My truck vs the cooler outside temps

[jdheff1982]

Ok, so a few weeks I installed an E-Performer 750 to replace the sh*tty 600 that was on there. That was when the temps were still in the 80's to 90's. Since then, the tmeps have cooled off and mthe truck is not liking it.

First start in the morning usually takes about 5 pumps just ot get it running. After that, it is a struggle trying to keep it between 1.5 and 2.0 K RPMS. If I lett off just a hair, the motor takes a nose dive to the 0 to 500 RPM range and getting it back up is erradic.

I know the hose from the brake boost is good and the dizzy line is good. Not so sure about the tranny line. The PO used clear tubing up to a certain point before it switches over to plair rubber hose. I haven't had any shifting problems, so I haven't replaced it.

Any adjustments I have made to the carb include the following,
1.) Increase accel pump stroke length to bottom hole. Truck was hesitating upon take off from stand still. The hesitation has decreased, it is still there and start up is more difficult than before. It used to take maybe 1 or 2 pumps at top hole, now it takes more on bottom hole.

2.) Idle mixture screws have mean adjusted, but not accurately. I was able to get on side to increase engine rpm, but the other side wouldn't do anything. I plan to rent a vacuum gauge this weekend and properly adjust it.

3.) I have idle set at 1000 rpms. When it is warm out, the rpms will drop to 700 or 800 rpms when in gear. Now that it is cooler out, the rpms are barely above 500. Even after driving the truck for 10 minutes from work at a near constant speed of 40 MPH, it was trying to die as I was slowing down to park at home.

One thing I have noticed is that idle and cruise performance seems erradic. One day, it might drive fine. Another day, it could be gasping for air at idle. Cruise is ok, but the motor misfires alot. Not sure if the wires are jumping or what. The spark plugs are only 2 months old.

The only constant that I have seen with the motor is only when my foot is in it. If I drive it around say above 2500 RPMS, the motor loves it and performs well.

Other than checking the trans vacuum line, I am unsure as to what else I can do to get lower rpm driveability. And please don't say that the carb is too big. These problems have slowly been creaping up as the temps have gotten cooler.

Any ideas and help would be appreciative. Thanks in advance.

[Redcap]

Carb is too big.

[jdheff1982]

Originally Posted by Redcap

Carb is too big.

Would you think it was too big if you spent $200 on a reman when a 600 reman was $50 more. I wouldn't think so.

Anyways, there should be a way to compensate. I mean, take a 4 banger, ppl are always increaseing throttle body size and increasing airflow. So why doesn't the same principle apply to carbs? I still doubt the carb size is the issue. As I mentioned, it ran fine during warmer temps and it runs fine as long as I keep my foot in it depending on how it wants to act. The problems come and go. I don't experience them everytime.

[Squareforceone]

I'm interested in this is as well my 305 with a stock 4bbl quadrajet is having a hard time starting in the mornings anything i could do

[Redcap]

Originally Posted by jdheff1982

Would you think it was too big if you spent $200 on a reman when a 600 reman was $50 more. I wouldn't think so.

Anyways, there should be a way to compensate. I mean, take a 4 banger, ppl are always increaseing throttle body size and increasing airflow. So why doesn't the same principle apply to carbs? I still doubt the carb size is the issue. As I mentioned, it ran fine during warmer temps and it runs fine as long as I keep my foot in it depending on how it wants to act. The problems come and go. I don't experience them everytime.

Considering that I have never paid more than $100 for a carb (in good working order, thank you Craigslist), I think someone took you to the cleaners.

[csb#356]

Throttle bodies on hondas are different than carburetors on your chevy. The throttle body is electronic and compensates for different amounts of air coming in and different humiditis, atmospheric pressures, engine temperature, etc etc. That carburetor can definately hurt the performance of your engine at lower rpm assuming it is a small block. Is the choke and fast idle working properly on this carburetor? Also if you want to increase the stroke of the accelerator pump you should move the pushrod to the top hole. If trouble is starting as air temperature gets lower and oxygen gets denser then I would look at the carburetor as the culprite

[jdheff1982]

Originally Posted by Redcap

Considering that I have never paid more than $100 for a carb (in good working order, thank you Craigslist), I think someone took you to the cleaners.

Nope, I won't buy second hand parts that are vital to the functionality of my truck from people I don't know. The e-Performer 750 was the cheapest carb from Jegs. Even cheaper than summit. And it has been reconditioned by the very people who made the carb. Imagine that! Basically got a new carb for nothing.

Anyways, my beef isn't about how much I spent on a carb. These things are not found on Craigslist in my area. Even asked my Uncle who drag races about getting a used one from one of his racing buddies. Apparently, they all use spread bore carbs or carbs way bigger than what I need. It's sad actually, Wichita has an International Raceway that is NHRA and we don't have any specialty shops.

The truck performs fine once I get it rolling. It's the fluctuation in idle speeds. Some days it holds fine, other day it's all I can do to keep the motor running.

It is probably something simple that I am unaware of. The only carb work I have ever done is on a nitro r/c. Obviously, what I know about them won't relate to the more sophisticated gas engines.

