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cgsmakaveli

Rebuilt Carb - Lost 1-2mph

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cgsmakaveli
Posted (edited)

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

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MadMan

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.

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Woodski

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.

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cgsmakaveli

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. 

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drh

What RPM and MPH are you getting now? And what prop?

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cgsmakaveli

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. 

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Woodski

@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?

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cgsmakaveli
Posted (edited)

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

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Falko

How did you tune the carb? might be running a little lean/rich with the settings since rebuild.

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cgsmakaveli

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

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jmack

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.

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cgsmakaveli

right now hitting a 1:1 ratio on RPM and Speed maxing our at 46 mph / 4600 rpm. Doesnt seem right. 

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Michigan boarder

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.

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cgsmakaveli

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?

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SkiPablo

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

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cgsmakaveli

put new spark plugs in last summer. thanks for the note. 

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justgary
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....

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drh
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?

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cgsmakaveli

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

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Michigan boarder

Would it make sense to purchase and install a wedge under the carb?  

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cgsmakaveli

worked good last 5 years that i have owned it. might make sense but trying to trouble shoot first. 

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cgsmakaveli

delco cap and rotor i believe. 

Anyone know the part for the fuel filter on a 1998 sportster?

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justgary

And you are sure that you don't have some crud in the jets, and the gaskets all seated ok? 

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cgsmakaveli
Posted (edited)
14 hours ago, drh said:

https://www.skidim.com/products.asp?dept=1063

4th line down - part # 0530

It's a shorter one for the Sportster

 

Do you know which dist cap and rotor? I believe it should be a Delco?

 

Updated: Think i figured this out. 

Edited by cgsmakaveli

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