1988 Merc 3.0L 2 barrel carb won't idle

[SamStrobert]

My son and I have a 1988 Mercury inboard/outboard 3.0L gas engine with a 2 barrel carb (tag 1389-9562)that starts easy, runs fine above 3000 rpm but will only idle if I hold the choke almost (2 or 3 millimeters) closed. It ran fine last year. I've put in new float and new spring jet in base of float bowl. I assume it is idle adjustment and don't know where this is. Is it hidden so I won't pollute?! There is a needle valve under the carb near the intake manifold that does not seem to do anything. I think this might be a high speed idle?

 

[JB]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

Moving this to I/O and Inboards

 

[tylerin]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

I assume you have covered the obvious things like you have good gas, filter ok, good spark plugs. timing

 

[SamStrobert]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

Yes, new gas (we cleaned the tank to get rid of a little condensate. Probably could have just used dry gas. There was some water in carb float bowl too), clean plugs, clean filter. So it started out with brand new gas. It ran well last year and I haven't changed the timing. It runs at idle very smoothly if I hold the choke almost closed. It runs at high RPM good too.<br />I think it is an idle mixture adjustment but I don't know how to adjust that. Can you tell me or point me to a web page picture?

 

[DJ]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

Sam,<br /><br />You are running lean. Indicative of a vacuum leak.<br /><br />Take a good look around the carb and see if any vacuum hoses were left unplugged, cracked, etc.<br /><br />Is your PCV hose (valve cover to carb base or air cleaner) hooked up?

 

[SamStrobert]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

There are three "hoses" to the carb. #1 is the metal gas line. #2 is a clear plastic hose that looks like a drain line as it would not support a vacuum. It is near the top of the carb and 3/8" in diameter. #3 is a 3/4" black short hose from the air filter to the valve cover. This is of course removed so I can hold the choke almost closed. The air filter is a metal multilayered set of disks that would only keep bugs out of the intake. I guess dust is not a problem for boats. <br />I agree that it appears like a vacuum leak because closing the choke compensates for the problem but there are no visible vacuum leaks so I was trying to find the idle mixture screws. The gaskets between the carb and the maniform appears to be in good shape. I did not remove the carb from the monifold. I did remove the top of the carb to replace the float and clean jets. <br />Are the idle misture screws adjustable? Where are they? I read somewhere that you have to drill through a plate to get to them to prevent people from misadjusting them?! Is there an idle jet that could of got clogged? I'm not even sure there is a seperate idle jet?

 

[McKenzie]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

If its a holley, there is a small screw on the port side of the carb on the metering block, right in back of the the fuel bowl. If you need a pic i can upload one

 

[McKenzie]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

A good way to find vacuum leaks is to get a spray bottle with some water in it and squirt away.

 

[SamStrobert]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

I don't know if the carb is a Holly. I've heard they use Rochester and perhaps Merc. carbs? A picture to download would be apprecited. My email address is sssiii@hotmail.com.<br />I will try to find the vacuum lead but is there an idle adjustment or a idle jet that could be clogged?

 

[Trent]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

That year had a Mercarb. One adjustment screw at the base for idle mixture adjustment. If that does not cure your problem you might have to tear it down and clean. Check this out if you think you need to tear it down.<br /><br /> Service bulleitin<br /><br />Here is another.... web page

 

[SamStrobert]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

Thanks. It appears that there must be somthing clogging up the idle jet. I guess I can't ream it out with a wire?

 

[Trent]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

Dont do that. You can damage the seat. You can try to spray some carb cleaner after removing the adjustment screw. I dont think it will help but its worth a try. If it does not help. Tear down the carb and clean.

 

[SamStrobert]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

Trent,<br />Thanks. That is an excellent web site. I have been searching for a exploded picture and/or description of how to rebuild or clean the carb and didn't find one. I will just be careful I guess. Thanks again for the web site.<br />Sam

 

[McKenzie]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

Might wanna try this, I copied it from another post and i've had good luck with its results.<br />

Get an outboard motor gas tank, connect it to your fuel pump and fill the tank with a gallon or two of gas and add a can of Seafoam. Get the engine running (you will probably have to use starting fluid). Run the engine until it empties the tank. If you are lucky, that will clean up this problem and save you the trouble of rebuilding the carb. If it doesn't work, it was worth a try and you gotta rebuild the carb. BTW, you can get Seafoam at NAPA.<br />

 

[damie]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

this carb for your year will be a rochester 2bl,<br />the mercarb was later although almost identical,<br />this idle screw should be 1 1/4 turns from closed.

 

[SamStrobert]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

Mariah,<br />Thanks for the 1 1/4 turn tip. It has no effect now because it must be clogged up with something. I am anxious to get to the boat and remove the carb to unplug this idle jet.<br /><br />When I remove the carb from the manifold will I see the restriction or must I take the carb apart? Hopefully it comes apart from the bottom because it doesn't look like I would get to the idle adjustment from the top without removing a lot of stuff (jets, venturi, choke, butterflies etc. Are there any exploded views of this Rochester 2B carb on the web?<br />Sam

 

[The Marine Doctor]

Re: 1988 Merc 3.0L 2 barrel carb won't idle

Sam, do you have a 2 piece carb. ie...the bottom plate is separate from the top. If so its most likely that your bottom plate is warped. Mercury knows of this kind of problem and there should be a parts bulletin. The replacement carb is 1 piece and will take care of the problem for you.<br /><br />TMD