SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

Carb Problem?

10K views 44 replies 12 participants last post by  christian.hess 
#1 ·
As part of a separate transmission cable replacement issue, I decided to hire a mechanic to rebuild my gunked up carburetor. In hindsight, I wish I had done it myself, but that is another story.
The engine now fires up on the first crank, but it wants to rev up high, and there is a lot of blue smoke coming out of the exhaust. There is also what appears to be a gas slick forming on the water behind the exhaust. And it sounds like it is spark knocking.
The oil pressure is 40 psi. No water in the oil, and the level hasn't dropped. The plugs look ok, except for two that are a bit black and dry(I am assuming from having to run it for an extended time with the choke, from a gunked up carb?).
Now the cabin of the boat smells like gas, and there appears to be a gas-like residue on the OUTSIDE of the carb and underneath it. The mechanic swears that there is a valve or piston problem and that the gas slick is an oil slick, but I know for a fact that it wasn't smoking/knocking/slicking before the repair.
I would greatly appreciate any insight on this problem. I will be checking the compression on the next trip down to the boat.
 
#2 ·
burning rich, very rich. Float not set properly and idle/mixture not set properly. Don't waste your time on a compression check.

Be VERY careful with "the boat smells like gas" as vapors/fumes can cause problems.

Get it fixed, properly or do it yourself. At this point you would be better off ordering a new carb and replacing it yourself, than to give this person more money to "repair" what he has already broken. No more money for him, till it idles smoothly. He is not a mechanic.

While you may have a valve or piston problem, that is secondary to the carb getting repaired.
 
#4 ·
Rebuilding a carb is more like watchmaking than general mechanic work. And even carb shops seem to screw them up more often than not. A whole new carb can be expensive, but if you can get a "major overhaul kit" for the carb, that's often ~$100 and with a gallon of gumout and an afternoon of patience you can put it back in new condition.

The overhaul kit usually includes detailed instructions, Some drill bits of wire gauges and a small steel ruler to make adjustments precisely are required, nothing exotic. Some needles or fine brushes to clean out the passages, all easily procured. The hardest part is just being patient and methodical. Take the phone off the hook, use some boxes or bags so the small parts can't run away, and take pix with a cell phone or digicam if there's any doubt about how a stack of things go together.

When it is done, if everything is rosy again, you keelhaul the alleged mechanic.
 
#5 ·
Rebuilding a carb is more like watchmaking than general mechanic work. And even carb shops seem to screw them up more often than not. A whole new carb can be expensive, but if you can get a "major overhaul kit" for the carb, that's often ~$100 and with a gallon of gumout and an afternoon of patience you can put it back in new condition.

The overhaul kit usually includes detailed instructions, Some drill bits of wire gauges and a small steel ruler to make adjustments precisely are required, nothing exotic. Some needles or fine brushes to clean out the passages, all easily procured. The hardest part is just being patient and methodical. Take the phone off the hook, use some boxes or bags so the small parts can't run away, and take pix with a cell phone or digicam if there's any doubt about how a stack of things go together.

When it is done, if everything is rosy again, you keelhaul the alleged mechanic.
Good points. I have been successful at doing what you described many times.
Had I known the Evinrude carb was $400 I would have pulled the old carb & brought it home with me for a try. But, due to distance & logistics, I just bit the bullet & ordered a new one.

You really don't have much to lose by trying a re-build/cleaning first, except you won't know if it worked until you re-install & test it, which takes time.
A new carb should work properly right out of the box, needing only low speed mixture & idle speed adjustment, as compared to a couple of hours "cleaning" it.

I like to lay out the parts, "up" side up, in sequence from left to right, in order of dis-assembly, on a large, clean towel to be reversed on assembly. Even if you have a good parts diagram or a good shop manual, good, close up digital pictures would be a big help. Suggest you "go slow" & be gentle. Some carbs have small spring loaded "check balls" most difficult if they spring out onto the floor. :D

Paul T
 
#6 ·
How could the machanic suggest that there is anything wrong with the carb, other that what he just did to it? It ran OK before, and crappy after. My best (very uneducated) guess is that it is the float. If you take the carb off (easy), and split it in two (easy), the only thing that may fly out is the float and float pin. The pin should have a rubber pointed end that seats into a hole. The hole needs to be free of crap. Also, as most A4 posts mention at some point, see moyer marine site.
 
