carb question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mhorning · 12-18-2003, 08:18 PM

Thought I'd throw this out to you guys. I have a quadrajet M4Med. It runs pretty well except when I first start it up. When I put it in drive it immediately dies. However, if I put one foot on the brake and the other on the gas and kick it into drive while giving it a little gas, it will immediately trim out an idle fine. I can then turn it off and turn it right back on and it will run fine. Any thoughts?

Jerdog · 12-18-2003, 09:14 PM

I've never had any luck with quadrajets. I would replace it with a Carter, or an Edlebrock, or even a Holley. I think the money would be well spent. With the price of fuel, it would pay for it self with the better gas mileage you would be getting. But if you decide to keep it I would look at the fast idle/ choke area. Maybe all it needs is a little carb cleaner in the right spots. Good luck.

**swervin ervin** · 12-18-2003, 09:40 PM

Hmmmm.... another Q-jet hater I see.

A Q-jet will give you better gas mileage than any square bore carb made. It's like anything else though, it needs to be tuned every once in a while. Nothing lasts forever. You couldn't run fast enough to give a Holley. Talk about gas drinkers, not counting the need to be constantly adjusting on the things.

Sounds like the choke needs adjusting or is not working. With the engine cold, start it up with the air cleaner removed. The choke should be closed but with about a 1/4" gap left for some air to get to the engine. If this is OK, how is the fast idle? Needs to be around 1200 to 1500 rpm in order for it to stay running. Let it run to make sure the choke opens all the way when it gets warm.

mhorning · 12-19-2003, 01:17 AM

Mike the choke seems to be working properly. It's at about 1/4 open when cold. And the fast idle is kicking on. It runs at about 1500 when cold, but then when I drop it into drive it dies. It's really weird. Like I said, If I force it to stay running it immediately levels out. But if I don't do this, it dies. Also, If I let it warm up for about 10 minutes and don't do anything to it, it will also run fine. I know it sounds like a choke thing to me too, but I think it's correct. Oh one other thing, not sure if this is related. It will diesel when I shut it off, after it has warmed up. Could my mixture be that cause of all of this?

*mike reeh* · 12-19-2003, 02:11 AM

Quote:

Originally posted by Jerdog
I would replace it with a Carter, or an Edlebrock, or even a Holley. it would pay for it self with the better gas mileage you would be getting.

^^^ *sigh* ^^^

apstguy · 12-19-2003, 02:24 AM

For two days I had my choke stick on me all the was on the freeway. Not only did it suck up alot of extra gas, but it got a little hotter than normal. The choke refused to go off. If I was idling and pushed the gas it would turn off. Once I reached cruizing speed it would turn on again. It dieseled too. It hasn't done it since which is weird. Point is chokes and be decieving. Try using choke & carb cleaner and clean it to see if it helps. Also, if it is an electric choke, pull the fuse and see if it changes the situation.

**swervin ervin** · 12-19-2003, 02:26 AM

Have you adjusted on it any, as in idle mixture screws? Of course I don't think this would cause it because you are above the idle circuit when it's at 1500 rpm.

Let's remember, every time stuff like this happens, it's not always the carb. I'm guessing your tuneup is in good shape.

Try this just for the fun of it. After it's warm and the choke is fully open, cap you whole hand over the air horn. Does it die? If not, this rules out any vacuum leak in the carb.

Russell · 12-19-2003, 02:40 AM

Hmm, sounds like the exact symptoms I've got, but mine runs like it has a HUGE camshaft in it when I first start it on really cold days, and on warmer days it will just have a serious lack of power, and struggle to build enough vacuum to shift gears....

I'll check the choke on it tommorow night, see if it is infact pulling off, and do a good old vacuum leak scan as well, carb cleaner around the base of the carb etc...

It was kinda odd, when I had the vac gauge on the truck, when I set the timing so I had normal engine vac according to the gauge, yet my timing was like an inch before the timing mark, and it ate gas faster than anything I had ever seen... Now when I have it set at proper timing, it gets good milage, but has all the annoying symptoms with that little tremor in the engine, and the vac gauge tells me I haven't got enough vac for a typical engine...

mhorning · 12-21-2003, 01:09 PM

Mike I've attached a page from the Delco manual I found online. Now my carb is a little different than the one illustrated, but I'm wondering, does this mean that the carb should be fully closed when cold for the initial start and that it opens to a 1/4 after ignition, then full when warm? I only ask because I've been making adjustments on the choke and the fast idle. I thought I had it figured out last night and I thought the choke was completely cold when I was working on it. Then, however, I woke up this morning to check the choke and it was completely closed. I should have hit the key to see if it would run this way, but I figured it must be wrong. Now if I am reading this correctly, I'm wondering if it should have been actually closed. Thought I'd get your thoughts.

