Rough Running A-65, Help

[rcefird]

1941 BC12-65 engine with about 800 hrs. New slick mags and harnesses with all leads checked and re-checked put in 1/07, timed 30 BTDC and re-checked. Compression checks 70-72/80 all cylinders, and re-checked. Just put in new spark plugs recently- checked, gap checked,etc(happens with old or new plugs). Here's the problem now: Cranks fine, runs fine, mag check at 1500 and 1800-fine. Fly for sometime, esp. when going to airports where have a long drawn out pattern (i.e. low rpm's for extended periods), and lots of taxiing-- then when run-up or go to full power will get lots of skipping and some backfiring/misfiring which is present on L or R or both mags. So far, after running at higher rpm's for sometime will clear up and away I go. I don't like it, and it certainly looks bad to all the airport sitters. Also, I use both Mogas and 100ll avgas (results same on both). When I look at the spark plugs, they look OK, maybe a little black, but no lead deposits, etc. Help me diagnose and fix this please. Is it carb too rich? Valves? What gives?
Thanks for your help, and sorry for the long post.
Randy

[Howard Wilson]

Re: Rough Running A-65, Help

Sounds like you're on the right track with too rich.

[flyguy]

Re: Rough Running A-65, Help

Don't take this for gospel, but from my experience and reading I believe that the idle mixture affects the mixture up through the low rpms and into the mid range rpms. You may be loading up the plugs and you just need to tweak the idle mixture control. Using carb heat will also make that bad condition worse. Watch out for the prop when you're tweaking.
DC

Just a thought, I never tried it this way--You might be able to do it by adjusting it 1/4 turn at a time with the engine stopped and carefully see if the rpm goes up or down after you have started the engine and the idle has settled down. Might work and be safer--don't know just an idea.
If you suspect the idle is rich you probably want to start by screwing the adjust screw in first, the idle rpms should speed up if it was too rich before.

[Ragwing nut]

Re: Rough Running A-65, Help

1941 BC12-65 engine with about 800 hrs. New slick mags and harnesses with all leads checked and re-checked put in 1/07, timed 30 BTDC and re-checked. Compression checks 70-72/80 all cylinders, and re-checked. Just put in new spark plugs recently- checked, gap checked,etc(happens with old or new plugs). Here's the problem now: Cranks fine, runs fine, mag check at 1500 and 1800-fine. Fly for sometime, esp. when going to airports where have a long drawn out pattern (i.e. low rpm's for extended periods), and lots of taxiing-- then when run-up or go to full power will get lots of skipping and some backfiring/misfiring which is present on L or R or both mags. So far, after running at higher rpm's for sometime will clear up and away I go. I don't like it, and it certainly looks bad to all the airport sitters. Also, I use both Mogas and 100ll avgas (results same on both). When I look at the spark plugs, they look OK, maybe a little black, but no lead deposits, etc. Help me diagnose and fix this please. Is it carb too rich? Valves? What gives?
Thanks for your help, and sorry for the long post.
Randy

Sounds like you are advancing the throttle to fast. There is no accelerator pump on Stromberg carbs and they will cough and stumble when advanced to fast.

Mike

[jstall]

Re: Rough Running A-65, Help

1941 BC12-65 engine with about 800 hrs. New slick mags and harnesses with all leads checked and re-checked put in 1/07, timed 30 BTDC and re-checked. Compression checks 70-72/80 all cylinders, and re-checked. Just put in new spark plugs recently- checked, gap checked,etc(happens with old or new plugs). Here's the problem now: Cranks fine, runs fine, mag check at 1500 and 1800-fine. Fly for sometime, esp. when going to airports where have a long drawn out pattern (i.e. low rpm's for extended periods), and lots of taxiing-- then when run-up or go to full power will get lots of skipping and some backfiring/misfiring which is present on L or R or both mags. So far, after running at higher rpm's for sometime will clear up and away I go. I don't like it, and it certainly looks bad to all the airport sitters. Also, I use both Mogas and 100ll avgas (results same on both). When I look at the spark plugs, they look OK, maybe a little black, but no lead deposits, etc. Help me diagnose and fix this please. Is it carb too rich? Valves? What gives?
Thanks for your help, and sorry for the long post.
Randy

