What could be wrong? (Updated 7.9.07)

Chromaflage · 07-01-2007, 06:42 PM

Saturday, while running out of Gari, the engine in my boat decided to not like to run at cruising speed - about 3200 RPM. It would run for a while, then the RPMs would drop and it would cough a little like it was fuel starved. I could only run it at about 1900 RPMs without it doing the same thing. What is perplexing is that only seemed to be a problem under load. While in neutral, I could run it up to 3000+ RPMs without a problem. But under load it wouldn't hold above 1800 or 1900. Here's what I plan to look for:

-check fuel/water separators
-check carb fuel filter
-check fuel tank vent for obstruction

I have a mechanical fuel pump and I suspect that it would either work or it won't. Any other ideas?

Thanks

CrF

Sea Jypzee · 07-01-2007, 07:13 PM

I'm no mechanic, but I have stayed at the Holiday Inn Express once. :grin:

On my prior boat, I had one engine that was cutting out periodically. Would run fine without a load as I recall, but when underway at cruise speed, the engine would cut out like what you describe.

After much investigation, a tune up, and carb rebuild, it turned out to be the fuel pick-up tube. There was a hairline crack in the thread of the tube that you couldn't even see easily...looked at it 3 times before we even found it.

Anyway, probably not likely to be your problem, but something to at least take a look at and is a cheap easy fix.

Quote:

Originally Posted by Chromaflage

Saturday, while running out of Gari, the engine in my boat decided to not like to run at cruising speed - about 3200 RPM. It would run for a while, then the RPMs would drop and it would cough a little like it was fuel starved. I could only run it at about 1900 RPMs without it doing the same thing. What is perplexing is that only seemed to be a problem under load. While in neutral, I could run it up to 3000+ RPMs without a problem. But under load it wouldn't hold above 1800 or 1900. Here's what I plan to look for:

-check fuel/water separators
-check carb fuel filter
-check fuel tank vent for obstruction

I have a mechanical fuel pump and I suspect that it would either work or it won't. Any other ideas?

Thanks

CrF

KeyWest · 07-01-2007, 07:15 PM

Over time, the fuel line could begin delaminating internally and restricting flow. Replacing any fuel hose might do the trick. I've seen this more than once.

Chromaflage · 07-01-2007, 07:22 PM

I just replaced all fuel lines - upgraded from B2 to A1 all around.

Metal Manipulator · 07-01-2007, 07:36 PM

Take it out for a test run. When you experiance the problem have a small bottle ready to squirt som fuel into the carborator if your engine speeds up you will know for sure that you have a fuel flow problem. Then you could put a gauge in the fuel line between the fuel pump and the carb to see if you have a bad fuel pump, doing this before it starts to lag. Then you can take a portable tank and bypass the boats fuel tank and determine if the fuel tank pickup has a problem. So many variables what do you do but search them out one at a time. I seem to have many of the problems and am becoming adept at finding them.

Grady252 · 07-01-2007, 07:56 PM

CMF I had the same thing happen on two different boats and it was the same thing both times.... When not under load it is using minimal fuel even at 3000 rpms....When you pump it up it is trying to suck large amounts of fuel and then it can't get the rpms...

Water in the fuel caused my problem on the first boat, and the second boat had rust in the steel fuel cell which caused the w/f separator to be plugged.....I had to change my filter a bunch......

The boat with water in the fuel, I had to empty the tank completely, and fill it back up and I added some heet to help get the water out.....

The second boat a new fuel tank was in order.....

I think you are on the right track. The only other time I had a similar symptom was from moisture under the cap of the mallory distributor with a pertronix kit..... Moisture will hold the RPMs down when under a load as well....

Good Luck!!

seasquid · 07-02-2007, 06:44 AM

Quote:

Originally Posted by Grady252

CMF I had the same thing happen on two different boats and it was the same thing both times.... When not under load it is using minimal fuel even at 3000 rpms....When you pump it up it is trying to suck large amounts of fuel and then it can't get the rpms...

Water in the fuel caused my problem on the first boat, and the second boat had rust in the steel fuel cell which caused the w/f separator to be plugged.....I had to change my filter a bunch......

The boat with water in the fuel, I had to empty the tank completely, and fill it back up and I added some heet to help get the water out.....

The second boat a new fuel tank was in order.....

I think you are on the right track. The only other time I had a similar symptom was from moisture under the cap of the mallory distributor with a pertronix kit..... Moisture will hold the RPMs down when under a load as well....

Good Luck!!

seasquid · 07-02-2007, 06:51 AM

Wow! This sounds like the EXACT same problem I have been having -- finally, yesterday it ran like it should.

Here is what I have found, among other non-related things. Moisture in the distributor. Same thing -- at the dock in idle or even in gear it runs terrific -- get that thing out in the ocean under load -- coughing, pinging, etc. I'm not sure where I'm picking up the moisture. Anyway, that is where I would look. Everybody was telling me a fuel flow issue, but that definitely was not it.

