Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
Hello Guest, we are proud to now have our Wiki online that is completely compiled and written by our members. Feel free to browse our Jeep-CJ Wiki or click on any orange keyword when looking at posts in the forum.
Recently (a few months ago, but went right into storage) picked up a 1979 CJ7 . Most of it isn't factory anymore, including the AMC 290 the PO put in it, and I have questions. The most pressing, now that I'm almost through that original tank of fuel, is what fuel to use. I've read that the 290's have high compression, so generally require a higher octane, but want the experts thoughts on non-ethanol 91 (the highest I can get around here) vs 93 with sta-bil I add. Or do I need to find something higher (there is supposedly non-ethanol 112 about 15 minutes south of me, but I've never checked it out). I'll be using this as much as I can in the summer in nice weather, but will go into storage for the winter, so ethanol probably isn't a big deal right now, but will be in a few months. Also, the exhaust is real bad smelling, so I'm hoping by emptying this tank, and putting in fresh, that helps the smell a bit.
I have many other questions, such as how to solve the cold hard start (it is an Edelbrock 4bbl), or how to keep it cooler just cruising around town (I've gotten it up to 230*), but fuel type first.
Do you have a 2bbl or 4bbl? Most likely it's the 8.7:1 2bbl and can easily run 89 octane but if you have the ultra rare 225 hp 290 4bbl it's 10.0:1 and probably needs 91.
The GEN-2 AMC V-8 was first introduced at 290 cu. in. (4.8 L), in 1966.
The 290 heads used smaller valves, 1.787″ intake, and 1.406″ exhaust, in order to preclude interference problems with the small bore.
The AMC 4-barrel carbureted motors were rated at 225 hp for 290.
The base 290 cu. in. V8 advertised 200 hp with a 2 bbl. carburetor and 8.7:1 compression ratio.
The optional 225 hp 290 used a 4bbl. carburetor and 10.0:1 compression ratio.
The 290 was manufactured from 1966 through 1969. AHPS
84 CJ7 4 banger-owned since new in 1984 bought off truck at dealership - rebuilding 258, T176 with Sniper EFI D300 4:1 Lomax gears Twin Sticked 1 piece axels with locker
Recently (a few months ago, but went right into storage) picked up a 1979 CJ7 . Most of it isn't factory anymore, including the AMC 290 the PO put in it, and I have questions. The most pressing, now that I'm almost through that original tank of fuel, is what fuel to use. I've read that the 290's have high compression, so generally require a higher octane, but want the experts thoughts on non-ethanol 91 (the highest I can get around here) vs 93 with sta-bil I add. Or do I need to find something higher (there is supposedly non-ethanol 112 about 15 minutes south of me, but I've never checked it out). I'll be using this as much as I can in the summer in nice weather, but will go into storage for the winter, so ethanol probably isn't a big deal right now, but will be in a few months. Also, the exhaust is real bad smelling, so I'm hoping by emptying this tank, and putting in fresh, that helps the smell a bit.
I have many other questions, such as how to solve the cold hard start (it is an Edelbrock 4bbl), or how to keep it cooler just cruising around town (I've gotten it up to 230*), but fuel type first.
Just to show what the VERY thorough and wordy Gemini reply looks like. IMO, way to much info!
Okay, let's break down your CJ7 fuel and running concerns:
Fuel Octane and Ethanol Content
* Understanding Your Engine: The AMC 290 could have high compression, but it depends on the specific build. Stock 290s from the late 60s had compression ratios around 9.0:1, which isn't super high but might benefit from premium fuel. However, being a 1979 CJ7 , that AMC 290 is from a few years before that, and most of those 290's were rated at closer to 8.5:1 compression, meaning a lower octane is usually sufficient. Since yours is a swap, and you don't know its history, you'll have to experiment.
* Ethanol Concerns: Ethanol is bad for older fuel systems. It can dissolve rubber components (fuel lines, seals, carb parts), attract water, and cause corrosion. Modern vehicles are designed to handle it, but vintage vehicles are not.
* Your Options:
* Non-Ethanol 91: This is your best starting point. Try it first. If you experience no pinging (detonation) or knocking, you're probably fine. It eliminates the ethanol problem altogether, which is a huge win for long-term reliability, especially in storage.
* 93 with Sta-Bil: This is a reasonable compromise if you can't get non-ethanol 91. The Sta-Bil will help prevent ethanol-related issues, especially during storage. However, it's still a band-aid. You're still exposing your fuel system to ethanol. If it's the only readily available option, use it, but be diligent with the Sta-Bil (follow the instructions exactly).
* 112 Octane (Non-Ethanol): This is almost certainly overkill. Unless you know you have a seriously high-compression engine that requires it (and the Edelbrock carb is jetted accordingly), it's a waste of money and could actually hurt performance. Engines are designed to run on a certain octane. Using a much higher octane than required doesn't give you more power. It just burns slower, and you might get incomplete combustion.
