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Rv7a hesitation problem

Gixxy

Gixxy

I'm New Here
Sorry if this is a bit of a rehash of a older subject. I have been using the search function and doing quite a bit of reading so far on the issue.

Equipment
RV7A with a 0-360
Slick Mags originally and now 1 Slick and 1 Emag (same issue both setups)
MA4-5 10-3878 Carb (I don't know what jet is in it)

On takeoff and touch and goes there is always a hesitation or bit of sputtering before getting full power. No throttle Jockeying is taking place. I always try for a nice smooth application of power. Never had any of my other aircraft do this.

The other thing it will do is start to feel like it?s eother loading up or starved of fuel while idling for very long. I?ve tried both leaning the mixture on the ground (my normal operation for all my previous aircraft) and have even tried to just leave the mixture in. I?m leaning towards something to do with the accelator pump but I really would love to hear a few extra opinions. I don?t think the carb has been overhauled since it was built in 2008. Been heavily considering a carb overhaul. We installed a emag at this annual and it still runs identical as before.

Only other thing I?ve noticed is while in cruise I swear there a tiny hiccup every once in a while. Something most pilots probably wouldn?t notice but I spend a lot of time listening to and feeling how my engines are running through the vibrations etc. Anyhow here are the ideas for fixes. I?ve been told to just fly it as is but I feel like it?s not really acceptable. I really don?t want my engine hesitating on a go around or when the power is needed immediately.

Check the jetting in the MA4-5 10-3878 Carb. I?ve seen some people drill out the jet to a larger size.

Get the carb rebuilt or possibly swap to a new 10-4164-1 carb ???

Ideas ???

Thanks in advance.
 
Gixxy said:
On takeoff and touch and goes there is always a hesitation or bit of sputtering before getting full power.
Click to expand...
I assume you have a Marvel-Schebler MA4-SPA carburetor, which has three adjustment holes for the accelerator pump linkage. My O-290-D2 (MA3-SPA) was stumbling when adding power for takeoff on a hot day so I adjusted the linkage to squirt less gas into the barrel. That helped. There's another thread about my problems here: http://www.vansairforce.com/community/showthread.php?t=141327
 
Planecrazy232 said:
I had this exact hesitation in my O-360 RV6A. I had the carb overhauled and had the "Mooney mod" installed. (google it). It is an actual Marvel part # and changes the model number of the carb to a -M. Worked like a charm on mine and is smooth as could be now. My work was done by D&G Supply.

See post #18 here:

http://www.vansairforce.com/community/showthread.php?t=29221&highlight=carb+mooney+mod&page=2
Click to expand...

I had similar issues with my MS10-3878. After reading about it on the forum I decided to try the M mod. I bought the mod kit (MS#666-660F) and the new float (MS#666-1002F) from ACS. The mod kit includes a new jet and restrictor. After installation the carb has worked perfectly. No longer lean on TO and smooth in flight.

Many suggestions on the forum were to drill out the main jet to a #38 or 39 instead of buying the kit. I was concerned about doing this so I decided to buy the mod kit as recommended by some others. The original jet in my carb was a #41 and the new one was a #40. The one thing I did not see talked about was the restrictor included in the kit. My understanding is this limits air to the economizer circuit which then increases fuel flow at high power settings only, whereas drilling the main jet increases fuel flow any time it is operational.
 
Overly rich accell pump shots tend to sputter and create black smoke. It is rough, not smooth. A Lean shot creates a smooth bog (power smoothly drops and after a second or two smoothly recuperates - more like a hesitation than rough running). If the hesitation occurs below 1200, you can try working the idle mixture. If the engine runs well after the acceleration, best to work with the accel pump adjustments. A jet only a few sizes larger will not typically resolve inadequate accell shot and if it is rich, will make it worse.

Have someone look for black smoke as you accelerate on TO. Any visible smoke would indicate too large of a shot from the accell pump and an overly rich transition.

Larry
 
Last edited:
thanks for bringing this problem up guys, suffering the same symptoms here. Cleaned the fuel filters & replaced the air filter, to no avail.
Now ordered the kit from ACS.

RV7 To Go, did you do the mod yourself, any issues?
 
DeeCee 57 said:
thanks for bringing this problem up guys, suffering the same symptoms here. Cleaned the fuel filters & replaced the air filter, to no avail.
Now ordered the kit from ACS.

RV7 To Go, did you do the mod yourself, any issues?
Click to expand...

Yes, I did the mod myself with no issues. My first time working on an aviation carb. The kit includes a drill bit for the restrictor hole. Apparently there are 2 sizes of holes in the body. I did not need to drill it out as mine was the correct size for the restrictor. Just make sure to get the mixture rod in the hole when reassembling. It is easy to miss and it won't run right if you do. I also installed the new "blue" float as per the SB.
 
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