O-360 won't idle

Working on my RV today, finally got the cowling fixed. Wanted to try a taxi test. The engine (Lycoming O-360 with Rotec TBI) starts really easy, but won't run under about 1500 rpm.

I've only run it once before, and that was running way to rich due to my wiring the primer switch backwards. Got that fixed. So, second time running this engine on this plane.

Start it up, if the throttle is far enough forward to have 1500-2000 RPM it starts up. Do need to stand on the brakes. Did an ignition test, both the mag and P-mag seem to be working correctly. Seems to respond normally to mixture. Throttle back, about 1500 rpm it starts running rough. Further back (1200-1500) and it just quits completely. Full throttle seems to work fine.

I'm not really an engine guy, any ideas for things to check? I could get video of it running if it would help.

Do plan on calling Rotec Monday, I have the day off, but it isn't a holiday in Australia.

Also not an engine guy... yet... but:

Air leaks on the intake side? Intake manifolds torqued to spec?

I would start with the basics. Idle setting screw position? Does the control line have full throw to hit both the idle and full power stops on the carb? Idle mixture setting?

Most likely scenario is too much or too little fuel for the air flow at lower RPMs. (i.e. too rich or too lean. Is this a carb or fuel injection? Different things to look at for each. Idle mixture is irrelevant after about 1100 or so RPM, so something more than that.

EDIT: I see you mentioned Rotec TBI. I am sorry, but I know nothing about those units and how they meter fuel. I am sure someone will step in or you could do some research on the web.

Larry

Sounds like you need to reset the idle screw to a better position. That the hex-drive located just above the fuel inlet, and depending on model, can be a pain to get to with the cowling on...Once you've dfone that, don't forget to set your idle stop on the throttle control - have that backed all the way out during testing, and when you find your sweet spot, set the idle stop on the throttle to match.

I just installed a new Rotec 48-4/5 on my 9 and am still tweaking it, but once you've odne that, it should idle smoothly down to around 600RPM or so.

vacuum leak

check all the intake pipe seals you may have a bad one. U can use the exhaust side of you shop vac to add air to the intake using a filter or fine cloth. Use soapy water to look for leaks.

Thanks for the help. Did turn out to be idle setting too lean. Spent most of today going over the idle steps in the setup manual. Now have it running good from 500-2000 RPM. Still doesn't run good at full power. Need to keep tweaking it.

What are the symptoms you're experiencing towards full power? Mine was fairly straight forward to adjust there, I just had to make sure the mixture arm had full travel to the rich stop.

I ended up using a bellcrank type setup for mine if that helps?

bifft said:

Thanks for the help. Did turn out to be idle setting too lean. Spent most of today going over the idle steps in the setup manual. Now have it running good from 500-2000 RPM. Still doesn't run good at full power. Need to keep tweaking it.

Click to expand...

What altitude are you at in Utah? 5,000 ish? may need to lean it a bit?

Thanks for all the help. Due to work and family commitments I wasn't able to get back out to the airport until today. Needed just a little bit more tweaking of the mixture arm position. Helped to go back over the installation instructions again as well. Now runs great from idle to 2200, which is all the static RPM I could get. Can't use full rich and full throttle, but the density altitude was around 7000, so should need to be much leaner than full rich.

Took a victory lap/first taxi test around the hangars. Feels like I'm almost there.