520 rich/misfire?

Aircraft powered airboat discussion.
Post Reply
fanofthesimplelife
Southern Airboat Member
Posts: 36
Joined: Tue Jul 05, 2016 1:19 pm

520 rich/misfire?

Post by fanofthesimplelife » Fri Oct 12, 2018 8:13 pm

just changed the oil and plugs in my motor because i noticed it running a bit rough and now out of the right cylinder bank at WOT it will smoke black not constant but puffs i was thinking maybe mag issue new plugs are ngk AB-6

User avatar
Slidin Gator
Site Supporter - IV
Site Supporter - IV
Posts: 673
Joined: Sat Feb 03, 2018 11:33 pm
Location: Jupiter Farms, Florida

Re: 520 rich/misfire?

Post by Slidin Gator » Fri Oct 12, 2018 8:23 pm

Puffs usually means a problem on a single cylinder. What do the old plugs look like?
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

fanofthesimplelife
Southern Airboat Member
Posts: 36
Joined: Tue Jul 05, 2016 1:19 pm

Re: 520 rich/misfire?

Post by fanofthesimplelife » Fri Oct 12, 2018 8:26 pm

black garbage probably only had 20hrs on them the back cylinder plug had a small rust spot by the tip it looked like a heat rust though not a water rust

Seadrift
Southern Airboat Member
Posts: 30
Joined: Tue Oct 04, 2016 5:28 pm

Re: 520 rich/misfire?

Post by Seadrift » Mon Oct 15, 2018 6:01 pm

8)
2000 Combee 18' / TIO 541 Don't laff, it takes me there and brings me back.

User avatar
Slidin Gator
Site Supporter - IV
Site Supporter - IV
Posts: 673
Joined: Sat Feb 03, 2018 11:33 pm
Location: Jupiter Farms, Florida

Re: 520 rich/misfire?

Post by Slidin Gator » Tue Oct 16, 2018 1:42 pm

With new plugs installed (no run time on them) start motor and immediately go to low-medium power to warm up. Once warm run it hard for a bit and shut down. Pull the plugs and see what you get. Looking to see if all cylinders are rich or just 1-2?

By black garbage, do you mean they are oil fouled or fluffy black from being rich?
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

fanofthesimplelife
Southern Airboat Member
Posts: 36
Joined: Tue Jul 05, 2016 1:19 pm

Re: 520 rich/misfire?

Post by fanofthesimplelife » Wed Oct 17, 2018 8:45 pm

fluffy black i pulled the plugs after i ran like you said all of them are this way

User avatar
Slidin Gator
Site Supporter - IV
Site Supporter - IV
Posts: 673
Joined: Sat Feb 03, 2018 11:33 pm
Location: Jupiter Farms, Florida

Re: 520 rich/misfire?

Post by Slidin Gator » Wed Oct 17, 2018 10:36 pm

It could be mags, but both would have to go weak at the same time for all plugs to show. Rich sounds like the correct diagnosis. All cylinders rich points to the carb. Did this just start or always done it? Recent change might indicate a stuck float. What carb? If Holley or similar a blown power valve is a good suspect. Otherwise it might just need jet tuning.

Did you recently add an air cleaner? That will richen the mixture some. I believe this is a new boat to you (??) so note any changes you made since it ran right.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

User avatar
John Fenner
Southern Airboat Member
Posts: 2833
Joined: Tue Feb 14, 2012 12:26 pm
Location: Miami(Cuba) Fl.

Re: 520 rich/misfire?

Post by John Fenner » Thu Oct 18, 2018 8:51 am

Need to know what carb, if MA6 the aneroid could have vibrated out, there is an MA4-5 version that has the aneroid as well, unsure of the # on that one, a runup and a gradual move of the lean rich lever could show a jet issue, also a stuck or plugged economizer valve could cause a rich condition.
I never finish anyth,,,.

GMAC 76
Site Supporter - V
Site Supporter - V
Posts: 1237
Joined: Sun Jan 04, 2009 11:12 pm
Location: LAKE PLACID FL.... LAKE ISTOKPOGA

Re: 520 rich/misfire?

Post by GMAC 76 » Thu Oct 18, 2018 3:21 pm

if and only if the carb is a MA-6AA helicopter carb and has not been converted or modified.....I had a very similar problem with an 0-540 and a 6AA carb last week and what had happened was the AMC unit had failed and was dumping unjetted fuel into the main nozzle

fanofthesimplelife
Southern Airboat Member
Posts: 36
Joined: Tue Jul 05, 2016 1:19 pm

Re: 520 rich/misfire?

Post by fanofthesimplelife » Sat Oct 20, 2018 7:43 pm

it has a ma4-5 carb

GMAC 76
Site Supporter - V
Site Supporter - V
Posts: 1237
Joined: Sun Jan 04, 2009 11:12 pm
Location: LAKE PLACID FL.... LAKE ISTOKPOGA

Re: 520 rich/misfire?

Post by GMAC 76 » Sun Oct 21, 2018 10:36 am

what is the 10-???? part number on the tag?

Post Reply

Return to “Aircraft Power Only”