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Carb problems still

C

captal

Contributing Member
"After the Edelbrock vs. Quadr

"After the Edelbrock vs. Quadrajet posts earlier, I changed out the poorly running/flooding Qjet with a new Edelbrock 1409. Of course all the adjacent stuff- breakerless ignition module, rotor, coil, plugs, I changed earlier when I was having problems with the Qjet. ANYWAY put on the new 1409 and fired the engine up. Took a few minutes for it to clean up but started running much better. Set the idle to about 800 RPM. All seemed pretty good. Went to adjust the mixture screws and ran into almost the same problem I had with the Qjet. I can run the screws all the way in and the motor idle doesn't change???? I ran the boat down the river and it seemed to do pretty well. Just to recap the set-up, I have twin 1989 270hp 350ci Crusaders FWC in a 29' Luhrs. I'm actually taking a few days off this weekend before I pull out what hair I have left. Any of you gurus have any ideas? I figured a new card shouldn't be leaking fuel from anywhere to bypass the mixture screws and let the engine still run. When I get back, I'm going to put on a vacumn gauge and do a few tests, do a full compression test, and check intensity of spark. Any other ides would be GREATLY appreciated! Thanks!!!!"
 
"Big Al:

I'd try it aga

"Big Al:

I'd try it again, but with the idle speed set between 550 and 600 rpm. The throttle plates need to be closed enough to ensure all the fuel is delivered via the mixture screws. If no improvement, hook up the vacuum gauge and see if the idle screws can control the vacuum to any extent.

If no difference still, get a fuel pressure gauge and make sure the fuel pressure at the inlet is less than 6 psi.

You didn't indicate any rich condition - gas smell readily detectable in the exhaust - make a note to check that, too."
 
"I was advised a while back to

"I was advised a while back to check things with a vacuum gauge and frankly, it is a nice tool to work with and they are not expensive. Pinpoints a great carb adjustment ..."
 
"OK back to the grind and back

"OK back to the grind and back to work on the boat. So to get everyone up to the current situation. Thanks guys, I did get a vacum gauge, lowered the idle speed, and got the ebrock tuned up. Did have needle wiggle at idle that smoothed out with just a little rpm. Crusader book says that might be worn valve guides but that is something I will work on later. Did have about 15in of vacum though.
So new glitch is, hate to start a new thread for this but, ran down the river fine. I'm happy basking in my mechanical accomplishments cruising along 30knots at 4000rpm. The starboard engine (the redheaded step child) spits, just about dies then runs right back up. Sounded more like an ignition problem to me than fuel. No other problem the rest of the trip. Next morning got back down to the boat and found about a quart of oil in the bilge and the motor low. Just a side note when I got the boat it was overfilled about 2 quarts. Looked all around the engine best I could anyway, and can find no apparent leaks. Going tomorrow with some lights and a mirror to see if I can find something. Any ideas from the gurus??? I know I probably need to crawl down in the bilge with the engine running to find the leak but not sure why the cough/die problem or if it might be related. Ahhh the joys of boat ownership. MERRY CHRISTMAS everyone!!}}"
 
"Ah, Big Al, running "down

"Ah, Big Al, running "down the river at 4,000 rpms" is really not a good idea! I know--people do it all the time. I hear them going up the river, their engines screaming alto at 4 grand and more. Yikes! (The piston speed of a SB Chevy at 4,000 rpms is frightful!)

If the motor was overfilled with oil--not good--it may have blown oil out of the breather or past the crank seals. Either way you're probably okay, but take it easy from now on. Okay?

On the sudden loss of power, that sounds like a classic case of water in the fuel or gas starvation (dirty filter, weak pump, filter BEFORE the fuel pump, etc.)

Good luck!

Jeff"
 
"BigAl:

I vote w/ Jeff - ch

"BigAl:

I vote w/ Jeff - change the fuel filters on your next visit. Check their contents to see if there is any water, too.

I'd suggest you find out why it was 2 qts too much. In addition to expelling the excess, it may cause the oil to foam. foamy oil is like air-entrained coolant - neither do their job very well."
 
