Trojan Boat Forum

The engines on our F36 convertible were originally 400's, but the previous owner replaced them with 440's and later rebuilt them. While there are a number of issues that I am looking at, one that has my immediate attention is a heavy gas smell that appears after shutting down the engines. It is quite noticeable in the salon for a couple of hours after using the engines, to the point of being overwhelming. Needless to say, this is a real safety issue!

Looking back at the records I got with the boat, the PO bought carb rebuild kits every couple of years, and also mentioned to me that there was a possibility that the shaft bushings were wearing out. Given that knowledge, I am going to replace the carbs with new Edelbrock marine carbs.

My question is which ones to use. The 1410's are the obvious choice as they are 750 cfm and the ones usually recommended for big blocks. On the other hand, if I calculate the cfm from an equation using a volumetric efficiency of 85% (my best guess), they would appear to be higher flow than optimal.

cfm = (cid x rpm x ve) / 3,456 = (440 x 4,000 x 0.85) / 3,456 = 433 cfm

For a dual plane intake like the Edelbrock 440 Performer that the PO put on the engines, Edelbrock recommends 120-150% larger for best performance. As far as I know, I have stock heads and Osco manifolds and risers, none of which should improve volumetric efficiency as I understand it.

So, it looks like I need a 520-650 cfm carb. The Edelbrock 1409 is rated for 600 cfm, which might slightly reduce power at full throttle, but we mostly cruise at hull speed and sometimes at ~3,000 rpm, so I do not feel like that should be an issue. I don't know if this would improve our fuel efficiency, but that would be a nice side effect.

On other forums, such as marineengine.com, other folks have used the smaller carbs on 440's with success, but I hate getting info on the internet, especially from folks that may not be in the same situation or have a vested interest.

What do you guys think? Am I missing something in the way I am looking at this?

I personally think for the cruising that you've stated, the 1409s would be fine. I replaced them on my boat, (350 Chevys) a few years ago.
The fuel burn is less, the idle quality and acceleration from no wake to plane is fantastic. I am not familiar with the 1410s so I can't comment. Regarding the fuel smell after shut down, this can be normal depending on how hard and the engine run time, especially under a good load. I sometimes will run the blower while headed to the dock and up to 10 minutes or so after engine shut down just to aerate the engine room. It definitely helps with the heat soak smell.

Sometimes it's better to not overthink your project.

In my opinion you are looking at it the right way...even 85% VE might be a bit optimistic unless someone has done some fancy valve work or casting flash cleanup.....the 1409 carbs will probably be just fine for what you are doing, and with that intake more carb signal will make tuning ,idle quality even better.....that is what I would use if it were me.......I put 1409's on my 360's and they are a world better than the old afb's that were there.....

Jamie, the 1410's are similar to the 1409's, but with larger primaries (1 7/16ths vs. 1 3/16ths). The secondaries are the same size on both (1 9/16ths). Also, the 1409's ship with smaller jets and metering rods: http://www.edelbrock.com/automotive/mc/ ... rine.shtml.

As for the gas smell, it is happening after a long idle with the blower on, and takes hours to go away, even with the blower on and the hatches, doors and windows open. I suspect that is different from the scenario you have encountered...

I guess my concern is that I feel like the 1409's should be OK, but at 600 cfm, they may be at the bottom edge of what will work well for the 440's.

In any case, thanks to you and Mike for your insights!

Not to be a worry wart.... but if the fuel smell continues for hours with all hatches, doors, windows open, after idling back in with blower on... I would be checking for a fuel leak in the lines, filters, or connection points. Also check the exhaust (mufflers) to make sure no drain plugs are missing.

I don't idle back in with the blower running but sometimes have a fuel smell for a bit (especially if the wind is over the transom - it blows the exhaust into the boat), but with aft door and hatches open it is normally gone within an hour.

Can you compare the 1410s to you have now ? I would worry about loss of top rpm if your were to sell it ,it would be a issue , Also with the small 1409 you would be into the secondary's sooner .

I decided to call Edelbrock's tech support and see what they thought about carb selection.

They said:

1) 85% VE is a good number to use.
2) At 4,000 rpm, there is no need to go over 600 cfm and I should not have any issues getting to redline at full power.
3) Throttle response would be better with the smaller carb.
4) Fuel usage is hard to determine, and is more a function of tuning than carb bore.
5) The secondaries would still be closed at 3,200 rpm with the 600cfm carbs.

At this point, I am leaning towards the smaller carbs. Price is the same for both, so that is not an issue. I did find a reference to somebody who was able to get to 4,600 rpm with built 440 marine engines using the 600 cfm carbs, so that substantiates what Edelbrock told me.

Captainmaniac, that is good advice about checking the fuel line connections. I am not smelling exhaust and not getting a lot of water in the bilge, so I doubt there is an issue with muffler drain plugs. The fuel smell is not present when running the engines, but happens after shutdown, and the carbs are wet with gas on the outside after shutdown. From other forums on the internet, this seems to be a chronic problem with the Carter AFB's once they get old and have E10 run through them. Unfortunately, none of the fuel docks in our area have straight gas, so we are running E10 with Starbrite. I will go over the whole fuel system, which has been on my list of things to do.

Getting a new to me boat is quite an adventure in learning all the details of its current condition and planning on improving it to my standards!

If you wanted to keep the AFBs you could clean them off and watch for leaks. Mine had floats set wrong and acted similar they would also flood and stall my port engine. But if your buying new who cares the 1409 will work fine for what your doing.

Check the vents on your fuel pumps. I had one leak when I first started the engine. It stopped after a minute or so, but I replaced it because that's not a good thing to have on a woody.