5.7 GL bogging under load

[garbageguy]

I have not been able to locate a model or serial number on the block. It's a Volvo 5.7 GL in a 1998 24 ft Wellcraft 240se cruiser with Volvo outdrive. The engine is black (charcoal?).

When cold starting, it takes a couple times to stay running, not a big issue (I think). When it fires and catches, there's a very brief whine but runs smooth. After temp comes up, I reduce throttle and it will idle fine at about 650. Underway, it runs fine until hard throttle-up and when rpms get to about 3100, it will bog. Let off throttle and can cruise off-plane OK all day. With less load in boat (just me), can get it on plane by coaxing throttle up, then down, then up a bit. It will run on plane at about 3100 rpm, but if try more throttle it will bog. Thoughts?

 

[jimmbo]

Re: 5.7 GL bogging under load

How old is the gas in the tank? It sounds like you might have gummed up jets passages in the carb. Which carb does it have 2 barrel Holley, 4 Barrel Holley? A couple of years ago my 5.7 GL with 2bbl Holley would act up around 4100 rpm, it would surge, WOT was ok. The surge was caused by the main jets were partialy clogged and were running lean, WOT because the power valve would open and would pass enough fuel to prevent the lean out. BTW My carb is jetted a bit too rich wide open and the power valve doesn't open till the manifold vacumn falls below 4.5 inches of mercury. Being lazy and not interested in taking the carb apart to clean it. I dumped a few cans of seafoam in the fuel tank, and using a small flexable tube I sprayed carb cleaner into the fuel bowl thru the vent while the engine was running at a fast idle, also spraying some into the carb throat to clean any air bleeds After several cycles of this I let it sit 15 mins and then took the boat out. It ran good after that.

 

[garbageguy]

Re: 5.7 GL bogging under load

It has 4 bbl, not sure of make. Thru what vent did you spray carb cleaner?

 

[mtymax]

Re: 5.7 GL bogging under load

i had same issue with my 2006 5.7 GI-F and it was the fuel pump... i tried everything and did full tune up, pumped out old gas and cleaned the tank, with no help... they finally replaced the fuel pump under warranty (phew) and the boat is perfect now... good luck!

 

[Maclin]

Re: 5.7 GL bogging under load

When was the last time the carb was serviced? It could have clogged internal passages and cannot meter enough fuel in to cruise. The fuel bowl could also be running dry. A carb rebuild is in order, then troublshoot problem after that. If it is a Holley then it has a power valve with a rubber diaphragm and those do not like a high concentration of carb cleaner so I recommend the carb be removed and taken apart, all parts cleaned and passages blown thru then rebuilt.

The fuel pump may be a factor, but in a carbed engine it can either fill the carb or not. By contrast, an EFI engine will not run at all if the fuel pressure is not high enough, that is how the injectors fire. On a carbed engine the fuel pump only has to get gas to the fuel bowl, the engine vacuum draws the fuel in with the air and the carb does the metering. Theer are many small air bleeds and fuel metering passages in a carb that need to stay open, all of those are involved in the metering.

 

[Maclin]

Re: 5.7 GL bogging under load

Also verify to us that you have replaced filters, recent tuneup, etc.

 

[garbageguy]

Re: 5.7 GL bogging under load

Thanks for the replies. The more I can learn, the better.

Boat new to me this spring. It had a tuneup before sale - dist cap and "internals", (plugs? not sure), wires, fuel filter/water separator, oil change, etc. I have also checked the screen filter at entrance to carb - it's clean. No water in separator. On initial sea trial it had some performance problems at about 3500 rpm, but Ok at all others including WOT. They tried to rebuild the carb, but had same problem - so they replaced it with a carb off another boat which ran fine, and I bought the boat. That current carb is a Rochester 4 bbl. I also just learned the previous carb had electric choke, current carb does not and they couldn't find a conversion kit, so current carb has no choke. That doesn't bother me (yet). I spoke with the mechanic from the marina where I purchased the boat (brokered deal), who did the carb work. He mentioned possibility that previous carb floats may have lost their bouyancy, even though he checked they were empty. Ever heard of that?

 

[Maclin]

Re: 5.7 GL bogging under load

The secondary barrels opening rate may be off, there is a wound up spring or similar mechanism that the air valve plate over the secondaries works against to keep from opening too soon or too much. If that plate is falling open too soon then it will cause a super lean condition and a big bog and the engine may not be able to recover as the carb struggles to meter in fuel. The fact that you can coax it up falls in line with this.

With engine off, and the top of the carb visible, press lightly on the larger plate that covers the secondaries, pressing on the edge at the back of the carb, farthest away from the pivot shaft it is attached with. It should have some resistance and also snap back fairly vigorously.

If it tends to fall open, or resistance is light then this may need to be adjusted or fixed if something has gone awry with that system.

