Getting fustrated with engine

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Austringer
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Getting fustrated with engine

Post by Austringer » Sun Dec 18, 2016 10:17 pm

Just rebuilt the carb and set the accelator pump at about .008 mils when sitting at high idle (choked). When starting from a dead stop, the engine just about dies on me unless I back off on the gas and short of nurse it past this massive dead spot. Once moving, no issue.

My compression is around 125-130 on all 4 cylinders and this is with choke and throttle plates wide open, engine turning over 4-5 times.

Time is set dead on mark and i get a rough idle unless I advance it about another 2-3 degrees, was worse before carb rebuild, next step is to take an new carb, swap out the accelerator pump and economizer assembly (the little rubber things) with the ones I put in this carb (for the new crappy gas situation) and try again. I set the idle at 625 and timed it at this speed. I'm also only getting about 14-15" of hg at idle off the special bolt for vacuum pressure. When 1500 plus rpm, getting a nice 18-19" hg.

Going to do a leak down test tomorrow to see how the rings and valves are. What should I expect as far as a percentage leak? Also going to change out the points to see if that makes a difference as well as set them to spec.

Other thing that is bothering me, getting a little bit more oil than I like in #3, (rear driver side). Spoke with Robert W and he said he has had the same experience.

Any suggestions on this would be most appreciated and this rough idle and flat spot is about to drive me up a wall and is making this vehicle not as fun to drive......
Jason Green
Atlanta, Ga

1958 M56 Scorpion #98
1969 M706
1974 M113A2
flame throwers, Class 3
and an avid falconer

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Austringer
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Re: Getting fustrated with engine

Post by Austringer » Sun Dec 18, 2016 10:19 pm

Thinking of pulling off the heads as well to check the cylinders, the engine was gone through 2-3 years ago and NOS cylinders put in, but I want to check for condition to be 100% sure, didn't see any silver dust in the engine oil when I changed it out.

I'm about ready to put new piston rings in (if the walls look good) and while I'm in there, check the rod bearings...

as you can tell, i'm a bit frustrated.
Jason Green
Atlanta, Ga

1958 M56 Scorpion #98
1969 M706
1974 M113A2
flame throwers, Class 3
and an avid falconer

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Bill H.
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Re: Getting fustrated with engine

Post by Bill H. » Mon Dec 19, 2016 7:05 am

Jason, where is your timing? Albeit your vacuum is there I'd suspect timing or electrical such as condenser breaking down.
Bill H.

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1962 AMC M422A1
1965 Stevens M416B1

2 Timothy 3:1-5

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Re: Getting fustrated with engine

Post by mspeters » Tue Dec 20, 2016 8:09 pm

in addition to isolating the ignition parts, including a coil swap, check the intake manifold for corroded through freeze plugs between exhaust and intake zones. You can inspect them with the carb off, or remove both exhaust heater pipes and shoot some carb cleaner through the exhaust section when it's running. Mine had 1/16" hole; the DPO could not find, they swapped to a Falcon carb, then gave up and pulled the whole engine. A tip-off could be needing full/max rich on the idle mix screw to obtain a stable idle. I can't get more than 16 inches vacuum at low idle.

Is the PCV valve replaced or clean ?

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Re: Getting fustrated with engine

Post by Austringer » Tue Jan 03, 2017 10:42 pm

An update on what I've done over the last few days, at least since my last post.

I pulled the cylinder heads off to check the cylinder walls and they look great, the guy told me they were new and I believe him.

I thoroughly cleaned the piston tops as they had some carbon build up, and did the same thing with the valves and combustion chamber on the heads.

Installed a complete new exhaust system from headers to the exhaust tip

Installed NOS carb with new accelerator pump and economizer valve thingy.

Pulled all the spark plugs and put them through the bead blaster (using crushed glass) to clean them up, set the gap to .030.

I pulled the distributor and installed a M151 electronic ign kit that I had extra since the lobes vs the flat spot are the same for the M151 and the Mite.\

Put everything back together cranked it up, set idle to ~650, confirmed timing was on the mark (~4 BTDC)

SAME darn PROBLEMS........