Also, when the boat was tuned up prior to the season, the mechanic put the wrong spark plugs in -- bigger issue than you would think. I wasn't even getting any spark off of one of them.

Anyway, that is where I would look. I have a Mercruiser 305.

I feel your frustration.

ss

HiTekRdNek · 07-02-2007, 07:30 AM

Kerry, I think WetFly and Grady 252 are on the right path.
I would look into the fuel system.
If you need some help gimme a PM.

Pilar · 07-02-2007, 07:52 AM

I get the condensation in the distributor too. Anytime I wash the motor some water vapor gets in the mallory distributor. Then when you run it later .. it's all good till the motor heats up and the water vaporizes and then condenses in the cap. If I think about it before the trip I'll use a hair dryer and take the cap off to blow hot air into the distributor base to dry it out.

Now I carry some Brakeleen and a rag. When it starts to bog we shut down and hose out the cap and dab up the solvent with a rag. After one or two of these no more problem till I wash the motor again.

My plan was to keep the new paint on the motor clean so it would last. And washing the motor everytime causes the water problem.

what to do?

TubeFly · 07-02-2007, 08:44 AM

I had a similar problem and mine turned out to be the fuel intake plug on the engine where the gas line connects, it had a tiny hairline crack. I found this out after replacing all the fuel lines etc.

Good luck-

Ryon

RatherBFishn · 07-02-2007, 12:02 PM

Lots of good advice, here is another possibility...
I had a similar problem once. After replacing everything (well almost) in the fuel line I still had a problem. It turned out to be crud in the bottom of the tank would get sucked up and plug the anti-siphon valve. The boat would often stop running for awhile and would then restart and idle fine. Apparantly, the debris would eventually fall back down and it would run fine until it got sucked up into the valve again. I had to drain the tank, remove and clean it. No problems since. Carbed Mercruiser 305. I ran the motor off a separate portable tank which helped to isolate the problem. Use Stabil or some other stabilizer to the fuel if you are going to store the boat for a few months. Fuel these days seems to varnish up pretty fast.

I have heard but cannot substantiate that an ignition coil can get hot and exhibit similiar behavior.

Good luck.

CATCH AND EAT · 07-02-2007, 12:26 PM

Kerry, I think the fuel system deal is the right track to look at. You might also check the coil, plug wires and plugs. Last year I had a complete tune up done on my old boat the Cindy Lou. Ran perfect at idle and up to about 2500 rpm and then it would miss and act like a fuel issue. Replaced all plug wires, plugs, coil, resistor AGAIN and what do you know. Perfect running motor.

Moral of the story? Even if it is new stuff it can be defective. Check the easy stuff bro. You might be surprised.

StickFish · 07-02-2007, 12:32 PM

When you stored you boat last year did you put in a fuel stabilizer?

Have you done any recent high altitude trolling with that boat? If so it might need som Sea foam treatment.

Could be carbon buildup

ron m · 07-02-2007, 12:41 PM

Good luck finding and fixing the problem, sounds like you've got a bunch of things to check now.
ron m

slabhunter · 07-02-2007, 12:57 PM

Good advice above.
I'll second checking the tank pickup for a partial blockage.
Good luck!

Chromaflage · 07-09-2007, 10:02 AM

Problem Solved!

After reading all of the advice here and speaking with a couple different mechanics, what I was experiencing was a fuel issue. Just in case, I pulled and examined spark plugs, checked the cap and rotor and traced electrical. All electrical equipment was in excellent condition. Then on to fuel.

I pulled and dumped both of my fuel/water separators - whew!! No water. That left only a couple options - a partial restriction somewhere. So I pulled and replaced the filter cartridge that is in the carb. The old one was about 15% restricted with some deposits. It still didn't seem to be enough to cause my problems. Then I noticed I actually had two fuel lines running from the fuel pump to the carb. One was the main fuel line that is threaded into the carb where the filter element is. The second one perplexed me. It was attached to a nipple on the carb that looked like it went right into the secondaries. Upon further examination, I noticed that it actually fed into the accelerator pump (leave it to Rochester). So I pulled the line off the carb to discover that it was completely clogged. I flushed the line, and removed and cleaned the nipple.

After all this, we did a shakedown on the CR from Chinook Landing to Rooster Rock. No problems. Last Saturday, we ran and motored around Yaquina Bay for several hours - no problem. Sunday, we ran 12 miles out for Coho. No problems. I believe that the unclogging the line to the accelerator pump solved the problem. Now, I'm working on prevention. There is no filter between the fuel pump and the connection to the carb. So I'm wondering if adding and in-line filter would be too restrictive?

Anyway, thanks to all who replied! I appreciate the input. I do believe I can be ready for another TUNA! run on pretty short notice.

