454 engine bogs down - ideas?

Discussion in 'Boats and Motors' started by PatSea, Jun 16, 2017.

  1. PatSea


    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
  2. Carb issues? Way way out there guess..

  3. UFM82

    UFM82 The one others want to be

    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?
  4. PatSea


    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.
  5. 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...
  6. 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...
  7. 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
    backfar likes this.
  8. 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.
  9. Im gonna say its not vapor lock....a marine engine should never get hot enough for vapor lock to happen...
  10. 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.
  11. clean off the spark arrest screens
  12. PatSea


    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!
  13. sherman51

    sherman51 florida ice fishing

    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.
    Dovans likes this.
  14. 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
    sherman51 likes this.
  15. Let me know if you need someone to rebuild your carbs!
  16. 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?
  17. PatSea


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

    crestliner TS redeye

    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.
  19. 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