#7 ·
"The hole needs to be free of crap. " And the pin needs to be "perfect" as well. If someone smashed up the tip (often "rubber") it usually needs a new one, which would be included in most overhaul kits. Or if the guy reamed out the hole with something too sharp, and it has been enlarged too much...that could ruin a carb and make it run rich forever.

You know boat projects, it rarely is over when you thought it would be.

Carbs are one reason that fuel-injected diesel engines became popular. (Until the owners get intimate with diesel and injection problems, anyway.(G)
 
#8 ·
As a marine mechanic I would hazard that the mechanic you hired didn't either set the float correctly or didn't set the needles correctly the choke is sticking or some combination of all the above the problem is not due to the valves or pistons. M2cw
 
#9 ·
Blue smoke indicates oil. Running fast is idle adjustment or vacuum leak. A float set extremely low can cause fast idle but not smoke too. I would also suggest, from your description, you have other issues. Is the base gasket on correctly, vacuum connections, breather?
 
#13 ·
I have taken the Zenith updraft carb apart several times for cleaning etc. It is quite easy to do - yourself. It is also quite easy to put the float pin in upside down - which will cause the symptoms the OP is experiencing - gas smell, dripping carb. Obviously I have done this.
A fuel tank with a lot of ethanol crud in it will also wreak havoc on the float needle, causing it to get stuck in the open or closed position.
There is an old expression: "If you want something done right you will have to do it yourself."
 
#14 ·
"A fuel tank with a lot of ethanol crud in it will also wreak havoc"

Any crud will do.

But the most important point is probably that if you can SMELL gasoline, there's probably a fire danger.

1. Call insurance broker, make sure boat is overinsured.
2. Buy marshmallows and sticks.
3. Attempt to repair engine. Using bronze, brass, or beryllium-copper non-sparking tools.

Stick to the sequence and you'll be happy whatever the outcome is.(G)
 
#15 ·
How about:

1.Opening every hatch, port, or other opening you can

2. Turn off the gas at the tank

3. Sop up any gas that is visible

4. Disconnect from shore power

5. Go have a long lunch

6. Remove carb & take it home to clean in a well ventilated garage

As others have mentioned, if you can smell gas, heap big trouble. :(

Paul T
 
#16 ·
I went down again this weekend. The smell in the boat wasn't quite as bad, but when the bilge pump kicked on there was more residue on top of the water when it exited the boat. I know now that shutting the gas petcock should be done after each trip. I traced every line and every connection, looking for a leak. I am in agreement with you folks that there is a float problem. I did not start the engine. The carb had some wet residue on it, so I cleaned it up and also the area underneath it. I left a clean white paper towel. If that thing is stained next weekend, then that HAS to be it. Either way, I know I need to pull the carb.

ALSO, the mechanic failed to seat the choke cable bracket correctly. Not sure if this has anything to do with it, but I thought I would mention it.

Thanks again for your advice.
 
#17 · (Edited)
#18 ·
First, not all "professionals" are experts, or conscientious . I am not even close to being an expert on anything. Fortunately, my Dad started teaching me how to work on engines about 68 years ago. I don't know what your mechanical experience level is so forgive me if I am speaking out of turn.

I would imagine that Community Colleges, or something similar, offer small engine maintenance courses? That & a good shop manual or equivalent, can take you far. It is my opinion that the more work you can do yourself, with some limitations, the better off you are. Carburetors & distributors are generally fairly simple. However, a diesel high pressure injector pump is not. Older gas engines are relatively simple & easy to work on, in my opinion.

Paul T
 
#19 ·
Newhaul-
"find a mechanic you can trust."
Reminds me of something Benjamin Franklin said, that any three men can keep a secret as long as two of them are dead. So any dead mechanic should be trustworthy, although, I'd still have reservations about some of them.

Paul-
I don't think you'd find engine courses in Community Colleges. In high school trade programs, yes. In "Trade Schools", yes. And some adult ed classes, like the New York State BOCES programs. But with a lot of the trade schools, the problem is that they are "student loan" mills, set up to take in anyone who is interested, get them signed up for government student loans, and then no one really pays a lot of attention to anything beyond getting those loan dollars. Sad to say, but a long-term racket. Asking a local car dealer's shop manager might get you a local referral, if there was one.
A good manual, and some you-tube videos, might be just as reliable a way to start.
 
#20 ·
Newhaul-
"find a mechanic you can trust."
Reminds me of something Benjamin Franklin said, that any three men can keep a secret as long as two of them are dead. So any dead mechanic should be trustworthy, although, I'd still have reservations about some of them.
Paul-
I don't think you'd find engine courses in Community Colleges. In high school trade programs, yes. In "Trade Schools", yes. And some adult ed classes, like the New York State BOCES programs.
Just a guess. I took night courses in welding at the local high school shop. If the OP does a search, he can probably find a course. If he has basic mechanical knowledge & basic tool skills & a good shop manual, he should be OK.

