AMC 360 misfire

[Zooguy]

Thanks for the suggestions. I feel like it is now the carb also. I don’t have a vacuum gauge but maybe I should get one. The plugs when I last pulled them looked good. I should try again though. I am pretty sure I don’t have vacuum leaks. And I have replaced the fuel lines with braided line and as far away from the exhaust as I can. I also put in a carb spacer incase it was transferring heat.
For my cam I actually put in a tamer one. It had one with a 292 open duration so I replaced it with a 252. It will mostly be a pavement queen.
Any suggestions on good mechanics to adjust the carb? I am ok with throwing a bit of money at it if I can’t figure it out. Again thanks for the input.

[renegade350]

With my holly truck avenger on an older 350, I get an annoying idle miss fire with the idle screws 1/16" of a turn either direction from being perfectly bang on.  I highly recommend a wideband O2 sensor with an A/F gauge, tuning a carb without one is a lost art, even going off of feel/RPM I was still way out until I used the gauge.  going from a 10 to 13.5 mixture will give you almost 1/3 better fuel economy.  The gauge will pay for itself x5 easily in fuel consumption and unnecessary stress after a few big trips.  (Going from 5-8 mpg to almost 12). 

It will also help diagnose future carb / engine problems including vacuum leaks, stuck chokes, clogged fuel filters, flooding, stumbles during power transitions (coasting to power), stumbles at 10-100% throttle, fine tuning the accelerator pumps and secondary's, backfires etc.

https://www.amazon.ca/AEM-30-4110-UEGO-Ratio-Gauge/dp/B00N3VGPYS/ref=asc_df_B00N3VGPYS/?tag=googleshopc0c-20&linkCode=df0&hvadid=292977936168&hvpos=&hvnetw=g&hvrand=6573167427041104759&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9001313&hvtargid=pla-377903111462&psc=1 

You need to be completely at 185F engine temp or hotter to accurately tune anything.  Is this an electric choke or mechanical? you didn't mention this at all in your previous posts.  If electrical, and it dies after 10 min it may not be opening causing a rich situation - possible electrical issue but incredibly easy to fix properly or just with a zip tie to troubleshoot.   I doubt it is anything else electrical, as they really only need two hot wires to work - 12 volt ignition to the distributor and starter crank power, the rest are just accessories.  It could also be the speed the choke is opening, possibly to soon?  Adjusted by turning the black disk on the side clockwise or counterclockwise. 

Timing is at 8....that's 8 degrees with no vac advance or total?  Idle total advance, vac + mech should be in the 25-40* range, usually the more the better, I dont know offhand what a 360 and your cylinder heads like but in that range. 

even if there is a huge vacuum leak, the miss should go away at WOT / zero vacuum.     


Keep in mind;
Idle screws are idle af ratio
mid range power is primaries and the idle mixture together.  Not just primaries. 
WOT is idle mixture + primaries + secondary's.  All three combined, plus the accelerator pumps if you really got on it.     

A properly tuned 360 should be able to really test your AMC 20 2 piece axle strength on pavement if you still have that rear-end.   

My services can be available with a complete holly jet kit, timing lights, vac gauges etc for a small fee   plus I cant even remember what a CJ7 is supposed to look like anymore.  I have spent enough time and money tuning a carb I could have changed over to fuel injection now but that's another story. 

[Zooguy]

I didn’t think of an O2 sensor. It sounds like it would help to dial it in only if I know what’s wrong. I’ve been told that maybe I have to adjust the butterfly valves on the bottom of the carb if my idle screws are going all the way in without stalling. Also I’m not sure if my choke is set properly. A gauge wouldn’t tell me what’s wrong, only that something is wrong. Those are just my initial thoughts so I will research a bit and get a better understanding.
I have an electrical choke on the side of the carb.
The timing was set at Idle and might be between 6-8. We didn’t check it at higher rpms.
It does have the AMC 20 in it. I checked the gears and it looks like it has 273 open, with T5 and 35’s. I don’t mind the gears since it will mainly be on the road. But I might change to 33s once the 35s wear down. They are brand new so that will be a while.
Thanks again  for the suggestions, I will research a bit and DM you for some help if I can’t get it right soon.

[cLAY]

Is  the carb new(fairly new)? Not something bought 2nd hand? If so the throttle plates should be set correctly and I would avoid playing with them as that would add a whole new set of parameters to the mix.

A vacuum guage lets you see whats going on as you drive, not as accurate as a O2 sensor but still handy and easier, also handy to watch while adjusting at idle and a fairly cheap.

Is your vaccum advance hooked to ported or manifold? Did you disconnect and plug it when setting the timing? If not then you might not have enough base advance timing. If you are not sure the difference on ported vs manifold then do a google search, easy to find.

[Zooguy]

It is a new carb, but since the cam that I replaced had a 292 open duration I suspect he messed with the carb a lot in order for it to run. With the internet research I’ve done, one possibility is the throttle plates and it seems to sound like my symptoms. I did try to use a vacuum gauge to tune it which seemed to help. It went up two numbers to 15. But the idle screws can still be bottomed out. I only tried the manifold vacuum when tuning it at Idle. Thanks for the suggestions

[Zooguy]

I took the carb off and adjusted the throttle plates so the the “gas port”? was squared off. The idle screws can still almost bottom out but it runs much better. It still stumbled a little at full throttle but much better than before. The air fuel gauge sounds appealing to tune it a bit better. So a step in the right direction. Thanks.

[Zooguy]

And two steps back. I took the Jeep out for a drive today and it started to act up after about 30 min. I am starting to think one of the issues is vapour lock. After I got home I saw a couple bubbles in the float bowl. Maybe a heat shield would help. I am also thinking of running the fuel lines in the frame. Thoughts?

[renegade350]

How close to the exhaust and manifold coolant passages are your fuel lines? you should be able to touch the fuel lines bar handed everywhere they run.   

[rws]

And two steps back. I took the Jeep out for a drive today and it started to act up after about 30 min. I am starting to think one of the issues is vapour lock. After I got home I saw a couple bubbles in the float bowl. Maybe a heat shield would help. I am also thinking of running the fuel lines in the frame. Thoughts?

Centuries ago, back in my carb days, we used aluminum heat shields and spacers between the carb and intake manifold all the time.  They work well and are super effective.  We would also wrap fuel line that were near  "hot areas"  with header wrap however now there are heat shield wraps that attach with velcro that are fantastic,  Mopac has a good selection.

[Zooguy]

How close to the exhaust and manifold coolant passages are your fuel lines? you should be able to touch the fuel lines bar handed everywhere they run.

The fuel lines were in some places about 6 inches away. My Jeep has run hot from the start. I ended up running the lines through the frame so it will hopefully be a non issue.
Thanks for the reply.

[Zooguy]

Centuries ago, back in my carb days, we used aluminum heat shields and spacers between the carb and intake manifold all the time.  They work well and are super effective.  We would also wrap fuel line that were near  "hot areas"  with header wrap however now there are heat shield wraps that attach with velcro that are fantastic,  Mopac has a good selection.

I ended up putting on a heat shield and some of the heat material around the gas lines. I ran the fuel lines through the frame also. I haven’t had time to get it out but when I started it the idle was about 1500 and hard to get down and stay steady. I will try to make some time this weekend.
Thanks for the suggestions, hopefully this will help.