carburetor suspect problems

[lukecono]

I have an early 1980s MerCruiser 5.7 and the boat takes a while to get running. I have to pump and advance the throttle multiple times (from 5-15 tries) cranking with no life until it fires up and must maintain 1500 rpms before bringing the throttle down to idle and not having it stall. The engine is still under 20 hours of run time since being freshly built by certified mechanic. The engine isn't stock and does have an aftermarket cam rods and pistons making 300hp instead of the 260. The other funny thing is that the boat does decide to idle at different rpms. Typically, after bringing the throttle back to neutral after waiting a few minutes at the 1500 rpms it'll sit at 900 rpms idle, I shift, and it drops to 700 rpms... that's the normal part. After on plane and coming off back to idle the boat again goes to 900 in gear and slowly walks itself down to its lobing 500-700 and stays there once in neutral. My biggest thing is having it start within first couple tries and my first suspicion is not enough fuel until that 10th try or so cranking. I haven't dug into it too much, but I think one of first places I should look is at the fuel accelerator pump and see if fuel sprays when I give it those priming throttle pumps. ANY thoughts?

 

[Bondo]

Ayuh,..... Welcome Aboard,.... No doubt a fuel delivery issue,.....

What carb,..??

 

[lukecono]

Ayuh,..... Welcome Aboard,.... No doubt a fuel delivery issue,.....

What carb,..??

I couldn't tell you honestly, I was just picking some brains and confirming what I suspected. DO you have a good way to test this? Pour some fuel down it or starting fluid? I've always been told to avoid starting fluid. I can get the carburetor serial number tomorrow sometime. You think fuel delivery is my starting issue? Is it normal to have to let it warm up at higher rpms and back it down?

 

[Bondo]

I couldn't tell you honestly, I was just picking some brains and confirming what I suspected. DO you have a good way to test this? Pour some fuel down it or starting fluid? I've always been told to avoid starting fluid. I can get the carburetor serial number tomorrow sometime. You think fuel delivery is my starting issue? Is it normal to have to let it warm up at higher rpms and back it down?

Ayuh,.... Sounds like the carb might need a rebuild,.... is it a 2bbl., or 4bbl.,..??
If the choke ain't workin' properly, havin' to rev it is likely,....

 

[kenny nunez]

In addition to the carburetor suggestions.
Something else to consider, if your distributor is a breaker point style check that the centrifugal advance is not sticking. Also check that the +or bat side of the coil is getting a full 12 volts in cranking mode.

 

[lukecono]

Ayuh,.... Sounds like the carb might need a rebuild,.... is it a 2bbl., or 4bbl.,..??
If the choke ain't workin' properly, havin' to rev it is likely,....

I'll be able to check tonight and tell you the carb. Is there any way to manually activate the choke?

 

[Bondo]

I'll be able to check tonight and tell you the carb. Is there any way to manually activate the choke?

Ayuh,..... If everything is working properly, advancing the throttle to Wot once, sets the choke,....

 

[lukecono]

Ayuh,..... If everything is working properly, advancing the throttle to Wot once, sets the choke,....

ill give that a shot tonight when I go to start it. Pulling the boat just for some bilge cleaning and I'll also get the carb for you. Much appreciated

 

[lukecono]

ill give that a shot tonight when I go to start it. Pulling the boat just for some bilge cleaning and I'll also get the carb for you. Much appreciated

Quick question as I'm looking into it more, is the linkage for the choke on the opposite side of the throttle linkage? I do know for a fact it's a manual choke. I keep reading also about this heat sensing coil, but I don't believe that pertains to me. Seems as i narrow it down my choke may be open and not behaving as it's supposed to more so than lack of fuel because it does eventually fire up.

