Missing 390
Thread Starter
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Senior User
Joined: Dec 2009
Posts: 281
Likes: 0
From: Alberta, Canada
Missing 390
Have a 68 390 in my 79 f250.
I have been hopping up the motor and mud racing with it.
I have a horrible miss on the #2 cylinder. it misses from idle and i cannot take it over 3000 rpm before it sounds real bad.
I had duraspark on it and changed to a MSD 7al-2.
I suspect a bent pushrod as i have spark on the plug and its as if its washed over. this is the only relitively clean plug the others have a bit of carbon on them. my carb is a little big but i think the new Msd box will fix the riches.
My cousin said the pushrod should be loose compared to the others. but its not.
I think its bent because how else could that plug be clean while the others are dirty. while still having spark.
But the thing that really messes with my head is that this is my highest compression cylinder.
Any help would be great
I have been hopping up the motor and mud racing with it.
I have a horrible miss on the #2 cylinder. it misses from idle and i cannot take it over 3000 rpm before it sounds real bad.
I had duraspark on it and changed to a MSD 7al-2.
I suspect a bent pushrod as i have spark on the plug and its as if its washed over. this is the only relitively clean plug the others have a bit of carbon on them. my carb is a little big but i think the new Msd box will fix the riches.
My cousin said the pushrod should be loose compared to the others. but its not.
I think its bent because how else could that plug be clean while the others are dirty. while still having spark.
But the thing that really messes with my head is that this is my highest compression cylinder.
Any help would be great
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
First things first, Compression test, then you have the knowledge that the engine is healthy or not. Changing components before your know what is wrong just cost money an rarely fixes anything. If compression is good, then change the plug, they are cheap and should be changed during pre-race season setup. A vacuum leak on the #2 runner could cause it ti be so lean as to not fire. The plug is clean because it is not firing and not firing all the fuel just washes down everything in the cylinder, including the rings and cylinder walls which will shortly cause you grief, so don't be running it until it is fixed.
I just had a thought, damn that hurt, I had a front main jet fall out and do this exact thing on my 428CJ.
I just had a thought, damn that hurt, I had a front main jet fall out and do this exact thing on my 428CJ.
Thread Starter
|
Senior User
Joined: Dec 2009
Posts: 281
Likes: 0
From: Alberta, Canada
First things first, Compression test, then you have the knowledge that the engine is healthy or not. Changing components before your know what is wrong just cost money an rarely fixes anything. If compression is good, then change the plug, they are cheap and should be changed during pre-race season setup. A vacuum leak on the #2 runner could cause it ti be so lean as to not fire. The plug is clean because it is not firing and not firing all the fuel just washes down everything in the cylinder, including the rings and cylinder walls which will shortly cause you grief, so don't be running it until it is fixed.
I just had a thought, damn that hurt, I had a front main jet fall out and do this exact thing on my 428CJ.
I just had a thought, damn that hurt, I had a front main jet fall out and do this exact thing on my 428CJ.
Also my truck smokes out the breathers more than any vehicle i've ever seen.
There is no fuel in the crankcase and i do have electric fuel pump(learned that lesson the hard way).
I have a new edlebrock carb on. I will throw on the old holley.and see if it runs.
this motor has been a son of a gun since i started swaping it in.
Has fought every step of the way.
