Skybrd Posted January 3, 2014 Report Posted January 3, 2014 I've encountered rough erratic idle after hot starts. While I'm taxing it's humbling to have my engine sound not right with up and down idle speeds. I've tried leaning and riching the mixture and one time I tried the boost pump for a few seconds. By the time I'm at the run-up area everything is back to normal and the run-up check out good. I think it's something to do with trapped air or vapor lock. The procedure I use for hot starts is: (less than 30 minute shutdown) leave the mixture to cutoff and throttle the same as shutdown. Crank the starter until it starts and quickly push the mixture to full rich. If its been over 30 minutes I push the mixture in full rich, give it a boost for about 1 second and return the mixture back to idle cutoff and do the same as before. Quote
Danb Posted January 3, 2014 Report Posted January 3, 2014 I believe most our engines are like women find what's works and that may be trial and error. POh good place to start, both my j models were different and my Bravo is different also. Quote
orionflt Posted January 3, 2014 Report Posted January 3, 2014 Starting procedures sound good, wondering if you have an induction leak that seats it's self after the engine is running for a few min... 1 Quote
Skybrd Posted January 3, 2014 Author Report Posted January 3, 2014 Starting procedures sound good, wondering if you have an induction leak that seats it's self after the engine is running for a few min... Yesterday when the engine was hot, a local shop checked compressions and spark plugs. Compression checked good and the plugs passed their test. If I had a induction leak wouldn't it show up on cold starts? Cold starts the engine runs fine. The mechanic checked the servo and didn't find anything there either. Could it just be trapped air from vapor lock? I found the Contiental engines have a return line to purge the system buy Lycomings don't. Quote
Skybrd Posted January 3, 2014 Author Report Posted January 3, 2014 I don't know if this has anything to do this. I usually lean my engine right after start to keep it from loading the cylinders. Is this the wrong thing to do after a hot start? Quote
Jeev Posted January 3, 2014 Report Posted January 3, 2014 This may help, I put about 40hrs on my J with a IO-360 in a week and follow the same hot start ops as you do. It got progressively harder to hot start and had a rough idle like you described but performed great at cruise power settings. Finally it wouldn't start at all hot or cold. ended up pulling the plugs, cleaned & re-gapped them and it ran and started up like a dream. I also lean aggressively on the ground. Worth a try. Quote
Skybrd Posted January 3, 2014 Author Report Posted January 3, 2014 They cleaned and gaps the plugs yesterday. When I get over my sinus cold, I'll go out and try it again. Thanks Jeev for your suggestion. Quote
orionflt Posted January 3, 2014 Report Posted January 3, 2014 When you have problem like that it can take some time to trouble shoot and can be something that seems unrelated. Thinking about it I remembered an issue I had a 152 that would start right up cold, but once it was hot it would not start. After hours of troubleshooting, checking the fuel system, timing and replacing plugs we pulled the mags checked and cleaned the points, internally retimed the mags. The problem went away, mechanically there is no good reason for it to start fine cold but not start hot but the mags were causing the issue, might be another place to look. Quote
EDNR-Cruiser Posted January 3, 2014 Report Posted January 3, 2014 Similar "problems" here with my M20F and her IO-360 A1A engine... - hot start is a tricky business and it depends on many factors how she behaves... In the end I follow roughly your procedure, too... - before idling I make sure that the RPM is somewhere in the 1200 RPM region. After shutdown I don't touch the throttle anymore. Starting the hot engine (up to 60 minutes depending on OAT) is then just cranking the engine until it fires and then slowly (!) push the mixture in. Afterwards the engine mostly produces some "hickups" for a minute or two when idling or running with very little throttle before it finally runs normal... - usually it helps when I open the throttle to almost full once or twice but that is not always welcome... The O-360 with its carburator is much easier to start when hot and can't be compared to the IO-360... - took me some time to get used to it after my transition from a PA28-181 with an O-360 to my M20F with the IO-360. Quote
aviatoreb Posted January 3, 2014 Report Posted January 3, 2014 High of -5F today - no hot start problems on such days is one benefit. 1 Quote
