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!

Rebuilt Carb - Lost 1-2mph


Recommended Posts

rebuilt a holley 4160 carb over the winter for a 1998 Sportster.

The boat seems to be running at about 1-2 mph slower than last year. 

Carb is angled as it was not sitting on a wedge. Floats are set to a small drip of gas. Do i want more gas in the float due to the angle?

Any thoughts? 

 

Edited by cgsmakaveli
Link to comment

To compensate for the angled carb (even worse when moving with bow up), the front float should be lowered, maybe 1/8", and the rear float raised the same amount.

Link to comment

Are you sure you have full throttle?  I am going to guess you did not reset the floats from previous year so in theory that should not be different -but- does your comment about the wedge suggest you had prior and not now?  If that is the case, you did change the float level via carb angle.

Link to comment

Yes to full throttle. I even disconnected perfect pass throttle cable. I never had a wedge. We did adjust the float levels after the rebuild but i will adjust once more based on MadMan's comment. 

Link to comment

Prop is good, dont remember the specs but it is the same prop as last year.

Hitting about 4,900-5,000 rpm at 47-47.8/9 MPH with glimpses of 48.

Have a BI tower and superfly mounted on the boat. 

Still have plenty of speed to foot but just not the exact same speed i had last summer. 

Link to comment

@cgsmakaveli:  What was your peak RPM and speed last year?  By prop is good you are getting the same RPM to Speed ratio as last year?  It would be beneficial to know the specific prop you are running.  Are the tower and superfly new?

Link to comment

I will check the prop when i am up north but i think it is an acme 3 blade performance prop 13x11.

However, everything else on the boat remained the exact same so i am isolating this to the Carb. The tower was on the boat, same prop, etc. I am pretty sure that i was always about 2mph lower then my rpm ( I put in a gps speedo last year). Therefore, im guessing the 5,000rpm should be more like 48 mph. 

Edited by cgsmakaveli
Link to comment

That is my thought, as noted above, floats are currently set for just a very slight drip of gas when checking levels. 

Link to comment

Do you know the exact peak RPM prior to rebuilding the carb? If RPM is the same, then speed should be the same - or at least it's being effected by something other than the carburetor. If RPM is less, then the carb is more likely the culprit.

Link to comment
  • 3 weeks later...

Probably good to check the simple stuff: distributor cap clean (they can corrode over the winter), clean out flame arrestor with carb/choke cleaner, change fuel filter.

My boat consistently ran 49mph at 4,900rpm.  This year I put it in the water and only had 47mph & 4,700 rpm.  Swapped out distributor and put fresh fuel in, and now I'm back to 49 & 4,900.

Link to comment

will try it this weekend. To confirm, will continuing to raise the float level on back barrell help gain some speed...more gas more speed?

Link to comment

i'm not an expert but I don't think float level has anything to do with your top end, unless you are running out.  But it doesn't sound like that.  I would look at your various linkages.   It could also just be this warm humid air - that can slow you down a bit.    A fresh set of spark plug might help you

Link to comment
35 minutes ago, cgsmakaveli said:

will try it this weekend. To confirm, will continuing to raise the float level on back barrell help gain some speed...more gas more speed?

If you go too far with the float level, it will probably start spilling into the throat and bog down because it is running rich.  If you don't have enough, it will bog down because it is running lean.  They sound different, but you should be able to get it set without hitting either extreme.

By the way, have you checked the base timing?  Improper spark advance will rob horsepower, so it's good to at least check it.  I don't know what kind of ignition you have, but I think I would also check the timing at wide open throttle to make sure the advance is working OK.  I really don't know how much you are looking for, but it could be anywhere from 30 to 60 degrees.  It should be based primarily on engine RPM, with possibly some retardation due to knock detection.

If you have mechanical advance (probably not), then surely take a look at the springs and fly plate under the cap and rotor to verify that they work.  You wouldn't be the first guy with rusted distributor springs....

Link to comment
22 hours ago, cgsmakaveli said:

will try it this weekend. To confirm, will continuing to raise the float level on back barrell help gain some speed...more gas more speed?

I think you may be right about this. Looking at the angle on mine with the wedge underneath I can image you would have a pretty significant angle without one which would push fuel to the back side of the bowl away from the metering plate. What that being said, did you change out the bowls or mess with the float settings when you did the rebuild? If not, then there may be something else going on. 

Was the secondary vacuum diaphragm and spring replaced during the rebuild?

Link to comment

Did not change out the bowls, did mess with float levels. 

Replaced all diaphragms. i think there still isn't enough gas in the back bowl . It is probably around a 15 degree angle

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.

Guest
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...