"Wow great responses! First I

"Wow great responses! First I usually don't run down the river at 4000 rpm, usually about 2800-3200. Just was running up to see how the engines would perform. Still had a little throttle left though. I did take off 2 quarts of oil before the run so the level was correct. Oil looks good too, no sign of water or foam. The power failure I believe to be ignition related. There was a loud pop, like a backfire through the carb, loss of power almost to cut off, then right back up to running. Doesn't a fuel problem usually kinda' stumble then pick up or die off? Filters are new. Timing is set right on the money. Bob, thanks for the great timing info. I'm going to hook my gauge back up and compare. Gonna' do a little more investigating today and see if I can find out anymore info. Thanks guy!!!"
 
I would check the oil to assur

I would check the oil to assure that it has not been diluted with gasoline. Oil cannot grow but the volume can increase because of gasoline. A leaking mechanical fuel pump diaphram can cause it. There are other ways this can happen. If you have that much gasoline in the oil you should be able to smell it and the oil will likely be very dark. I know from experience that at 2 quarts too much oil the excess will leak into the bilge.

Chuck Hanson
 
If your old carb was leaking f

If your old carb was leaking fuel or running too rich that could be a source of fuel contamination of oil. If you have gas in the oil you need to change the oil before running the engine again. I have seen main bearings wiped out by gas diluted oil. I have heard of crankcase explosions that blew the oil pan and valve covers right off an engine. I just changed the upper intake (plastic) on a '96 chevy pickup that back fired and blew the intake to pieces.
 
"Chuck has a good point: IF yo

"Chuck has a good point: IF you have a mechanical fuel pump, and IF the diaphragm is leaking gas into the engine, that would explain both of your problems: A lean out will cause the backfire at speed, then be okay when you back off the gas.

Jeff"
 
"Just an idea but we had the s

"Just an idea but we had the same problem on a 454 from a mainship and blew an engine before we where able to find the problem, the oil was breaking down and caused bottom end to go. Fault was traced back this past fall to a bad fuel pump, the diafram inside the pump had a small tear and was leaking fuel back up into the carb, engine seemed to run fine but we never where able to adjust the air fuel mixture right. Once the pump had been replaced problem was solved and the air fuel screw worked! just an idea."
 
That's why newer fuel pump

That's why newer fuel pumps have three lines on them; one takes fuel leaking past a bad diaphragm to the carb instead of the oil pan. Good idea.

Jeff
 
"yes! and if the fuel pump has

"yes! and if the fuel pump has a small leak like us the line carries the fuel and dumps it back in the carb. we never got the adjustments right and in the end we where always running a little lean. After one season like that we popped, when the new engine was installed and the same problem started we called in a tech who pulled the line on the carb from the bottom of the fuel pump and fuel was running out, urika!"
 
"that's why the tygon tubi

"that's why the tygon tubing is installed; to permit frequent inspection.

the tygon is very tolerant of fuel, even with ethanol....unfortunately, it doesn't care for the heat of a marine engine installation. when it starts to harden up, get brown, and lose it's translucence, it's time for renewal."
 
"First give me the dunce award

"First give me the dunce award. Started checking out the oil in the bilge problem and found out it was just a film on top of the bilge water. Just looked like oil from up top. I think the original overfull problem was probably something the previous owner done, but that’s a whole other story.
So back to the backfire problem. Running along about 3000 rpm, got a backfire, loss of power almost to shutdown, then ran right back up. Motors been running fine since. Hate to get off shore and have the problem rear its ugly head. Good ideas above though. I do have new fuel filters but wouldn't a fuel filter or bad gas/water be a constant problem? I do have the tygon tube and it is clear. After the loss of power the engine has been running fine. I have a new ebrock carb and set the idle mixture with a vacuum gauge. The only lean adjustment would be to change jets. Again after the power loss, the engine has been running great. So do I quit worrying and just keep going till the problem comes back or does anyone have a theory??"
 
If all is good then go run it

If all is good then go run it and just keep an eye out for the problem. could have been a hiccup.
 