CrF

Chesapeake · 07-09-2007, 10:17 AM

I would add one of the high flow inline glass tube type filters, but I'm not sure they are recomended for marine use.

I use them on my Toyotas and they are very nice. They have a simple plastic screen type element that can be easily cleaned or replaced, and just a quick look will tell you if it needs maintenance.

They look like this (but not so flashy):

HOGGEMIN · 07-09-2007, 12:11 PM

If you go with the glass type filters check the ends periodically as they get loose on a rare occasion. My friend pulled into PIR for tech inspection with flames coming out from under the hood. But yue I would put in some sort of a high flow inline fuel filter.

Chromaflage · 07-09-2007, 12:19 PM

Sweet idea! Thanks!

fyshndad · 07-09-2007, 12:30 PM

I got one of those glass filters to put on my fuel line after the trouble I had last week
I always had them installed but when I got the Merc the dealer said I did not need one as the Merc has its own filter and had removed the one I had installed on the fuel line
Well.... let me just say this.....that Merc filter would require someone with fingers the size of an infants to check it.. nearly impossible to replace even if I could get it out
So the glass filter is going inline right after the squeeze ball

Glad to see you are on the water again Kerry and great seeing you at the OTC

Chromaflage · 07-09-2007, 12:32 PM

Quote:

Originally Posted by fyshndad

Glad to see you are on the water again Kerry and great seeing you at the OTC

Likewise, Hank!! And thanks again for the stickers!

CrF

Skipper · 07-09-2007, 12:50 PM

Hi Kerry,
Glad you solved yet another boat problem, and were able to get out fishing.

You can add to your signature
"Cobia Boat Problem Solver Extraordinaire"

Cheerio'
Skipper

Billfisher · 07-09-2007, 12:56 PM

Quote:

Originally Posted by Chromaflage

Likewise, Hank!! And thanks again for the stickers!

CrF

I'm glad you got this fixed! I had almost the same deal that Nancy did, carb rebuild, new fuel filters, etc. etc., and it was the screen on the inside of the fuel intake hose (in the tank.) Screen gone, problem solved! That was 3 TUNA! trips boogered up before it as fixed though! Now, go whack some fish!

-D

Chromaflage · 07-09-2007, 01:14 PM

If the boat name "almost perfect" wasn't already taken, I might rethink "Aqua Velvet."

In all seriousness, though, I am getting to know her pretty intimately.....and that's the upside. But, knock on fiberglass, we're ready to hit the TUNA! grounds at short notice. Come on SW winds

Quote:

Originally Posted by Skipper

Hi Kerry,
Glad you solved yet another boat problem, and were able to get out fishing.

You can add to your signature
"Cobia Boat Problem Solver Extraordinaire"

Cheerio'
Skipper

fishindude · 07-09-2007, 01:33 PM

thanks for sharing the experience. I bet this will help others with the same set up as yours. Glad to see you got it fixed. Really an inexpensive repair but very time consuming.

fishbait · 07-09-2007, 02:06 PM

Kerry,

Glad you finally got this one solved, and nothing wrong with some intimate knowledge now and then.

Orca · 07-09-2007, 03:45 PM

Chromaflage,

The second line on the fuel pump is the vent line. On a car, the body of the pump just vents out to the engine compartment. If the diaphram ruptures on the car, fuel spills out of the pump on to the ground, engine quits, and all is well. On the boat, they run the vent line back up to the carb and vent into the bowl. If the diaphram ruptures on the boat, then the fuel heads up to the carb bowl rather than into the bilge. If the bowl fills on the boat, then it overflows into the carb barrels and down the manifold.

If your vent was blocked the fuel pump was not vented correctly and not pumping enough fuel to run at higher RPM. You can get new pumps that are marine certified with dual diaphrams without vent tubes. I just bought one of these and will be doing away with vent tube on install.

Grady252 · 07-10-2007, 06:01 AM

CMF,
The vent is important part of the function, however, it is not common for them to get clogged. They usually don't have anything in them, they are simply a vent unless you're pump fails. If you replace the vent line it is likely that you will never experience this problem again.

Good Luck!!

Quote:

Originally Posted by Orca

Chromaflage,

The second line on the fuel pump is the vent line. On a car, the body of the pump just vents out to the engine compartment. If the diaphram ruptures on the car, fuel spills out of the pump on to the ground, engine quits, and all is well. On the boat, they run the vent line back up to the carb and vent into the bowl. If the diaphram ruptures on the boat, then the fuel heads up to the carb bowl rather than into the bilge. If the bowl fills on the boat, then it overflows into the carb barrels and down the manifold.

If your vent was blocked the fuel pump was not vented correctly and not pumping enough fuel to run at higher RPM. You can get new pumps that are marine certified with dual diaphrams without vent tubes. I just bought one of these and will be doing away with vent tube on install.