Also, since you have no method to close the choke and open automatically with engine heat then be sure the choke is open all the time. Choke plates are designed to be drawn to the open position as airlfow increases, but it could be sticking. With no choke mechanism in place make sure the choke plate does not interfere.

 

[Maclin]

Re: 5.7 GL bogging under load

Carb floats can take on fuel if they leak, metal ones can leak where brazed together or even get pinholes in them. But, as your mechanic mentioned, there would be some evidence of this.

 

[skywidget]

Re: 5.7 GL bogging under load

(My wife) has a 5.7 "EFI" and we're experiencing similar bogging. It will run if we ease up to 2700 RPM and remain steady. Then when the throttle is just pinched up it boggs acting like you pulled the throttle back to idle. No way it will throttle all the way up without sneaking up on 2700. It's just been serviced by an outfit that being taking care of this boat for about 6 years with no issues. I'm the "new" husband and have worked on lots of cars and motorcycles but not any experience on boats. Not familiar with the Penta obviously.

Since the answers (and question) was about carbs, I thought I might dovetail here to see what's you guys think.
Or should I start a new thread?

Help appreciated...wife is getting testy. (just kidding)

Jeff

 

[jimmbo]

Re: 5.7 GL bogging under load

Thanks for the replies. The more I can learn, the better.

They tried to rebuild the carb, but had same problem - so they replaced it with a carb off another boat which ran fine, and I bought the boat. That current carb is a Rochester 4 bbl. I also just learned the previous carb had electric choke, current carb does not and they couldn't find a conversion kit, so current carb has no choke. That doesn't bother me (yet). I spoke with the mechanic from the marina where I purchased the boat (brokered deal), who did the carb work. He mentioned possibility that previous carb floats may have lost their bouyancy, even though he checked they were empty. Ever heard of that?

Well that answers a few questions but adds other variables to the story. My guess is the motor originally had a Holley 4bbl on it, these, in late marine apps use electric chokes and do have hollow brass floats. Sounds more like they didn't want to spend the money on rebuilding the original carb properly and stuck whatever they had laying around on it and got rid of it. Or Perhaps someone wanted the Holley 4bbl for their boat and did a swap. I would ask for the old carb back and go over it carefully, Holley is not a complicated carb. As for the Q-jet that they stuck on, Oh Boy. Try to find out what it was on, make, displacement. Also get the number of the carb. It should be stamped in the port side of the bowl assembly near the front bolt that holds it to the manifold.

You say you are able to get it up to 3000 or so rpm. It is possible the secondairies are not opening. there is a lockout to prevent either the secondary throttle shaft from opening or the air valve above the throttles from opening when the choke is not fully open. You will need to watch the carb to see if the secondaries are opening when the throttle is pushed to wide open. Fortunatly you can do this at the dock or in the garage, wherever the boat may be. With motor off shift into forward and advance to full power. With flame arrestor off try to push the air valve on the carb open(looks like a big choke valve on back half of carb).

A) If airvalve does not open is the choke fully open? Check for a little tang on the starboard side of the choke housing, if the choke isn't fully open it locks out the air valve. If valve opens, does it open smoothly or is it binding or sticky? look down to see if the secondairies are fully opening

B)If it opens does it open smoothly or is it binding or sticky? While it is open look down the opening and see if the secondairy throttles are open fully. If they are not, close airvalve and retard throttle. Check to see if choke is fully open. and repeat. Here a system phyically locks the secondairy throttle shaft from rotating unless the choke is fully off If not, fully open choke and readvance the throttle, open air valve and check again. This method is the more common one on the late Q-jet.

Hope that makes some sense

 

[Maclin]

Re: 5.7 GL bogging under load

Thank Jimmbo, I forgot about the secondaries being locked out until the choke opens up, actually was not sure the Qudrajets did that, I know the Thermoquads do and that can cause problems when the choke is not setup (or bypassed!) correctly.

 

[Maclin]

Re: 5.7 GL bogging under load

skywidget, if you are serious about getting your issues diagnosed and fixed quickly (and staying newly married!) then start a new thread

There are several systems on the EFI engines that can cause that, and none of those systems even exist on a carbed engine.

Post the year, full model#, serial number of the engine and drive to get the best advice.

 

[skywidget]

Re: 5.7 GL bogging under load

Thank you kindly sir. I'll take your well appreciated advice. Not much on forum stuff.
Just got off the lake troubleshooting. Took the air filter off the throttle body to look at the the two fuel sprays and one side is shutting down when I throttle up. I'm hoping trash on the one side. I'll post another thread though!

Thanks again,

 

[garbageguy]

Re: 5.7 GL bogging under load

Maclin and Jimmbo - thanks for the detailed responses and ideas. Can't wait to get back on it this weekend and apply your suggestions. Will post back with updates.

 

[garbageguy]

Re: 5.7 GL bogging under load

RESOLVED: Turns out the carb filter was in backwards. Hate it was something so stupid, love it was that easy.