Another 3.0 question

[Marlin1]

Howdy everyone! I've got another 3.0 question to ask. I have A 1977 18 foot Marlin with An OMC 3.0 4 cylinder motor.She runs good but she wants to stumble from an idle to half throttle.When I give it gas slowly she revs up just fine but when I'm trying to move out of the way she wants to stumble before it takes off.I had the carb rebuilt last week but I just dont know how to adjust it.It has A Rocheaster 2 barrel on it and it has 2 air fuel mixture screws on it.I gave it A tune up with the new carb,points,plugs,cap rotor.Points are set at .16.Any help would be appreciated.Thanks

 

[Don S]

Re: Another 3.0 question

For one thing, you need to set your points by dwell not gap. That alone could be the problem.<br />Adjusting the carb properly will probably take care of the stumble.<br />Could also be the accelerator pump is bad. Does a good stream of fuel squirt in the carb when the throttle is opened? You can check this with the engine OFF.

 

[gregs]

Re: Another 3.0 question

Look to see if you have a clogged filter on your carburator. You should have a fitting that your fule line runs to. Remove fuel line, the remove the filter.

 

[Marlin1]

Re: Another 3.0 question

New fuel filter,good stream into the carb.<br />Its been A long time since I had anyhting with points and I have never set anything with A dwell. Last car I owned with points was A vw bug and the points were set at .16 also.<br />Can you tell me how to set the points with by dwell?<br />Is that the same thing as A volt meter.Sorry for the dumb question I just havent heard of setting it with a dwell meter in A long time.Thanks

 

[Don S]

Re: Another 3.0 question

I had an old VW, and anything from .010 to .040 worked, but on a boat, you really need the accruacy of a dwell meter.<br />Any auto parts store sells them and ebay probably has a bunch of them, many are very inexpensive, but they do the job and aren't fancy. Depends on the meter on how it's set up, but they have instructions that are very easy to follow.

 

[Boatist]

Re: Another 3.0 question

Points gap on a 1980 140 HP 3.0L 181 CI is .019. <br />Dwell is 31 eo 34 degrees. Condenser is .18 to .23 microfarads. <br />I dout you are blowing the spark out.<br />Accelerator pump is usually the cause. <br />I guess a lean Carb could do it also.

 

[Marlin1]

Re: Another 3.0 question

Can someone tell me how to adjust the carb?<br />It has 2 screw air/fuel mixtures. I dont know witch is witch.The book does not tell you how to adjust the carb.Only to adust the two screws till max rpm is achieved then set idle.<br />I tried adjusting while it was in the water but I dont know witch is air and fuel or maybe both of them are so I didnt have much luck with it.

 

[Big-E]

Re: Another 3.0 question

i wasn't aware you should adj points with a dwell meter. I did mine with a feeler gauge. Guess i should go and steal dads dwell meter. Allthough if the gap is right via feeler gauge shouldnt dwell be accurate? <br /><br />Big-E

 

[Fishermark]

Re: Another 3.0 question

Accurate dwell is more important than point gap. Of course dwell is affected by point gap, and you can usually get the dwell "close enough" by using your feeler gauge and setting point gap, but using a dwell meter is much more accurate. Adjusting point gap is a fairly "subjective" thing, whereas a dwell meter is hard to get wrong!

 

[Marlin1]

Re: Another 3.0 question

Ok ran it again just on the hose not in the water and its seems to be doing alot better,but my question still has not been answered. How do you adjust the carb?<br />I had the whole thing rebuilt and they said I would have to adjust it as soon as I put it on.I tried to get them to do it but they have about A month waiting list to get in.Too many boats not enough people to work on them. Any takers?

 

[Big-E]

Re: Another 3.0 question

In your clymor/FSM should be a procedure on adj carb. If you dont have either one i sugest buying one. I have a mercarb and it only has one adj skrew, also when i had the car rebuilt they said not to play with it.. which i havn't !! <br /><br />good luck ,<br />Big-E

 

[Boatist]

Re: Another 3.0 question

Adjusting the carb can be done many ways. What I do is turn in each screw until it hits the stop. Must turn in gently as if turn hard will damage the jet. As you turn it in count the turns closely. Say one screw is 3 and 1/4 turns and the other is 4 and 1/4 turns. I add the two numbers 3.25 plus 4.25 equals 7.50. Now I devide by two and get 3.75 or 3 and 3/4 turns. Now I set both screws at 3 and 3/4 for a starting point. Start engine and let it warm up, make sure the choke is open and engine has reached normal running tenperature. I set the RPMS to 600 and then keeping track of turns I turn it in or out 1/4 turn. If the RPMS increase and the engine smooth out You are going the right dirrection. Keep the adjustments even. If nessarry readjust the idle speed to stay at 600 RPMS. When you find the point where each screw turned either way decreases RPMS or causes engine to stumble you have reached your best adjustment.<br />Still at this point you should note the number of turns out then take it for a test run. If test run is good then your done. If not then from this point change screws 1/4 and do another run. Always keep track of your number of turns. When you get it where it runs best your done. <br /><br />I still bet it is the acelerater pump.<br /> <br />Your manual will give you a starting point also.