My 78 L48 w/auto takes at least 5-10 minutes to warmup and run right; sometimes longer. Is this normal?

Starts with 3 to 4 pumps of gas on second try when its dead cold in morning, then starts with 0-1 pump of gas the rest of the day. It just does not seem to idle smooth or stable until it warms to 200 F; then its fine.

It just seem to be temper mental and cold nature; until it's warm. It'll idle rough 900-1200 rpm in idle and in Park after 2-3 minute warmup and throttle kicked down (temp `170F); then if i try to put it in drive it'll die. Then restart and either let it warm up more or drive off and give it gas to keep it from dying. First couple stop signs or lights; it may want to die or runs rough idle (550 - 800 rpm).

Then once it warmed up to 200 F; its fine; idles stable 650 rpm in drive and stopped or (900-1000 rpm in park or neutral). Timing set at 6 deg btdc, total advance 34-38 deg. Until it cools down after sitting an hour or two; then it's back to needing a warmup.

Again is this normal? Carb or vacuum issues? other ????

 

Need some details - such as what carb, intake manifold, cam, and exhaust.

 

Completely Stock, Original Quadrajet, Original Manifold, original Cam, and orginal 2-1-2 exhaust, car has only 74k miles. Recently (last year) put in new plugs, wires, cap, electronic distributer module.

 

Definitely something is not right. It should never take that long for the car to stay running. Mine takes a couple of times to start when it's been sitting for a week or more, but if I drive it every day, it starts instantaneously every time. The first place I'd start is making sure the choke is working properly. Email Lars for his q-jet choke set up paper for the best Q-jet help you'll probably ever get.

 

I would like said before in the post, check the auto choke. Pull the air cleaner and observe the choke action.
- Before starting when cold, pump the gas 1 time and make sure the choke is completely closed.
- After start the primary butterfly should be open about a 1/4" as a vacuum break.
- Engine should be running at around 1200rpm. Choke should slowly be opening. About 1/2 way open, if you jab the gas it should drop in rpms but not to idle rpms.

As far as having to pump the gas 3-4 times when cold in TN, the gas in the float bowl is low or disappearing. 1-2 pumps is normal,and the rest of the day, maybe putting the acc down 1/2 way is "normal". Suspect a leak out the bottom well plugs of the carb and into the intake or being pulled back in the fuel line. Fuel filter have a spring behind it?

Also, there is a heat riser on the right exhaust manifold that routes hot exhaust gas back under the carb for cold start drivability. When the engine is cold look at it and see if you can move it freely by hand. If not, spray it with penetrating oil til it moves freely.

All in all these are items to check and go ahead and email Lars at V8FASTCARS.COM and ask him to send a copy of the Q-Jet papers to you via email. Reality is if the Q-Jet is origional and the car is a 78 and you have 70k + miles, it probably needs a cleanout and some work. Good luck.

JSP

 

I'll download Lars papers (and read) and check choke operation, but I know choke is wide open when engine is warm and I've checked timing.

Car is started aproximately once a month, I need to drive it more, but hate when it stumbles?

 

I did not get he once a month before. Then it is possible the gas in the fuel bowl evaporates and you have to pump 3-4 times to draw it up to the bowl. The cold blooded nature of the car is not totally normal where you have to wait till it is 200 degrees before it is stable. In additional to the carb I would check the t-stat opening and closing. If the engine stays cold from an open t-stat then it is cold until it finally come up to operating temp. Try opening the radiator cap before starting and see if coolant is circulating before the t-stat opens. Put a thermometer in the coolant and see what temp the coolant does start really circulating. Just maybe you also have a stuck open t-stat.

Another point of general interest - is this the 1st carb car you have dealt with and are comparing cold drivability to fuel injection cars? They are not the same.

 

Thanks for all the advice. Did not have time to tinker with car last night, but this morning I did open the hood before going to work. I was tempted to drive it but was in a hurry.

The choke is fully closed and the the heat riser is free but stiff (need to spray pentrating oil); coolant is green but a little low.

So I'll look at it more tonight; since hood is open. Also, it is time to change coolant in several of my vehicles. Then I'll check the t-stat or replace it.

As for owning carb cars; I've owned seven (3 with quads); I've been lucky carbs were never the problems. I've rebuilt a couple 2 bbls (more than 6 yrs ago); had 1 quad rebuilt twice. I like older cars when they run right, esp no computer; it's fuel, air, or spark.

But new cars; do spoil one; that is jump in and go and no cold natured. And Old car require tinkering and regular driving to keep them running.

