Missing at 3000rpms

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416 scamp

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Going to race this weekend for the first time in 4 years.... Change plugs and wires.... still has a miss at 3000 rpms... What you guys think it is?
 
416 scamp said:
Car has sat for 4 years also... got it back on the road 2months ago
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Has the miss been there ever since you got it running again? Reason i ask is besides the fuel system, what else comes to mind is running the times in you signature i'm pretty sure you have a decent size solid cam in it. If the rocker shafts were installed the whole time it sat, several of the valves would have been in the open position and could have weakened a few valve springs.
 
Yep.. Had miss ever since i got it running again. Running a .570 solid... That could be a possibility
 
OldmanRick said:
Has the miss been there ever since you got it running again? Reason i ask is besides the fuel system, what else comes to mind is running the times in you signature i'm pretty sure you have a decent size solid cam in it. If the rocker shafts were installed the whole time it sat, several of the valves would have been in the open position and could have weakened a few valve springs.
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My first guess.
Sitting with the valve open doesn't do the springs any favors , so I'd check seat pressure first.
I chased a miss at around 5,100 for a couple weeks figuring it was ignition.
It sounded just like it was banging off the chip.
Then I looked at the fuel system second , because I was pretty sure that everything was cool there........it had good pressure , so that pointed me at the ignition.
It was neither. LOL
 
Is it under a load only(driving) or in -n- parked as well?

If its only under a load, i woud be looking at the fuel system. IF not, i thing "OldmanRick" has you on track.
 
I have been chasing a similar problem. I started a thread on the electricle forum, but I think I have eliminated all possible elec./ignition problems. Is there a way to test seat pressure with the heads installed on the car? Would a compression test reveal anything? I have three cylinders showing 150 psi, all the rest are at about 175. I rolled each cylinder up to tdc and put about 30 psi of air into them. None seemed to leak out the intake or exhaust, but they all sounded like air was leaking past the rings into the crankcase.
 
Yup. greymouser7 did the same thing to his. That was my first recommendation when we popped it off after several years. Although we're probably gonna go back through the whole thing. I guess.
 
70net440 said:
Is there a way to test seat pressure with the heads installed on the car?

Just realized this question. For me the answer is yes and no. I've used a tool similar to the one pictured below. As far as testing a unknown spring i don't believe these are accurate enough. What i did was bench test for the proper tension and right after installation i ran them with the tool to get a number. Didn't really matter what the tool showed, i would document whatever the readings were for later. Then whenever the valve covers were removed or i suspected something was up i would do a quick run thru to confirm whether any pressure was lost or inconsistant.
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The one in the picture is wildly inaccurate as far as actual pressure , but will tell you if any springs are softer than the others.
If it says 180 lbs , it could be anywhere within 30 lbs. of that.
But if they all say 180 , but two say 130 , you know you are looking at the problem.
 
Does that tool attatch to the rocker arms, or do you have to remove them? I saw one in Jeg's with a dial gauge, kinda pricey though.
 
70net440 said:
Does that tool attatch to the rocker arms, or do you have to remove them? I saw one in Jeg's with a dial gauge, kinda pricey though.
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The one i had, with the rocker in place, hooked over the pushrod side and applied pressure to the tip of the rocker when pulling down. Depending on different style rockers some of these may not work on all of them? I would check with the manufacturer to make sure before buying one. You're right about the cost of some of the high end models. Probably more accurate, but geeze:D
 
If you have an MSD box with a rev limiter check the pill. I've seen guys have a bad 7000 pill that would activate at a lower rpm. OR check the fuel VOLUME. See how long it takes to fill a one gallon jug from the pressure side if your fuel pump (if electric). Wish I could remember how long it was suppose to take. I'm sure someone here knows. OR go with the valve spring thing.
 
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