Randy: At first blush, I would be suspicious of two things, either a carb that is or has developed problems and might be running too rich? check soot and stack to see if it is staying clean i.e. brown or white, not black and not alot of soot on belly and belly pan just aft of the firewall. Next I would be suspicious of the valve guides getting leaded up and sticking valves. On that, boy, it can be a problem, might try some marvel mystery oil in the fuel then goto a straight diet of mo-gas for a few hrs, to see if that cleans up the lead problem, 100LL has about 8 times the lead that the old 80/87 had so it can cause problems, particularly in engines that the guides were set up tight. Just Ideas. but seems like what your are describing is coupled to time and low power or rpm which is cooling cylinders down after flying for awhile
that could cause valves to stick if they are really on the edge, but also a carb could do it too. If the valve guides turn out to be the problem
they will have to be reamed, I've seen this on 0-200's quite a bit, that run a full diet of 100LL, not all but some, it again depends on how the guides were set up in the beginning, and also how well they are oiling. That can be done without pulling the cyllinders, its a funky job but
a good A&P guy can do it, (you actually drop the valves out into the cylinder, then work em back with a couple of screwdrivers or a graber
its wierd but can be done, see it done several times a year, in fact we just did a 0-200 on a Cessna 140 a month ago

J Stallings
Alva, Ok

J Stallings
Alva, Ok

[crispy critter]

Re: Rough Running A-65, Help

1941 BC12-65 engine with about 800 hrs. New slick mags and harnesses with all leads checked and re-checked put in 1/07, timed 30 BTDC and re-checked. Compression checks 70-72/80 all cylinders, and re-checked. Just put in new spark plugs recently- checked, gap checked,etc(happens with old or new plugs). Here's the problem now: Cranks fine, runs fine, mag check at 1500 and 1800-fine. Fly for sometime, esp. when going to airports where have a long drawn out pattern (i.e. low rpm's for extended periods), and lots of taxiing-- then when run-up or go to full power will get lots of skipping and some backfiring/misfiring which is present on L or R or both mags. So far, after running at higher rpm's for sometime will clear up and away I go. I don't like it, and it certainly looks bad to all the airport sitters. Also, I use both Mogas and 100ll avgas (results same on both). When I look at the spark plugs, they look OK, maybe a little black, but no lead deposits, etc. Help me diagnose and fix this please. Is it carb too rich? Valves? What gives?
Thanks for your help, and sorry for the long post.
Randy

Randy,
How long has this problem been going on and how much has the outside air temp and humidity changed where you are at? Also,do you run straight 100LL all the time,and what is the elevation where you typically fly from ?
While your getting back to me on the questions asked above, here are a couple things to do and/or check..... Remove,check,clean,gap,and rotate all spark plugs.Check the idle adjustment mixture on the back of the carb(it should be set at 1 1/4 to 1 1/2 turns out,depending on elevation,etc.). Also check your mag timming to make sure one mag has not slipped or something....unlikely this would cause the problem you described but it might be possible.

[rcefird]

Re: Rough Running A-65, Help

Thanks for the replies everyone. Mike, I'm not advancing the throttle too fast, I understand that aspect of the engine and I'm not talking about a cough or sputter, it is running rough for sometime before clearing. Kevin, I am in NC--elevation 350ft. temp 63-73 degrees. As far as gas, I run mostly auto 87 or 89 octane, only occasional 100LL or sometimes I mix about 1 gal. of 100 with 4 gal. of auto. This has been going on only for the past two weeks. I have heard some of the old timers around here talk about adding MMO to the oil to prevent sticky valves, how much would they add to the 4qts of oil in an A-65?
Kevin, I haven't messed with my carb. before, should I check the idle mixture to see if it is at 1and 1/4 to1/2 turns as a baseline? I was planning to check the spark plugs again if I have the same problem the next time I go out.
Thanks everyone
Randy