* The Best Approach:
1. Start with Non-Ethanol 91. This is your ideal scenario.
2. Listen for Pinging: When you drive, pay very close attention to whether the engine pings or knocks, especially under load (going uphill, accelerating hard). Pinging sounds like rattling marbles in the engine. If you hear it, you need higher octane.
3. If you hear pinging: Try the 93 with Sta-Bil. If the pinging disappears, you're good to go.
4. If you still hear pinging:Then you need to investigate why. It could be a compression issue, timing advanced too far, or other engine problems. Only then would you consider extremely high-octane fuel, but honestly, it's more likely you have another problem.
Exhaust Smell
Old fuel is almost certainly contributing. The bad smell could also be caused by a few other issues:
Rich Fuel Mixture: A poorly tuned carburetor (especially an Edelbrock) can cause the engine to run rich, meaning it's getting too much fuel. This leads to unburned hydrocarbons in the exhaust, which smell terrible.
Catalytic Converter (or Lack Thereof): If your CJ7 originally had a catalytic converter, it might be missing or faulty. Catalytic converters clean up the exhaust.
Exhaust Leaks: Even small leaks can cause exhaust fumes to enter the cabin.
Hard Cold Start
Edelbrock carburetors can be tricky to tune. Here are some common issues and solutions:
Choke Adjustment: The choke is crucial for cold starts. Make sure it's closing properly when the engine is cold and opening fully as the engine warms up.
Accelerator Pump: This mechanism shoots a squirt of fuel into the intake when you press the gas pedal, aiding starting. Make sure it's working correctly.
Idle Mixture Screws: These control the air/fuel mixture at idle. They need to be adjusted properly for smooth running.
Vacuum Leaks: A vacuum leak can lean out the mixture, making the engine hard to start. Check all vacuum lines and fittings.
Overheating
230°F is definitely too high for cruising around town.
* Cooling System Inspection:
* Radiator: Is it clean and free of debris? Is it the correct size for the engine? (An undersized radiator is a common problem). Consider the core count in the radiator. The more cores in the radiator, the more coolant volume, and the more it will reject heat.
* Thermostat: Is it working properly? (Sometimes new thermostats are faulty). What temp thermostat is in it?
* Water Pump: Is it flowing coolant properly?
* Coolant Hoses: Are they in good condition?
* Fan/Fan Clutch: Is the fan providing adequate airflow? Is the fan clutch engaging properly when the engine is hot?
Timing: If the timing is off, it can cause the engine to run hot.
Lean Fuel Mixture: A lean mixture also causes overheating.
Airflow: Make sure there is nothing obstructing airflow to the radiator.
In Summary
1. Fuel: Start with non-ethanol 91. Monitor for pinging.
2. Exhaust Smell: Fresh fuel is a good start. If the smell persists, investigate the carburetor, catalytic converter, and exhaust system.
3. Cold Start: Check the choke, accelerator pump, idle mixture screws, and vacuum lines.
4. Overheating: Inspect the entire cooling system.
Your CJ7 is a project, but with a little patience and diagnosis, you can get it running smoothly and reliably!
Do you have a 2bbl or 4bbl? Most likely it's the 8.7:1 2bbl and can easily run 89 octane but if you have the ultra rare 225 hp 290 4bbl it's 10.0:1 and probably needs 91.
The GEN-2 AMC V-8 was first introduced at 290 cu. in. (4.8 L), in 1966.
The 290 heads used smaller valves, 1.787″ intake, and 1.406″ exhaust, in order to preclude interference problems with the small bore.
The AMC 4-barrel carbureted motors were rated at 225 hp for 290.
The base 290 cu. in. V8 advertised 200 hp with a 2 bbl. carburetor and 8.7:1 compression ratio.
The optional 225 hp 290 used a 4bbl. carburetor and 10.0:1 compression ratio.
The 290 was manufactured from 1966 through 1969. AHPS
Just to show what the VERY thorough and wordy Gemini reply looks like. IMO, way to much info!
Okay, let's break down your CJ7 fuel and running concerns:
Fuel Octane and Ethanol Content
* Understanding Your Engine: The AMC 290 could have high compression, but it depends on the specific build. Stock 290s from the late 60s had compression ratios around 9.0:1, which isn't super high but might benefit from premium fuel. However, being a 1979 CJ7 , that AMC 290 is from a few years before that, and most of those 290's were rated at closer to 8.5:1 compression, meaning a lower octane is usually sufficient. Since yours is a swap, and you don't know its history, you'll have to experiment.
* Ethanol Concerns: Ethanol is bad for older fuel systems. It can dissolve rubber components (fuel lines, seals, carb parts), attract water, and cause corrosion. Modern vehicles are designed to handle it, but vintage vehicles are not.
* Your Options:
* Non-Ethanol 91: This is your best starting point. Try it first. If you experience no pinging (detonation) or knocking, you're probably fine. It eliminates the ethanol problem altogether, which is a huge win for long-term reliability, especially in storage.
