2002 Sportster Holley 4150 Carb Issues

[SpencerK1992]

Looking for some help here.

My 2002 sportster with Holley 4150 carb runs great at skiing speed but despite my best efforts, it will not idle well and sputters in low gear. I had the carb rebuilt 5 years ago when I purchased the boat and while the idle and low gear speed has never ran particularly well, it seems to be getting worse. I adjust the idle speed and mixing but after running the boat or skiing and going back to neutral it is all over the place. 

Is it worth another rebuild or should I buy a new carb? 

Unfortunately, it appears that Holley no longer sells a 4150 with vacuum secondaries, only mechanical. I don't know if the 4160 will work as it is single gas feed and I am not sure what is entailed in that conversion process (i.e. new pump? Definitely new, longer fuel line?)

Any help is appreciated, I love skiing behind this boat and it runs great but since I am often skiing in the course I really need better idle and low gear speed!

[solorex]

If you are confident your rebuilt was done correctly, then maybe your issue isn't the carb?  Check your grounds first and foremost.  Check you ignition coil?  Have you done a new cap rotor in a while?  how are your spark plugs and plug leads?  Have you checked the timing?  If your timing is off this could affect your idle.  How about fuel filter?  Do you run ethanol fuel?

[SpencerK1992]

I put in new spark plugs, cap, and rotor this spring. Have not checked ignition coil or timing, I'll have to do some research on those!

[justgary]

@solorex mentioned plug wires also.  If yours are original it is time to replace them.  They do go bad with age.

[SpencerK1992]

Sorry, I forgot to add I did install new plug wires as well!

And yes, I do run ethanol fuel. 

Would all these factors contribute to poor idle? Do I need a new carb?

Edited May 7 by SpencerK1992

[justgary]

I would at least clean your existing carb or maybe rebuild it again before buying a new one.  Poor idle could be just gunk in the throat near or on the butterfly, debris in a jet, a leaky bowl gasket, bad float valve, improper float level, etc.

Carb rebuild is easily a DIY activity.  I would buy a kit and a gallon can of carb dip and have an enjoyable evening.  The can of dip works a whole lot better than the spray cans at removing gunk.  Compressed air is a bonus too, but if you don't have that you can use the spray carb cleaner as a substitute after the dip.

[Woodski]

An additional few items to check:  1.  check to see if there is a vacuum leak at the intake manifold, any old rubber plugs and the potential of a leaking intake gasket.  To check, spray some starting fluid around the gasketed joints and if the idle picks up, presto.  2.  when the distributor cap is off, check that the rotor is firmly attached and there is no slop in the rotor (rotational play) as the distributor gear could be worn (checking timing will show scatter at idle).  3. and start with making sure base timing is correct (~8 deg BTDC).

[waterskiercu]

Sounds like we have a similar problem. Mine is an '01 with a Holley (not sure which one...4150?). I had mine rebuilt last year and initially ran well but by the end of the summer, was having some stalling issues (vapor lock??) and lower than normal idle (500-ish). The good news is, while doing yearly maintenance in the driveway, it fired right up and held it the idle, albeit lower than prescribed. I believe cap, rotor, wires were all done back in 2017 so that may be an issue. My knowledge only goes so deep. What I've learned on this forum is it literally could be 25 different things. Anyways, I'm going to bite the bullet and take it to Malibu tomorrow. Hopefully they still have a few techs on hand familiar with the old school stuff. I know they sent the carb rebuild to a third party local guy. Head tech said my boat is literally the only carb engine they service these days. 

[Woodski]

@waterskiercu - per your comment on lack of carb knowledge at the dealer, perhaps a more successful approach would be to have a carb specialist mechanic tune it, good source will be the local hot rod, 70’s pony car community.  Car show, local drive in A&W etc will be a hang out.  You’ll supply the water feed knowledge for the raw water pump.

[waterskiercu]

Funny you mention that. Local car shop I go to offered to take a look -- head guy said he's well-versed on boats. Problem is they kept putting me off; said they are swamped, will do it next week, etc. I'm already missing out on days on the lake so Malibu will have to do. Plus, I'm not sure it's the carb. I was hoping fuel filter change would help but no dice. I look at today's modern boat and can't help but think that when mine pulls up to the shop, guys are excited to take a break from working on electronic screens and power wedges. I'll report back any findings. 

[waterskiercu]

My issue ended up being a bunch of fouled spark plugs. Cap and rotor were in good shape. He also adjusted front float on carb. Head tech said I am literally the only true ski boat they've worked on this spring. The end is nigh, gentlemen.