Mercruiser will not work without a lot of revs

Hi guys, new boater here. I have a Bayliner 2052LS Capri with a 3.0 mercruiser. 1998. I just can't get the engine to tick over without a lot of revs. I have cleaned the air filter and intake. Running fresh fuel, cleaned all wires and terminals etc etc. she cranks okay with some power applied, but dies when the throttle is eased off. Any help would be fantastic. Thanks.

Re: Mercruiser will not work without a lot of revs

When was the last full tune up?

and what was done/replaced during it?

Re: Mercruiser will not work without a lot of revs

Hello and welcome aboard.

Sounds like it might be a fuel problem, specifically a clogged idle circuit in the carb. If you have a timing light, put that on one of the spark plug wires and watch it as the engine dies. If the timing light continues to fire as the engine dies down, you most likely have a fuel problem. If the spark stops dead THEN the engine dies down, you have an electrical problem....

Chris.....
BTW, please post engine serial number when asking a question. For Mercruiser engines, serial numbers are king (engine, drive and transom). Year is less relevant (and sometime completely meaningless as the engine and the boat may not be the same year)...

Re: Mercruiser will not work without a lot of revs

Thank you for the replies. With regards to servicing, it was done around a year ago. Oil, plugs, leads etc, according to the guy who I brought it from. I have the transom serial number which is OL287387. Drive seal number is OL406238, Engine number is 0L097202 Apologies if I sound a little stupid. This is my first inboard. All I had before was a 14ft Dejon with a 20hp outboard that was kept on my driveway! :facepalm: It is an Alpha one Mercruiser, with a Chrysler engine 3.0l according to the paperwork. One chap at the marina did say though that it was not a carb that I was looking down, but a single point injector.

Re: Mercruiser will not work without a lot of revs

The chap at the marina is wrong. That's a 3.0 litre GM engine, nothing to do with Chrysler... And it has a MerCarb carburetor...

It does sound like the carb needs to be removed and cleaned out. Not a difficult job. Have you ever pulled a car carb apart? It's the same....

Chris.....
BTW, nothing sounding stupid in your questions, that's EXACTLY what we want to see in every new thread from everybody, engine, drive and transom serial numbers.... And I also once had a 14ft boat with a 20hp Merc on it...

Re: Mercruiser will not work without a lot of revs

this is the engine (well duh....I know).... I have had to resize the picture, so I hope you can see it! I have not removed a carb from a boat engine before. I have removed a twin choke webber years ago to change the vacuum diaphragm though. Will i need new gaskets, jets reset etc? A bit reluctant to maybe kill her completely when she is so close to going out on trips. I'm sure you understand my trepidation.

Re: Mercruiser will not work without a lot of revs

Yep, the re-sized photo was smaller than the thumbnail... :facepalm:... Oh well, at least I saw enough to be able to say, completely and unequivocally, that the engine in that photograph is a 3 litre GM engine, and the thing under the round thing on the port side of the engine (flame arrestor, not air filter) is a carburetor... Besides, you provided the engine serial number and I was able to look up what it was (that's the value of the serial number and why we ask)....

Removing carb. Easy. First thing you'll need is the manual.... For that, I have this -> https://docs.google.com/viewer?a=v&...ZDU4ZS00NzcwLWI1MGYtMTQwMzc3MTJiYTdl&hl=en_GB

Download and SAVE.... Now, open it up to section 5, part B... All about your carburetor.... Page 15 of that section steps through the removal process. If you're happier taking the carb to a shop, find one that has experience with Rochester carbs. Also, take a gasket set with you. Marine gaskets can vary slightly from standard automotive. The gasket set for that carb is 3302-810929. (from a Merc dealer or on-line shop)

If you're up to doing the job yourself, we're here to help.... It's not a difficult job, but you will need a few tools. Small is better when working with these components. The usual assortment of screwdrivers, spanners and simple hand tools is usually enough. NO HAMMERS!!!! :facepalm: You'll also need an accurate small measure (I use a 6 inch steel rule and a vernier caliper) and a source of DRY compressed air (I use SCUBA tank air as it's about as dry as it gets!). A few tins of carb cleaner (NOT brake cleaner, that stuff's dangerous!!!) and you should be good to go.

Just keep the work bench clean and tidy (and by clean, I mean, CLEAN! Your current problems are caused by dirt, so clean is good ), work slowly and check everything twice, and work in the order the book calls out. And read the procedure through a few times before tackling the job....

As I said, we're here to help you if you think you need it. One more thing. If in ANY doubt, ask, before you screw it up....

Chris.....

