compression test results

[mexgrizzly]

Have a problem with my 83 CJ stuttering at moderate throttle over 2500 RMP. It has a 258 with a weber 32/36 carb and GM style HEI ignition. The stutter goes away if I floor it and open the second barrel of the carb.

Checked the timing and it seems right at 12 BTDC, emissions sticker says 13; vacuum and centripedal advance seem to be working right according to the book. Get a tiny bit of knocking at WOT on a hot day. Readjusted the Weber per Redline instructions, went well except had to turn the idle speed screw in a aprox. 4 turns to get 600 RPM. Redline instructions are not clear if this is OK or not.

Did a compression test recently and need some help with the results. All 6 cylinders are at 160-170, book says they should be at 150 psi. Note I am using an Autozone loaner tool but it was new when I loaned it. I squirted some oil in 3 of the cylinders and got 200-210 psi. The book says high pressure indicated carbonization. It also says a significant increase in compression with oil added indicates the rings are bad. Do I have both here?

-Andy

[ZAEDOCK]

Andy,
Your rings would be bad if your initial check was very low(i.e. 40-50 psi) and when you added oil, it went up considerably. A baseline check of 160-170 psi is good. There will always be slight leakage which will be less when you add a little oil.

You may have some carbon build up in there though. Try using some AutoRx www.auto-rx.com/index.html
I belong to a well known motor oil forum and AutoRx is highly recommended.

Now, your engine stumble. It sounds like the carb needs some help. How long has it done this? Is it a new carb? When you pulled the plugs from each cylinder, what did they look like? Did you check for vacuum leaks? Is the powervalve still good(backfire's kill powervalves)? What size jets do you have(I think there are two styles for a Webber too). Did you adjust the accelerator pump linkage?

Unfortunately, it's going to take some trial and error.

-Joe

[mexgrizzly]

Joe,

This is a long story so get a comfy chair, a cold beverage and I will tell the story.

It started driving back from Paragon '05. On long hill climbs it would lose power like I had taken my foot off the gas even though I hadn't. I had a fuel pump on me so as a wild guess we replaced it on the way back but it did not improve. It didnt' reoccur for most of last year so I didn't stress about it too much. It was worse this year when I put it back on the road, I do put sta-bil in the gas when I store it. So far this year I have, replaced the fuel filter, dropped the gas tank, emptied the old gas, blew out the fuel lines with compressed air, installed GM HEI, and new bosch platinum +2 plugs.

After the HEI the stalling problem only occured above 3000RPM which I could live with to go to Paragon '06. The idle started creeping up at Paragon but still below 1000. After Paragon I started looking for more reasons. I checked vacuum lines, and in the process discovered the carburetor was loose on its mounts. I took the mounting plates out and put them back on with blue locktite. After that I checked the timing and readjusted the Weber 32/36 carb (the carb is a bit over 2 years old). It runs great from idle up to 2500 RPM, then stutters unless it is floored.

The plugs had a black sooty dry covering like it was running rich, they all looked the same. I am not familiar with the power valve, can you elaborate? I do have the vacuum connection to the EGR valve capped off, don't know if this is a good idea or not. The jets are whatever came with the Weber. Don't know how to adjust the accelerator pump linkage, will need to refer to the Weber book.

I have been recommended to run some top engine cleaner made by ACDelco to clean out any carbon buildup. Haven't done it yet, need to find a supplier.

Hope this helps.

-Andy

[ZAEDOCK]

A power valve is a spring loaded valve that opens under low vacuum conditions (i.e. when you get into the throttle) to let more fuel into the engine to make more power. If the diaphram is ruptured on the power valve, fuel can leak by and cause a rich condition.

Here's some cool reading: en.wikipedia.org/wiki/Carburetor

Before I started Jeeping, I used to drag race my Malibu. Out of all the spark plugs out there, Bosch would foul every time. IMO, there just isn't enough tip to get a good spark. That little electrode dot fouls easily with a carb'ed engine. The best plugs that I've used in my Malibu have been Champion and Accel "U-Groove". Even the cheapie Autolite at Wal-mart are OK.

Anyway, I have a Holly two-barrel sitting around some where if you want to borrow it to see how she runs.