 

Good on the observations. Then you know the difference of carb vs EFI and a good carb and a bad carb runner. The one other thing is how is the vacuum at start? A 78 - 350 should be pulling high teens at cold start and when warm and idle pull 16-18" unless there is a cam with lots of overlap. Later,
JP

 

Don't "download" any of my papers - I do not post any of my papers on-line, and all my papers posted by others are obsolete and out of date. Request the papers you want directly from me to assure you are getting current information:

V8FastCars@msn.com

These cars, when new and set up right, started and ran perfectly when cold. There should not be any cold-start or cold-running issue if things are set up right - you shouldn't be able to tell the difference between this and fuel injection.

Lars

 

Email sent. requesting latest Lars qjet papers. Thx

Tonight I plan to look at choke, and heat riser, and t-stat ops. By weekend; change coolant and maybe t-stat.

 

Most likely the choke 'heat' tube is clogged so it can't work properly. I suggest that you remove the carb, clean out any caked up carbon & crud in those areas needing it, do a rebuild on the carb and make all the set-up and adjustments to carb and choke shown in the Chevrolet Chassis Service Manual for your car. Good rebuild kits can be purchased at NAPA, along with nitrofil float {ref. Lars' papers} for very little money. Or, you can send it to Lars for rebuild [if you request it via his e-mail and he is willing]. The latter is the best way to go; doing it yourself is the next best way, IMO.

If you get all the 'stuff' you need to do the work and the correct reference materials (in advance), the rebuild and set up should easily take less than one day to complete.

 

Got to play or troubleshoot some more.

Car sat for two days needed to pump 3 times and it started; choke was fully closed. Heat riser free but stiff. Air cleaner top off. Started running about 1800 rpm high idle; after about 2 1/2 minutes it idles down and dies. Choke has fully opened.

Won't stay running and dies several times. Restart and hold pedal to about 1200-1500 rpm. Warms up to about 170 - 180 F. Finally stays running about 1150 rpm. Lapse time about 8-10 minutes.

Adjust idle to 1000 rpm, at about 200 F at 15 minutes, and t-stat open and water is green and circulating. Engine running quasi-stable at 15 minutes.

Decided to spray carb with carb cleaner; engine speeds up. Let idle return to stable; plug rear port (air cleaner conn); spray down choke area; engine speeds up; spray around base of carb; engine speeds up.

I'm guessing; but I believe I have a big vacuum leak around carb between carb and manifold gasket; thus need replace that gasket and old rubber hoses. It looks like the hoses are mostly original and stiff; thus need to replace and adjust carb. Was original engine paint sprayed with carb installed. Looks like gasket has some blue overspray on it.

The choke appears to be opening up; maybe need to adjust high idle speed later.

Could this be the problem, one big vacuum leak.

 

Yep. The big clue is the engine speeding up when you spray the base of the carburator. A vacuum leak would cause the symptoms you have.

 

when was the last time the plugs were replaced?

 

However, I also have a question about your base ignition timing. A couple days ago I looked at the factory manual for a '77 and the base timing is 12 degrees.. Is six degrees right for your engine? More base advance typically makes for a better idling engine. -Jeff

 

I thought I was getting warmer when the idle was changing. Now i have to change the carb manifold gasket and retune carb.

Less than a year ago, I replaced plugs and wires, distributor cap, and electronic module (it went bad; failed). I'll pull a plug later to see how thay are?

 

I'm sure the car can take more advance, right now it set to emmission tag specs: 6 deg btdc and 600 rpm in drive (auto). Later after I get it running like it should, I have been told to set timing between 8-12 depending on gas and ping?

 

I'll get this carburator adjusted right yet. Back to square one.

I pulled the carb off, and replaced the carb to manifold gasket, it was stuck on the botom of the carb, it was so dry and brittle it broke in half as I removed it. (removing the fuel line and the brake booster vacuum line (bbvl) was a PITA). The the bbvl has rounded corners and a twist in the line, I'll have to replace later?

The car runs smoother sealing that huge vacuum leak; I'll have to wait until tomorrow to adjust the carb; it's late and neighbors may not appreciate revving noise after 9:15 pm.

I'll start with checking timing; then adjust idle and idle mixture screws. Then the driver will be back in business for a weekend cruise. Off course, I'll have to go around a big block tomorrow when carb is fully adjusted.

Thanks for all the help. Thanks to Lars for his tuning papers; I've read them twice.

Tomorrow, this issue hopefully will be history.

 

Cold nature is history. Timing set at about 6 or 7 deg BTDC, idle at about 900 in park, about 600 in drive. Car runs great; choke is ready to go in about 2 minutes. did not really have to adjust mixture screws, kinda off just smoothed out idle.

It is still a 3 pumps of gas and it starts the first time, then it is none or one pump the rest of the day.

It's ready to go on a long cruise. Now its timing to change oil, coolant, and trans fluid. Freshen up every thing for summer.