5.7 Mercruiser will not idle

[rworkman6]

I have a 97 Maxum 2300sc with a 5.7 Mercruiser. I bought the boat last year and it had been used very little for 2-3 years. The boat has never ran well at idle so I got my brother-in-law to help me rebuild the Mercarb 2BBL a couple of weeks ago. I put the carb back on and it ran and idled perfectly. I had 3 great boating days, but when we went out on the 4th it suddenly went back to its old ways...only worse. Now I cannot get the boat to idle at all and it bogs terribly when the throttle is applied. We took the air horn off and checked the float and spring needle and seat. We even changed the the needle over to a solid needle. It seemed to help a little but will still not idle. It appears there may be gas dripping into the bowl at idle and that the carb may be flooding out at idle. The boat runs perfect at 1600RPM and above. We are out of ideas and hope someone can provide a solution. Otherwise, I guess I am heading to a mechanic and will lose several weeks of our short Illinois boating season.

 

[jtmarten]

Re: 5.7 Mercruiser will not idle

Did you set the float level? Pull the top off and see if the float is full of fuel. Maybe some debris in the needle/seat? What type of fuel pump? Fuel pressure too high for needle/seat to stop the flow? Any fuel in the fuel pump safety line?

 

[rworkman6]

Re: 5.7 Mercruiser will not idle

Originally set float to factory specs when rebuilding, but we lowered it a little last night thinking it was too high. We also put the original spring needle/seat back in then even switched to the new solid needle that came with the carb kit. Nothing made a difference. It is a mechanical fuel pump and I have not checked the pump safety line. Would gas in that line indicate a torn diaphram? Can you adjust the fuel pressure on that pump? I just cannot understand why it ran so well after the rebuild then reverted back to the original idle problem after a few trips on the lake. Frustrating.

 

[John_S]

Re: 5.7 Mercruiser will not idle

If you see fuel dribbling down and collecting on the butterflies, the needle/seat has an issue or too much fuel pressure. If it is coming out of the clear hose than your fuel pump has ruptured and needs replacing.

I went through a similiar problem on my 5.7. After replacing/checking increasing needle seat pressure, would seem to help, but would "act up" again. I broke down and rigged up a way to measure the fuel pressure. Pump was putting out 9-10lbs at idle. New pump fixed it, and there is not a pressure adjustment.

 

[Silvertip]

Re: 5.7 Mercruiser will not idle

The fact that the engine was pressure washed is very likely the cause of the problem. The reason there are few suggestions is that a pressure washer can screw up lots of delicate things including electrical connections, of which there are many. While you may have 12 volts present on the ignition, is it present while cranking? Have you checked for spark at the coil wire? No spark at the plug wires does not mean the ignition electrics has failed. It may be the fact that you doused the cap with WD-40 and it is arcing inside the cap. Replace the cap and try it. If it runs, flog your brother-in-law with the old one and don't let him do you any favors in the future.

 

[John_S]

Re: 5.7 Mercruiser will not idle

The fact that the engine was pressure washed is very likely the cause of the problem. The reason there are few suggestions is that a pressure washer can screw up lots of delicate things including electrical connections, of which there are many. While you may have 12 volts present on the ignition, is it present while cranking? Have you checked for spark at the coil wire? No spark at the plug wires does not mean the ignition electrics has failed. It may be the fact that you doused the cap with WD-40 and it is arcing inside the cap. Replace the cap and try it. If it runs, flog your brother-in-law with the old one and don't let him do you any favors in the future.

Cross threaded? http://forums.iboats.com/showthread.php?t=415035

 

[chopsticks]

Re: 5.7 Mercruiser will not idle

I also have a 5.7 merc with a 2 bbl mercarb in a 2355 Bayliner . It ran fine before it was winterized and now it won't idle. (A docking nightmare) I use startron at every fill upas well as when winterizing. I have read some forums about replacing the carb with an aftermarket unit, but I did not see any 2 barrel carbs. Any info would be appreciated.

 

[Bondo]

Re: 5.7 Mercruiser will not idle

The boat has never ran well at idle so I got my brother-in-law to help me rebuild the Mercarb 2BBL a couple of weeks ago. I put the carb back on and it ran and idled perfectly. I had 3 great boating days, but when we went out on the 4th it suddenly went back to its old ways...

Ayuh,.... My guess is, there's Crap in the rest of the fuel system,....
Tank, lines, fittings, All are suspect...
What's in the Filters,..?? Anything,..?? Water,..??

Probably have to pull the carb,+ reclean it....

Welcome Aboard,+ Same answer for You too Chopsticks.....
You probably need a Rebuild...

 

[rworkman6]

Re: 5.7 Mercruiser will not idle

I have the carb back off and on the workbench now. When I opened it up everything looked very clean. I did think about crap in the lines, tank, etc working back into the carb. That would explain it running great for 3 days then bad on the fourth. Also pulled the fuel/water filter and screen filter in the carb and both were clean. I took the cover off of the electric choke and I am not sure it was properly assembled before. Should the butterfly spring be set to snap to the closed position? My butterfly had no spring tension on it at all. When I catch the coil onto the choke lever it snaps it closed. Is this correct? Thanks!

 

[rworkman6]

Re: 5.7 Mercruiser will not idle

Thanks for all the help. I think I may have it fixed. Before deciding to replace the fuel pump I decided to completely start over and tear the carb completely apart. I basically did another rebuild...and when I just put it back on the boat ran perfectly. I am not getting my hopes up since it ran well when I put it on after the first rebuild. I am thinking that the float may have been getting hung up on that spring wrapped rod that goes down to the power valve. They are awfully close together. Thanks again!

 

[John_S]

Re: 5.7 Mercruiser will not idle

Thanks for all the help. I think I may have it fixed. Before deciding to replace the fuel pump I decided to completely start over and tear the carb completely apart. I basically did another rebuild...and when I just put it back on the boat ran perfectly. I am not getting my hopes up since it ran well when I put it on after the first rebuild. I am thinking that the float may have been getting hung up on that spring wrapped rod that goes down to the power valve. They are awfully close together. Thanks again!

If it acts back up, check for that fuel puddling.