Fuel line sucking air?

[Green Boater]

Hi all!
I think the carb on my Mercruiser 3.0 is sucking air in where the fuel line screws into the front of it. The rpms increase momentarily when I spray carb cleaner around it. Can I use the white teflon thread tape to help seal it up or will the fuel melt it and gum my carb up?
Many thanks in advance!!

 

[Bondo]

Re: Fuel line sucking air?

I think the carb on my Mercruiser 3.0 is sucking air in where the fuel line screws into the front of it.

Ayuh,... That ain't the problem, that fitting sees only pressurized fuel...

Yer spray musta been hittin' the leak elsewhere...

 

[Green Boater]

Re: Fuel line sucking air?

Same for the fitting for the screen filter? I sprayed around the gasket area - but didn't notice an increase in RPM.

 

[RogersJetboat454]

Re: Fuel line sucking air?

Same for the fitting for the screen filter? I sprayed around the gasket area - but didn't notice an increase in RPM.

Screen filter as in the flame arrestor, or as in a fuel filter on the carb? Anything related with fuel into your carb is going to be pressurized by the fuel pump. If there were a leak, fuel would be coming out rather carb clean going in. Sounds like you are have either found a vacuum leak close by that is getting some of the spray (you need to pinpoint where), or some of the carb clean is going into the throat of the carb, and making up for a lean condition. You didn't say why you are testing. I assume this is for a running condition? Are the mixture screws in proper adjustment? Have you checked the intake manifold gasket for a leak? How recently has the carb been rebuilt.

 

[Green Boater]

Re: Fuel line sucking air?

Screen filter as in the flame arrestor, or as in a fuel filter on the carb? Anything related with fuel into your carb is going to be pressurized by the fuel pump. If there were a leak, fuel would be coming out rather carb clean going in. Sounds like you are have either found a vacuum leak close by that is getting some of the spray (you need to pinpoint where), or some of the carb clean is going into the throat of the carb, and making up for a lean condition. You didn't say why you are testing. I assume this is for a running condition? Are the mixture screws in proper adjustment? Have you checked the intake manifold gasket for a leak? How recently has the carb been rebuilt.

I sprayed around the fitting for the fuel filter that's inside the carb. Makes sense what you guys said about the fuel being pressurized from the pump.... I did get a noticeable increase in rpm when I sprayed cleaner into the venturi - so, you're saying this would indicate the fuel mix is set too lean? If so, is it screw needle in or out to richen it up a tad? The carb only has one adjustment screw externally (exception being the idle speed screw). Don't think it has any vacuum lines - the only hose I see looks like a return(?) (please correct me if I'm wrong - it's the only way I'm gonna learn!) to the fuel pump.
The reason I was asking these questions is that I had some trouble keeping it running the other day - it was like it was starving for fuel at idle and would shut off. May have just been some junk in the fuel. I added a can of Seafoam and it seems to be running much better today - but still not where I want it. Checked the point gap - it was spot on.... Had to readjust the timing, it was 2* off. I'm at least 3rd owner on this boat, having only purchased it about a month ago. I know the carb hasn't been rebuilt for at least 13 months.
I greatly appreciate your inputs and any suggestions guys!!

 

[mpdive]

Re: Fuel line sucking air?

Putting a volatile mixture down any carb is going to change rpm's even one that's running great. Are you sure your idle speed is set right? If the idle speed is too low the engine will want to die out. First make sure your idle speed is set correctly. Idle speed is sometimes wrote on the top of your spark arrestor. It's usually around 600 rpm"s. Verify that first before making any adjustments.

 

[Green Boater]

Re: Fuel line sucking air?

Another issue I need to deal with..... The fuel gauge is off, and until last week, the trim indicator gauge was off (fixed it), the voltage gauge is a little off, so I'm almost willing to bet some bevies here that the tach is also off... I backed the idle off as low as I could get it without the engine shutting off - according to the tach, it was still running between maybe 950 - 1k rpms.... any lower and it would shake and shut off. It sounds really smooth reading right at 1k, or between 1k and 1100. I'm sure that darn thing is off. Any suggestions or sources for one of those (affordable) handheld meters to check the RPMs??

 

[RogersJetboat454]

Re: Fuel line sucking air?

Putting a volatile mixture down any carb is going to change rpm's even one that's running great. Are you sure your idle speed is set right? If the idle speed is too low the engine will want to die out. First make sure your idle speed is set correctly. Idle speed is sometimes wrote on the top of your spark arrestor. It's usually around 600 rpm"s. Verify that first before making any adjustments.

It will change the RPM's, no doubt. If the engine has a perfect mixture, or running rich, adding fuel will drop the RPM's. If adding fuel raises the RPM's, then the engine is running lean.

 

[RogersJetboat454]

Re: Fuel line sucking air?

Another issue I need to deal with..... The fuel gauge is off, and until last week, the trim indicator gauge was off (fixed it), the voltage gauge is a little off, so I'm almost willing to bet some bevies here that the tach is also off... I backed the idle off as low as I could get it without the engine shutting off - according to the tach, it was still running between maybe 950 - 1k rpms.... any lower and it would shake and shut off. It sounds really smooth reading right at 1k, or between 1k and 1100. I'm sure that darn thing is off. Any suggestions or sources for one of those (affordable) handheld meters to check the RPMs??

Well, since you should have a dwell meter for setting your point's dwell, why not get one of these?;

http://www.google.com/products/catalog?hl=en&sugexp=bvre&cp=8&gs_id=o&xhr=t&q=dwell+meter&gs_upl=&bav=on.2,or.r_gc.r_pw.&biw=1366&bih=587&wrapid=tljp1315848767585012&um=1&ie=UTF-8&tbm=shop&cid=9289534976178941780&sa=X&ei=N0JuTpjSBaTl0QH1z_H1Bw&sqi=2&ved=0CDUQ8wIwAA#

Sears, and auto parts stores may carry a version of this if you don't feel like going through mail order.