12-18-2003, 08:18 PM	#1
mhorning Registered User Join Date: Jul 2003 Location: Corning, NY Posts: 158	carb question Thought I'd throw this out to you guys. I have a quadrajet M4Med. It runs pretty well except when I first start it up. When I put it in drive it immediately dies. However, if I put one foot on the brake and the other on the gas and kick it into drive while giving it a little gas, it will immediately trim out an idle fine. I can then turn it off and turn it right back on and it will run fine. Any thoughts? __________________ 63 Chevy C10 86 Chevy K10

12-18-2003, 09:40 PM	#3
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Hmmmm.... another Q-jet hater I see. A Q-jet will give you better gas mileage than any square bore carb made. It's like anything else though, it needs to be tuned every once in a while. Nothing lasts forever. You couldn't run fast enough to give a Holley. Talk about gas drinkers, not counting the need to be constantly adjusting on the things. Sounds like the choke needs adjusting or is not working. With the engine cold, start it up with the air cleaner removed. The choke should be closed but with about a 1/4" gap left for some air to get to the engine. If this is OK, how is the fast idle? Needs to be around 1200 to 1500 rpm in order for it to stay running. Let it run to make sure the choke opens all the way when it gets warm. __________________ Mike 1985 Chevy C-10

12-19-2003, 01:17 AM	#4
mhorning Registered User Join Date: Jul 2003 Location: Corning, NY Posts: 158	Mike the choke seems to be working properly. It's at about 1/4 open when cold. And the fast idle is kicking on. It runs at about 1500 when cold, but then when I drop it into drive it dies. It's really weird. Like I said, If I force it to stay running it immediately levels out. But if I don't do this, it dies. Also, If I let it warm up for about 10 minutes and don't do anything to it, it will also run fine. I know it sounds like a choke thing to me too, but I think it's correct. Oh one other thing, not sure if this is related. It will diesel when I shut it off, after it has warmed up. Could my mixture be that cause of all of this? __________________ 63 Chevy C10 86 Chevy K10

12-19-2003, 02:24 AM	#6
apstguy LED King Join Date: Jan 2003 Location: Sacramento, CA Posts: 2,088	For two days I had my choke stick on me all the was on the freeway. Not only did it suck up alot of extra gas, but it got a little hotter than normal. The choke refused to go off. If I was idling and pushed the gas it would turn off. Once I reached cruizing speed it would turn on again. It dieseled too. It hasn't done it since which is weird. Point is chokes and be decieving. Try using choke & carb cleaner and clean it to see if it helps. Also, if it is an electric choke, pull the fuse and see if it changes the situation. __________________ Tyler 1985 C10 305 w/ Bowtie OD TH700R4 3.42 LSD 202,000 miles 2006 Ford Focus ZX3 5-speed Stick 2016 Chevy Spark EV Gone: 2002.5 VW GTI 24v VR6 Gone: 2008 VW R32

12-19-2003, 02:40 AM	#8
Russell Professional Grade Join Date: May 2003 Location: Fort McMurray, Alberta Posts: 7,915	Hmm, sounds like the exact symptoms I've got, but mine runs like it has a HUGE camshaft in it when I first start it on really cold days, and on warmer days it will just have a serious lack of power, and struggle to build enough vacuum to shift gears.... I'll check the choke on it tommorow night, see if it is infact pulling off, and do a good old vacuum leak scan as well, carb cleaner around the base of the carb etc... It was kinda odd, when I had the vac gauge on the truck, when I set the timing so I had normal engine vac according to the gauge, yet my timing was like an inch before the timing mark, and it ate gas faster than anything I had ever seen... Now when I have it set at proper timing, it gets good milage, but has all the annoying symptoms with that little tremor in the engine, and the vac gauge tells me I haven't got enough vac for a typical engine... __________________ 1995 Chevrolet 2 Door Tahoe (6.6L LBZ Duramax / ZF6 / NP241 with 1 ton solid axle swap)

12-18-2003, 09:14 PM	#2
Jerdog Registered User Join Date: Feb 2003 Location: Bakersfield, CA Posts: 38	I've never had any luck with quadrajets. I would replace it with a Carter, or an Edlebrock, or even a Holley. I think the money would be well spent. With the price of fuel, it would pay for it self with the better gas mileage you would be getting. But if you decide to keep it I would look at the fast idle/ choke area. Maybe all it needs is a little carb cleaner in the right spots. Good luck.

12-19-2003, 02:26 AM	#7
swervin ervin You get what you pay for Join Date: Dec 1999 Location: Cherryville, NC Posts: 4,798	Have you adjusted on it any, as in idle mixture screws? Of course I don't think this would cause it because you are above the idle circuit when it's at 1500 rpm. Let's remember, every time stuff like this happens, it's not always the carb. I'm guessing your tuneup is in good shape. Try this just for the fun of it. After it's warm and the choke is fully open, cap you whole hand over the air horn. Does it die? If not, this rules out any vacuum leak in the carb.

12-21-2003, 01:09 PM	#9
mhorning Registered User Join Date: Jul 2003 Location: Corning, NY Posts: 158	Mike I've attached a page from the Delco manual I found online. Now my carb is a little different than the one illustrated, but I'm wondering, does this mean that the carb should be fully closed when cold for the initial start and that it opens to a 1/4 after ignition, then full when warm? I only ask because I've been making adjustments on the choke and the fast idle. I thought I had it figured out last night and I thought the choke was completely cold when I was working on it. Then, however, I woke up this morning to check the choke and it was completely closed. I should have hit the key to see if it would run this way, but I figured it must be wrong. Now if I am reading this correctly, I'm wondering if it should have been actually closed. Thought I'd get your thoughts. Attached Images __________________ 63 Chevy C10 86 Chevy K10



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