3.7LX Mercruiser

[dirtdiver]

I have ann 89 3.7LX mercruiser with a quadrajet cab, its been running fine up until yesterday. I was crusing along at about 3200 rpm and after a few minutes of running the engine started boging down. It would run at about 1900 and if you would push the throtle open more it would start to die out. I replaced the condesner and points as well as the cap and rotor. Same thing happend today. I checked the little debrise seperator deal. and there didnt seem to be any water in it. I also tried regaping it after it had been dying out. I followed the book and used a feeler gauge ti gap it.... Any ideas?

 

[Don S]

Re: 3.7LX Mercruiser

I checked the little debrise seperator deal.

What is that ???????

Do you have a water seperating fuel filter? Looks like an oil filter, only for gas.
Did you take it off and pour it into a container and look for water.
If you don't have one, I would suspect water in the carb as your problem, and not ignition, or possibly an air leak or plugged fuel system somewhere.
Have a look at this thread. http://forums.iboats.com/showthread.php?t=283269

 

[Bifflefan]

Re: 3.7LX Mercruiser

There is a fuel filter in the carb right where the fuel line connects. it probably plugged up.
Mine was packed full of really fine sand once, that had made it through then other filter.

 

[dirtdiver]

Re: 3.7LX Mercruiser

It looks like a filter but no filter, kinda like a bowl. I'm going to check the filter on the carb, I think theres on there but Im not totally sure. I just read a post of someone having similar trouble but different motor, and their problem was the filter. I just dont see how it will run fine and then stop.

 

[EddiePetty]

Re: 3.7LX Mercruiser

......and there's yet another filter in that little sheetmetal can on the top of your mechanical fuel pump!!!!

FWIW...Ed in 'ol Virginny

 

[dirtdiver]

Re: 3.7LX Mercruiser

......and there's yet another filter in that little sheetmetal can on the top of your mechanical fuel pump!!!!

Thanks, I didnt know there was on there. The one on the carb I should be able to get at an auto parts store, but I guess the one on the pump I'll have to get from a boat part store?

 

[EddiePetty]

Re: 3.7LX Mercruiser

but I guess the one on the pump I'll have to get from a boat part store?

...got mine at our local mon 'n pop NAPA store!!!

Ed

 

[dirtdiver]

Re: 3.7LX Mercruiser

Thanks again. Im going to go change those filters now and try it out.

 

[dirtdiver]

Re: 3.7LX Mercruiser

Well I only found one fuel filter and that didnt fix it. Changed the coil and that didnt fix it. took the carb apart and cleaned it and it still runs the same. Just took apart the fuel pump and {t looks ok. Im stumpis one. do anyone have any other ideas?

 

[Bifflefan]

Re: 3.7LX Mercruiser

When you say you cleaned the carb, do you mean you took it apart, soaked it in carb dip, and then installed new gaskets and a float?
or shot it out with carb spray and put it back together.

I still think its a fuel problem of some sort.

 

[dirtdiver]

Re: 3.7LX Mercruiser

Could the fuel line from the tank to the pump be pinching itself off? Its rubber. Maybe the pick ups in the tank are cloged

 

[dirtdiver]

Re: 3.7LX Mercruiser

Its also back firing when it sputters out. i dont know if that makes a difference

 

[mdlee]

Re: 3.7LX Mercruiser

Are you sure the fuel pump is working correctly? An ez way to check your fuel pump is: disconnect your fuel inlet line going into the carb, place a hose on the line and run it into a clear container, turn the motor over. This test will confirm that the fuel pump is pumping, once you confirm the pump is working you will need a fuel pressure gauge to confirm the correct pressure. If all is right coming from the pump than you can eliminate the pump from your trouble shoot. Which will give you about a 90% chance that the problem is in the carb. Quadrajet carbs are VERRY hard to rebuild.

 

[dirtdiver]

Re: 3.7LX Mercruiser

I'll try it. What its doing just doesnt make sense, it runs great from 900 to 1700 rpm. Any higher and it backfires thru the carb and dies out. It does the same thing in the water or in netural hooked up to a hose.

 

[dirtdiver]

Re: 3.7LX Mercruiser

My newest idea is the mech advance is messed up on it. It kinda makes sense. Any thoughts?

 

[pasogrande]

Re: 3.7LX Mercruiser

I have a similar problem. My boat has two 3.7LX motors. They both idle perfectly, but when running one bogs down at 3000 rpm, and sometimes dies. After many tests, we switched the carbs and the problem went with it to the other engine. With just one engine running the problem comes in at about 2500 rpm. We stripped the carb (Rochester Quadrajet) and everything looked fine, but we did adjust the float level a little. No change. Tomorrow I will borrow a similar carb and see if it is the same.
btw, a carb "expert" told me some years ago that a carb cannot cause backfiring. Maybe timing.

 

[dirtdiver]

Re: 3.7LX Mercruiser

Problem solved. It was the mech advance sticking. It runs like a champ now