out of the charcoal canister.  Sadly took me 3 times taking it apart and cleaning the bits out to figure that out.   Found out from those that worked on this era car back in their heyday that the quick fix for that issue was to shove a universal inline fuel filter in the line between the carb and canister to catch the chunks.  It worked.  Guess the guy I sold the car to drive it daily for another 2-3 years before it rusted out too bad to keep going.

The other thing that surprises me about the carb guy is he apparently has no fix?   Doesn't suggest that if you find say one from a 197x  xxx that he can mod that to work on the 78 or for an extra $ he can fix the flaw in the 78.     Seems to me that 'hot rod' carb guys like the 77-79 Cad carbs because they are 800? CFM?   I think only a very few other carbs were 800's and they came as rare super option packs at the tail end of the real muscle cars so there just were not many out there and people want them to get as close as possible when making clones.    I could be wrong and there is a flaw in the 78 design and I just got lucky when I dealt with them.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Dave Shepherd

 I was a Cadillac employee in 78 and that carb did not present chronic performance issues, yours need to be gone thru and richened up some also there is a filter in the inlet fitting that is often overlooked.

76eldo

Is this problem mInle when the car is cold?  Does it go away when the car is warmed up and running for about 10 minutes?

A lot of the Eldorados do this. My 76 does it when it's on choke when you first start it.

I had a carb done by Isgro many years ago and was happy with the carb work but it was painted not plated and discolored almost immediately. It was not for a Caddy.

Google Bowen carburetion in Levittown Pa.

They are fantastic and I'd talk to them about your problem.

I've had carbs done there with good results and they replate them to look like new and more importantly get them to run like new.

Every carb is run and adjusted on a test motor after rebuilding.

Good luck.

Brian
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

Jakes

Brian... 
Quote from: 76eldo on May 30, 2015, 09:12:24 AM
Is this problem mInle [typo: mainly] when the car is cold?  Does it go away when the car is warmed up and running for about 10 minutes?

Yes, the bog/sag occurs only when the engine's cold.  As I drive it the problem gradually lessens (getaway from lights, stop signs, etc) until the engine's at operating temp. and there's no more problem -- yeah, after ~ 10 min or so.  Then, accels from stop are smooth and sure, no hesitation... although from time to time you get this very slight "stair-step" response as the engine revs from stop, but it doesn't bother me.

The car now has 15,400 mi on it.  The previous owner bought it in 2009 with less than 8K miles on it.  He changed the fuel filter at that time.  He put about 6K miles on it before I bought it last Oct.  My theory is that a combination of gas (possibly un-StaBil-ized) sitting in the carb for long periods of time and the dreaded ethanol gummed up the innards and perhaps deteriorated the pump plunger.

Glad to hear that rebuilding the M4ME Q-jet doesn't seem to result in problems, as per TJ's and Dave Shepherd's comments.  Hope that's the same thought from others who have yet to reply.  I have a feeling Larry Isgro had a bad customer experience with this carb and decided never again... I don't blame him.

A million thanks, Brian, for the recco. about Bowen.  Joe Caristo (I think you referred me to him) also likes Bowen.  I'll probably call them.  Regards...
Paul
'78 Eldo. Custom Biarritz Classic

76eldo

It would be nice to see if there is a choke adjustment that will lessen this cold problem.

Don't forget that modern cars are injected and computerized which allows you to turn the key and slam it in D and drive off.

Older carbureted cars do have to arm up a bit and that helps.

My 76 runs so well after it warms up I just live with letting it warm up for a few min and feather the gas for the next few minutes and afterthT it's great.

Brian
Brian Rachlin
Huntingdon Valley, Pa
I prefer email's not PM's rachlin@comcast.net

1960 62 Series Conv with Factory Tri Power
1970 DeVille Conv
1970 Eldo
1970 Caribu (?) "The Cadmino"
1973 Eldorado Conv Pace Car
1976 Eldorado Conv
1980 Eldorado H & E Conv
1993 Allante with Hardtop (X2)
2008 DTS
2012 CTS Coupe
2017 XT
1956 Thunderbird
1966 Olds Toronado

bill06447

The heat stove/air cleaner flapper valve needs to be working properly. Also the EFE (heat riser) valve in the right side exhaust manifold needs to be operating properly, including the temperature valves feeding both of them. I don't care who says that exhaust heat riser valve isn't necessary, it is, and the car won't run well cold if it's not working properly.

You need to adjust the choke via a measurement taken with the choke heater removed-not by the "hash marks" on the cover. The procedure is described in the Rochester manual. Alternatively, tick the choke cover a notch "rich" and give it a few drive cycles-repeat until you get the driveability you can live with. I put a rebuilt carb on my 78 and it was not adjusted properly from the rebuilder-took me a bit to get it straightened out to where it worked well on MY car.