But with a lot of the trade schools, the problem is that they are "student loan" mills, set up to take in anyone who is interested, get them signed up for government student loans, and then no one really pays a lot of attention to anything beyond getting those loan dollars. Sad to say, but a long-term racket.
Interesting, I didn't know that

Asking a local car dealer's shop manager might get you a local referral, if there was one.
A good manual, and some you-tube videos, might be just as reliable a way to start.
I forgot about you tube, right, I have seen some of those, like how to time a VW diesel, something I have done many times. Brought back some memories.
It is absolutely amazing what you can find on the internet.

Paul T
 
#24 ·
Pulled the carb this weekend. Was easier than I thought.
More gas found under it again. This time I left absorbent pads and sealed off everything, just in case the local insects were looking for a nice nesting spot.

Going to take it apart. Thanks again to all for your advice. The one thing I can't understand is why is it running rich while ALSO having a leak? Could a high float level cause leaking?
 
#25 ·
Running rich implies too much fuel which is consistent with your carb dripping gasoline. It is leaking because there is too much fuel.
Yes, it is probably the float valve/needle that needs re-thinking.
I'd get the carb rebuild kit from Moyer (new gasket, jets, float needle etc).
 
#27 ·
If you are shutting off the gas at the tank, the leak may be from a loose fitting or a crack in the carb body, assuming the tank is higher than the carb. If the tank is higher & the fuel
is left on, & the float is set too high, or not closing, the leak could be from the float?

Paul T
 
#28 ·
Update: took the carb apart and examined it closely. The float was indeed functioning. I also pushed the float down in a cup of water to see if it had any leaks. No leaks. Put it back together and installed it.
The engine fires up, runs steady (no more knocking), but still smokes. There is also what still appears to be some oily residue on top of the water from the exhaust. The oil pressure was steady at 40 psi. Oil level the same- not drinking oil. Set the mixture screw to one and half turns out. Tried turning it in half a turn and also the other way a half a turn. Doesn't stop the smoking/oily residue. I can't figure it out. Left absorbent pads under the carb. Going to see if it is still leaking on the next trip.
I guess checking the combustion is the next step. The only other thing I can think of is the Marvel Mystery Oil that is in the gas. I add a few ounces per gallon.
 
#29 ·
I used to run all my 2 strokes at 50:1, which is about 2-1/2 ounces per gallon. Looks like you are running about the same ratio in a 4 stroke, which could be the reason for the smoking. If you can run a separate tank, an outboard tank, perhaps, without the oil, & after a while the smoking stops, there is your cause.

Not sure about the leak, but it is evident because the oil in the fuel doesn't evaporate, like the gas does.

Paul T
 
#30 ·
I generally don't believe in magic elixirs, my faerie godmother told me they are all worthless. But I must confess that I've only heard good things about MMO, from people who have had, ah, intimate relationships with engines. Even in that context, I'd also say run that fuel out, or switch your fuel supply to a smaller "just gasoline" mix to see how it runs. Is there a chance you misread or miscalculated, and added way too much MMO?

I knew someone who misread and added 1/4 cup instead of 1/4 tablespoon of vinegar in a chocolate cake mix. Um, yummy. (Not!)
 
#31 ·
Yes, it is like cooking with wine- very easy to add too much!
Thanks for the tips, not giving up on this thing yet.
Would it be safe to disconnect the fuel line from one side of the engine side of the Racor filter and put the fuel hose down into a 2 gallon gas tank? I could plug the Racor and move the gas tank into the cockpit, away from any possible sparks.
 
#32 ·
Not quite sure if I am following your layout? However, I think if you shut the fuel off at the tank, disconnect, & drain the hose from the inlet side of the filter, & replace it with the hose from the outboard tank, which could be in the cockpit, hose length allowing, you should be OK?

Or, you could drain your onboard tank & re-fill with straight gas?

Paul T
 
#33 ·
One final update- something told me to try pulling the carb one more time. Downloaded the carburetor video from the Moyer site, which actually addresses quite a few frequent issues. Removed the float valve seat and blew on it by mouth. Also used a sharpened dowel to clean out any tiny grit. Something must have worked right because she ran much better this time. No blue smoke and no residue on the water. After about one minute, however, a bunch of RUST came out of the exhaust, and then water stopped coming out.
Blockage in the exhaust or somewhere in the cooling system?
 
