What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

I think I have a carb ice issue...

cjensen

cjensen

Well Known Member
Searched the forums today, and didn't find anything *SPECIFIC* to my setup...so, I'm asking for 1) General thoughts on what I'm experiencing, and 2) SPECIFICALLY, anyone with my setup, which is O-360, MA-4 carb, and Sam James intake, to chime in.

I have 35 hours on my 7 now, and I get this exact same problem from time to time. That problem would be, after a cruise configuration power reduction (doesn't matter if the mixture is already full rich or not), I am getting a VERY noticeable engine stumble. I don't know if it would actually quit because I always push the throttle back in when it happens, and it smooths right back out. It's an attention getter, but I half-expect it now. As I get closer to my 40th hour, I need to get this corrected. It does not happen on every flight. In fact, it hasn't happened at all in the last five or so hours. Yesterday while pulling the power to enter the pattern, it did stumble. It was humid, and temps were in the high 30's/low 40's.

It has never done it while in the pattern shooting stop n go's. This sort of leads me to believe that it's a carb ice issue. After a 15-20 minute cruise set up (or longer), it occurs, but not all the time.

After my pattern entry, and subsequent take off's and landings at that airport, it did not do it in the pattern, and it didn't do it on my return leg to my home airport.

Thoughts? :confused::confused::confused:
 
Check your idle mixture.

It may be too rich. When you close the throttle, you are within the idle circuit of the carb. If the idle mixture is too rich, the windmilling prop can force an extra rich mixture.
 
I'll double check that Mel...my A&P buddy asked me that same question, and I shut it down too quickly to check that yesterday. But, I do check the shutdown RPM increase from time to time, and I get the 50rpm rise or so. It could change tho, so I'll confirm it...
 
I'm probably no help, but I too have a random engine stumble issue(20.2hrsTT). It has happened 2 times now on the ground while taxiing and once running rough in the air.

I fairly certain the roughness while airborne was a fouled plug. I have FI, so no carb ice is ruled out.
My taxiing stumbles have been after landing from significant high cruise with a rich mixture. bump of the throttle and all is smooth and I can't reproduce it. I'm thinking it's an overly rich mixture situation.

just saw Mels post, I'll need to check that again, I haven't check my idle rise since we first ran the engine. I don't shutdown with my mixture but use move the purge valve to ICO.
 
Last edited:
I used to fall into #2 there and never had the issue you're experiencing.. flown in all kinds of temps and humidities..

my carb was 10-4164-1, if that helps any...

I'd be looking along the lines of what Mel suggested first..
 
Usually the Lycoming with its heated carb riser, buried in the oil pan, has very little trouble with carb ice unless you're in a region of really high absolute humidity, not relative humidity. With your Sam James intake system, what would you estimate the total length of your inlet is from the opening to the intake valve. Sometimes you will find on some planes that the engine will stumble going through a certain rpm, usually about 1400 rpm to 1800 rpm. This is thought to be due to anti-resonace of the inlet system. You should see some of the videos of a cloud of gasoline-air particles sitting right above a carb at certain rpm. Some induction systems claim that their filter box design eliminates this.
 
Although I know of a few cases of carb ice in Lycomings, I have personally never experienced it Chad. I would lean towards mixture adjustment as well. It has always interested me that if you have the engine leaned perfectly at cruise power, you have to richen it up to prevent stumbling when you pull the power back for descent. Counter-intuitive, but seems to hold true for the 320's and 360's I have owned. Didn't work that way for the 235, interestingly enough.

Paul
 
cjensen said:
Wouldn't it tend to do it on every flight if it was an idle mixture adjustment tho?
Click to expand...

Is there any correlation to OAT? At a given setting the mixture will be tend to be richer in warmer temperatures (because the inlet air is less dense).

I have the same engine/carb and have never (?) experienced icing.
 
Chad,
I'd put money on idle mixture and/or idle speed.
If the mixture is too rich and rpm set too low, the engine could be loading up with the throttle at idle.
Just another point of view. I had that situation once with a new airplane where the engine quit on final but it was hardly noticeable with a fixed pitch prop. It was noticeable when exiting the runway with no response to throttle movement.
This was with an Ellison system but the same thing could be going on with your carb.
As previously mentioned, setting idle mixture is a compromise of sorts as the setting is fixed and will be affected by OAT.
 
