Top end sputter (120 PSI)

Top end sputter (120PSI?)

Hi Guys,

First time thread here and really could use your help:

Have been trying to pinpoint an issue with my 56 CJ6 that has a 231 odd fire out of a 76 Skyhawk (I think). The guy I bought from only had only about 30-50 hours on the engine (Have rebuild receipts form NAPA) and the darn thing coughs, sputters and loses power in 3rd and 4th gear, and seems a little hesitant when cranking the starter. Tried all of the following: Set timing at 12 degrees, new plugs, wires, and cap. Rebuilt carb, replaced air cleaner, and fuel filter.

Thought maybe I had a burnt valve so I did a compression check and all the cylinders were 119-120 PSI. Although I know that the consistency is good doesn’t that sound low for an engine with 30-50 hours on it? I am wondering if I am a tooth off on the valve timing but wanted some opinions before I tore the timing cover off.

Thank you in advance for your help.

 

Welcome!
Check ignition advance?

 

Good call!
I eye balled the distance between 0 and 12 and when revved, it's hovering in the 35 range. If you you can suggest a more accurate way to measure I would be happy to try it.

 

What I did for mine, Mine is a chevy but should still apply. I went to a performance shop and bought a timing tape which has the degrees printed on it, that would be the simplest way, but mine wouldn't stay on the balancer and flew off. So, I made my own... I cleaned the timing tab off and took a piece of paper and pencil and scrolled the timing marks onto the paper then transferred them to another, marking each mark accordingly (my tab marks end at 16*, so my tape started at 18*) and taped it to the balancer where the timing mark is so I could read the timing in the upper rpms. You have to make sure to have to home made timing tape on so the numbers go in the correct direction. This is a simplified description but you should be able to figure it out. Good luck..
::If you actually go buy a timing tape you have to give them the diameter of your balancer.
it is only like $8

 

wonder if the front cover is a 231 or a 350. i think the timing marks are different between the two. you could have the distributor a tooth or so off? the vacuum advance needs to be disconnected and plugged when checking timing. sounds like it is working with you saying when revving it moves to 35. i thought mine was set at 5* to 6* but it has been a while. i also set it by ear and performance and tightened down the dist. just make sure your at top dead center on the compression stroke and pull the cap and see if it's going to hit number one. then look at what the timing mark is at.

 

Timing light with the advance feature.

 

Sounds good!
I will forgo the cost of the advance timing light and mark my balancer and jeepcj suggested. I'll also take a picture of the balancer and post later this evening after I get home. definitely double check the rotor at TDC and post my findings.
Thank you!

 

Check with your parts supplier. They may have one in their tool lending program.

 

Most oddfire timing covers have the tab cast into the cover. Most evenfire covers have the timing tab bolted on and is plastic. A pic is still a good idea so we can compare location to a known unit.

 

Got home from work too late so this will have to wait until the weekend. I did however manage to get a picture of the timing cover.

 

that looks like the one i have on mine. i had either a 225 or 231 cover on there and when i replaced it i could only find one from a 350.

 

OK.
Set the timing at 12 degrees and reconnected the vacuum advance. When the engine is revved, the overall advance is at 35 to 36. The Jeep is still sputtering in 3rd and the gear on the open road, and missis intermittently at idle. Also, it is stumbling when you romp on the gas sitting still and sometimes backfires out the exhaust, and sometimes the carb. Also noticed that the timing is jumping 2-3 degrees at idle. Is it possible the Dist. is worn out?

Still wondering if the valve timing is not set correctly due to the compression check being at 120 along with the other issues. Even worse I think I have a rod knocking @ 1500-2000 RPM....

 

Rod knock, or pre-ignition detonation? (Timing advancing too fast or too much?)

If the dist shaft/bore is worn loose, it will cause the point gap to vary, and therefore the dwell/timing to wander. A dwell meter ought to reveal this, if so. And the timing "jumping" at idle could indeed be a sign.

Grab the distributor rotor/shaft and see if it shakes from side to side. It shouldn't.

Your symptoms as most recently described might also fit with an intake vacuum leak. Vacuum gauges are really inexpensive.

 

I used the carb cleaner spray method to detect vacuum leaks but didn't think about using a gauge. What should the vacuum be?

 

The Dist (HEI) doesn't seem to have any play in the shaft. The dwell is hovering around 22, and the vacuum

 

Sorry, the vacuum is at 19 both at idle.

 

This is just one of many guides available.

Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine

If no vacuum leak, then maybe your carb is running lean on the high speed circuits?

 

sounds like what my F134 was doing when i had installed the spring on my points incorrectly,. it caused the points to "float" at higher rpms. i reinstalled the spring correctly and it was fixed for mine.