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carb. problems

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IMG_20181105_194315_828
2015 Hamant
Paw Paw Mound 2009
Chaos
Race
Sunset at Ridge
A

Anonymous

Guest
well here we go. ive finelly got my boat running. takin it out twice now runs great. even on dry ground. i just cant get the darn thing to idle.its a lycoming 0540,and im not sure on what kind of carb is on it i can find out if it it might help any. ive played with the idle screw,and the f/a mix screw. ive been told by a auto mac. friend of mine to turn the f/a mix in all the way and back it off 1 1/4 turns and start there.(notice i said auto mac. nither him or i both know anything about aircraft) once i started playing with the idle now when it cranks up (cold) it wants to spit and sputter,and backfire like i dont know what. but once it warms up it smothes out but still woulnt idle is this normal for aircraft moters? and also what rpm should it idle at? it seems when i try to hold the throdal at about 800 rpm its just starting to stall, its hard to tell my throdal is kinda delayed it seems. well if anyone has advice i would greatly app.
 
Kenny where are you from?


It should be a Marven Carb on there, either a MA-4-5 or a MA-6-AA. Has this been an on going problem or some thing that just started? Sounds like the idle circuit is partially plugged. If you are mechanically inclined with auto carbs then this one will not be a problem for you to work on at all. I would suggest taking it down and soaking it, pull the check valve under the accelerator pump out and make sure its not plugged and also pull the A/F mixture screw out and insure there is nothing in there restricting it. (I had a similar problem and it was a piece of O Ring behind the A/F mixture screw causing me havoc. Idle rates will vary, Lycoming says don't go below 500 RPMs but my 0540 idles a 300 RPMs with 35 PSI of oil pressure.



I have both of the schematics at home on those carbs, I can fax them to you if it will help. I should be home around Tuesday.


Kevin
 
im from kiss. fl.
ive only had the boat a week. it wasnt running when i got it ive already had the carb off and all apart twice. cleaned it. it looks clean but you know how looks go. i had to replace all the intake gaskets and drain the fule cell. (boat had set for 1 year+) like i said boat runs great ,i checked for vac. leaks with carb clean everything seems good i couldnt seem to find any leeks. plugs are good both mags are workin plug wires are new fule pressure is good, compression on all cyl. good(well i say good its all around 110 or so )any way im lost i just cant seem to get it to idle
 
I assume it’s a straight valve 0540. 110 is a little low, with 75089 pistons I am running 175 per cylinder.

What plug gap are you running? Should be around .020" to .025",,, a mag will not have enough juice at idle to jump a wide gap.



Just some thing else to check
 
Kenny,
Like KB27-99 Said.
Check the low speed circuits in your carb again. Especially if you have not been able to find any major vacuum leaks.

Sometime it takes me three or for tries to find the problem, or find one thing and miss something else.

As he stated that those carbs are pretty darn simple compared to a quadrajet for example. Just take it apart and study the idle circuit passages.
Shoot something through them to make sure they are not restricted. Spray carb cleaner in each hole you locate. This will help you trace the passeges, and figure out how the low speed fuel delivery works, and you may easily find the blockage.

Watch your eyes, as it's easy to shoot carb cleaner right in your face if your not careful.

Keep looking for that smoking gun problem, like the piece of o-ring he had found in his carb. Just take your time, and you'll find it, or convince yourself that the problem is not in there.

If you can't find the problem in the carb, go back to checking for intake leaks.

Proper plug gap Will make a big difference at idle also, so that good advise. As he said that's probably not the major problem here.

It will make your engine idle alot better when you have the fuel delivery issue sorted out.

You can fix that thing Kenny, and you will be feeling darn good about what you've done when your standing there watching it idle, and checking your throttle response.
 
Kenny,

There might be another source to your misery - as there was to mine. I bought an 0-540 that had been sitting for a long time, too.

My problem was at the fuel tank outflow nipple. Old fuel had gone to pot and there were threads of gunk that looked like wood strings clogged into the check valve passage at the tank nipple.

Cleaned it out and - wallah - purred like a kitten.

As to compression, your numbers are on the low side, but you may have the 0-540 version that is designed to run on - 92 octane.
 
still no go im going to try takin the carb off one more time and see what that does. all my plugs are at .025. the fule tank is all clean i dont know . i was told by the prev. owner that all he ran was 92 and it ran fine should i try putn ouctan boost in it ?
 
Check the condition of the accelerator pump. If that leather gasket is not holding it's shape, it will not idle well. There is a check valve under that plunger that has a little ball in it. If there is trash in that valve, behind the valve, or between the valve and the check valve, things don't work right.
 
I had the same problem. I cleaned the carb several times, replaced the accelerator pump, and finally gave up and sent the carb to southeast fuel systems, and traded it for a rebuild. The problem turned out to be the idle circuit. With a core the carb was $270 and now the engine runs and idles fine. They also test the carb on a test engine and tune it for your motor. Their number is 321-632-2762.
 
thats a cocoa or rockledge phone number not to far from kiss. I can find out where they are located if you would like
 
kenny they are located at 415 gus hipp blvd rockledge fl 32955 its about a block from my shop if you need me to stop by for any reason I would be glad to
 
thanks croc 1 i app if u could give me a cross sterat th at would held i lived in cocoa for a while so i kinda know my way around where is it in referance to 520 and us 1
 
I would go to http://www.mapquest.com click get directions! put in your address and their address it will give you a highlited printable map and text directions . from 520 take I-95 south 1 exit to fiske blvd mile marker 195 take a right go over 195 take 1st right barnes blvd (lowes store) go east to us1 go north about 1 mile past blinds of all kinds (my shop) go left at guss hipp good luck ( barnes blvd is the road that has the rockledge airport on it if you remember that )
 
i had the carb apart again and it looks like the little rubber gasket or leather on the valve(lol its so old lookin i cant tell) any way its cracked and split in places and kinda disformed outher than that every thing is clean i took it all apart and used breakcleen and air to clean it out(and even put a lil oil on the ring hopen it wouyld help) any way it still aint idlein could it be that or could it be that gasket between the 2 parts of the carb cause i aint replaced that yet
 
If that is the gasket on the plunger (accelerator pump) that is hard and cracked, it will cause bad idling problems. The leather gets that gas on it and when it sits up, it becomes stiff.

If you buy it from a aircraft supply, you can pay as much as $75 (the first one I bought I got taken). Give Jr Jurnigan a call, he gets them for less than half that. Or look at the aircraft supply companies, can get them there for about $45 - $55.

If she idles really rough when you start up and then smoothes out on idle after she warms up, you might have a stuck valve. That is the classic way they start showing up.

Good Luck
 
Pat,

Those are outrageous prices for technology that is 70 years old, and it is probably because they are certified parts. I'm surprised someone has not tried to adapt a modern neoprene part to the carb for airboat applications, hopefully at 1/10 the price.

Jim
 
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