OEM Carburetor and CFM for 2003 Sportster LX

[physicsmatters]

Hi All,

I am having along term problem with my 2003 Sportster LX, Indmar 5.7L Vortec.  It starts and runs fine and I can accelerate quickly up to about 3/4 throttle but if I punch it all the way it coughs and frequently dies.  The boat has had this problem since I bought it about 5 years ago.  About 4 years ago I paid a local mechanic to replace my existing Holley (which he said was for a car) with a new boat Holley. Though it runs better I still can not punch it.  Since then I have replaced virtually all fuel related components except the gas tank with I removed and cleaned.  All to no avail.  I recently took my boat to a different local mechanic - who I like and he seems to know his stuff.  He says the new Holley (600 - 650 CFM?) is too small and I need a 750 CFM for my engine.  He does not like Holley carburetors and would install a new Edelbrock (weber).  He guarantees this will fix my problem.

I would like to know what carburetor was on the boat when it was new and what the CFM is for that carburetor.  I have searched the web and can not find this spec.  If I could show the previous mechanic he installed the wrong carburetor I would try to get my money back.

Do I need a 750 CFM carburetor?  From looking at the forms on this site it seems others are using carburetors with 600 to 650 CFM.

Thank in advance for your assistance.

[drh]

See this thread:

Near the bottom there's a link for the OEM Indmar carb. It's a 600 CFM 4150 Holley, vacuum secondaries, electric choke.

If your mechanics have narrowed it down to a fuel issue (ruled out timing, compression, etc.) then it sounds like the secondaries may be opening too soon if the engine is bogging at full throttle (unless you mean black smoke when you say it coughs - then you may have the opposite problem). Is the carb vacuum secondaries or mechanical? 

 

Edited April 7, 2021 by drh
Said the opposite of what I meant

[Woodski]

It sounds like the secondary jets may not be delivering the fuel as they should.  Debris, wrong size, float level may be a contributing factor to what sounds like a lack of fuel delivery when you open the secondaries. Any chance the carb is not level, that could contribute to several issues.

indmar’s come with Holley’s, Mercuisers come with Weber’s which are same as the Edelbrock mentioned.  Both work fine and each have personal preferences.

[physicsmatters]

Hi DRH and Woodski,

Thanks for your responses.  It turns out I have a Holley 4150 #0-80559 carburetor.  That's a 600 CFM marine carburetor with Electric Choke and Mechanical Secondaries - a double pumper.  After reading DRH's reply and the thread he suggested I called Holley directly.  A very nice and knowledgeable guy talked me through the few things that are likely the cause of my problem - I had no idea Holley was this accommodating, I was truly impressed. 

The first is something I have wondered about for a while; when you set the float levels on a Holley, they always tell you to have the carburetor setting level, but as you know, the engine in a ski boat sets at an angle so shouldn't you set the float levels with the carburetor at the angle it will be when mounted on the engine?  The Holley tech said that is correct, set the floats with the carburetor mounted on the engine and the boat floating in the water.    That is the first thing I am going to try.

If that does not fix it, he recommended increasing the size of my Accelerator Pump Discharge Nozzles by 1 size.  If that doesn't work he said I could go up one more size.  He believe one of these adjustments should fix my problem.

This is the most promising news I have had so far!

I will let you know how this works out but it might be a few weeks - there is a legal battle going on over the damn that controls our lake and right now there isn't enough water to safely run my boat.

Please let me know if you see anything wrong with my proposed approach. 

Thanks again for your help and support!

[drh]

I hope that a simple float adjustment is all you need! I went through that process myself a few years ago - I did it on the trailer and then fine tuned on the water - I think it was pretty close just on the trailer. I've always thought that the secondary fuel level wouldn't hurt to be a little high when floating since anytime you need that the bow will be even higher and pushing fuel farther away from the metering plate.

[physicsmatters]

Thanks  drh, that is helpful, encouraging and validating.

[Woodski]

The engine sits pretty close to 15 degrees so you can just adjust the trailer tongue to get very close.  There should also be a wedge plate on the intake manifold to level the carb, at least the Merc’s have them for that reason.  Can’t say for sure for your application since I have not seen one.

[physicsmatters]

Thanks, I don't have wedge plate but it would make sense to have one given the design of the stock Holley carburetor.  I wonder if that's my problem, I am missing that wedge plate?  You do not have a wedge plate on your Indmare 350, correct? 

[Michigan boarder]

The wedge place on my Echelon looks like this:

 

[drh]

The Indmars do have a similar wedge plate

[physicsmatters]

15 hours ago, drh said:

The Indmars do have a similar wedge plate

Well it seems my saga is coming to an end.  I am pretty sure I do not have a wedge plate on my intake manifold and I am using a carburetor that needs to set level to work correctly.  

Apparently I need a wedge plate on top of my intake manifold, but before I buy one, is anyone out there using a Holley carburetor on a straight inboard Indmar engine  - setting at about 15 deg - without using a wedge plate? 

Obviously I can search for It but does anyone know where I can get a wedge plate for my engine? 

Thanks so much guys!