Page 3 of 3

PostPosted: Sat Sep 24, 2005 5:02 am
by lazflyn
Shannon,

I have just tried to eliminate a cracked cylinder head by swapping heads with the good engine. Wish I had read your post sooner concerning looking at the piston, because I was just looking at them while the heads where off. I'll give you the numbers tomorrow when I swap the heads back to where they belong. Just for your info, swapping heads didn't do anything. It still hangs up at 3/4 throttle. I was doing a touch and go on a farmer's field and when I applied power, the problem engine acted up. I cycled the throttle a few times and it finally cleaned out and went to full throttle. Also, for your info: When I tune it at the start of the day to get it to run at full throttle, I find that I have to first richen it. Then, when it smooths out, I lean it to get the rpm's back up. I end up pretty much right back where I started before I touched the needle. Something seems to have changed though with all I've done because it is not as hard to get tuned right. Sometimes I don't even have to tune it, it just works for that day. Weird.

I just thought of something to about the rpm and change in sound. From my experience, the Rotax 185 has a very distinct sound at 4300+ RPM. Below that they don't sound the same as at that higher rpm. At around 4000 rpm is what I like to "put" around at as that is the rpm that the engines get noticeably quieter. And it is also at that rpm that I can just maintain level flight. The reason I bring this up is that it is at this "transition rpm" range that it has the problem. It will either stay at the 4000 quieting operating rpm range, or it will kind of jump into that characteristic 185 sound at high rpm and run smooth. Just thinking out loud.

MarkDJ.

PostPosted: Sat Sep 24, 2005 1:40 pm
by JPXman
would a bad bearing cause this problem? sounds like some kind of harmonic resonance thing - sometimes you can vibrate the bearing just right to operate normally, but at other times the bearing wobbles and causes the engine to bog down? just a thought from a non-rotax 185 guy.

PostPosted: Sat Sep 24, 2005 10:19 pm
by Billm
I know virtually nothing about 185's but to me this kindof sounds like the muffler
may have a loose baffle and shut off sometimes (like when the frequency and the
pressure are in sync to shut it down.)
Just my 2 cents worth.
Bill

PostPosted: Sun Sep 25, 2005 8:13 pm
by Guest
Mark,

A couple things that I don't think have been mentioned here that might be of interest to you.

There were LOTS of lousy carburetors shipped on the 185's right after Tillotson moved their production to Ireland (early 1983, IIRC). Seems they didn't clean them properly after machining operations. Little pieces of metal got trapped behind the plugs and would cause all kinds of trouble. Sometimes it shows up on older carbs too. For about $100 US you can buy a new carb. I think they are now up to the forth revision of the HL series.

Also, "IF" you have the early style exhausts - the ones where the mufflers are mounted right on the side of the cylinders - you should try upgrading to the later style (the muffle behind the engine over top the nacelle). The engines with the early style did not run as smoothly, and had certain rpm's where they weren't as happy to run. Too much exhaust gas is pulled back into the cylinder from the muffler, which messes up the mixture. It makes the engine touchy to tune, and they don't produce as much power. When everything is perfect, they run OK, but if the carb or ignition system is marginal, you can have trouble.

Chappy

PostPosted: Mon Sep 26, 2005 5:21 am
by ozzie
just to really confuse you, remove the muffler check it and the port for heavy carbon build up including blocked and loose baffels then swap carbies if the prob goes to other engine completley tear down the carb including the welch plugs clean it and blow it out with compressed air and fit a new kit including needles. when hunting for carbs i found that nearly all types could be bought for well under 100 bucks. oh make sure that the orifice for the staic air pressure that act on the diaphram is clear and functioning as this could also cause problems as the air pressure changes from day to day. ozzie

PostPosted: Mon Sep 26, 2005 12:41 pm
by Guest
Mark,

A couple things that I don't think have been mentioned here that might be of interest to you.

There were LOTS of lousy carburetors shipped on the 185's right after Tillotson moved their production to Ireland (early 1983, IIRC). Seems they didn't clean them properly after machining operations. Little pieces of metal got trapped behind the plugs and would cause all kinds of trouble. Sometimes it shows up on older carbs too. For about $100 US you can buy a new carb. I think they are now up to the forth revision of the HL series.

Make sure the small passages in the engine/carb gaskets/carb base, that powers the carb diaphragm, are unrestricted. Sometimes gasket material gets smashed down in them, which will keep the carb fuel pump section from working well enough to pull enough fuel.

Also, if you have the early style exhausts - the ones where the mufflers are mounted right on the side of the cylinders - you should try upgrading to the later style (the muffle behind the engine over top the nacelle). The engines with the early style did not run as smoothly, and had certain rpm's where they weren't as happy to run. Too much exhaust gas is pulled back into the cylinder from the muffler, which messes up the mixture. It makes the engine touchy to tune, and they don't produce as much power. When everything is perfect, they run OK, but if the carb or ignition system is marginal, you can have trouble.

Chappy (I sent this yesterday, but for some reason it never went through.)

PostPosted: Mon Sep 26, 2005 12:48 pm
by Chappy
Mark,

A couple things that I don't think have been mentioned here that might be of interest to you.

There were LOTS of lousy carburetors shipped on the 185's right after Tillotson moved their production to Ireland (early 1983, IIRC). Seems they didn't clean them properly after machining operations. Little pieces of metal got trapped behind the plugs and would cause all kinds of trouble. Sometimes it shows up on older carbs too. For about $100 US you can buy a new carb. I think they are now up to the forth revision of the HL series.

Make sure the small passages in the engine/carb gaskets/carb base, that powers the carb diapham, are unrestricked. Sometimes gasket material gets smashed down in them, which will keep the carb fuel pump section from working well enough to pull enough fuel.

Also, "IF" you have the early style exhausts - the ones where the mufflers are mounted right on the side of the cylinders - you should try upgrading to the later style (the muffle behind the engine over top the nacelle). The engines with the early style did not run as smoothly, and had certain rpm's where they weren't as happy to run. Too much exhaust gas is pulled back into the cylinder from the muffler, which messes up the mixture. It makes the engine touchy to tune, and they don't produce as much power. When everything is perfect, they run OK, but if the carb or ignition system is marginal, you can have trouble.

Chappy (OK, I'm signed in now, maybe this will post.)