Trouble tuning 340.

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What else was changed when the exhaust went in? Are the plug wires in the correct spot? 18436572... and pressed firmly on... how fresh are the plugs?
 
pishta said:
If your car has hydros, you should be able to crank adjuster to zero (finger tight on the pushrod) then turn it even more and the valve will not move as there is .060 preload minimum on those hydros with no oil pressure. Solids will move once snugged. Check TDC on balancer to #1 rotor phasin and plug wire order. Simple to swap a pair of wires when your rigging it up or just drop the drive in 1 tooth off. Even some solids will have a snap ring so thats not 100% unless you see no snap ring at all, thats a solid lifter for sure.

Well now, we got more info. If it idles poorly in gear, your mix is off. If you installed headers, its gonna lean it out, if you went back to manifolds your probably fat. IF you got an exhaust leak (318 manifolds on a 340 head) its gonna run like crap and sound terrible. Same as a vacuum leak, may run but youll be chasing the idle. Start spraying the manifold gaskets and carb with water from a spray bottle and listen for the idle to change.
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I have shorty headers. I set the idle mixture screw 1 1/2 turns out from tight and then adjusted it with a vacuum gauge to get as much vacuum as possible. Plugs are new, but have a lot of carbon on them when examined.
 
cmcknight said:
I have shorty headers. I set the idle mixture screw 1 1/2 turns out from tight and then adjusted it with a vacuum gauge to get as much vacuum as possible. Plugs are new, but have a lot of carbon on them when examined.
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Ok, good. We have a student with some actual sense. That's good. Most people don't even know what the mixture screws are. I think we can actually help you. Do you have any way to post a video of the car running.....if it will run? I don't care how crappy. If we can hear it run, that will help. It sounds like a low compression engine someone put too large of a cam in. Don't fret. If it is, it can be made to run.
 
RustyRatRod said:
Ok, good. We have a student with some actual sense. That's good. Most people don't even know what the mixture screws are. I think we can actually help you. Do you have any way to post a video of the car running.....if it will run? I don't care how crappy. If we can hear it run, that will help. It sounds like a low compression engine someone put too large of a cam in. Don't fret. If it is, it can be made to run.
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I can post pics/video tomorrow.
 
Check your plug wires a third time. If you could adjust idle for highest vacuum at 15, thats not too bad with a cam. Stocker will give you closer to 20. Tough to nail down. Clean plugs, test wires on ohm meter. Spray the carb with cleaner around the bleeds.
 
pishta said:
Check your plug wires a third time. If you could adjust idle for highest vacuum at 15, thats not too bad with a cam. Stocker will give you closer to 20. Tough to nail down. Clean plugs, test wires on ohm meter. Spray the carb with cleaner around the bleeds.
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I agree with this except using carburetor cleaner to test for vacuum leaks. Please use water in a squirt bottle. You don't want to literally throw gas on a fire.
 
What carb?
RustyRatRod said:
I agree with this except using carburetor cleaner to test for vacuum leaks. Please use water in a squirt bottle. You don't want to literally throw gas on a fire.
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Your no fun... :poke:. Maybe some of us like walking on the wild side...
 
You have some really odd numbers there.

You are going to WOT when doing the compression test I hope?

14-15" of vacuum & such low cranking compression sounds to me like broken rings......or the compression ratio is very low. Doubt it is a cam timing problem with 15" of vac, but severely worn lifters/lobes might give low compression readings. I doubt that a 'tune up' is going to fix this problem.
 
RustyRatRod said:
I agree with this except using carburetor cleaner to test for vacuum leaks. Please use water in a squirt bottle. You don't want to literally throw gas on a fire.
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Yeah...my post #24 said use water spray on intake for vacuum leaks...use carb cleaner in the carb throat.
 
What is your cranking pressure with a squirt of oil into the cylinder? The oil will “help” seal a very worn piston ring. So if your pressure increases a bunch. You may have very worn rings. Don’t get discouraged.
 
the 71 engine with the 360 heads and .039 headgaskets, should have a compression ratio of about 10/1.
There is no street cam that you could install even moderately close to correctly, in your 340 that could generate pressures as low a 100psi, or even 130psi.
My guess is that your gauge is in error, or your rings are capitalD- DRY, or you did not perform the Compression test correctly. So I urge you to repeat the test with a different screw-in gauge.
Reset the lash to what has been suggested; lightly oil the rings as has been suggested, and then pump out the excess, then; crank the engine with all sparkplugs out and the throttle at WOT. Crank as long as it take to see two successive same or nearly the same, pressure readings. Make sure you start with a fully charged and properly working battery, and that the cranking speed at the end of the test is about the same as when you started.
If your pressure with a different gauge is still as low as 100psi, then you are correct, your pressure is way to low,and your low-rpm performance will be very disappointing.
If the pressures are all very close to the same, then we can look at cam-timing, but more likely a cam-replacement is in your future.
If the pressures are NOT all very similar, then I would recommend a Leak-Down test.
If the results of that test are pitiful, then I would recommend to remove the valve gear, and do the LD test with the pistons at the bottom of the bores instead of at the top.
 
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