With my motor setup, should I be running the idle mixtures richer than edelbrocks suggested lean-best setting?

[hatzie]

Your Carb has crud intermittently blocking one of the low speedcircuits or the carb is too big. Since you paid $200 for it I'd return it. Get a 600 CFM Rochester Quadrajet rebuilt by a reputable shop not the high volume outfts. I've consistently had issues with the Asian Edelbrock carb quality.

[motornut]

this past weekend I replaced my (guessing oringinal ,almost 34 year old)305 fuel pump
and with no fuel filter before it,when i undid the line up to the carb filter
couldn't believe the rusty crud that came out
i guess it just kept pushing up against the filter,didn't get caught in it
i too had miss fires and hesitation....but the truck fired right up after better then before
havn't driven it yet but the way it started and idled ....just made me smile

that and check the distributer weights move freely/mine were siezed

[jdheff1982]

Well, I think I found a partial contributor to my prob. I was out making idle mixture adjustments. After each adjustment, I would drive the truck to see if the idle to whatever still had hesitation. After the 1st adjustment, I had only 1st gear and reverse. I thought that switching the vacuum lines on the carb was the problem. Nope, when I went to grab the trans line, it was loose. Further inspection, I found the live completely burned through bny the headers.

Stupid PO used aquarium tubing from trans to the smaller hose going to carb. I have some reinforced rubber hose that I will replace it with. I am hoping fixing that will help the overall performance. Mainly first start of the day. It'll get fixed tomorrow.

Ediit, when I adjust the IMS, I need to aim at increasing engine RPM while adjusting, regardless of direction I am turning the needles. I followed the instructions and the engine didn't really idle up any until the IMS where nearly in as far as they will go. Although today, I backed them of and the engine rpms increased and the off idle hesitation decreased.

[jdheff1982]

Originally Posted by hatzie

Your Carb has crud intermittently blocking one of the low speedcircuits or the carb is too big. Since you paid $200 for it I'd return it. Get a 600 CFM Rochester Quadrajet rebuilt by a reputable shop not the high volume outfts. I've consistently had issues with the Asian Edelbrock carb quality.

I'll replace the fuel line first to see if it helps any. But I think I am beyond the return period from Jegs.

[jdheff1982]

Here is a pick of the blown vacuum line for the tranny:



As I mentioned before, the PO didn't know jack **** about this stuff. I am thinking about hooking the tranny to the PCV line and keeping the dizzy on full advance (that is if it is even advancing at all). Damn, I need more money....

[motornut]

good catch,
yup looks fishy to me lol
wonder if it colapses under suction too?

[tucsonjwt]

Just checking, have you made sure that your choke is fully open when the engine is warm?

[78 Chevyrado]

It's likely the temp change. to get the most from a carb, you have to retune for different temps, like a 20 degree spread.

On my edelbrock, I figured this out long ago, so i have a note in the calibration kit which parts and settings are for summer and which are for winter.

if your in the season of ever changing temps like me, ie; 30 degrees in the morning and 80 degrees in the afternoon, its going to run crappy at least half the time.

The only set it and forget it remedy is EFI.

Before you change your settings, take note how it was setup on a hot day, you can stick it back just like this in spring/summer and it will work fine.

This is how cars were back in the day. people didn't notice much because a full tune up was every 5-10k or so depending on the car. so that covered the seasons.

My edlebrock has a summer and winter setting. in between when the temps fluctuaute a lot it runs crappy half the time. that is life with a carb. you are the computer for a carb. gotta set idle mixture, sometimes jets n rods and sometimes choke depending on the weather, whereas EFI does this 2,000 times or so a second, at all times.

[406 Q-ship]

Originally Posted by hatzie

Your Carb has crud intermittently blocking one of the low speedcircuits or the carb is too big. Since you paid $200 for it I'd return it. Get a 600 CFM Rochester Quadrajet rebuilt by a reputable shop not the high volume outfts. I've consistently had issues with the Asian Edelbrock carb quality.

Edelbrock carbs are not made in asia. They are cast in the Southeast US and assembled in California.

Is the choke working properly? Fuel is changed this time of the year to a winter blend that can be propblematic in some areas.

[jdheff1982]

I have not been using the choke as of yet. I still need to do some adjusting on it.

Here is a picture of the contraption the PO used to connect 2 hoses together for the tranny vacuum line. The clear brown tubing went to tranny, the black hose went to carb.

EDIT> the hose ending at the carb is a 3/16". Will this be the same size needed for the tranny nipple?

[1LowToy]

Let's see if I can simply explain that your carb is too big for the application. The air flow and jetting is designed to be 14 parts air to 1 part fuel, vaporized to make combustion. Your trying to get the amount of air flow needed for a 14:1 ratio from an amount of engine vacuum and air flow. So if you have a carburator designed for a motor with an extra 100 cubic inches of vacuum and air flow your not going to get 14:1 air fuel ratio.