Still only getting 15 inhg of vacuum on the vacuum gauge

When I try to give it some throttle... it wants to die as the vacuum goes to pretty much zero and I have to back off on the throttle until it catches itself, gets some vacuum and then I can tease it into accelerating.


After this disappointment, I pulled the plugs again and conducted a leak down test on each cylinder at TDC, and the average for each cylinder was around 25% which is well in the green on the testing kits I have....

After doing this, well during, I remembered the PVC valve and the comment made earlier about making sure it was clean etc.

I removed the covers from the top of the engine to expose the pvc valve, then installed everything back minus the cover and left the little heater pipes off to test something that was mentioned earlier..

With the PVC valve removed, I started the engine and put my finger over the brass fitting to cut off any air getting in that way. With my finger on the brass fitting, still 15 PSI. I then reconnected the line to the pvc valve and sprayed starter fluid around the carb gaskets.. no effect... then around the intake manifold to cylinder head gaskets... no change.... then into the header area where the little pipes go in... no change.

I'm pretty much at my wits end with this thing and trying to figure out what the hell is wrong with the vacuum pressure and why it basically dies when I try to even slowly accelerate it. something is killing the ability to create a vacuum and I can't figure out what the hell is causing it.

Please help...

Thanks
Jason Green
Atlanta, Ga

1958 M56 Scorpion #98
1969 M706
1974 M113A2
flame throwers, Class 3
and an avid falconer


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Babadave
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Re: Getting fustrated with engine

Post by Babadave » Thu Jan 05, 2017 8:54 am

I think mspeters may have already hit the nail on the head with your problem. manifold vacuum leak.
man.jpeg
man.jpeg (97.4 KiB) Viewed 793 times
My engine actually ran with this manifold installed. :?:

Pull yours and check it VERY carefully ? Sometimes just spraying starter fluid won't locate the problem. Especially if the leak is between the heat riser plenum, and the manifold plenum.

Good luck !
"We've been looking for the enemy for some time now. We've finally found him. We're surrounded. That simplifies things."
Lewis Burwell "Chesty" Puller

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Austringer
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Re: Getting fustrated with engine

Post by Austringer » Thu Jan 05, 2017 9:10 am

Got it fixed last night, I did everything mentioned by the previous poster regarding the PVC valve, heat riser etc. I ended up abandoning the timing light and mark and timed it with my vacuum gauge and engine analyser (RPM). With modern gas (higher octane), i needed to advance the timing about 15 degrees to achieve max vacuume at approx 650 rpm. Once max vacuum was achieved, I backed off the vacuum around 1.5" and settled with 16" and she now purrs and the dying at acceleration has gone away 90% unless I basically go wide open from idle (which would kill vacuum in most engines). She starts right up and runs well. Adjusted the idle mixture as well until I had 650 rpm and maintained the steady 16" vacuum. Turns out the timing I needed on this one was about 15 deg BTDC. Also, no pings or pre-ign under acceleration and load (light and heavy).

Now it's fun to drive again. :-)
Jason Green
Atlanta, Ga

1958 M56 Scorpion #98
1969 M706
1974 M113A2
flame throwers, Class 3
and an avid falconer

renovate7
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Re: Getting fustrated with engine

Post by renovate7 » Sat Apr 22, 2017 5:25 pm

I had a heck of a time setting the timing on my GMC inline 6 in my DUKW. Ended up timing it by ear with tach attached to number one wire. Turned the distributor till I got max rpm and backed it off a bit. Runs very well. It was designed for 73 octane fuel. Even using the formula of so many degrees change based on an increase in octane just didn't work. The ear is mightier than the timing light, some times.

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Bill H.
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Re: Getting fustrated with engine

Post by Bill H. » Sat Apr 22, 2017 7:01 pm

Glad it's fixed bro! :wink:
Bill H.

Welfare, a modern day career choice.

1962 AMC M422A1
1965 Stevens M416B1

2 Timothy 3:1-5

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