# 454 engine bogs down - ideas?



## PatSea (Oct 10, 2004)

I have a cruiser with twin 454 engines. They run fine and seem to be strong. The only problem I have is the sb engine bogs down in certain situations. If I've run out on the lake, shut them off to drift fish, then start them to make a move, they start ok, but when I power up to 3000 rpm to get on plane, the sb engine bogs down, sputters and seems to be running very rich by the smell of the exhaust. I immediately throttle back to idle, wait 20 seconds or so,then throttle up again and it runs ok. Then it runs fine as we cruise to the next location. It only does this after the engine has been run for awhile. In other words, it doesn't do this when I first power up as I leave the harbor. Seems like it might be some type of vapor lock situation. This engine has done this maybe once or twice each season for the last several years but this year it is doing it more frequently. Any ideas to solve? Thanks


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## Dovans (Nov 15, 2011)

Carb issues? Way way out there guess..


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## bigdogbull (Apr 19, 2012)

carburator for sure .


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## UFM82 (Apr 6, 2004)

Sounds like the carb is leaking fuel into the cylinders after you shut the engine down. Once you start back up, allow it to clear and lean out it runs fine. I'd pull the carb, look for a leaking needle seat or incorrect float level. (I'm assuming this isn't an EFI engine.) It doesn't exhibit the same issue when it's cold since the fuel in the carb would have drained into the intake manifold evaporated due to the time elapsed before trying to start the engine again. Does the SB engine start easily enough cold?


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## PatSea (Oct 10, 2004)

UFM82 said:


> Sounds like the carb is leaking fuel into the cylinders after you shut the engine down. Once you start back up, allow it to clear and lean out it runs fine. I'd pull the carb, look for a leaking needle seat or incorrect float level. (I'm assuming this isn't an EFI engine.) It doesn't exhibit the same issue when it's cold since the fuel in the carb would have drained into the intake manifold evaporated due to the time elapsed before trying to start the engine again. Does the SB engine start easily enough cold?


Both engines start reasonably well after they've set idle at the dock for a week or two. I have to pump the throttle several times but they start. And they run ok and when I power up to cruise the first time the engine doesn't hesitate or bog down. It only does it after I've cruised for awhile, turned it if, then start to power up to cruise again. And once I'm able to clear it the engine cruises ok. Hope this makes sense and thanks for your insight.


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## bigdogbull (Apr 19, 2012)

sounds like a needle and seat ... I would get both carbs checked out rebuilt at the same time. I would bet he other isnt too far behind...


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## backfar (Sep 24, 2014)

100% carb....im thinking the needle vavle on the float is sticking....you can try to run seafoam though it...if that fails to fix it, your going to have to take it apart and clean it...


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## firemanmike2127 (Mar 17, 2013)

I'd agree with the needle & seat being a good area to investigate. I know that you stated that the engine smells rich when you get it fired back up, but if your engine is equipped with a Quadrajet here's another possibility. Water in the bowl can obstruct one of the main jets & cause the engine to bog down pretty badly. Once you slow down & the water globule has a chance to move away from the jet, the engine will start readily & make good power again. I've seen this numerous times in marine applications. The main jets in Rochester 2 & 4 barrel carburetors sit in the very bottom of the bowl unlike a Holley, where they are located in the side of a metering block. I always like to inspect the fuel inside any carbs that I service to ensure that there aren't other upstream issues in the fuel system that need addressed. Mike


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## Misdirection (Jul 16, 2012)

The easy way to check for vapor lock in the tank is to crank your gas cap open and/or check your vent. But I agree with others, it's a carb issue.


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## backfar (Sep 24, 2014)

Im gonna say its not vapor lock....a marine engine should never get hot enough for vapor lock to happen...


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## Misdirection (Jul 16, 2012)

backfar said:


> Im gonna say its not vapor lock....a marine engine should never get hot enough for vapor lock to happen...


On one of my 454's the vent was blocked one year and only when it was hot would bog down around 3200 rpm. In that case the person who waxed it taped the vent shut and forgot to remove the tape. Easy fix to remove the tape. So maybe not a vapor lock but it was starving for fuel.


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## tagalong09 (Jul 25, 2012)

clean off the spark arrest screens


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## PatSea (Oct 10, 2004)

Looks like I'm in for a carberator rebuild (make that 2 carberator rebuilds). But first I'm going to put on new fuel/water separators and run some Seafoam through the engine. Question: What is the best way to run the Seafoam as I have 80 gallon tanks. Do I introduce it directly into the carb or do I put it in the fuel tank. Thanks for all the help! There is a wealth of knowledge of all types on here!