Bill

35-709

Funny, both of my 472s (a '71 and a '73) run just fine cold without a heat riser, about one extra minute of warm up time and they are ready to go.  There are many of us that have gotten rid of that troublesome part.  Rapid acceleration should wait for a complete warm up, heat riser or no.

 
1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

bill06447

It's possible there is a vacuum leak in the heat riser system. Once the car warms up there would be no vacuum to it; a vacuum leak while cold could cause the lean stumble described.

Bill

Jakes

Greetings gentlemen... here's the latest in my saga of cold drive-away problems.  Today, as soon as I fired her up I checked the position of the lever on the EFE valve (heat riser) that's hooked to the vacuum actuator.  Looked like full vacuum was being applied by the TVS judging from the change in position of the lever which indicated that the heat riser valve was closing properly.  Of course it's possible the TVS may be bad by cutting the vacuum to the EFE valve at a temp. colder than spec. thus causing the riser valve to open sooner than it should.

Some of you suggested letting the engine warm up for a while before moving out.  Today I did that for about 10-12 minutes after unloading the choke from fast idle and it helped a lot.  I still had some bog/sag but it was much more manageable.  However, it continued to bog/sag a bit at lights/stops even after the engine was fully warmed up (I think, because there's no gage), but even less than when I started out.  After a while there was no problem at all.

Sent an email to Bowen Carburetor (Brian Rachlin's and Joe Caristo's recommendation) the other day but have had no response yet.  Guess I'll call them tomorrow and see what they say.  Appreciate all your input.  Regards..
Paul
'78 Eldo. Custom Biarritz Classic

35-709

I am still of the opinion that your accelerator pump is not doing its job, especially if you are still having the problem when the car is fully warmed up eventhough it is not quite as bad.  There are plenty of good carb shops that are not afraid of that carburetor and can put it right for you with an overhaul.  I have recommended Daytona Parts (carburetor experts) here many times.

http://daytonaparts.com/ 

1935 Cadillac Sedan resto-mod "Big Red"
1973 Cadillac Caribou - Sold - but still in the family
1950 Jaguar Mark V Saloon resto-mod - Sold
1942 Cadillac 6269 - Sold
1968 Pontiac Bonneville Convertible - Sold
1950 Packard 2dr. Club Sedan
1935 Glenn Pray - Auburn Boattail Speedster, Gen. 2

Jeff Moffo

Hi Paul,
Hope all is well with you.

If it makes you feel any better, my '76 does the same thing.  Once warmed up, it is fine.  Actually, when I get it on the road and move it for a bit, the sag/bog goes away.  But it takes a little while.
My accelerator pump needs to be replaced.  It is not that difficult to do, just have not done it yet.  I suspect your pump's washer has deteriorated.  That should help with the "stair-step" jump at lights.  (Mine does that too, sometimes.)
Lastly, when the car has had old gas sitting in it from the winter (even with Sta-Bil), it does this even more.  Trying to get my tank down a little by driving the heck out of it when the weather is good and then fill it with fresh gas.  Usually helps out, too.  Just some thoughts on my experiences.  Seems Brian's '76 is a distant cousin with the same "family" issues!

Good Luck. 
Jeff
Jeff M
North Jersey
Best of all, it's a Cadillac....
'76 Coupe DeVille - Claret (Sold)
'73 Series 60 Fleetwood (Sold)
'76 Coupe DeVille-Dunbarton Green

Scot Minesinger

My 1970 with stock carb on stock 472 engine runs fine when cold.  Now it is not as powerful and great when warmed up, but it works as I remember they did when I drove these cars in high school.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

"Cadillac Kid" Greg Surfas 15364

Paul,
Have you pulled and checked the spark plugs?  A plug that is beginning to get fouled will miss fire untill it is warmed up and then perform okay.  That is until it gets more fully fouled.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

"Cadillac Kid" Greg Surfas 15364

Paul,
If un modified, there are several temperature sensitive systems in your emissions controls which come into play before the car is warmed up. Trying to guess from 3000 miles away can go on for ever, however, if the plugs look good I would start checking vacuum lines and connections witht eh help of a factory service manual to find the culprit. Yours is in the last generation of trying to make the "big blocvk" motors comply with emissions standards, so the system (emissions) is complex and sensitive.  The fact that it does smooth out when warm is a good sign that there is probably nothing seriously wrong, but it will take some looking at. 
I second (or third) the idea that there is nothing intrinsically wrong with your carburetor.  It was fine tuned for your emissions system, and should work well if it (emission system) does.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-