 

[tank1949]

I have an early 1980s MerCruiser 5.7 and the boat takes a while to get running. I have to pump and advance the throttle multiple times (from 5-15 tries) cranking with no life until it fires up and must maintain 1500 rpms before bringing the throttle down to idle and not having it stall. The engine is still under 20 hours of run time since being freshly built by certified mechanic. The engine isn't stock and does have an aftermarket cam rods and pistons making 300hp instead of the 260. The other funny thing is that the boat does decide to idle at different rpms. Typically, after bringing the throttle back to neutral after waiting a few minutes at the 1500 rpms it'll sit at 900 rpms idle, I shift, and it drops to 700 rpms... that's the normal part. After on plane and coming off back to idle the boat again goes to 900 in gear and slowly walks itself down to its lobing 500-700 and stays there once in neutral. My biggest thing is having it start within first couple tries and my first suspicion is not enough fuel until that 10th try or so cranking. I haven't dug into it too much, but I think one of first places I should look is at the fuel accelerator pump and see if fuel sprays when I give it those priming throttle pumps. ANY thoughts?

Lots of years on a gas tank and the crap that can settle in it or in pickup tube or water/fuel filter. I suspect to start there. Hope that your tank can be easily removed, or at least pickup tube easily removed. My old tanks had screens in pickup tubes that were somewhat clogged up with crap. Gas tanks generate lots of condensation unless completely full of gas. You might consider an electric pump to recycle gas to catch contaminates.

 

[lukecono]

Lots of years on a gas tank and the crap that can settle in it or in pickup tube or water/fuel filter. I suspect to start there. Hope that your tank can be easily removed, or at least pickup tube easily removed. My old tanks had screens in pickup tubes that were somewhat clogged up with crap. Gas tanks generate lots of condensation unless completely full of gas. You might consider an electric pump to recycle gas to catch contaminates.

Thank you, I'm sure it would be much beneficial to do something like that, but the tank has been taken care of by last couple of owners. Winterizing tanks been full to avoid condensation with stabil and fuel water Seperator is relatively new. I don't think this is my long starting issue but just a good recommendation for any older boat. If gas contamination was the issue I would have bigger problems and Definity while running but starting is the only thing that's giving me an issue.

 

[dubs283]

Is the ignition system a thunderbolt or conventional (points)?

 

[lukecono]

Is the ignition system a thunderbolt or conventional (points)?

its a thunderbolt ignition system, I have two wires that ride next to my carb that aren't connected and are most definitely for my electric choke. I think i've narrowed this down to the choke. Boat runs great minus the initial start.

 

[nola mike]

Quick question as I'm looking into it more, is the linkage for the choke on the opposite side of the throttle linkage? I do know for a fact it's a manual choke. I keep reading also about this heat sensing coil, but I don't believe that pertains to me. Seems as i narrow it down my choke may be open and not behaving as it's supposed to more so than lack of fuel because it does eventually fire up.

Who knows? You still haven't told us what carb you're using. And afaik no mercs came with manual chokes.

 

[lukecono]

Who knows? You still haven't told us what carb you're using. And afaik no mercs came with manual chokes.

I haven't got down to the boat yet. I'll snap some pics of it hopefully tonight. And yes, I'm learning along the way, I did realize since then that it is electric.

 

[dubs283]

its a thunderbolt ignition system

Is the module the early style 4-5" square, 1.5" wide box mounted to the post exhaust riser/elbow?

 

[lukecono]

Is the module the early style 4-5" square, 1.5" wide box mounted to the post exhaust riser/elbow?

It’s the older one the 4-5”

 

[lukecono]

Here’s the images of the carb. The choke was zip tied open permanently. I don’t have the linkage there or any choke even there…

Thank u all for the ideas so far but found the issue now it’s just how to go about it … YouTube it is

 

[dubs283]

Given the older style ignition module present I'll note if the sensor in the distributor has been replaced with the latest style sensor I've experienced a timing jump at idle of anywhere from 4-8 degrees. This would account for the varying rpm at idle speed you're experiencing.

I cannot tell from the photos if the setup has a newer style sensor

Couple things I do see in the pics is the throttle return spring is installed incorrectly and the plug wires are wire tied in a bundle on the odd side

 

[Scott06]

The reason the choke is zip tied open is the aftermarket aluminum intake does not have the choke stove capability in the exhaust cross over. Quadra jets liek this use a divorced choke with a heated spring in the manifold. Someone removed this. A place like cliffs carbs should have An electric choke conversion or advance the throttle on cold starts .

i ran my mercarb with choke forced open for years was onky an issue starting in cold weather in the fall