Number 3 cylinder not firing

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MG Midget Forum: Number 3 cylinder not firing
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Oct 03, 2007 08:18:44
eparke

Okay, here we go. After doing some searches on this site, and getting some ideas but not totaly convinced, I would like to put it out there for all of you experienced techicians on these cars.
After installing a new condensor I was able to get this thing running again. It idles rough though, as if it were actually built for the purpose of being an earth compactor.
I did the spark check. Then I pulled each spark plug wire off-one at a time. The problem lies with number 3. Good spark at all cylinders. I then took a compression check. 120lbs in #3. Then I switch the spark plug AND wire with the #1 cylinder because #1 had the largest drop in performance when I pulled that wire. Same problem, #3 had no change when disconnected. Another spark check showed it had good spark. I played with the vaccum advance fine adjustment, and was able to get it to idle a little bit more smoothly but the #3 cylinder still not firing.
Could it be possible that the cam is worn down so much as to not be letting the intake or exhaust valves open? Blown head gasket - with 120lbs compression?

Oh, one other thought...each of these carbs - with the float bowls had an overflow tube or something coming off of them. There is a slight dribble of gasoline coming from each of those tubes. Could this be related to my #3 cylinder problem? I would think not, but then again - I am new to this/these cars.

My next plan is for tonight I will pull the valve cover off and verify that the valves are functioning. I will also look for a leak in the intake manifold on #3.

Any suggestions will be greatly appreciated, and I will post the results here. Thanks to all who make this site possible.

Oct 03, 2007 08:40:42
kuz1

What kind of compression in the other cylinders? what does the plug look like, gas /oil fouled, or just sooty? Are you getting spark to #3? (hook a timing light to the 3 wire) . If your getting spark , adjust your valves , and fix your carb float problem. If your not getting spark check your cap.





Oct 03, 2007 10:10:41
eparke


Kuz1,

When I checked the compression last week, I had 130lbs in hole #4, and 145 in holes 1 and 2. I have very good spark to all spark plugs. The spark plug in hole #3 was wet when I pulled it. It could have been oil because I took a lit match to the end of it and it did not burn, so I don't think it was gas. The plug I pulled from hole #1 looked very good (kind of tan colored and dry).
When I pull the valve cover off tonight, I will adjust the valves. Hopefully you are on to something there, I don't see how it would matter because it's getting good compression - but like I said, I'm a noob here and will follow all ideas presented. I will also look into the floats as suggested.
Thank you sir for your input. I'll post the results.

Oct 03, 2007 10:37:01
kuz1

I'd look at the float issue too. The cam worn catastropically would give you way low compression. The stuff not burning on the plug , isn't an absolute that it is not gas fouled. Liquid gas in the cylinders ussually sucks up all the oil it can. If you disconnect your coil and hang a white piece of paper over the number 3 plug hole , then crank it, you can get a fair idea of what kind of liquid your getting in the cylinder.

Oct 04, 2007 18:17:56
TT

Eldon.

I had the same problem when I first got my Midget, no. 3 cyl. was missing (no change in engine when I pulled the #3 plug wire). Had 150 lbs. of compression in all cylinders. I checked the valve lash on #3 and it was way too tight. After I adjusted the lash, the miss on #3 went away.

Don't know if this will help, but it worked for me.

Tom

Oct 04, 2007 19:57:42
eparke

Keith and Tom, thank you both for your input. The problem has been solved (well, mostly).
I installed new spark plugs and ordered new cap, rotor and wires. The new cap, rotor and wires have not arrived yet.
I, for some reason or another thought that when I pulled the #4 plug wire, there was a drop in RPM just like the wires from #1 and #2. Well, I did it today and did not get a change in RPM's. I decided that maybe the 2nd carburetor was not feeding gas. I started the engine and sprayed starting fluid into the 2nd carburetor and the RPM's increased. I then sprayed the fluid into the 1st carburetor and it did not increase, if anything, it started to choke out. It made sense to me that there was no fuel getting to #3 and #4 cylinders. I removed both carburetors and blew into the hose going from the float bowl into the jet and the 2nd carburetor's hose was plugged again. I initially did this same procedure and cleaned them both out, when I wasn't able to get the engine started in the first place. Well, after cleaning out that hose again and re-installing the carbs, I fired it up and new right away that the engine was running much better. It started much easier and the engine was pretty smooth. Also I didn't need the choke to get it started. Before, I couldn't run the motor without the choke closed.
I once again pulled the #3 plug wire and it did drop in performance just a little bit. Pullilng #4 wire there was a big drop in performance. So at this point I don't know if #3 is pulling it's load like the others but atleast it is hitting at this time.
Another thing is that I now know that this engine is worth putting the time and money into.
Once again, thank you for your help and comments.

Oct 07, 2007 15:38:00
dte948

Eldon,
Get a grip, Do you have spark at #3 or not? You seem to have the problem identified but don't want to fix it. Make sure you have spark at #3 or not!
Dave

Oct 07, 2007 16:03:01
eparke

Dave,

I clearly stated several times that I had spark at #3. As I said in my last post the engine is running pretty smooth. I believe all I need now is just a little bit of tuning the carburetors.
As far as not wanting to fix it? Believe me, I have spent much time on this thing in the past few weeks.

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