bertram31.com

Greetings to all the Faithful:
After 3 or 4 years of following your posts, and absorbing a lot of great tips and useful information, I am finally, with some help from Capt. Patrick, able to join in.

My name is Bill, and for the past 27 years I have been happily owned by a 1979 28 Flybridge Cruiser ( I tell outsiders I own the boat, but I believe that you will understand what I mean). During that time I have had just about every part of the boat apart in order to replace, refurbish or update her. During the winter of 2012-13 I completed the biggest project of all, pulling the original engines, refurbishing the engine compartment, updating the wiring and instrumentation and repowering with 5.7 GM Vortec engines.

This year, with 50 hours on the clocks, I have developed a problem with the starboard engine that has me stumped, and I welcome any suggestions or thoughts as to the cause. It seems pretty simple: both engines start immediately, idle fine and run smoothly up to about 1500 rpm. As I continue to accelerate the starboard engine starts to slightly vary rpm. It is pretty subtle at this point: for example, if I set the throttle at 1800 rpm it will drift in and out of synch by 50 rpm or so. At 2000-2200 rpm it hits a flat spot: it does not want to take the gas, not missing, not stumbling, just not speeding up.

If I push the throttle past this point it will go to cruising speed, but will not hold a steady rpm. It does not stumble or vary like it is starving for fuel; rather it is a momentary drop and immediate return to the former throttle setting. The best description I can give is it like the ignition switch was opened, then closed again, faster than any human fingers could move it. My normal cruise range is from 2800 to 3200 rpm; it does the same drop across that range, but it seems to lessen as the rpm increases. At 3400 I don't see any rpm drop at all. My gut says this is not a fuel problem; how could it starve for fuel at 2200 rpm, yet not miss a beat at 3500?

I think I have addressed all the usual suspects: fuel filters changed, spark plugs replaced (all seem to be firing fine), ignition module changed. Engines have Delco Voyager ignition systems: base timing set at 8 degrees, full advance 26 degrees at 2500 rpm. New fuel lines from tank to carbs, common fuel pickup for both engines in tank, new carter electric fuel pumps set at 7 psi. Carbs are Edelbrock model 1409. What am I missing here?

Bill,

I'd put money on your problem being somewhere between your throttle and the carb... All of your symptoms sound like a cable, throttle, or linkage problem. Check to make sure that all mechanical linkage between the throttle and carb are operating smoothly and at full throw, both in and out. Make sure that nothing mechanical is slipping or sticking. Check the return spring on the carb linkage for wear or weakness. Make sure that the cable is secure, no sharp bends, and that the cable jacket is secured along the path between carb and throttle. The cable jacket must be secured by tie wraps in at least two or more places along the run...

Bill

Welcome

It does sound like the throttles are drifting some how. If you can, when you run her, if someone can open the engine hatch and watch the throttle on the carb to see if it moves.

I'm gonna put my money on the carb.

At the intermediate speeds you are relying on the primarys and I suspect it may be sarving for fuel.

But when you hit the high RPM the secondarys are open and providing ample fuel.

I have never been a fan of Additives or Potions to "Fix" problems but recently I have had to eat my words. I would run the fuel tank down low and then add SEA FOAM to the fuel and take her for a spin around the harbor.

From there you can swap carbs from one engine to the other and see if the problem followed the carb.......if it does and the Sea Foam does not do the trick......get the carb rebuilt.

Welcome to our SANDBOX Bill

Keep us posted

I say a carb problem. Possibly water, dirt or sludge in bowl slopping around and partially clogging jets. Or maybe a weak accererator pump

Thank you everyone. I will check the cable for any slop. I checked the filters for water, none present. The corrosive ethanol they force us to use here in NY stripped every particle of dirt from the fuel system years ago (along with melting the bowls on my original Racors, dissolving the insides of the original fuel pumps and turning the fuel hoses into mush--but that is another story . . .).
The next step, I think, will be to switch the carbs.
I am most concerned about the momentary rpm drop at cruise--you can feel the boat give a little jerk every time it happens, and I worry about the strain it might put on the engine and drive train.

Thanks again for the input.