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## sherman51 (Apr 12, 2011)

have you checked to see if the choke might be sticking? sound like it could be sticking closed and opens back up when you throttle down. that would account for the bogging down and the gas smell. check the simple things 1st.
sherman


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## firemanmike2127 (Mar 17, 2013)

Sherman brings up a good point......an electric choke thermostat could possibly be closing, but generally a warm engine is very hard to start if the choke shutter is closed. Another observation you could make would be to inspect inside the carburetor throat after the engine is shut down. You'll have to remove the flame arrestor so ensure that the battery & ignition switches are BOTH OFF prior to doing the inspection. DO NOT RUN THE ENGINE WITH THE FLAME ARRESTOR OFF !! Look down inside the carburetor venturi to see if fuel is leaking past the needle & seat assy & running down into the intake manifold. You should not see any dripping fuel if the needle & seat are sealing AND adjusted properly. Mike


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## EyeCatchEm (Jan 6, 2014)

Let me know if you need someone to rebuild your carbs!


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## RJohnson442 (May 14, 2013)

Just use water down the carbs it will actually work better than sea foam to decarbonize. To check for vaporlock After running it for a while and warmed up remove the air filter and have someone shut her down. Do you see gas still pouring into the carbs? What type of carb are they and do they have mechanical or vacuum secondaries?


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## PatSea (Oct 10, 2004)

RJohnson442 said:


> Just use water down the carbs it will actually work better than sea foam to decarbonize. To check for vaporlock After running it for a while and warmed up remove the air filter and have someone shut her down. Do you see gas still pouring into the carbs? What type of carb are they and do they have mechanical or vacuum secondaries?


RJohnson, I don't understand your comment about using water to debarbonize the carb. Can you explain? Thanks.


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## crestliner TS (Jun 8, 2012)

If you slowly pour water into the carbs as the engine is running it will clean the carbon. There are good videos on you tube.


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## slimdaddy45 (Aug 27, 2007)

If they are q-jet carbs Ive never seen one run right after a rebuild I had one on a 454 in a pickup and I rebuilt and had mechanics rebuild it and it never ran right so I took it off and threw it away and put a spreadbore Holly on it plus it gave me 4 more miles per gal than the junk q-jet they run good when there right but once you have trouble with replace them is my opinion on them


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## firemanmike2127 (Mar 17, 2013)

I'm not trying to discredit slimdaddy45 here but Quadrajets have gotten a bad rap because a lot of people don't know how to properly set one up. There have certainly been cases of bad/defective/worn out carburetors but I feel that the Quadrajet is an excellent carburetor when properly adjusted. The secondary air valve tension is critical to ensure a smooth transition from idle/part throttle engine speed to wide open throttle. This is particularly important in marine applications where you have to accelerate hard to get a boat up on plane. Like anything else, it takes some time & experience to learn. I was fortunate to have an old friend who drag raced in the Stock & Super Stock NHRA classes who shared his knowledge of those carbs with me. I have several hotrods so I'm pretty familiar with the Holleys & Edelbrock carbs as well, & I have definitely had a Holley carb center section that was junk. Mike


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## UFM82 (Apr 6, 2004)

Using water to decarbon an engine can work but it can cause issues to. The water turns to steam and basically blasts the carbon loose. The downside is if the carbon is bad enough a chunk can break loose stick on top of a piston or under a valve and cause problems. Sometimes you'll hear a knock while doing the water treatment as the carbon comes loose but usually it clears. But if it sticks under a valve the engine will drop that cylinder and it may not clear. Sea Foam dissolves the carbon and allows it to turn off as opposed to just being dislodged. It works, but be careful.


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## PatSea (Oct 10, 2004)

UFM82 said:


> Using water to decarbon an engine can work but it can cause issues to. The water turns to steam and basically blasts the carbon loose. The downside is if the carbon is bad enough a chunk can break loose stick on top of a piston or under a valve and cause problems. Sometimes you'll hear a knock while doing the water treatment as the carbon comes loose but usually it clears. But if it sticks under a valve the engine will drop that cylinder and it may not clear. Sea Foam dissolves the carbon and allows it to turn off as opposed to just being dislodged. It works, but be careful.


I don't feel comfortable doing the decarbonizing with water. How do I introduce the SeaFoam to the carberator?