Take the worry out

Carb temp probes/ gauges are great for peace of mind. My 7A O-360 has not had carb ice yet (360hrs), but when going through humid cool air I will moniter my carb temp on my EIS. Also had a Tiger with an O360 that had a carb float get heavy after less than 100hrs and one year after reman. It did what yours is doing in the early stages of failure. Does boost pump make it worse? Gene
 
Last edited:
Engine Stumble

Boy, does this sound familiar! I had this problem on my first RV-6A, O-320-D1A engine. It took me months to finally find the issue. It turned out to be the specific 10-#### carb model and the way the bowl vent was setup. I can't remember the 10-#### of the bad carb, but how the bowl is vented into the intake area was the cause of the problem. A different 10-#### carb solved the problem.
After a LOT of instrumentation was setup on the intake, the problem turned out to be a turbulence issue that caused the bowl fuel to foam, causing the engine to stumble (110 MS max stumble time, but VERY noticeable). The stumble would occur just after throttling back, and as the airspeed increased to a point where the intake RAM air pressure began to exceed the engine intake suction. At the crossover point, the engine would stumble, especially in cold, dense air.
Changing to another MA-4 carb with another 10-#### that had a different bowl vent method solved the problem....
So try a different carb and see if it makes a difference......



cjensen said:
Searched the forums today, and didn't find anything *SPECIFIC* to my setup...so, I'm asking for 1) General thoughts on what I'm experiencing, and 2) SPECIFICALLY, anyone with my setup, which is O-360, MA-4 carb, and Sam James intake, to chime in.

I have 35 hours on my 7 now, and I get this exact same problem from time to time. That problem would be, after a cruise configuration power reduction (doesn't matter if the mixture is already full rich or not), I am getting a VERY noticeable engine stumble. I don't know if it would actually quit because I always push the throttle back in when it happens, and it smooths right back out. It's an attention getter, but I half-expect it now. As I get closer to my 40th hour, I need to get this corrected. It does not happen on every flight. In fact, it hasn't happened at all in the last five or so hours. Yesterday while pulling the power to enter the pattern, it did stumble. It was humid, and temps were in the high 30's/low 40's.

It has never done it while in the pattern shooting stop n go's. This sort of leads me to believe that it's a carb ice issue. After a 15-20 minute cruise set up (or longer), it occurs, but not all the time.

After my pattern entry, and subsequent take off's and landings at that airport, it did not do it in the pattern, and it didn't do it on my return leg to my home airport.

Thoughts? :confused::confused::confused:
Click to expand...
 
Intake tubes

You might want to check your intake tubes where they go into the oil sump for tightness. I had the same issue on mine, and they went away when I put some sealant where the tubes go into the sump. I think what was happening on mine is that when you throttle back, the suction increases, and sucks more air throught the tubes than you would when checking idle mixture on the ground since RPM is much higher.

Lycoming makes a special tool ($$!) to roll the tubes into the holes which would probably solve the problem.

Recently teh stumble has started happening again, so I am thinking my sealing job has probably come loose.

I posted on this subject a while back so you can check the archives on the responses then as well.
 
This is a sometimes common problem if you have a 10-3878 carb and your engine needs a 10-3878M carb. You can get the carb modified by installing a "M Kit" What P/N carb do you have?? I think you are going to need a 10-4164-1 or 10-3878M to solve you problem.
Good Luck,
Mahlon

?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
I too have had a stumble when rolling back on the throttle. It happened was when I was throttling back on the downwind. Definitely got my attention. It seemed to go away after 30-40 hours T.I.S. and I haven't noticed it for a while.
 
Last edited:
David-aviator said:
the engine quit on final but it was hardly noticeable with a fixed pitch prop. It was noticeable when exiting the runway with no response to throttle movement.
Click to expand...

Hmmm! (thinking to self...)

I'm rolling out after landing...
Slowing......
slowing...
slowing
turning off at the taxiway and throttle up...
No throttle response and the prop isn't turning:confused:
I wonder if my engine quit:(

Sorry, just laughing at the way you noticed that your engine quit on final.;)

Have a great day!
 
This is the jetting of the carb, nothing else. We had this problem way early on with the early RV's before we realized what was going on. Van hadn't incorporated the airboxes with the filters yet, so we had full ram air. I was one of the early RV-4's (10 or 11, I think) and it pretty regularly stumbled right after a reduction in power after a climb, but NOT always. Temperature seemed to have an effect on it, and that would make sense and temperature can certainly affect the mixture at a particular power setting due to it's impact on air density. I assure you the first few times it happened I had it turned back to the airport faster than you can blink (that's easy with an RV-4!). After a while I just got used to it, until we finally drilled out the jet a little.

Vic
 
Sorry for missing all these...was out of town today...

LOGGY said:
Are you using 100 LL.......?
Click to expand...
Yes, 100%

Alan Carroll said:
Is there any correlation to OAT? At a given setting the mixture will be tend to be richer in warmer temperatures (because the inlet air is less dense).

