Mercruiser 888

[Scott06]

Do you think that will make quite the difference?

Kenny has been around the block maintenance wise. Obviously he would not be suggesting it if he didn’t think it was part of the issue.

Likely the carb set up for a universal automotive application is not either sized or jetted correctly for marine loads and the altitude u are running at

What do the spark plugs look like

 

[mauro.]

Sorry about that and my late reply the spark plugs are white but not glazed that is actualy a good point with those jets I guess automotive engines usualy dont run at 4500 rpms for a long time

 

[ROY WILLIAMS]

Sorry about that and my late reply to the spark plugs are white but not glazed that is actually a good point with those jets I guess automotive engines usually don't run at 4500 rpms for a long time

MCM 888 engine max 3800-4200 rpm ....

 

[Scott06]

Sorry about that and my late reply the spark plugs are white but not glazed that is actualy a good point with those jets I guess automotive engines usualy dont run at 4500 rpms for a long time

There a couple things. A marine carb is built to with bowl vents such that if it overflows it dumps the gas down the throttle bores , also does not have a fast idle cam, jetting is likely a tad richer as marine engines run cooler due to open cooling system. The fuel and vapor control on a marine carb is a safety control so gas vapors that would drop out the engine compartment in a car don’t build up in a closed engine bay and explode.

yes you are correct a automotive application doesn’t run under the same load constantly like a marine application. Same reason they don’t use vacuum advance distributor, marine will not be at part throttle high vacuum cruise ever. hence the power valves enrich the mixture at different vacuum numbers.
if you can post some pics of the plugs when you say white that may mean you are running lean and may have be prone to detonation.
this is the best old school spark plug reading chart /explanation I have seen

Wallace Racing - Spark Plug Reading

 

[mauro.]

Thank you so much will post pics shortly.

 

[Scott Danforth]

Sorry about that and my late reply the spark plugs are white but not glazed that is actualy a good point with those jets I guess automotive engines usualy dont run at 4500 rpms for a long time

Your running lean. Your plugs should be toffee colored

My 1986 RX7 with a transplanted 1994 GM 3.4 V6 ran 4500 RPM an hour each way on my daily commute. Put 100k on the car before I sold it

 

[mauro.]

This is one of the plugs, I took out three and they all looked alike. Hope you can see enough looking at them now I almost think they are running rich

 

[Scott Danforth]

Your running lean

 

[mauro.]

what size jets would you recommend?

 

[Scott Danforth]

What carb, and what are you starting with?

 

[mauro.]

I don't recall jet size I thought it was a 53 is that possible? carb is the Holley 2300 but with the auto line part number. so they did some modifications to the throttle plate it has the idle mixture screws in there instead of the metering block as far as i can tell that is the only difference

 

[Scott Danforth]

All Holley carbs have idle mix screws on the primary metering block.

Post the list number on the choke horn

 

[mauro.]

list number is 4308-1
the tag says autoline c-7080

 

[Scott Danforth]

4308-1 is for a 1964 IH.

It's not in the Holley library, however it's only listed as 275 CFM on an IH site

Your motor needs about 400 CFM

If sticking with a 2-barrel, I suggest a Holley 500 CFM marine carb

 

[mauro.]

This means not enough air going through right?

 

[Scott06]

This means not enough air going through right?

yes it is the equivalent of running while someone is choking you. As SD mentioned most 5 L engines need 400-500 cfm vs the 275 you have.

I run a Edlebrock 1409 on my 5.0 chevy vortec and it is just about perfect size.

Do you have a 4 bbl intake or is it 2 bbl.

 

[mauro.]

it is a 2bbl intake and so that is why I hear a bit of a sucking sound when at WOT right?

 

[mauro.]

I meant due to the carb.

 

[Scott06]

it is a 2bbl intake and so that is why I hear a bit of a sucking sound when at WOT right?

yes - if you look at how they rate the CFM of a 4 bbl vs a 2 bbl they use a higher vacuum to measure the cfm of a 2 bbl - 1.5" of mercury is used for 4bbls and 3 for 2 bbl carb.

So and old school way to tell is to hook up a vacuum gauge at WOT of the carb is correctly sized vacuum will be down to 1" or less. If the carb is too small there will be more vacuum as the engine is trying to overcome the restriction. this is why the power or enrichment circuit on carbs is signaled off of vacuum - as throttle opens and you get closer to WOT and want a richer mixture for max power vacuum drops.

Since you have a slightly hotter cam depending on the wallet it might be worth it to get a 4 bbl intake and carb. Of course it is easier for me to spend your money but generally you will find with the smaller primary throttle bores of a 4bbl you get better midrange throttle response

 

[mauro.]

I am aiming to spend not a whole lot more as i already spent too much In that case i will probably stick with 2bbls, do you have any suggestion where I could find a good marine carb at a good price that ships to Canada?