5.0 bogs, won't accelerate off idle

[Cheif531]

I will try and make this as short as possible but still get the facts across...

I was curious to see how much gas was left in my tank when the gauge indicated it was one quarter full. I siphoned out 14 gallons and put it in the cars and let the boat sit, empty for a few weeks on the trailer. When we decided to take the boat out I put in 3 ounces of Stabil Marine additive and 28 gallons of regular 87 gas from the Shell station. It had sat for three or four weeks without any gas or being ran.

Prior to this the boat ran great. Good acceleration all the way up to 4700 rpm and 46 mph. Oh, it is a 1998 Chaparral 1930SS with about 370 hours. Engine Serial #0L046720

Now, I put her in the water it had a hard time starting, I figured because of the lack of gas and sitting for a while. Put her in reverse, engine stumbled and ran rough when I tried to accelerate to back off the trailer. Idles fine to come alongside the dock.

I let her warm up good while I parked the truck. We got underway and idled out into the Intercoastal. Once clear of the no wake zone I punched it, and it fell flat on its face running rougher than you can imagine and almost stalling. I throttled back and it idled fine and even a little off idle but tried to accelerate again and it ran like crap. I could throttle it up in neutral and it would run up to 35-4500 rpm no problem but under load it runs like crap.

managed to get back to the dock but getting back on the trailer was tough without good power to run it up on the bunks.

I have since checked all the fuel lines, check valve and fuel filters. I emptied the fuel filter into a glass jar to look for water and found nothing out of the ordinary.

Today I took off the distributor cap and found some condensation but do not know if that was there the day we went out which was the weekend before Christmas.

Any Ideas or help will be greatly appreciated.
Thanks in advance....MIke

 

[Bondo]

Re: 5.0 bogs, won't accelerate off idle

Ayuh,.... Welcome Aboard,.... Did ya take a peek at the spark plugs,..??

Is this motor Carbed, or Efi,..??
Is the fuel flowin' through it,..??

 

[Fun Times]

Re: 5.0 bogs, won't accelerate off idle

Engine Serial #0L046720

Is a MERCRUISER 5.0L ALPHA GEN+, Merc carb with an electric fuel pump.
MERCRUISER - (5.0L H.P. (1998) Serial No: 0L046720 Model No: 4M11025LS Parts Catalog No: 81659698

Any condensation inside the distributor cap would definitely make the engine run rough/not accelerate while under load but rev up fine while in neutral. With the weather the way it has been lately, I would think condensation would be a big problem right now.

 

[Cheif531]

Re: 5.0 bogs, won't accelerate off idle

Thanks for the quick response's...

I have not checked the plugs yet....that was next on the list.

I was going to get a new cap and rotor today...might just as well get a set of plugs and wires to go with them. The previous owner was not the best at regular maintenance so I know the plugs have not been changed.

I will try and get a test run in this Saturday and let you know the results.

thanks again
Mike

 

[tazrig]

Re: 5.0 bogs, won't accelerate off idle

...The previous owner was not the best at regular maintenance

That being the case you better also replace the water pump impeller. It should be changed every other year regardless of hours. You won't know you have a bad impeller until it sneaks up and bites you. For the small cost better just to replace it. along with engine and drive oil if you haven't already. Here a link to an OEM service Manu@l for your motor.


Boatinfo - Mercruiser Service Manual nr. 9 - 1985-1988 - GM V8 Engines

See section 1C for maintenance items and the proper schedules for them.


Manual for your Alpha One Gen 2 drive:

Boatinfo - Mercruiser Service Manual nr. 14 - 1991-Current - Sterndrives Alpha One Gen II</

 

[Cheif531]

Re: 5.0 bogs, won't accelerate off idle

Thanks for the links to those manuals they will definitely come in handy.

I did the impeller on a 120 I/O back in 1976, can't imagine it is much different. What I have never done is service the outdrive u-joint. I guess that should also be on my to do list before I get into the season again.

You guys are great, thanks for your help...

 

[littlebookworm]

Re: 5.0 bogs, won't accelerate off idle

Letting the boat sit with no fuel and a drained tank may have allowed some of the junk in the bottom of the tank to clog the filter screen on the pick-up tube. You might have to pull the picl-up tube and clean the screen.Definitely do the major tune-up and outdrive service. In addition, I suggest you change the engine oil and filter and check the PVC valve, if your engine has one. Just pull the valve from the valve cover and shake the valve. You should hear the piece inside (the valve) moving back and forth. If it's just an open tobe to a hose, just reinstall and forget about it. Lubricate all grease fitting on the outdrive and steering and squirt oil on all the other pivot points. Good luck and let us know how it works out. Hy

 

[Scott Danforth]

Re: 5.0 bogs, won't accelerate off idle

pull the spark arrestor and watch as someone gives it throttle. if you do not see a nice shot of fuel, my guess is there is crud in the accelerator circuit.

the crappy florida gas coupled with sitting for a while without fuel and I am leaning toward needing a carb rehab. OK, the really crappy florida gas.

 

[jeromeb]

Re: 5.0 bogs, won't accelerate off idle

After you've gone through your ignition system, if the problem still persist, check the carburetor accelerator pump. Pull the spark arrester and work the throttle, (engine off). Two streams of gas should squirt each time you open the throttle. Sitting for a period of time dry can cause it to deteriorate.

 

[searay3]

Re: 5.0 bogs, won't accelerate off idle

If after all the checks listed above still results in idle only operation, don't rule out the coil. I have had this same issue prior with a 1987 4.3lx. Rebuilt carb, new wires/plugs, fuel filters water separator and it still would bog at throttle up. Coil was original, tbIV ignition. Replaced the coil (cost about 30 bucks, blaster coil), she came back to life.

 

[Cheif531]

Re: 5.0 bogs, won't accelerate off idle

I did not get her into the water today as planned. Rain in the area and 60 degrees just does not make for a nice boat ride. Going to try during the week to get her out..

Never thought about the coil, will definitely keep that in mind. I did get a new cap and rotor put in...fires up right snappy when i hit the switch.

 

[FuelishBehavior]

Re: 5.0 bogs, won't accelerate off idle

Ethanol to carbs is like cholesterol to arteries.... I'm learning slowly, change fuel filters regularly, and learn how to rebuild a carburetor. Please God, give us back our regular gasoline! Corn is for consumption not fuel.

 

[Cheif531]

Re: 5.0 bogs, won't accelerate off idle

Ok, Gents, Thank you for all your help.

I put a new cap and rotor on and put the boat on Lake Tarpon today.....It ran like a top. Well over 45 mph at just over 5000 rpm. I know, I know don't run it like that.. I always keep it under 4500 at the most and I cruise around 3-3500. But, today was special..

Love the fact it was 70 plus out on the lake and the sun was shining bright..

Take care and smooth sailing.....until next time
Thanks again
Mike