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## FISHIN 2 (Jun 22, 2005)

Firemanmike, I too have a quadrajet that I believe is a culprit, motor starts fine, throttles up good but only getting 2200 rpms out of engine. It just bogs down after about 1/2 throttle. It a 4 cylinder mercruiser in a Thompson boat. I first had backfiring at 1/3 throttle, replaced the points with electronic module , changed coil, changed gas lines, added a fuel/water separator, put new fuel filters in carb and fuel pump. Still at a loss as the culprit that robs my power. Where are you located, a carb rebuild is about my next move. I noticed my old coil said to use with a resistor but haven't been able to find one on engine, new coil said use no resistor, could that be a problem but cant find one on my system. Thanks a lot, Mike


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## RJohnson442 (May 14, 2013)

FISHIN 2 said:


> Firemanmike, I too have a quadrajet that I believe is a culprit, motor starts fine, throttles up good but only getting 2200 rpms out of engine. It just bogs down after about 1/2 throttle. It a 4 cylinder mercruiser in a Thompson boat. I first had backfiring at 1/3 throttle, replaced the points with electronic module , changed coil, changed gas lines, added a fuel/water separator, put new fuel filters in carb and fuel pump. Still at a loss as the culprit that robs my power. Where are you located, a carb rebuild is about my next move. I noticed my old coil said to use with a resistor but haven't been able to find one on engine, new coil said use no resistor, could that be a problem but cant find one on my system. Thanks a lot, Mike


The resistor is usually in the line itself. They'll usually have a thicker softer insulation than the rest of the wire harness. They usually have a rubber tab or tag attached to them to identify but fall off all the time. Running the new coil you need a full 12 volts for it to work properly. High rpm it's firing so fast it can't keep up to charge and fire. Run a dedicated wire from the battery to the coil.


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## firemanmike2127 (Mar 17, 2013)

FISHIN 2......I don't want the administrators to think that I'm 'fishing' for business here. I'll send you a PM & you can give me a call for some advice on your problem. Mike


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## firemanmike2127 (Mar 17, 2013)

For those following this thread.....It sure sounds like a tuning issue FISHIN 2. Specifically.....not enough tension on the secondary air valve. This is assuming that your tune-up interventions were all done correctly & the advance mechanism in the distributor is working properly. Mike


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## firemanmike2127 (Mar 17, 2013)

PatSea.....we're you able to determine if the needle & seat was properly sealing in the carburetor on your starboard engine ? Mike


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## PatSea (Oct 10, 2004)

Mike, 


firemanmike2127 said:


> PatSea.....we're you able to determine if the needle & seat was properly sealing in the carburetor on your starboard engine ? Mike


I'm not at the boat now, probably won't be back up for a week or two. I'll update this when I get back up there and can check it out. I appreciate all the help from you guys, at least I have a direction to proceed.


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## KaGee (Sep 8, 2006)

Quadrajet on a 4 cyl? Hmmmm.


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## firemanmike2127 (Mar 17, 2013)

Probably a 224 cu. in.engine that Mercruiser made in Mexico back in the late 70's thru the early 80's. They were available in 170 HP 2 barrel versions & rated @ 190 HP when equipped with a Quadrajet. They had a closed cooling system & an interesting combination of internal components. The rotating assy consists of a 460 Ford connecting rod & piston topped off by a single Ford 460 cylinder head to make a long stroke 4 cylinder with a pretty decent torque curve. Mike


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## Uncle Paul (Jul 10, 2004)

firemanmike2127 said:


> Probably a 224 cu. in.engine that Mercruiser made in Mexico back in the late 70's thru the early 80's. They were available in 170 HP 2 barrel versions & rated @ 190 HP when equipped with a Quadrajet. They had a closed cooling system & an interesting combination of internal components. The rotating assy consists of a 460 Ford connecting rod & piston topped off by a single Ford 460 cylinder head to make a long stroke 4 cylinder with a pretty decent torque curve. Mike


Interesting combination of internal components, Had a buddy that had two of those engines in his Sea Ray and he lost a lower unit on one engine so he shut it down, problem was it was the engine that had the water pump for the heat exchanger for Both engines and overheated the running one. Went through two dealers and a couple of machine shops before a Mercury Racing dealer could tell us what components we needed to order for that engine and as I remember it took a very long time to get the parts. But when all done they were a very strong engine for a 4 cyl like you said big on touque.


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