Well, I'm about at my wits end with a starting problem that has come up recently. My stock '53 B model has always been a good starter cold, hot or warm. But lately I have had the darndest time getting it started after about a 30-90 minute stopover after flying. Cold, she fires right up after 2 shots of prime. And hot starts after a brief break for fueling (10-20 minutes) don't seem to be a problem. But wait an hour after shutdown to go to dinner or something, then try to start has consistently been a problem the past 3 months. I'm not doing anything different than I have been doing in the past, so I don't think I'm the cause. I leave the throttle alone, mixture rich and pull the starter. It acts like it wants to catch for a few blades, firing about 4 or 5 times then quits. I have tried priming with primer and with the throttle accelerator pump and that doesn't work so I don't think it's fuel starved. But also have been careful not to flood it with endless shots of prime by only giving it one shot to see if it wants gas. Eventually I seem to get it started by trying several variations of throttle and mixture but can't seem to find a consistent method. It's like it just decides to start arbitrarily despite what I do, so I keep cranking in about 7 second intervals and letting it rest at least 30 seconds to several minutes between cranking sessions. Several times this procedure has almost run me out of battery power and delays from 1/2 hour on up to over an hour. It also does it with either Mogas or Avgas, so I don't think its a fuel quality problem either. It seems to finally start after 3/4 of my battery power is gone and my passengers are looking at me real funny
My A&P thinks its flooding or has too rich a mixture, but why does it start Okay hot? He has not pulled the cowlings off to check things out yet though. He sorta acted like it was my fault and didn't seem overly eager to jump on the problem. This problem if affecting the way I fly, I now plan my stops to either be for a full cool down or a quick turn around and it really bites. To tell the truth, I don't trust it anymore to reliably start warm and in the Alaska bush, this is not a good thing. Any Ideas or thoughts are welcome...
Bruce,
I have a freind with a 1957 172 straight tail. 0300 engine. He had simular problems, it turned out to be the Mag or Mags.
I do not remember the cause exactly, he had them checked and I think rebuilt and no more problem.
I really do not see why you have the problem either, sounds like something that is intermitent, but 3 things make and engine run,
Spark, Fuel, Compression. It has to run if these three are correct. If the fuel is consistant and the compression is constant, that leaves the spark.???
I hope you find the trouble, please post your results so if others have problems too.
Dave
Bruce, I had similar trouble about a year ago. The airplane was sometimes kinda hard to start. Then one day it just flat wouldn't start when I was over at a nearby airport. Ran the battery down several times. Monkeyed with the mags,plugs,etc. Finally got her started,ran like crap at lower rpm's, but it got me home Pulled the mags & had them tested per the Slick manual,they were fine. The mechanic asked how many hours on the plugs-- after checking, I told him "only about 450". "There's your problem" he said-- I couldn't believe it but he insisted. I bought new plugs,put her all back together again, & it fired right up & ran great. He said the resistors ( the "R" as in REM40E) break down over time,and eventually the mag spark just ain't enough to fire the plug,especially at the lower (cranking) rpm. He said if you get 500 hours out of a set of plugs you're doing good.
Good luck,hope ya get it figgered out.
Bruce, we got to get to the basics. We need spark, fuel and air to make fire. we know cold you have what you need cause your able to start the engine, and after brief shut downs your not having any problems either, hum. After the hour shutdown and when you use your primer do you feel it or hear it draw fuel? Can you see if you have fuel in your gascolator? on the other extreme do you see fuel dripping out of the airbox. Also check your induction system for lose hoses and the such (do you get any lean popping when you do manage to get it started) ? Pull the prop thru by hand ( mags off ) how even is the compression. Has this been only a summer thing? have you done any maint in that time to where you could of disturbed something? This is what I would think of checking first with out taking anything apart. mabee some of the other members can come up with some other t/s hints.
Good luck
Vic
Vic
N2609V
48 Ragwing
A Lanber 2097 12 gauge O/U Sporting
A happy go lucky Ruger Red label 20 ga
12N Aeroflex
Andover NJ http://www.sandhillaviation.com
Thanks for the responses guys. Eric, can't (or at least shouldn't) be the plugs. We installed new Unison plugs at annual in December, only 50 hours on 'em. Vic, yes I can hear and feel the fuel draw when using the primer and there is fuel in the gascolator. No lean popping on startup either. Also no other maintenance since annual either. problem did not happen in winter, just started this spring. Also no fuel dripping out the airbox because I have checked during these problems to see if ther is fuel running out.
Sounds like you have something that is affected by the changes in temperature from the engine being cold to being hot. Works when it is small, and works when it is big, but not in the middle - that item is probably inside one of your mags since it sounds like you have ruled out bad gas. You might have a combination of weak items, seems like it should fire on one good mag, but if one mag goes South, and you have weak ignition leads, carb gaskets allowing air in, etc, the combination of one mag failure along with some other items could be causing your problem. It would help if you could get a loaner mag so you could identify which one is failing during the cool down period. GOOD LUCK!
Do a mag check with it hot after a hard start, it could be a bad mag coil. The coils get hot after shut down and can break down, but run fine and produce good spark when not heat soaked.
Well it looks like the votes are leaning towards the mags or mag coils. Initial runup still is ok, with about a 50-75 RPM drop on each mag. I have not checked them immediately after one of these problem starts yet, (probably because I'm so damn glad it started) Will do that next time. These slick mags do have about 1000 hours on them now, however. For once, I'd also like Gahorn's take on this but where is he when you need him? I think my next plan is go flying for a while, then land and park in front of my A&P's hangar then let HIM try to get it started after an hour...
Well it turned out that the mags needed new points is all. My A&P had them inspected at a shop that put in a points kit and off we go. Cost $300 to have them yellow tagged but they were not "overhauled" per se. Why they seemed to be temperature sensitive on startup is still up for grabs. Thanks again to all for the help.
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I think my next plan is go flying for a while, then land and park in front of my A&P's hangar then let HIM try to get it started after an hour...