fuel problem with straight 4 Mercruiser I/O

[nopEda]

Hi,

I've got a straight four cylinder Mercruiser some info led me to believe is a 470 2bbl. 1976-1979, though other info told me it's a 140 hp 1973 Vega. I don't know what to think about all that, and I'm sure no mechanic. Anyway, since the weather has gotten cooler it no longer will idle, though the temperature may have nothing to do with it. I'm in GA around Atlanta so it's not very cold. It has a clear inline fuel filter that got real dirty so I changed it, but it still won't idle. There also may be a filter where the line goes into the carburetor, but I don't understand the fitting there. There's a large part that screws into the carb, and then a smaller part behind it which the line goes into. I don't know if I should hold the smaller part and loosen the large part, or try to undo both at once. When I turned it a little the small part turned with the large part. I tried holding the small part and putting some pressure on the large part to see if they would break loose, but didn't want to put too much pressure on it before trying to find out how it goes together. Here is a photo of what I'm trying to describe:

IMG_0631.jpg Photo by sazzyazz | Photobucket

Is there another fuel filter in there?

I don't think it just needs the idle speed increased with the set screw because that might make it idle too fast to go in gear. Does anyone know what I should try to do? Maybe new spark plugs because it has been a while...could that be the real problem? It doesn't sound like it's skipping to me but I don't know. Like I said I'm no mechanic.

Thank you for any help with this!
David

 

[achris]

Re: fuel problem with straight 4 Mercruiser I/O

Hello David,

I can confirm you have a GM engine (either 120hp or 140hp) and not a 470....

In your case I would start with a basic tune-up, including new plugs, points, rotor and cap....

Here's the basic rundown of what I suggest.....

Standard troubleshooting for an engine.

Engines require certain things to operate properly... Basically they need the correct fuel/air mixture to be compressed and then fired at the right time.

So, in this order.

1. Compression tests.
2. Check spark plugs, replace if needed.
3. If points, replace, along with condenser and rotor. Check and adjust, if needed, points cam dwell angle.
4. Inspect distributor cap, rotor and leads, replace if necessary.
5. Check spark quality (needs to be a nice BLUE spark drawn over 1/2").
6. Set timing. Check timing advance is working correctly.
7. Check/change fuel filters and check that the fuel system is not sucking air.
8. Check fuel pump pressure.
9. Check for full opening of the carb. Also ensure choke is opening fully when the engine is warm.

...Is there another fuel filter in there?

Yes, so you do need to break it open. The large part should stay in the carb, and the tube nut should unscrew.

 

[84EdH]

Re: fuel problem with straight 4 Mercruiser I/O

Yes, follow the sequence in the list Chris posted. When you get to fuel filters, there is a filter inside the big nut shown in your pic. You hold the big one still and back the small one out. Then back the big one out. There is a spring and a filter in there.
Carefull with the small one it is easy round off if your wrench slips. A line wrench is best.

 

[84EdH]

Re: fuel problem with straight 4 Mercruiser I/O

Just posted over your edit:facepalm:

 

[Fishermark]

Re: fuel problem with straight 4 Mercruiser I/O

I can confirm you have a GM engine (either 120hp or 140hp) and not a 470....

Just a quick question to the original poster - is that a photo of your actual carb? Or is it a picture similar to your setup? I ask not to say it is wrong to post a photo of something that is not specifically yours, but any information given to you about your engine is going to be based on you having the engine in the photo. And if that is not yours, then we do not know if you have the infamous 470 or not.

Let us know. Thanks!

 

[ziggy]

Re: fuel problem with straight 4 Mercruiser I/O

is that a photo of your actual carb?

it's my pic fm.
my 2gc on my L6, on lime time....

op, yep, big nut stays stationary, small nut gets loosened. on my 1975 set up there is a fine mesh screen inside. mine has had some crud in it too.

that's rust from my fuel tank inside the screen filter your looking for.

 

[Fishermark]

Re: fuel problem with straight 4 Mercruiser I/O

Hey Ziggy - I knew it looked familiar! ;-)