When you changed the spark plugs.......did you make sure to use the correct heat range plug for your engine???

hb

Michael wrote:I say a carb problem. Possibly water, dirt or sludge in bowl slopping around and partially clogging jets. Or maybe a weak accererator pump

This is where I'd start looking. You said filters are clean...could be. Could still get dirt and water in bowls on some carbs. Only takes a drop of water or speck of dirt for those systems. Starving for fuel till secondaries open, but once they do your off.

Accelerator pump is a quick check, give it a pump or two.



Welcome aboard, to bad you decided to wait till you had a problem to join us. But better late then never!

Carl

Just wanted to post a quick update. I checked the throttle cable; properly secured all along its' length, no slop or movement at the carb. The accelerator pump is working; however, on this carb it is adjustable: on the actuating arm there are three different holes the linkage can go into, thereby changing the stroke and amount of fuel delivered. It was set on the innermost hole; I moved it to the middle, went for a ride and lo and behold the hesitation on acceleration is almost completely gone, so it looks like fuel supply is the issue.
When I changed the plugs (gap set to .045) I noted that after 50 hours the insulators were still white, indicating (I think) running lean. I never worked on Edelbrock carbs before, but it seems that this model was designed for use on high performance cars: it is designed so that jets and metering rods can be easily changed without removing the carb, and it comes with detailed instructions on how to calibrate different jet/metering rod combinations. So I think I am going to try going one or two steps richer on the primary jets.

Thanks again for the help. This site is the best!

Tooeez wrote:Just wanted to post a quick update. I checked the throttle cable; properly secured all along its' length, no slop or movement at the carb. The accelerator pump is working; however, on this carb it is adjustable: on the actuating arm there are three different holes the linkage can go into, thereby changing the stroke and amount of fuel delivered. It was set on the innermost hole; I moved it to the middle, went for a ride and lo and behold the hesitation on acceleration is almost completely gone, so it looks like fuel supply is the issue.
When I changed the plugs (gap set to .045) I noted that after 50 hours the insulators were still white, indicating (I think) running lean. I never worked on Edelbrock carbs before, but it seems that this model was designed for use on high performance cars: it is designed so that jets and metering rods can be easily changed without removing the carb, and it comes with detailed instructions on how to calibrate different jet/metering rod combinations. So I think I am going to try going one or two steps richer on the primary jets.

Thanks again for the help. This site is the best!

Carbs for cars and boats are different...

The part I consider most important is Marine carbs to not vent fuel outside the carb...not sure if it goes into the throat to the intake or what...all I know you do not want fuel venting/dripping/going into your bilge. Some parts may be SS and brass or whatever...but that is secondary to the Big Bang possibility. And of course a fine if the CG picks up on it or if you ever had a fire and your insurance company saw it was not a marine carb you can forget collecting.

The Edelbrocks are Carter AFB clones. I you need a rebuild, Carbs Unlimited does a good job on them. They replace yours with a rebuilt one that has been test run and has a 6 month warranty.

http://www.carburetion.com/weber/weber.htm

Thanks, guys. These are marine versions, no vents or hose barb connections and CG compliant. I'll let you know how the jet change works out.

Tooeez wrote: These are marine versions, no vents or hose barb connections and CG compliant. I'll let you know how the jet change works out.

Just figured I'd pass on the info in case you didn't know....

After hanging out at the beach all weekend waiting for the new jets to arrive I ran into a friend back at the dock. During our conversation he mentioned that he had traced an intermittent fuel starvation problem to a sticky anti-sipion valve. I figured it was worth a look, so I pulled the starboard valve. It was free and clean, except for a small piece of aluminium--smaller than a grain of sand, on the tank side of the ball. It surely made no difference in the fuel flow, but the thought came to me that if that valve never opened enough to allow that tiny piece to pass how much of a restriction is it causing in the fuel flow? After the repower my fuel filters are even with the top of the tank, so I don't need the valves any more, so I took it out and went for a spin--engine came right up to speed, held steady rpm and never missed a beat. So today, life is good. Thanks again to everybody, and I look forward to my chance to help out someone else.

I am sure glad that you and your friend found that problem.....never in a life time would I have guessed that one! !

Good for you

hb

This problem showed me (once again) that you have to keep an open mind when presented with a puzzle. When I started I would have bet the farm it was electrical, because of the sharp way the rpm dropped and then returned to its' former setting. After the responses to the post I redirected my attention to the fuel system. It's great to be able to talk to experienced, knowledgeable people who understand what they are talking about and are willing to share their knowledge.