Yes a 750 CFM carb will work on a 350, but you will need more cam and yes a higher idle speed to get it. End result a high idle high performance high RPM motor if your heads have enough air flow.

So my best advise is the 600 CFM carb for a closer air/fuel ratio and better perfomance overall.

[jdheff1982]

Seriously, you all need to back off on the size of carb I have. I'm not rich and can't go replacing things at will. I have to make do with what I have. When I bought this carb, I was looking at price and brand. I saw jegs had the 750 reman'd on sale for $200. That was cheaper than a reman 600 by 40 or 50 dollars.

The truck had a stripped down 600 performer on it to begin with. It ran like **** then too. After I installed the 750, I was able to start the motor w/o having to pump 15 times.

I think the progressive loss of driveability has something to do with an open vacuum line to the tranny and I need to spend more time adjusting the IMS. If I have to, I'll get the calibration kit and try to adjust that way.

BTW, the cam that is on the truck is the most agressive Comp Cams put out in the Big Muther Thumper line.

Are there not air restrictors made that would cut down on the over all air intake I could use during the winter?

[INSIDIOUS '86]

BTW, the cam that is on the truck is the most agressive Comp Cams put out in the Big Muther Thumper line.



this is your problem you have NO NONE vacuume to actually give a usable signal to the carb for your idle circuit to even work

i have the smaller thumpr and it was a pain in the ass to tune and it doesnt like the cold either but it would do better if i had a stall converter which is a good idea but i can get by without YOU cannot you must have a higher stall converter with the bigger cam and your timing needs to be run up on the initial About 14* to start and an adjustable vacuum advance canister to get your total timing and drivability

a smaller carb is more sensitive to flow of air

so when you put it into gear your converter is stalling and killing your engine cause its to tight fix that and half your battle is over the other half is edelbrocks are CRAAP with big cams on the street but you can get by get a tuning kit and start with the weakest springs since there is no vacuume hardly made by the engine the springs are open and its eating fuel hence why when you adjust the IMS all the way to almost bottom you are then getting an adjustment

[1LowToy]

Let me guess you power brakes don't work worth a damn either as you probably have a wopping 13 inches of vacuum. With that cam you need at least a 3000 rpm stall speed torq converter, 456:1 gears, larger port and larger valve heads to get any RPM.

What you really need is a nice RV cam that will give you a mild lope at idle, more torq and more rpm top end. Change cams and enjoy your truck. Trust me on this. I have a 69 Cuda with all the goodies. It gets a wopping 3,5 MPG and has been in the garage for nearly 30 years. Yeah I'm going to change cams too.

If you wanna build a thumper for the street get a sugar momma with an unlimited supply of credit cards

[jdheff1982]

Originally Posted by 1LowToy

Let me guess you power brakes don't work worth a damn either as you probably have a wopping 13 inches of vacuum. With that cam you need at least a 3000 rpm stall speed torq converter, 456:1 gears, larger port and larger valve heads to get any RPM.

What you really need is a nice RV cam that will give you a mild lope at idle, more torq and more rpm top end. Change cams and enjoy your truck. Trust me on this. I have a 69 Cuda with all the goodies. It gets a wopping 3,5 MPG and has been in the garage for nearly 30 years. Yeah I'm going to change cams too.

If you wanna build a thumper for the street get a sugar momma with an unlimited supply of credit cards

If anyone cared to check out the truck specs at the link in my sig, they would find the heads have been port and polished with the valves enlarged. It also has a 2700 to 3000 RPM stall converter. Flat top pistons, Scat crank and rods, and full roller rockers. My brakes actually do work even w/o a vacuum canister.

I believe the progressive loss of low driveability is due to the blown tranny vacuum line and poorly adjusted IMS.

[rs72z]

Originally Posted by jdheff1982

If anyone cared to check out the truck specs at the link in my sig, they would find the heads have been port and polished with the valves enlarged. It also has a 2700 to 3000 RPM stall converter. Flat top pistons, Scat crank and rods, and full roller rockers. My brakes actually do work even w/o a vacuum canister.

I believe the progressive loss of low driveability is due to the blown tranny vacuum line and poorly adjusted IMS.

How does the trans shift? I it doesn't have vacuum to it it will shift late and hard.
What is your timing set at? Initial and total. If timing is to low it will do exactly what you are describing.

[jdheff1982]

Originally Posted by rs72z

How does the trans shift? I it doesn't have vacuum to it it will shift late and hard.
What is your timing set at? Initial and total. If timing is to low it will do exactly what you are describing.

as of now, tranny don't shift. before, it would shift around 2000 to 2500 before going into second. once the engine warmed, shifting was sooner. it doesn't shift hard either.

timing is unknown at this point. the marker is hanging over on the passenger side. the balancer needs replacing.

[rs72z]

Originally Posted by jdheff1982

as of now, tranny don't shift. before, it would shift around 2000 to 2500 before going into second. once the engine warmed, shifting was sooner. it doesn't shift hard either.

timing is unknown at this point. the marker is hanging over on the passenger side. the balancer needs replacing.

You need to get that problem fixed before you do anything else.