 

[Green Boater]

Re: Fuel line sucking air?

Thanks guys - I appreciate it!

 

[mpdive]

Re: Fuel line sucking air?

It will change the RPM's, no doubt. If the engine has a perfect mixture, or running rich, adding fuel will drop the RPM's. If adding fuel raises the RPM's, then the engine is running lean.

Notice I said CHANGE rpm's. I realize what your saying.

 

[mpdive]

Re: Fuel line sucking air?

Another issue I need to deal with..... The fuel gauge is off, and until last week, the trim indicator gauge was off (fixed it), the voltage gauge is a little off, so I'm almost willing to bet some bevies here that the tach is also off... I backed the idle off as low as I could get it without the engine shutting off - according to the tach, it was still running between maybe 950 - 1k rpms.... any lower and it would shake and shut off. It sounds really smooth reading right at 1k, or between 1k and 1100. I'm sure that darn thing is off. Any suggestions or sources for one of those (affordable) handheld meters to check the RPMs??

You have a definite fuel delivery problem if you can't get it to idle smoothly at 600 rpm. You either have a vacuum leak, carb need rebuilt or your mixture screws are set way lean..Also timing etc......

 

[mpdive]

Re: Fuel line sucking air?

Notice I said CHANGE rpm's. I realize what your saying.

That didn't come out right...Sounds like I was being "snippy". My apologies.......

 

[Green Boater]

Re: Fuel line sucking air?

Borrowing a tach/dwell meter from a friend today...I'll see exactly what the idle rpms are. I'm thinking the fuel mix was running a little lean - I backed the needle out 1.5 turns and it actually "sounds" better. Do they still make those old style fuel mixture testers?? Trying to remember if you hook the sensor up to the #1 plug - something like that.... Man, that was YEARS ago last time I used one!!

 

[Volphin]

Re: Fuel line sucking air?

Before you adjust your mixture, verify that engine timing is correct. Then...

How to set idle mixture: Before you fire up the engine, attach a vacuum gauge to the intake or base of the carb. Slowly turn each idle-mixture screw in until it gently bottoms out and count the number of turns it takes. Do this for each idle-mixture screw and then return them to their original positions. If all the idle-mixture screws are not adjusted the same, do that now. Remember to always adjust both screws the same amount. This will help balance the idle mixture and allow the engine to run as smoothly as possible. If the carburetor is new to the engine, start at 1?-turns out (counterclockwise) from full in.

Now start the engine and set the idle speed to around 850 rpm with the idle-speed screw. Note the reading on the vacuum gauge. Next, turn one idle-mixture screw in ?-turn and note the change on the vacuum gauge. If the vacuum reading increases —say, from 14 inches to 14-? inches —then move to the other screw and turn that mixture screw in ?-turn as well. Again, note the vacuum gauge reading; if the gauge continues to climb, then adjust each idle-mixture screw in another ?-turn. On most carburetors, turning the mixture screw in (clockwise) leans the mixture, while counterclockwise (out) enriches the mixture.

Initially, if the engine stumbles or the vacuum drops when turning the mixture screw in, turn both screws out about a ?-turn and evaluate the results. The goal of adjusting the idle-mixture screws is to achieve the highest possible idle vacuum at a set idle speed. If the idle speed increases after you adjust the idle-mixture screws (which is likely), be sure to adjust the idle speed back to the base speed. This is important because a higher idle speed will increase the vacuum reading. Maintaining a standard idle speed will make it easier to evaluate changes to the idle-mixture screws.

V

 

[RogersJetboat454]

Re: Fuel line sucking air?

Borrowing a tach/dwell meter from a friend today...I'll see exactly what the idle rpms are. I'm thinking the fuel mix was running a little lean - I backed the needle out 1.5 turns and it actually "sounds" better. Do they still make those old style fuel mixture testers?? Trying to remember if you hook the sensor up to the #1 plug - something like that.... Man, that was YEARS ago last time I used one!!

If you are getting your hands on a dwell meter, now would be a good time to throw in a fresh set of points. Set the dwell THEN set the timing. This will eliminate any questions that the primary ignition is up to snuff, and you will have the confidence that you have a new set of points which you KNOW have been set up properly.

 

[Green Boater]

Re: Fuel line sucking air?

Thanks guys. I installed new points, condensor, cap, plugs and wires about 2 weeks ago. I've triple-checked the gap on the points - they're still spot on, according to specs. Gonna have to wait until Friday to verify the idle rpm with a dwell/tach meter. Regardless of outcome, the carb will be undergoing a rebuild as part of the winter prep this year. Not sure yet if it's a Rochester or what - may have to post a pic and see who can ID it for me. No markings on the carb itself, but the spark arrester has "Mercruiser" stamped on it.

 

[kidafa]

Re: Fuel line sucking air?

quick question guys..... How do you tell if your engine has "Points" or not?

 

[RogersJetboat454]

Re: Fuel line sucking air?

If you replaced the points with out a dwell meter, use this opportunity to check your dwell. You can install points with out one, and most of the time get away with it, but you may be surprised how much better it runs if you properly set the dwell. Again if you do this (which I strongly suggest), set the dwell then set the timing.

 

[RogersJetboat454]

Re: Fuel line sucking air?

quick question guys..... How do you tell if your engine has "Points" or not?

Quick response....
Start your own thread with details about your engine (make, size, model number, year). Don't Hijack someones thread...