Author Topic: Engine running rough  (Read 4009 times)

emptyhead

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Engine running rough
« on: April 20, 2017, 06:56:48 PM »
Back ground on the engine was built by a reputable engine builder. Was rebuilt about three years ago and finally at a point where I can run it. Its running rough no matter what I do play with the distributor. Checked and double checked the timing and plug wire till I was sick of it. When I pull either 1 2 or 3 cylinder plug it wants to die but when I pull 4 5 and 6 pretty much nothing happens whether I pull one of them or all three. Getting spark to alll 6 cylinders I checked with spark tester. All cylinders are at between 118 and 120 psi. At this point don't know which direction to go. Anyone have some suggestions it would be great. Thanks.

Monkeypirate

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Re: Engine running rough
« Reply #1 on: April 20, 2017, 08:36:49 PM »
Sounds like a irritating situation you have! How strong is your spark? compression is good, so if the spark is strong that means you are not getting fuel into the cylinders. I'd check the lifters first and then look for an obstruction in the intake.  Best of luck!

steve-0

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Re: Engine running rough
« Reply #2 on: April 20, 2017, 08:54:30 PM »
are the plug wires going to the correct cylinders?

some unlikely things
carbon tracks in the cap or on the rotor
loose distributer shaft
bad spark plugs

emptyhead

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Re: Engine running rough
« Reply #3 on: April 21, 2017, 01:14:38 AM »
Switched plugs around the different cylinders still the same. Checked continuity on all wires and good. Triple checked wire timing. Even tried swithing around wires from 4 5 and 6. Engine ran the asame no matter what. Tried both the old distributor and a nos in the box one and still the same. Running out of options. Thanks guys

Smadge

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Re: Engine running rough
« Reply #4 on: April 21, 2017, 04:25:08 AM »
If the compression is good it's usually fuel or spark.  You know you're getting spark.  When you pulled the plugs, they should be soaking wet with gas and you should have a heavy gas smell at the exhaust.  If not, it may be the lifters like Steve said.
1941 M2A1 Autocar (restoring)
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WayOffTrack

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Re: Engine running rough
« Reply #5 on: April 21, 2017, 07:10:39 AM »
I'm wondering about lifters too since 1-3 is the same lifter block. I think they have to be preloaded with oil to charge them before they are assembled.

Smadge

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Re: Engine running rough
« Reply #6 on: April 21, 2017, 09:21:44 AM »
Correction:  I agree with Monkeypirate's assessment of the lifters!
1941 M2A1 Autocar (restoring)
MVPA# 36810E

yd328

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Re: Engine running rough
« Reply #7 on: April 21, 2017, 11:55:48 AM »
Just curious, was the oil filter filled with oil prior to starting and did you do prime the motor before starting it?

Gary

emptyhead

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Re: Engine running rough
« Reply #8 on: April 21, 2017, 02:46:15 PM »
I'll pulled off the head yet again and all my valves are rising and falling as they should. Pulled the intake a exhaust manifold off just to make sure non of the ports are blocked. Have any of you guys ever had to time the valves. It mentioned something about it in the Tom but couldn't find it. Thanks so far.

vj

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Re: Engine running rough
« Reply #9 on: April 21, 2017, 03:57:55 PM »
I would try using the infrared thermometer to check the temp on each exhaust tube at the block, if one is low in temp. that will be the bad cyl.  Back in the old days we used water, if a lot of steam, that was the good cyl.

8683jb

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Re: Engine running rough
« Reply #10 on: April 21, 2017, 04:53:41 PM »
Did you run a vacuum check? About all that's left is valve timing. I would check it with a degree wheel and dial indicator, not just by the marks (sometimes they're not too accurate and can cause you to chase your tail - ask me how I know). At this point, I'd sure start with that. If it's off enough, none of the rest of it matters. Keep us posted and good luck.
« Last Edit: April 21, 2017, 05:02:26 PM by 8683jb »
'42 Autocar M2A1

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R.E.Co.

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Re: Engine running rough
« Reply #11 on: April 21, 2017, 08:32:47 PM »
I hate to be an obvious fella, but is the fuel filter partly plugged? If you only get alittle fuel into the carb and its gasping for air that could make it run rough to.  If you know the engine is timed correctly and you have spark, then its fuel related issue.  Carb might not be opening right or something.  Its a long shot but one you can cross off your list if all checks out.
1941 White M2 Halftrack

steve1973

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Re: Engine running rough
« Reply #12 on: April 21, 2017, 09:13:13 PM »
Did you happen to check to see if the intake going to the front cylinders are plugged? This happened to Don with Zelda. The front three cylinders were partially plugged due to something getting sucked down the carb.

Steve A.

emptyhead

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Re: Engine running rough
« Reply #13 on: April 22, 2017, 04:31:30 AM »
That's why I pulled off the manifolds to make certain intake and exhaust ports where open. Will put everything back together and go through the carb today and tomorrow and see what happens. Maybe it's a fuel issue. 4 5 and 6 are feed from the right side of the carb. Maybe something is going on there. Thanks for all the help so far guys will keep you posted.

steve1973

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Re: Engine running rough
« Reply #14 on: April 22, 2017, 06:40:36 AM »
I don't believe that the intake I'd divided like some manifolds are. I did think of that though. How is your Camera? It could be warned bad on some front lobes. How about timing gears, they might be off one tooth. Are you running with the air cleaner hooked up? That might be plugged up.

Steve A.