A performance question. When accelerating at WOT, in first gear, my car will wind up fairly quickly to about 3500/4000rpm and then the rate of increse seems to slow considerably. The distributor has a curve very similar to that of the '64 specs,a pertronics unit, the secondaries on the carb open(fully?), I can hear them anyway, and it has an 097 cam. I was curious if this was normal for the 340 shp. Thanks
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Re: '63 340 SHP
3500-4000 is when it should really start to pull. Test that that counterweighted aux. air valve opens freely by pressing it with a soft tool like a wood or plastic stick, then with it open, have someone in the cockpit floor the throttle and check that the lever on the carb is pulled to the stop and all the butterflies fully open. If not, adjust the pull rod as required to be sure it pulls the lever to the stop, and also check that the other joints in the linkage to the pedal are secure. If the secondary butterflies don't open fully with the lever on the stop, adjust the seconardary linkage on the RH side of the carb IAW the '63 Corvette Shop Manual.
The 340 HP distributors can be problematic. The '64 L-76/84 quick advnace is good and you should also install the '64 L-76/84 vacuum can because the OE "210 15" can is not matched to the engines manifold vacuum characteristic, but this won't affect WOT - just idle quality and low speed/load operation.
The shaft should be checked for tight clearance to the bushings, the breaker plate should fit snug and not wobble, the end play should be shimmed up to two to seven thou, and the 28-32 oz. points should be used. Ignition breakup is usually accompanied with backfiring through the carb. If the engine just "lays down" but doesn't misfire, it's probably being chocked due to lack of airflow, so the carb checks as above should be the first order of business.
Duke -
Re: '63 340 SHP PS
If the engine just "quits" like someone turned off the key, the fuel filter may be clogged, and it's just running out of fuel.
DukeComment
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Re: '63 340 SHP PS
Thanks Duke for the info on the carb., that will be my first check. I have the 236 vac.can on the car and the fuel filter is relatively new. All that really occurs is that the rate of rpm increase slows, no misfires or any other symptoms. The distributor end play is within specs and as I stated it has a Pertronics unit. Once i check the carb I'll install a new fuel filter to sure. I'm getting about 48 degrees of total timing with the initial at 10. ThanksComment
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Re: '63 340 SHP
make sure the heat riser valve is not stuck closed OR installed up side down. i found the some installed up side down and that is how the engine actedComment
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Re: '63 340 SHP
Mine moves freely and the counterweight moves in a downward diretion. Is that the proper orientation?Comment
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Re: '63 340 SHP
sound correct,did you try shimming the points spring with foam rubber to increase the spring tension?Comment
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Re: '63 340 SHP
It has a Pertronics unit, no pointsComment
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Re: '63 340 SHP PS
Jim,
If the 48* total timing that you posted wasn't a misprint, then I know one problem that the engine has. You probably should be around 38*, not 48*. That would probably be happening around the same RPM that you noticed the perf dropping off. Anything near 10* initial and 36-38* total should be in the ballpark.Comment
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Re: '63 340 SHP PS
I think he's talking about "total cruise timing". Above 2500 it's 10+24+16 = 50 plus or minus a couple degrees tolerance.
You guys need to start specifying WHICH "total timing" you are talking about. There are three:
1. Total WOT timing (total of initial and full centrifugal)
2. Total idle timing (total of initial, vacuum, and maybe some centrifugal)
3. Total cruise timing (total of initial, vacuum, and centrifugal at whatever "cruise" RPM you choose)
Being as how the '64/65 SHP/FI centrifugal is all in at 2500, at any cruise RPM above 2500 the total with be intial plus all the centrifugal and all the vacuum advance.
DukeComment
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Re: '63 340 SHP
I wonder if the Pertronics is the problem? If you can read a dwell angle at idle, rig up some test leads so you can place the dwell meter in the cockpit and take it for a ride. Or just free rev it to 5000 or more. That's the way I check for point bounce.
Good points or a good electronic switch should maintain nearly constant dwell angle all the way to the redline. Some electonic swithes actually increase dwell with revs, but it should not decrease.
Do the throttle linkage/carb checks first. Your syptoms sound like the the secondaries aren't opening and it's just air starved.
If you remove and empty the fuel filter you should be able to blow through it easily. If not, it's clogged and the engine can rev up to the midrange, then just quit like someone switched off he key because the fuel flow can't keep up with demand, and it just "runs out of gas". Then you back off and it starts firing again and is normal until the next episode of WOT.
DukeComment
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Re: '63 340 SHP
install a fresh set of plugs,make several full throttle passes to the red line,push in the clutch,kill the ignition,coast off to the side of the road. pull several plugs,if they are dark you have ignition problems and if they are white you have a fuel problemComment
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Re: '63 340 SHP PS
Duke, yes, your correct , total cruise timing. After reading and learning from your post of Jan. 2004 I should differentiate specifically in my posts. ThanksComment
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Re: '63 340 SHP PS
At Dukes suggestion I checked to see if the secondaries were opening. They were, but not completely! A simple adjustment of the throttle linkage corrected the problem and the difference is amazing,really winds right up and the shifter sounds like a diamondback rattler. Thanks DukeComment
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