Loading up below 1300RPMs after hours of use.

[imp0ster]

Brand new Edelbrock 1409 600cfm. Merc 355 from late 2013. Engine has around 20hrs on it now. The entire engine had a tuneup earlier the year. Entire fuel system is new. Gas is clean. Water separator is clean. This only happens after about 1.5hrs of idling or after I let the boat sit for hours after running a decent amount of time. I can actually hear the engine running differently in the low RPMs and if I plop it in neutral and WOT the throttle twice it clears up. It spits if I ease into it but runs great cruise - WOT.

I'm an EFI tuner so clueless here. What in the carb will cause this? The plugs definitely show she's running rich.

 

[jimmbo]

rewording my response

 

[Bondo]

Brand new Edelbrock 1409 600cfm.

Ayuh,.... Rick Stephens just put one on his motor,....

Rick can tell ya All 'bout tunin' it,.....

I believe the link to the Bible for that carb is in Rick's thread,....
Read the book, 'n you'll understand the carb,....

Great carb, I love 'em,....

 

[imp0ster]

Any chance you have a link? I looked in stickies and searched his name and came back with a ton of hits.

 

[Bondo]

Ayuh,..... Try this, then pm Rick,....

 

[imp0ster]

thank you I shot him a PM. It's like something heats up and gets stuck.

 

[Rick Stephens]

Thought I would bring this back here instead of PM, so anyone can chime in with ideas and correct or expand anything I suggest.

The manual for that carb is findable on this page, t second link is EPS Carburetor Owners Manual.

http://www.edelbrock.com/automotive/misc/tech-center/?query=1409&submit=search

That carb is so easy to take apart and clean. That is the first step. Make sure all the passages are open. Edelbrock recommends you use Simple Green and compressed air and not carb cleaners. They have a coating on the carb that gets damaged with the high volatility cleaners.

Next is check float level. If in doubt, replace the float's needle valve.

New gaskets and needle valve are a auto parts store item. You can use the kit for the 1406/1409 models and pretty much anyone will carry it.


I would absolutely be checking spark plugs if you have a new engine and new carb. No matter who or how it was set up, it is easy to pull a plug and be certain of mixture and hard (read expensive) to replace valves that got too hot or holed pistons.

Rick

 

[imp0ster]

I already checked the plugs and they're trashed like I knew they would be. I'll ask my father to clean the carb. he's the carb guy. I'm the laptop ECM guy. It will probably be a week or two.

 

[Rick Stephens]

I already checked the plugs and they're trashed like I knew they would be..

Post pictures of plugs. That will help a lot.

 

[imp0ster]

No Title

Well this could be the problem. Dumped the carb out. I'll take it to dad for cleaning then retune it

 

[imp0ster]

float bowl crudded up. metering rods covered in crap. This is a brand new carb, brand new fuel line, emptied cleaned and filled tank. All this crap had to come from when we rebuilt the floor/stringers/bulkheads and or the fuel pump. When I puled the fuel line to the carb it was empty telling me the check valve at the tank is garbage. I thought mechanical pumps had a check valve in them too?

 

[Bondo]

I thought mechanical pumps had a check valve in them too?

Ayuh,.... A mechanical fuel pump consists of 2 check valves, 'n a diaphragm,....

 

[imp0ster]

thanks! Looks like mine be bad!

 

[NHGuy]

I'd also recommend re cleaning your fuel tank.
It really has to be pretty much perfect or you are spitting in the wind.

 

[imp0ster]

I'm placing an additional filter in line before the water separator for now. I sealed the floor in for this season so tank access is pretty much impossible. If you click on my link in my sig you'll see what I mean. The end of this season we'll pull the tank cover and finish the nidacore job. I'll pull and clean the tank again.

I just put the carb back on and the new water separator in. We'll see how it does after tuning and a day out. Anymore BS and I'll have to assume the fuel pump is just totally toast. I haven't bought a new one. I'm waiting on underwriting to finish cleaning up their stupid mess so I can lock down my new house. Damn priorities.

 

[imp0ster]

took some cranking to get the gas back up to the carb but once it fired I didn't have to play with the throttle. Idled perfectly then I dropped the idle speed to 650 from 900 and started messing with the screws. I turned them lean until I heard the engine choke then added a bit of fuel until it smoothed out. No matter what I could not get the idle speed higher with the mixture screws even backing the idle speed screw out more. It's weird but at least it seems to be idling better. I'll probably have to mess with it more when I buy the replacement fuel pump.

Thanks again peoples

 

[NHGuy]

Sorry for the long wait, but you probably have it exactly right..
I am in the middle of this on my engine and I've done a lot of reading on the subject so thought this would be a good post for all to have as reference.
Since the Webers in our boats are direct cast from the same Carters as the Edelbrocks are I think the Edelbrock method is a very good process.
This is adapted from Edelbrock Carb Brochure #0033. Idle Mixture section..
Edelbrock wants you to get highest rpm with each mixture screw starting from a predetermined lowish rpm. Say 700.
Do one side then the other til they equal.
Example: warm engine idle set to 700, turn down mix til it stumbles. back out til smooth and no longer increases engine speed. If it increased more than 40 rpm reset to original rpm. Do the other side the same way.
Now, reset to intended idle. Retrim mix screws again for max rpm only. Reset to correct idle. Turn down mix enough to get a 20 rpm drop. Reset idle to desired value.
This is what Edelbrock calls a lean best idle. Mercruiser does NOT say to do the lean down step. So if your results are poor you may want to add back in the 20 rpm via the mix screws, then retrim the idle speed.
BTW if you have a thunderbolt V this needs to be done with the distributor lock out wire (purple/white) grounded, or the ignition will try to correct rpms on you while adjusting!
I am going to give this a separate post, might be a keeper.

 

[imp0ster]

Also FYI the mechanical pump versions of these motors act the complete opposite of a electric pump. When they're bad you see it at idle when it heats up and the diaphragm gets enough heat into it. Once the RPMs build the pump hits the pressure point and runs fine. Electric pumps will either just run like crap from the get go or fail at higher RPMs with or without heat depending on its failure.

Mine was a dirty carb and a shot mechanical pump. With as little as my boat weighs with a new 355 and all new parts and a brand new Enertia Eco 19 I'm going to pull a compression test then leak down to see why I can't even get 50mph out of it. It's semi moot since a built 383 will go in it but at least when I sell the engine I can be honest about it with someone