Jump to content

Welcome to TheMalibuCrew!

As a guest, you are welcome to poke around and view the majority of the content that we have to offer, but in order to post, search, contact members, and get full use out of the website you will need to Register for an Account. It's free and it's easy, so don't hesitate to join the TheMalibuCrew Family today!

2001 Sportster LX engine carb and timing specs

Recommended Posts

Hello, I have a 2001 Sporster LX that I bought in 2019. Great boat. Have put 200 hrs on it in 3 seasons.

Over the winter, I pulled the motor to fix an oil leak and go through the motor and rebuild the carb.

Looking at the specs it states this boat had the Vortec 310 with timing set at 10 degrees BTDC.

Local boat mechanic that has worked on these from the early 90's to now told me they came from the factory with the Holley 4160 carb.

Several questions after the rebuild and discovering some things on the motor. It's not as quick out of the hole and using more fuel. But I was running 4 degrees BTDC. Just found the 10 degree spec. Hopefully some experts can help out and clear some things up.

1. The build sheet says Vortec 310. The heads on it are not Vortec style. Did Vortec in the marine motors mean the same thing as in say a chevy truck or was it more marketing verbiage?
2. The local boat mechanic took 1 look at the carb and said it was not stock and too big for the motor. He stated it should be a Holley 4160 and I think he said 450 CFM. Looking up 4160 marine carbs I see them listed at 450 and 600 CFM. Anyone know if the stock carb was 4160 and what the CFM should be?
3. The timing specs I have for this motor is 10 degrees BTDC @1000 RPM. The distributor is very basic with no crank position or cam sensors and no centrifugal magnets to advance timing. The distributor only advances it 4 degrees above 2000 RPMS to a max of 14 degrees BTDC. Is this correct? Seems low.

Just trying to make sure I have everything correct so as not to burn a piston or other damage.

Thanks in advance!

Link to comment

You need to start the engine, run it up to operating temperature, plug a timing shunt into the Delco distributer, and connect the shunt wire to a 12 volt power source to put it in timing mode to set the timing or do carb adjustments.  It is important to only connect or disconnect the shunt wire while the engine is running.  If the engine stalls, disconnect the wire before restarting the engine to avoid damage to the ignition module.

Link to comment

I've got a 99 Sportster with the same engine and it has Vortec heads - I think you can distinguish by vertical intake manifold bolts and valve cover bolts in the center instead of around the perimeter. You should have had true Vortec heads from the factory but who knows what happened over the last 20 years since.

OEM carb is the Holley 4150 (float bowls attach on each end) or 4010 (float bowls are accessed by taking the entire top of the carb off). I think the 4150 is the most common. It should be electric choke, vacuum secondary but I'm not sure of the CFM.

Timing is correct at 10 deg initial but I set mine to 11 or 12. I think full advance adds 20 degrees above base (but I would verify that) so I figured 32 was safe. I didn't want to buy the shunt so I used a wire to jump the pins and an alligator clip to get 12v to the third pin. Sorry I do not remember which pins are jumped. Search on here or google and I'm sure you can find out. 

Link to comment

Think of your engine as an air pump.  A 5.7 liter engine pumps 5.7 liters of air every two rotations (a four stroke engine).

5.7 liters = 347 cubic inches = 0.201 cubic feet,  so 0.201 * 5,200 RPM / 2 strokes = 523 cubic feet per minute maximum at normal wide open RPM.

Anything over about a 550 to 600 CFM carb is a waste on these engines.

Link to comment

Thank you all for your replies. DRH, you are correct, who knows what has been done in the 17 years before I purchased it!

I called a couple of well respected inboard parts places this morning. For the carb, one said most all the 350 Chevys were fitted with the 4160. The other said 4150. My current carb is a Holley and has fuel feeds to both ends. Just not sure yet which model it is and boat is 60 miles away.

Both vendors confirmed the 10 degrees BTDC and should advance 20 or so degrees. As for the shunt, one of the part suppliers said they sell new OEM distributors and since mine is carbed, that it was just a matter of installing and set timing. They said if I had FI then I would need the shunt. The other sells a Pertronix distributor.