"just bought a silverton 4 wee

"just bought a silverton 4 weeks ago and 2 sea trials later, sign on the boat. finally got to strech her legs yesterday and had the same problem as Big Al with the loss of power and even lost the port engine and had to limp back in on 1 engine. i drained the main fuel line fuel/water separators and had a little debris, but no water. just found the engine fuel/water separator but havent removed it yet, nor the carb filter. engines purr at idle, and even at taxi. is there any test on the engines in the slip besides morring like crazy and not pulling the pilings out of the harbour? i really dont want to limp back in again.
thanks
bruce"
 
"Water in the gas does all kin

"Water in the gas does all kinds of weird things and, with "evil-nol" fuel, you'll get more water in the gas.

It appears that water doesn't separate out in the separators like it used to with the old gas. So, even though you drain the separators regularly--and don't see any water--it's still there and may be getting though to cause carb misfires.

The bottom line: Drain the separators regularly, change the filters more often, and keep fresh gas onboard. We ran a bunch of small refuelings of 20/ 30 gallons each this year instead of one big fill up. That seemed to help.

Jeff"
 
Bruce: When I first got my boa

Bruce: When I first got my boat had the identical problem. Idled in the slip but got out on the river engine would cough and shut down. Did all the fuel things and still had the problem. Found out I had a bad ignition coil that was breaking down under load. Easy to replace and usually under $20. Might help.
 
"Al,

I had a similar proble

"Al,

I had a similar problem and it turned out to be a dirty anti-syphon valve. Removed, cleaned, replaced valve and no problem since.

Erich"
 
"Erich, Where is the anti-syph

"Erich, Where is the anti-syphon valve? And I am going to do these other tests also. Thanks for all the good replies. Will update you all after new years.
HAPPY NEW YEAR!
talker.gif

Bruce"
 
"Anti Syphon will be near the

"Anti Syphon will be near the gas tank in most cases. Look for a canister type fitting near or on the shut off valve at the tank. However possible someone could have installed this some where along the way.

Some racor filters have antisyphon valve that is internal.

What about vacuum leaks? Intake manifold, fittings, Baseplate etc."
 
"The anti-siphon valve on my S

"The anti-siphon valve on my Silverton with '90 454 Crusaders is located at the top of the pickup tube on the fuel tank (see photo). I used one of those plumbers basin wrenches to remove it as there was little room between the top of the tank and the cockpit floor.

Erich
247565.jpg
anti-siphon valve
 
"a lot of the older anti-sipho

"a lot of the older anti-siphon fittings are integral with the pickup fitting. also seen some with the built-in hose barbs used at the pickup fittings. Usually, an easy way to ID the likely culprits are to llok for the aluminum fittings."
 
"Hey guys, I'm learning ab

"Hey guys, I'm learning about my new/used boat every minute. I found the anti-syphon valves and they are in good shape, maybe replaced recently, anyway the ball/spring is free of any obstruction, ie: travels freely when you shake it. I pulled the port carb and drained the fuel, engine mounted filter, carb filter, and in line filter. Now the fuel line is dry, meaning the fuel pump is not priming. The genset with electric pump is on the same fuel tank/line and it will not prime either. Is this vapor loc or does that have to do with the engine. How can I prime the fuel line. Line is approx. 20' with an additional 12' to the gen set.
uhoh.gif

Thanks-Bruce"
 
"shouldn't be any need to

"shouldn't be any need to prime the fuel line, the engine pump should pull the fuel fine. You can help by adding some fuel to the carb bowl, usually thru a vent tube. If you do this be VERY CAREFUL & CAUTIOUS. Keep the fuel containers off the boat, use the blower, clean up spills, etc.

If neither will prime, have you checked for any shutoff valves that are not open? If they are open, and neither will prime, there is an air leak somewhere - split or cracked hose maybe.

Only other thing that comes to mind is the pickup itself. sometimes the vertical tube will fatigue and fall off. quick check for that is to pressurize the fuel line, slightly, and listen at the tank for bubbling - no bubbling means the pickup tube isn't 'wet'. In this case, you can usually hear the air coming out of the vent."
 
"Here's a great applicatio

"Here's a great application for one of those "Migthy-Vacs". This little jewel is used, among a zillion other applications, for bleeding brakes. in this case, you'd hook it to the fuel line and pull a vacuum. Either fuel would come rushing out, no vacuum would be produced (air leak somewhere), or a vacuum would build (blocked line, shutoff valve closed, etc.)

Could you borrow one from an Auto Zone store or ??

Jeff"
 
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