Compression test readings: Re-carb backfire..

[bob westphal]

Ed,

Are you the same one that had the carb backfire earlier in the week? Are you still getting the popping? No one has asked this question or mentioned valve timing in your recent thread. Your readings are quite low across the board and are indicitive of a jumped timing chain. A used or average well worn engine would have a compression reading around 85 psi. The WOT therory is like Don said 'bunk'! I've been working on cars for 55 years and I never saw any difference when I tried it after someone told me about the therory over 50 years ago. If you do squirt oil in the cylinders, use an oil can with a flexible spout to get by the valves. However the amount of sealing that would take place by oil around a poorly seated valve won't make enough difference to mislead a diagnosis.

Bob

[Ed Griffin]

Bob,

If the title to the post was carb backfire then it was most likely me. I just carried it over to another thread. Reason for the above title with "re" in it.

Before Don made his post abt the WOT being bunk i had already tried it. The results were posted to compare with the compression test done without the WOT and there was a small differance. Actually an odd differance because I lost, gained and had no change in the results of the psi.

I was'nt able to make any progress today and try the wet test yet so I cant say anything. As far as the WOT method this was the only time I've ever done it that way. After a long time of reading Don's post's and seeing what he has accomplished I take what he says as the truth.

However, my main goal is to get my car back on the road. I miss it and enjoyed driving it as a daily driver when it was running. I just didnt get enough time on the road with it before it crapped out and I dont know it's past history which would be a big help.

There are various issues with wiring, added relays and some other items I was hoping to get to before the car did die on me. None have anything to do with the primary electrical but basically what I'm saying is I didnt get the chance to find out just how good or bad of condition the motor was in.

I do know it was running fine enough to make 30 mile trips to a buddies shop on several occasions and on the last trip there this is when my car just out of the blue started to stumble and lose power. I didnt want to get stuck on the hwy so at the first exit which was just in time, I had to keep my foot on the gas or pump it to keep the car from stalling and this is when i got a backfire through the carb. Once i reached the stop sign I noticed the car was trying to stall so i never let up on the gas, turned the car on to the overpass, another carb backfire and was going to park it on the other side of the overpass. Since the car did not die on me I pulled back on the hwy and headed home. The car never did backfire again but stumbled the rest of the way. To me it was like a bad plug wire. With that thought and the fact that I did know the car hadnt been tuned in at least 2 yrs by the previou owner I thought this was most likely the trouble and thats when the nightmare began with putting in the long spark plugs. That was about a yr ago.

This recent thread has been about the results i got when trying to get the car tuned after installing the heli coil and the back firing through the carb i was getting as I was trying to tune it. This is my first attempt at trying to get her rolling again since she broke down last yr.

If i hadnt have been so dumb to put in the long spark plugs the kid gave me I would have already done a compression test a long time ago and either have got her running again or found that I need a rebuild.

I will be trying the wet test and posting the results in hopes to get more ideas from those that post but I will also be trying to go over the manuals as well so that maybe I will be one step smarter and can pass on what i've learned as you guys have done.

The advantage to many who post here is they've been doing this for years or even make a living at it. Growing up I was the guy who would stand to the side and offer what help I could provide but never quite understood what made what work. It's not as though I've been one to farm out work that needed to be done over the years but everything I have done in the past was by manuals and trial and error.

When it comes to times like these I'll ask questions on how to not always because i dont know but sometimes i need the assurance that I am not going the wrong direction. Thats what makes this forum so great in my opinion. Because of people like Don, you and all the others who have offered their insight and past experiance.

Finally at 49 yrs of age I've found a place i can ask and get some straight answers to my mechanical questions and check to see if i have comprehended what the manuals tell you or dont tell you.

Posts like yours usually either get printed or put in a folder in my computer or even both for future use and I thank you for it, Ed Griffin

[Lou Earle]

Your description of the sudden drop in power and suddenly backfiring thru carb sound a lot like gas starvation to me. I have had that happen on a model A when 1- the carb base bolts got loose and air leaked in and 2- when the fuel line or tank exit hole got blocked by a piece of trash in the tank.

One other thing I Can think of causing it-maybe- the set screw on the dist came loose and it rotated to cause a backfire.

i was a bit skeptical on your readings- I cannot having an engine that low and running well. Also a blown head gasket can cause the backfiring and power drop. If you have a torque wrench try and torque a few bolts to 70 lbs. if they are loose that means that the last time worked on and gasket replaced the head was not torqued the SECOND time after running- I have had 2 "shot" engines- with blown head gaskets because failure -I believe- to re torque them. Both engines turned out to be brand new rebuilds.

Also check for intake leaks- I spray starting fluid around the intake and if speeds up u have found your leak.

There might be other things causing the problem but i know the above can all cause power loss and backfiring

Lou

[Normspeed]

Ed, another thing to check regarding the sudden power loss. Bad vacuum advance. These are sneaky, they fail internally and you won't know unless you either put a timing light on and check the advance with the motor running, or put some suction on the advance line and see if it holds. With a bad advance you can get truly awful performance including stuff like a good idle and bad acceleration, or good idle, good acceleration but surging at cruising speeds at light steady throttle. Backfiring can happen too.

[norrism1]

Leaking condenser will do it too!

[Lou Earle]

Leaking condenser will do it too!

I did not know that- will it go bad at anytime or are there warnings?

Lou

[Plymouthy Adams]

when the points burn out..you have been warned..actually the first sign of condensor break down is that it will run and idle without problem out of gear..all the way through the rpm scale..however load it down and its instant fall on its face..will not pull itself off a spot of peanut butter...AC Delco condensors were notorious for this in the early seventies..only line to trust was KEM brand in the gold and yellow box...better points also as they had the phenolic breaker cam.