Super Dave Posted January 3, 2014 Report Posted January 3, 2014 If I'm reading correctly, you aren't having trouble with hot starts; it's just that the engine is running erratically after a hot start? My guess is that there is nothing wrong with your engine or start technique, it's just that things are still too hot under the cowl for a minute or two after startup. Try leaving it full rich and running up to 1500RPM for a few seconds after a hot start, then throttle back and lean normally. Quote
Marauder Posted January 4, 2014 Report Posted January 4, 2014 I agree with Super Dave. My IO-360 will run rough a little after a hot start. I think the fuel is still boiling in the spider and is leaning it out a bit. Cruiser -- I corrected my English... Quote
Cruiser Posted January 4, 2014 Report Posted January 4, 2014 I thought "pops" were raw fuel igniting in the exhaust ? Quote
kmyfm20s Posted January 4, 2014 Report Posted January 4, 2014 When I do a quick turn around hot start as soon as I get in the cockpit and the prop is clear I push the mixture and throttle in and let it sit there until I get everything situated for take off. When I'm ready to star I put the throttle at idle and pull the mixture back out. I go through my startup check list as usual but DON'T PRIME. When it starts up its runs like it was never shut down. My theory is it allows all the vaporized fuel to purge out of the lines and removes the air bubbles. It also doesn't flood the engine. Try it, I learned it here on MS on another thread and has worked perfectly. Quote
Skybrd Posted January 4, 2014 Author Report Posted January 4, 2014 When I do a quick turn around hot start as soon as I get in the cockpit and the prop is clear I push the mixture and throttle in and let it sit there until I get everything situated for take off. When I'm ready to star I put the throttle at idle and pull the mixture back out. I go through my startup check list as usual but DON'T PRIME. When it starts up its runs like it was never shut down. My theory is it allows all the vaporized fuel to purge out of the lines and removes the air bubbles. It also doesn't flood the engine. Try it, I learned it here on MS on another thread and has worked perfectly. Good information, I'll try it as well as some of the other suggestion. I was wondering if this is related to a problem with the old Bonanza's with the Bendix PS5C pressure carburator. It needs the mixture to be left at full rich after stopping other wise the next start will have a bad idle. Quote
Shadrach Posted January 6, 2014 Report Posted January 6, 2014 I have no problem with hot starts. However, when taxiing after a hot start the plane has always had an ever so slight "surge" sound at idle speeds (say 900rpm); Its more audible than visablemon the tach. It did this before and after the servo was rebuilt. Moreover I have heard others do it as well. I just assumed it was normal... Quote
Guest Posted January 7, 2014 Report Posted January 7, 2014 Skybrd, Check tha the anti flood valve on the bottom of the engine above the muffler is working correctly. Although it looks like a standard AN elbow it actually has a small plastic ball inside which is supposed to be sucked closed by the engine vacuum on start up. If it is leaking air is entering the engine but is not passing through the injection servo. It can cause irrational idling. Clarence Quote
tony Posted January 7, 2014 Report Posted January 7, 2014 How do you check that? because there have been times I have seen fuel dribbling out of mine after a shut down on a warm day. Skybrd, Check tha the anti flood valve on the bottom of the engine above the muffler is working correctly. Although it looks like a standard AN elbow it actually has a small plastic ball inside which is supposed to be sucked closed by the engine vacuum on start up. If it is leaking air is entering the engine but is not passing through the injection servo. It can cause irrational idling. Clarence Quote
Alan Fox Posted January 7, 2014 Report Posted January 7, 2014 The surging is the fuel boiling in the spider and lines , At idle there is not enough pressure in the lines to keep it from boiling , that is why it goes away when you add enough power, perfectly normal , annoying as hell..... 1 Quote
M016576 Posted January 7, 2014 Report Posted January 7, 2014 The surging is the fuel boiling in the spider and lines , At idle there is not enough pressure in the lines to keep it from boiling , that is why it goes away when you add enough power, perfectly normal , annoying as hell..... Damn tractor engines.... Quote
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