Link to comment

I am positive the stock carb on the indmar 310hp is the Holley 4150, 600cfm with vacuum secondary and electric choke.  At least it was on my 1998.  They seem to be getting pretty rare.

Link to comment

The Delco distributor on carb engines changes the timing advance using the programming in the ignition module since it does not have physical advance weights and springs like older distributors that use centrifugal spark advance.  The ignition module timing advance needs to be turned off to properly set the timing, that is what the shunt does.  If the distributor in your engine has been replaced with a different one, then follow the timing instructions from that distributor manufacturer instead.

Fuel injected engines with a MEFI ECM and Delco distributor only use the ignition module programming to get the engine started, then ignition advance is controlled by the ECM.  A shunt can't be used on MEFI fuel injected engines because the ECM harness is connected to the shunt port.  For setting ignition timing on MEFI the pins on the diagnostic connector can be jumped or a diagnostic tool is connected to put it in base timing mode.

Link to comment

Again thanks for the replies. I need to get the # off the carb and check it. Also ordered a shunt so I can set base timing, but I have a feeling that the ignition module is bad since it is only advancing 4 degrees.  Here is a pic of the carb. From the looks it appears to be a 4150. Just not sure what CFM it is rated for.                                                                                                                        20190503_205158_resized.thumb.jpg.7cc6a42923c39980ff0d020f67b0029b.jpg20190503_200835_resized.thumb.jpg.2cc27874540797cb7937a0eeb0d31dcd.jpg

Link to comment
Posted (edited)

Well found the # stamped on the carb to be 6R 7072 B

That # is not on the Holley list and when I google it a 7072b shows up on Ebay with the same stamp but one fuel port.

Tech at marine shop insist it is too big of a carb for the engine. Of course he also insisted that you set the ignition at 10 degrees and that's it. No shunt, no nothing.

Not sure what I have now. Anyone with more knowledge would be appreciated.






Edited by vwztips
Link to comment

Check the vertical part of the choke housing for another number.  You may need to clean it a bit to get it to show better.

Link to comment

Thank you sir. 75021-1 which is a 4105 and 600 CFM.

So the local boat tech is batting 0 for 2. Wrong on timing procedure and wrong on carb.

Thanks for all your help. Now to try the shunt and set timing.





Link to comment

On to timing. I made up my own shunt so I could set base timing.

Before connecting shunt I brought engine up to temp and set timing to 10 degrees BTDC.

Once up to temp I connected the shunt to 12VDC and RPM dropped. Is that normal?

I then set engine to 1000 RPM and set timing at 10 degrees BTDC.

Removed the shunt and checked timing without shunt and it was 24 degrees BTDC. Revving up to 2500 RPM it gets to 28 degrees BTDC.

It seems to run good and sounds normal. I have not gunned it yet and only run it on water to 2500 RPM. Wanted some feedback and answers to questions below before I run it hard.


Once base timing is set properly, is it useless to check timing without the shunt?

Does this timing sound correct? 24 degrees BTDC at idle and only advancing 4 degrees at 2500 RPM?

Thank you.

Link to comment

Update: Played with it some more today.

After setting base timing at 10 BTDC then disconnecting shunt I am show 24 BTDC at 750 RPM and 31 BTDC at 3000 RPM

Out of curiosity went and bought another ignition module from O'reillys. They didn't have a GM unit but the one they had was made in the US.

Installed the O'reilly ignition module, set base timing again at 10 BTDC. After pulling the shunt, with this module the timing at 750 RPM is 13 BTDC and 20 BTDC at 3000 RPM.

From my understanding, most 350 Chevys seem to want 28 to 32 BTDC at 3000 RPM.

Again, wondering if I need to disregard timing values without the shunt connected. Just concerned about the 24 degrees BTDC at idle 

Edited by vwztips
Link to comment

@vwztipsSomething sounds off. It's been a few years since I did this process on mine but I don't remember the timing fluctuating that much with shunt in vs out. I do know that when you plug in the shunt is it normal for RPMs to drop. 

Are you using an adjustable timing light or using the marks on the balancer to check advance? I tried to use the adjustable feature on my cheap timing light at first and got very inconsistent results. 

Link to comment

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Restore formatting

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...