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  #1   IP: 24.61.95.61
Old 09-26-2019, 09:23 AM
ArtJ ArtJ is offline
 
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Engine stumbles on startup

I have a late model A4 in my 1970 Tartan 34

It has been running great all season. I installed a new carb in the
spring. I have electric fuel pump. Igniter elect ignition as well as
protective dropping resistor with coil.

Yesterday, the engine started perfectly a ran for a couple of minutes
then started to stumble and died. I attempted to restart to no
avail. I tehn noticed the smell of gas and checked the throat of the
carb and it had gas dripping out of it. I also noticed gas and gas stains
in the bilge. I cleaned all of it up. Looked at the choke to see if
operating properly believe it is but could not easily look in the
barrel.
I may have 2 separate issues, can excessive gas cause flooding and a shutdown? I noticed elsewhere that someone had to replace fuel shutoff
due to a starting problem. I thought that the draft of the carb
precluded flooding? or could the choke being on cause a excess of
fuel to drip out stuck float? leaking main fuel shutoff?
the tank height causes gravity flow of fuel on the Tartan 34

Do I have 2 problems?

Comments Appreciated

Art
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  #2   IP: 97.93.70.7
Old 09-26-2019, 10:17 AM
Dave Neptune Dave Neptune is offline
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Art, there are a few ways for fuel to leak out of the throat.

First and most common would be a stuck float. Do you have filters on the fuel line?

Second and not as common is a compromised float. That is a float with a leak that can hang down leaving the needle open. This will usually cause a flood of fuel not just a leak.

Third and not so common would be lugging the engine or leaving the choke on. An updraft carb running rich, with the choke on or lugging can cause a poor fuel mix and that poorly mixed fuel will stick to the walls on the way up only to leak back down as it is liquid and not vaporized fuel.

Only in a serious over-rich situation will the excess fuel stall the engine.

Do be sure you have a good spark too.

ANY CARB MOUNTED WITH A POSSIBLE GRAVITY FEED SHOULD HAVE A FUEL SHUTOFF VALVE FOR SAFETY!!!!!!!!!!!!!!! A good place to mount the valve is on the fuel pressure gage in front of the carb.

Yes an updraft carb can flood an engine!!

Dave Neptune
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  #3   IP: 97.93.70.7
Old 09-26-2019, 10:20 AM
Dave Neptune Dave Neptune is offline
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Part II, does your scavenge tube still function? IE is the tube "clear and free of obstruction" and are the fittings tight?

Dave Neptune
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Old 09-26-2019, 10:51 AM
ArtJ ArtJ is offline
 
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Thanks Dave apreciated


I have ordered a new shutoff valve today. the original is probably 50 years

I will install it to carb.
I will recheck scavenge tube connections

I was wondering about the choke being on. I will check more carefully
tomorrow. The only thing that threw me off was the quantity of fuel and the stains in the bilge Can the choke being on cause lots of fuel to be coming
out of the carb?

. It has run perfectly till yesterday
The carb is new and new filters in the spring,

Thanks Appreciated
Art
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  #5   IP: 97.93.70.7
Old 09-26-2019, 10:57 AM
Dave Neptune Dave Neptune is offline
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Art, if the choke is on it will draw an excess of fuel that is not very atomized into the throat and a lot of it will stick to the sides only to "run down" the throat and out. It is the scavenge tube that reroutes (sucks) that fuel back into the intake manifold. If there is to much fuel the engine will flood!

Do a visual check of the choke by removing the flame arrestor.

Dave Neptune
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Old 09-26-2019, 11:04 AM
ArtJ ArtJ is offline
 
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Smile

Thanks Dave

The choke is normally spring loaded to be open I believe, but I will
check to be sure.

Much appreciated

Art
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  #7   IP: 97.93.70.7
Old 09-26-2019, 11:42 AM
Dave Neptune Dave Neptune is offline
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The choke is probably a manual cable control and not automatic. What kind of carb?

Dave Neptune
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  #8   IP: 24.61.95.61
Old 09-26-2019, 11:57 AM
ArtJ ArtJ is offline
 
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It is a manual choke. It is a zenith late model carb brand new this
spring bought here at mmi. The clamp holding the choke cable
has been making the choke tighter than before to operate last year

I need to check this tomorrow at the boat
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  #9   IP: 32.211.28.40
Old 09-26-2019, 01:06 PM
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Al Schober Al Schober is offline
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Sounds to me like the float valve in the carb. It's supposed to shut off the fuel flow when the bowl is full. Sounds like it has a piece of grit in it that's keeping it from closing. New Carb? Then it's new grit!
I spent a few weeks (months?) one summer tracking down a similar problem. Turns out the fuel filter between the pump and the carb was corroding internally, sending rusticles into the float valve!
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Old 09-26-2019, 01:49 PM
ArtJ ArtJ is offline
 
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Thanks Al

I was tired yesterday doing some mounting of hardware and didn't go too deeply into the problem when discovered.

My initial thoughs were choke and float stuck

But was mislead by the engine shutting down like when the choke is left on too long. I believed (incorrectly?) that if the carb is over filling it was
impossible to flood the carb.

Can I try tapping the carb if stuck float or what other remedies?

The carb is difficult to remove due to very tight area I have the
scratches to prove it

I also must check the choke better as per Dave N.

Thanks

Art
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  #11   IP: 32.211.28.40
Old 09-26-2019, 04:09 PM
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Al Schober Al Schober is offline
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Tapping the carb costs you nothing - well, if you don't hit it too hard.
How old are your filters? Does a magnet stick to them?
If you have smutz coming down your fuel lines, it's going to keep coming.
I don't think the choke is the issue.
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Old 09-26-2019, 07:01 PM
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Thanks for the input

I will start by banging the carb slightly

The filters are new in may
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Old 09-26-2019, 07:20 PM
Dave Neptune Dave Neptune is offline
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Art, a good practice is to not re-use a fuel line "end" as pulling them off of a barb often tears the inside a bit. And these bits often get stuck in the carb especially the needle & seat.