Re: Mercruiser will not work without a lot of revs

You sir, are a star! I will crack on and see how it goes. Thank you so much for your help. Supreme Mariner status is obviously well deserved. I will let you know how I get on. Thanks again.

Re: Mercruiser will not work without a lot of revs

Right, carb back on, crystal clean, new gaskets etc, I cleaned the fuel filter whilst there, even though this was clean anyway. Started her up, no probs starting, died at low revs. :grumpy: just can't get her to tick over. Timing out maybe? In fact , I had her rumbling over for around 5 mins on medium revs just to get some fuel through and heat into the engine, and she died....even with decent revs. A sucking air like noise then nothing. I'm going grey with stress, will this kill the love for my boat and boating?......season coming to an end but still no trip out. :-(

Re: Mercruiser will not work without a lot of revs

How many turns are the mixture screws out

Re: Mercruiser will not work without a lot of revs

Two and a quarter turns out (idle mixture needle on right side of carb as you look at engine). Also not sure where the idle screw at the top of the carb is suppose to be at. The mixture needle also had some slight ware on it, so may need replacing. I sprayed some carb cleaner into the hole when I removed it, even though it should be clean! I can't seem to find anywhere that tells me the exact setting of these two adjustment screws.

Re: Mercruiser will not work without a lot of revs

Anyone there?

Re: Mercruiser will not work without a lot of revs

Yes, we're still here.... There should be no adjustment screws on the top of the carb. It should have one idle mixture screw near the base, and the idle speed screw on the throttle cam... Post photo (large enough to see this time ) of the screw in question...

Re: Mercruiser will not work without a lot of revs

Deff sounds like a clogged idle circuit in carb. What about the choke? Is it closed when engine is cold? Could also be a vacuum leak.

Re: Mercruiser will not work without a lot of revs

Hi achris, yes that's what I meant, I didn't explain it clearly. If I put both of them all the way in, is there a "guesstimate" of how many turns back out would be the correct settings? The manual says 1 1/4 turns out to start engine, then adjust when engine is warm.....that's the problem! XJdriver, I have had the carb off and cleaned using an ultrasonic cleaner. It was replaced in gleaming condition. Where would the idler circuit be on the carb? The exploded view from the service manual doesn't show it. Or I'm looking in the wrong place? Thank guys. Mike.

Re: Mercruiser will not work without a lot of revs

Mike,

The 'idle circuit' is part of the drillings and porting inside the carb. After you cleaned it all, did you then blow all the passages out with CLEAN dry compressed air?

I posted up some 'cut-away' views and operational pictures of a carb. This is the thread -> http://forums.iboats.com/mercruiser...-how-does-mercab-work-623283.html#post4343446

Those drawings are from the Merc Service training school handbook.

Which particular carb do you have? There are 2, you should have a red tag with a number on it (or it might be on the side of the carb somewhere.). If it's 3310-807504, then the initial setting for the idle mixture is 1-1/4 turns out form LIGHTLY seated.... If it's the other one, then the book just says "factory setting'... Whatever that means.

Chris......

Re: Mercruiser will not work without a lot of revs

Emeraldsnake said:

Hi achris, yes that's what I meant, I didn't explain it clearly. If I put both of them all the way in, is there a "guesstimate" of how many turns back out would be the correct settings? The manual says 1 1/4 turns out to start engine, then adjust when engine is warm.....that's the problem! XJdriver, I have had the carb off and cleaned using an ultrasonic cleaner. It was replaced in gleaming condition. Where would the idler circuit be on the carb? The exploded view from the service manual doesn't show it. Or I'm looking in the wrong place? Thank guys. Mike.

Click to expand...

Ultrasonic cleaners are good at making the outside nice and pretty, kind of a hit and miss at cleaning the passageways inside the carb. Your best bet is to get a nice big can of carb cleaner with a straw, take the carb apart and go to town on it, and also what achris mentioned about the compressed air. You should be able to see the idle circuit ports if you view the carb from the bottom with the throttle plates closed.

Re: Mercruiser will not work without a lot of revs

Used carb cleaner and an air compressor to clean, blow through and dry everything. I did notice on replacing the carb that the brass covers that swing over the pots (sorry, poor terminology), were fairly stiff. The carb number is 807504 8302.

Re: Mercruiser will not work without a lot of revs

Success! Got her ticking over sweet. I moved the choke to the right a bit, wound the idle screw all the way out, then in 3 turns once it had reached the idle cam, then put the idle mixture needle all the way in, then out two and a half turns.But................she now dies when I put the revs up a bit or try to go into gear. I'm nearly there, I'm guessing she just needs a final few tweaks. Any ideas?

Re: Mercruiser will not work without a lot of revs

Oh, and the rev counter doesn't work. So that's making it a tad more difficult.