[jstall]

Re: Rough Running A-65, Help

Thanks for the replies everyone. Mike, I'm not advancing the throttle too fast, I understand that aspect of the engine and I'm not talking about a cough or sputter, it is running rough for sometime before clearing. Kevin, I am in NC--elevation 350ft. temp 63-73 degrees. As far as gas, I run mostly auto 87 or 89 octane, only occasional 100LL or sometimes I mix about 1 gal. of 100 with 4 gal. of auto. This has been going on only for the past two weeks. I have heard some of the old timers around here talk about adding MMO to the oil to prevent sticky valves, how much would they add to the 4qts of oil in an A-65?
Kevin, I haven't messed with my carb. before, should I check the idle mixture to see if it is at 1and 1/4 to1/2 turns as a baseline? I was planning to check the spark plugs again if I have the same problem the next time I go out.
Thanks everyone
Randy

If you put MMO in the oil, be sure that you consider how old the engine is smoh, in both time and yrs, and what the possible sludge situation could be, the MMO will break some of that loose, and things can get really wierd, so be ready for that. MMO recomends about 20% mixtures by volume, so in 4 quarts a pint or so would be max, also in the fuel try some there also. I have use MMO in radials, and didn't have good luck with it, it caused oil pressure relief valve to stick and act up. Check the carb adjustment 1st, thats relatively easy, then try some marvel, but stay close to home until you feel good about the effect on the internal portion of engine, check the oil and see how dirty its getting, and if in fact alot of sludge is breaking loose you might want to do a early oil change.

JS

[rcefird]

Re: Rough Running A-65, Help

Kevin and flyguy
I'm leaning toward the carb. issue/idle mixture issue. It seems like pulling carb heat does worsen the issue, and the problem seems to occur at airports where I have prolonged decent at low rpms (with carb heat on).
Randy

[3Dreaming]

Re: Rough Running A-65, Help

A leaking primer could also cause problems too. The low power settings could be pulling raw fuel through the primer into the engine. Tom

[flyguy]

Re: Rough Running A-65, Help

Do the simple one first. Just twist the idle mixture in 1/4 turn and see what happens. Bet it will speed up.
DC

[rcefird]

Re: Rough Running A-65, Help

Thanks guys. Thanks JS, I remember reading that about MMO in one of the groups. My engine is old, will probably stay away from that route. I think I will try leaning first. When people use MMO in their gas, how much do they put? And is it enough to have any effect like in oil? My guess is not since it is mainly contained in the cylinder.
Thanks
Randy

[astjp2]

Re: Rough Running A-65, Help

Mags can also cause a problem, the coils break down when they heat up. Causing rough running. Lean your mixture out when taxiing and before takeoff, the mixture actually works on a stromberg if it is rigged right. Tim

[robbie]

Re: Rough Running A-65, Help

It's on the can but its about 4 Oz's per 12 gal.
I use it in my gas, don't know how much it helps but it's cheap, and with auto gas it might give some additional top lubrication.

[jstall]

Re: Rough Running A-65, Help

Thanks guys. Thanks JS, I remember reading that about MMO in one of the groups. My engine is old, will probably stay away from that route. I think I will try leaning first. When people use MMO in their gas, how much do they put? And is it enough to have any effect like in oil? My guess is not since it is mainly contained in the cylinder.
Thanks
Randy

I don't know just off hand but its on the can or container, don't remember, anyway, double contanier amounts and I don't think it will hurt and it shouldn't hurt anything.

I'm kinda thinking like the others though, it sure could be that carb, those carbs are kinda crude. Mine acts very wierd in the mid range when cold From what I understand there is no good transition on those carbs from idle to fast, and many have a habbit of stumbling.

JS