It is a good practice and not really expensive to just put on new lines to keep everything neat and clean. I would usually install my fuel lines a few inches to long then cut them off. After cutting I would have a "fresh" end to deal with.

I'd install a pressure gage while at it. Can really aid in diagnostics.

Dave Neptune
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  #14   IP: 108.34.253.10
Old 09-26-2019, 08:20 PM
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Hello Artj.

As a fellow Tartan 34 owner, one of your comments got my attention, namely, that the carb is difficult to remove due to the very tight engine compartment.

I agree that there isn’t much room between the carb and the battery compartment. But in my experience at least, the main “knuckle scratcher” is detaching the scavenge tube. The fuel line, throttle, and choke cables are more accessible. My recollection is that it helps to remove the flame arrestor before moving the carb down and forward.

Of course, if you have an oil or fuel filter mounted across from the carb, access would be worse.

best regards,

Jack
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Old 09-26-2019, 11:16 PM
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romantic comedy romantic comedy is offline
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I find that the carb is easy to remove on my T34.

Sounds like a stuck open float valve.

Why did you get a new carb? This is often a big clue.

Also the choke cable may need to be lubed.

Last edited by romantic comedy; 09-26-2019 at 11:21 PM.
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Old 09-27-2019, 07:40 AM
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Thanks for the new posts guys

I will keep in mind all suggestions

BTW my carb is extra hard to reach because of FWC, Oil filter and cables for
4 batteries and Oil cooler


Best Regards to all

Art
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Old 09-27-2019, 11:54 AM
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If you can reroute some of those items that restrict access to the carb, your life will be easier, because carburetor removal is a common task with these engines. I had an oil filter once but removed it, and never saw the need for an oil cooler. I just change oil every 50 hours. Make sure your scavenge tube is tight. Float valve inspection is in your future. Check floats for leaks. Moyer's carburetor rebuild kit includes a small pointed wooden dowel for dressing the float valve seat. You may be able to make one without buying the whole $100 kit. (Buy the kit anyway) It is a hardwood dowel 3/16", tapering down to a point in 5/16". A pencil sharpener might produce the right taper, I don't know, but it is a similar angle. It should match the point on the valve needle. But dressing the seat won't solve the problem of junk in the fuel. New filters and a fuel pressure gauge would be good.
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Old 09-27-2019, 09:55 PM
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Quote:
Originally Posted by Dave Neptune View Post
Art, a good practice is to not re-use a fuel line "end" as pulling them off of a barb often tears the inside a bit. And these bits often get stuck in the carb especially the needle & seat.
I prefer to use flare fittings for fuel lines that require frequent disassembly such as at the carb inlet.
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  #19   IP: 24.61.95.61
Old 09-28-2019, 09:24 PM
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Carb fixed

On Reviewing Don's short video in carburetor troubleshooting,
The number one most common issue is a stuck float.
Don's first solution is to remove the main passage plug and flush with
fresh fuel by using the priming bulb or the electric fuel pump
bypassing the oil pressure shutoff valve, which i did by use of a jumper
clips from the lead on the pump to the battery terminal on
the starter and let it run for 20 seconds for a good flushout.
This had immediate results and the engine started immediately
and smoothly wit no fuel dripping from the carb barrel.

Cautions I shut the main power switch off before adding jumpers and again'before removing- don't want a spark to occur wit fuel vapors.
I also cleaned up the bilge thoroughly before starting the engine
and ran the blower until i was certain no vapors were present.

Kuddos to Don Moyer tips!
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Old 09-29-2019, 02:37 PM
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Glad the fix was an easy carb flush to unstick the float valve, for now. No carb removal required. Don's videos are worth every penny. The question remains why did the float valve stick?
This is another reason why I am keeping my mechanical fuel pump. You can manually flush the float valve briefly without electricity, before starting. No danger of sparks in fuel vapor as when bypassing the OPSS with the power switch on, a situation you wisely avoided. Also, no fumes or spills are created trying to direct fuel into a jar from the main passage, although that is a good way to look for fuel problems. You didn't report any particles in the gas you pumped through the carb for 20 seconds, so that's good.
Using the hand bail underneath the mechanical pump forces gas past the float valve until the floats rise to close it. I like to pressurize the fuel line this way before starting, as it starts with less cranking. This acts as a priming bulb, but is USCG approved. You can hear the gas squirting through the float valve until the bail has no resistance and the fuel pressure gauge goes up. I believe this flushes the valve and helps keep it from sticking. That, and the use of MMO in non-ethanol fuel. IMO, the MMO keeps the rubber tip of the float valve needle lubricated, and non-ethanol fuel doesn't degrade the rubber.
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Old 09-29-2019, 10:01 PM
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Come on guys - the problem is NOT a stuck float. It's smutz in the float valve seat. When you remove the main passage plug, the bowl drains and the valve opens fully. When you hit it with fuel, the smutz is flushed out of the valve seat (usually) then the valve will work again.
I have heard of floats that develop pin hole leaks, get gas in the float, then won't close the valve. But I've never seen one.
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Old 09-30-2019, 12:42 PM
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Quote:
Originally Posted by Al Schober View Post
...I have heard of floats that develop pin hole leaks, get gas in the float, then won't close the valve. But I've never seen one.
I have. The right side chamber is half full of gas and sloshed when shook next to the ear. The float is balanced on the screwdriver edge, and you can see that the balance point is way off-center to the right.
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