I have the same engine/carb and have never (?) experienced icing.
Click to expand...
Doesn't seem to be...it has happened at 70+ and 20...I'm leaning away from the carb ice problem...
GeneL said:
Carb temp probes/ gauges are great for peace of mind. My 7A O-360 has not had carb ice yet (360hrs), but when going through humid cool air I will moniter my carb temp on my EIS. Also had a Tiger with an O360 that had a carb float get heavy after less than 100hrs and one year after reman. It did what yours is doing in the early stages of failure. Does boost pump make it worse? Gene
Click to expand...
I plan to add the carb temp probe now. Good assurance. Boost pump has never been on when it stumbled.
Fred.Stucklen said:
Boy, does this sound familiar! I had this problem on my first RV-6A, O-320-D1A engine. It took me months to finally find the issue. It turned out to be the specific 10-#### carb model and the way the bowl vent was setup. I can't remember the 10-#### of the bad carb, but how the bowl is vented into the intake area was the cause of the problem. A different 10-#### carb solved the problem.
After a LOT of instrumentation was setup on the intake, the problem turned out to be a turbulence issue that caused the bowl fuel to foam, causing the engine to stumble (110 MS max stumble time, but VERY noticeable). The stumble would occur just after throttling back, and as the airspeed increased to a point where the intake RAM air pressure began to exceed the engine intake suction. At the crossover point, the engine would stumble, especially in cold, dense air.
Changing to another MA-4 carb with another 10-#### that had a different bowl vent method solved the problem....
So try a different carb and see if it makes a difference......
Click to expand...
Very interesting info here...and Mahlon's response below seems to match up.
lcnmrv8r said:
Yeah Chad- I have to agree that it's the carb setup. I have a stumble there occasionally as well. Gets your attention. It happens around 3/4 throttle when I am pulling back. It doesn't happen all the time but I can replicate it. Freds post puts it pretty well.

Good luck on the next five hours till freedom
Click to expand...
Yep, right about 3/4 throttle is where it's happening. Thanks for the data point!
mahlon_r said:
This is a sometimes common problem if you have a 10-3878 carb and your engine needs a 10-3878M carb. You can get the carb modified by installing a "M Kit" What P/N carb do you have?? I think you are going to need a 10-4164-1 or 10-3878M to solve you problem.
Good Luck,
Mahlon

“The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
Click to expand...
Thank you Mahlon...I'll check my part numbers this weekend.

Thanks for the info guys!! It doesn't match what my shop is thinking (carb ice), but they don't work on, or fly RV's...;)
 
mahlon_r said:
I think you are going to need a 10-4164-1 or 10-3878M to solve you problem.
Good Luck,
Mahlon
Click to expand...

I just checked my engine info here at home, and my paperwork indicates that I have the 10-4164-1. Will have to verify, but seems as tho I have the correct carb on the engine...:confused:
 
If you have an OK part number, can you borrow a carb from a buddy to try??
Really sounds like a carb issue.
Good Luck,
Mahlon
"The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
I have an O-320 in my 9, it also stumbles when it is in idle on final, carb heat on helps it not do that as bad, I have adjusted the idle mixture in both directions and drilled the jet, still does it. It never cuts off completely, just stumbles,,wish I could figure this one out. My carb is a 10-5135 overhauled by Kelly.
 
Maybe sucking fuel through the primmer if you have one. Try disconnecting and plugging the primmer system, if installed.
Good luck,
Mahlon
?The opinions and information provided in this and all of my posts are hopefully helpful to you. Please use the information provided responsibly and at your own risk."
 
DakotaHawk said:
Hmmm! (thinking to self...)

I'm rolling out after landing...
Slowing......
slowing...
slowing
turning off at the taxiway and throttle up...
No throttle response and the prop isn't turning:confused:
I wonder if my engine quit:(

Sorry, just laughing at the way you noticed that your engine quit on final.;)

Have a great day!
Click to expand...

This happened with the Cozy MKIV and the engine in back, that airplane was slick as a baby's bottom and would glide forever with no power. I used to haul it back to idle on downwind leg and not touch the throttle until on the runway. No flaps, just a speed brake on the belly. Ben Ellison about went nuts when I told him what happened and he admonished me to reset the idle stuff before next flight....OK, OK, but it sure runs well otherwise. I was having lots of fun flying that airplane. :)
 
Carb Ice experiences

Hi Chad - I had carb ice events 3x and none of them was like what you are seeing:

#1 was right after takeoff (!) in a C150 powered by a continental. It was in the 50s out but very very humid from the cornfields. Engine ran rough and RPMs droppped. Pulled carb heat, turned towards lower terrain (Iowa, thats easy) and slowly climbed. AFter a while the roughness went away and the RPMs returned.


#2 and #3 were behind a Lycoming O-235. Both times the OAT was in the 40's, and very humid again... but the kicker was I was vectored over a big food plant next to the aiport. It produces lots of steam. I didn't fly thru the plume but I think the plant produces a lot of local humidity. The engine ran rough but the RPMs didn't drop. It really got your attention. I think what was happening was the ice was forming / melting and the water was running through the engine.

The first time this happened I asked for a return to the airport. Tower decided to declare an emergency for me (!) without telling me and rolled the rescue trucks. Got to meet nice rescue people. I think they were just looking to practice.

Keep us posted on your experiences as you resolve the issue. I bet the carb is flaky.
 
You must log in or register to reply here.
Back
Top