* 93 with Sta-Bil: This is a reasonable compromise if you can't get non-ethanol 91. The Sta-Bil will help prevent ethanol-related issues, especially during storage. However, it's still a band-aid. You're still exposing your fuel system to ethanol. If it's the only readily available option, use it, but be diligent with the Sta-Bil (follow the instructions exactly).
* 112 Octane (Non-Ethanol): This is almost certainly overkill. Unless you know you have a seriously high-compression engine that requires it (and the Edelbrock carb is jetted accordingly), it's a waste of money and could actually hurt performance. Engines are designed to run on a certain octane. Using a much higher octane than required doesn't give you more power. It just burns slower, and you might get incomplete combustion.
* The Best Approach:
1. Start with Non-Ethanol 91. This is your ideal scenario.
2. Listen for Pinging: When you drive, pay very close attention to whether the engine pings or knocks, especially under load (going uphill, accelerating hard). Pinging sounds like rattling marbles in the engine. If you hear it, you need higher octane.
3. If you hear pinging: Try the 93 with Sta-Bil. If the pinging disappears, you're good to go.
4. If you still hear pinging:Then you need to investigate why. It could be a compression issue, timing advanced too far, or other engine problems. Only then would you consider extremely high-octane fuel, but honestly, it's more likely you have another problem.
Exhaust Smell
Old fuel is almost certainly contributing. The bad smell could also be caused by a few other issues:
Rich Fuel Mixture: A poorly tuned carburetor (especially an Edelbrock) can cause the engine to run rich, meaning it's getting too much fuel. This leads to unburned hydrocarbons in the exhaust, which smell terrible.
Catalytic Converter (or Lack Thereof): If your CJ7 originally had a catalytic converter, it might be missing or faulty. Catalytic converters clean up the exhaust.
Exhaust Leaks: Even small leaks can cause exhaust fumes to enter the cabin.
Hard Cold Start
Edelbrock carburetors can be tricky to tune. Here are some common issues and solutions:
Choke Adjustment: The choke is crucial for cold starts. Make sure it's closing properly when the engine is cold and opening fully as the engine warms up.
Accelerator Pump: This mechanism shoots a squirt of fuel into the intake when you press the gas pedal, aiding starting. Make sure it's working correctly.
Idle Mixture Screws: These control the air/fuel mixture at idle. They need to be adjusted properly for smooth running.
Vacuum Leaks: A vacuum leak can lean out the mixture, making the engine hard to start. Check all vacuum lines and fittings.
Overheating
230°F is definitely too high for cruising around town.
* Cooling System Inspection:
* Radiator: Is it clean and free of debris? Is it the correct size for the engine? (An undersized radiator is a common problem). Consider the core count in the radiator. The more cores in the radiator, the more coolant volume, and the more it will reject heat.
* Thermostat: Is it working properly? (Sometimes new thermostats are faulty). What temp thermostat is in it?
* Water Pump: Is it flowing coolant properly?
* Coolant Hoses: Are they in good condition?
* Fan/Fan Clutch: Is the fan providing adequate airflow? Is the fan clutch engaging properly when the engine is hot?
Timing: If the timing is off, it can cause the engine to run hot.
Lean Fuel Mixture: A lean mixture also causes overheating.
Airflow: Make sure there is nothing obstructing airflow to the radiator.
In Summary
1. Fuel: Start with non-ethanol 91. Monitor for pinging.
2. Exhaust Smell: Fresh fuel is a good start. If the smell persists, investigate the carburetor, catalytic converter, and exhaust system.
3. Cold Start: Check the choke, accelerator pump, idle mixture screws, and vacuum lines.
4. Overheating: Inspect the entire cooling system.
Your CJ7 is a project, but with a little patience and diagnosis, you can get it running smoothly and reliably!
Yep, that's a lot of words... Will probably put a couple gallons of non-eth 91 in the next time its out, and do that a couple of times to try and get all the old fuel out.
I've played with carb mixture screws some based on watching some videos, but there may be a bigger issue that I don't know how to figure out. The RPMs just bounce all over once I do get it started. It mostly stabilizes when it is warm though.
The electric fans do kick on when it gets around 190* or so, and it is fine when idling, but once you start driving it, it can get pretty hot. There's really no shroud around the rad, so not sure if that's not helping, or it is just undersized.
Yep, that's a lot of words... Will probably put a couple gallons of non-eth 91 in the next time its out, and do that a couple of times to try and get all the old fuel out.
I've played with carb mixture screws some based on watching some videos, but there may be a bigger issue that I don't know how to figure out. The RPMs just bounce all over once I do get it started. It mostly stabilizes when it is warm though.
The electric fans do kick on when it gets around 190* or so, and it is fine when idling, but once you start driving it, it can get pretty hot. There's really no shroud around the rad, so not sure if that's not helping, or it is just undersized.
If it's an Edelbrock 4bbl intake I would bet it's the factory 2bbl low compression 290. Why change a 4bbl intake to another 4bbl intake?
The most accurate way to dissertation the compression ratio is run a compression test. Do you have a compression gauge you can test with?
