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#11
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Can hydraulic lifters cause inadequate full power?
On Oct 12, 8:03 pm, wrote:
We've put new points and condensers in both, including internally (and of course externally) timing them. No change. I've done full-power mag checks and misfires would be apparent in that case. New plugs make no change, either. One other possibility: A bad plug lead or two. They can be open (arcing internally) or shorted (arcing to the coax). They often won't show up on mag checks but will, like a bad resistor in a plug, cause some roughness if trhe mags aren't timed pretty close together. The firing of the early mag can create enough pressure rise that the second has trouble firing its plugs. I would doubt that yours are that far apart. : If the carb is a Marvel Schebler/Precision Airmotive unit, have : the ADs been done with regard to the two-piece venturi and fuel : nozzle? Venturi AD's checked and CW. Restriction or mixture would show up as low MP or abnormal EGTs anyway, no? Neither is the present. The two-piece venturi had the risk of losing its secondary venturi into the engine. The AD-mandated one-piece has squared-off support arms that disrupt airflow around the nozzle and a second AD required a new nozzle to try to fix this. The new nozzle made things worse on some engines, so a third AD allowed the reinstallation of the old venturis and nozzles, to be checked every 100 hours for looseness. Except that Precision had recalled all the old parts and crunched them. I know of one rebuilder that dresses the secondary support arms and achieves better running. EGTs won't show anything, since it's random turbulence around the venturi that screws up the atomization. My 60-year-old Bendix/Stromberg is a better carb than any of these MA-3s or -4s. What does all the money get us? Maybe Tempest will fix these problems. They've purchased the carb line from Precision. Dan |
#12
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Can hydraulic lifters cause inadequate full power?
On Oct 12, 9:03*pm, wrote:
* * * * We've put new points and condensers in both, including internally (and of course externally) timing them. *No change. *I've done full-power mag checks and misfires would be apparent in that case. *New plugs make no change, either. Advance the static spark timing on both mags by a degree or two more than where it's sitting at now (e.g. 26 or 27 deg BTC instead of 25 deg) and see if that makes a noticeable improvement on static RPM and takeoff power. |
#13
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Can hydraulic lifters cause inadequate full power?
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#14
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Can hydraulic lifters cause inadequate full power?
Obviously you have checked the tachometer for accuracy by now. I
agree you should not have to go out of spec with the ignition timing, but at least make sure it is set on the slightly high side (i. e. up to the + 1/2 degree from spec. And you should at least witness (or do) the timing check. My O-320 seemed very sensitive to seemingly minor timing variances. BTW make sure the 180 degree timing is correct too - just in case your mag ignition point cam is not symmetrical. |
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