#36 · (Edited)
.............. After about one minute, however, a bunch of RUST came out of the exhaust, and then water stopped coming out.
Blockage in the exhaust or somewhere in the cooling system?
Slab Rust !!!!!
Very common on marine exhaust manifolds, especially on engines that are drained of cooling water when seasonally or long term stored on the hard.
What happens is that as the cast iron rusts it penetrates deeper into the casting exposing the 'stratifications' of the casting when it was made. Such flakes can easily block the outlet of the manifold causing overheat problems that mysterious go away when the engine is shut down (and the slabs fall back to the bottom of the insides of the casting).
Rx. - Remove the exhaust manifold, and get inside the manifold with a stiff wire and break loose the loose 'slabs'. DO NOT use any non-inhibited acid to clean out this manifold EVER again - only inhibited boiler descaling compounds such as RydLyme, etc. if there is significant 'fouling'.
Once you shake and blow out all the loose and broken up slabs from the inside of the manifold, perform a 'pressure hold' test on the manifold to validate that the manifold does not have a pin hole leak between the gas side and the water side of the manifold. Put a temporary 'cap' on one of the water 'nozzles' on the manifold to totally block flow, apply a pressure gage to the water hose that you will apply and connect to the 'other' nozzle and apply 30-40 psi pressure, shut off the valve to the hose and watch the pressure on the gage to 'hold steady' for 15-30 minutes .... and with NO water coming out of any of the gas passages.

To prevent slab rust, always use an antifreeze with 'rust inhibitors' when laying up the engine for long periods of time; AND, whenever possible always run the engine for long periods of time (such will form a 'protective' BLACK form of rust ... in the engine and in the manifold).
These manifolds are no longer easily or commonly available, so take care of what you have: run the hell out of the engine and always add antifreeze with rust inhibitors when long term storing the engine.

BTW the carburetors on such engines have whats known as an emulsion tube that meters the correct ratio of fuel/air. The emulsion tube are small brass tubes with a closed end and with quite a few holes in the sides of the tube. If you get 'any' dirt or debris in any one of those small 'side holes' in the emulsion tube the entire fuel/air mixture will radically change. ALWAYS inspect and clean the emulsion tube when suspecting air/fuel ratio problems - the main jet only controls fuel flow TO the emulsion tube. (You can convert these 'fixed' jet carbs to adjustable needle valve control to extend the time needed for routine emulsion tube 'maintenance and cleaning'). Best is to keep small 'dirt' out the carb in the first place by applying a precise 10µM 'filter' between the fuel pump and the carb ... even if you already have Racors, etc. in the fuel delivery system.

hope this helps
 
#34 ·
yes...I would not run the engine

take off manifolds...descale and clean exhaust ports well also clean all your water flow passages

you are deifinitely gunked up...the blue smoke could of been from overheating every time you got restricted flow in the system
 
#37 · (Edited)
WORD

a tip on emulsion tubes is to remove them and soak them in a cleaning solution

to not attempt to use dowels or sharp objects or anything that is harder than brass

not only will you damage them physically you will damage flow and precise metering not unlike a jet or in EFI the tip of the injector

do not use 3m pads either as they score the tubes and again mess with flow

I have always had GREAT results by either buying deep claen carb cleaner solution or boiling all brass and or metal or die cast parts in pinesol then let sit overnight

you can also invest in ultrasonic cleaning

what rich says is spot on...

you scale and slab rust as he calls it is what I was reffering to. its also very possible again that your blue smoke was heat related and not even close to being carb related

for the most part blue smoke can always be associated with overheating and bad piston rings aka "oi burningl" in engines with valve stem seals this first...

again caused by overheating or drying up of the seals.

the common black smoke I have found on a4s is mostlt from bad timing using the points systems...basically owners dont adjust as frequently as they should per the manual. best bet is to go electronic if you havent already done so

you need a ballast resistor on some conversions.

on the a4 you will have best luck fixing your engine by taking off manifolds, and cleaning all passages once water flow is restored to stock or better and water pump is working correctly AND exhaust system is clear you are good to go on carb work

number 1 rule on engine diagnosing is to fix ONE THING AT A TIME. that way you can pinpoint fault and check improvements in gradual steps.

this is ESPECIALLY TRUE of carb work and TUNING.

the good news is the a4 carb is so damn simple.
 
  • Like
Reactions: RichH
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top