Rebuilt Carb - Lost 1-2mph

[cgsmakaveli]

8 hours ago, justgary said:

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

I guess it is always possible but i did the rebuild with a buddy that knows what he is doing. 

[cgsmakaveli]

Running an acme 13x13 Prop. 

From reading, it has been recommended the Sportster runs a 13x12.6. However, i'm still just using last year performance for my baseline.

Installed the Dist Cap and Fuel Separator this weekend. Also used some brake cleaner on my flame arrester and re tuned the carb with the warmer weather (originally tuned in 55 degree temps while raining) 

All in all, picked up about 100 rpm with max performance at 4740rpm  per via perfect pass and analog readout.  With the Tower, Super Fly, and Boom (w/ extension) 1 spotter in the boat, and a barefooter behind the boat, it pulled a hard 44 mph, soft 45 mph. Can't complain to much about that speed but still think i should be int he 4,800-4,900 rpm range. 

Secondly, getting a little hesitation when my back barrels open around 3,000 RPM pushing to open throttle. Fuel accelerator works the way it should as we played with both extremes and it still occurred. From reading it sounds like the new spring installed during the rebuild is allowing the diaphragm that controls the back barrels to open too soon. So next i plan to order the Holley  20-13 spring kit to see if this fixes the issue.  Unless anyone has some additional insight. 

[Woodski]

@cgsmakaveli Are you running the Acme 425?  That actually may be a bit tall for your boat, your era boat did probably come with a CVP 13 x 13 but the Acme CNC props tend to run a bit less pitch to get the same speed:rpm ratio of the older props that have less blade area.  My comment does not really pertain to your issue as you indicated you could pull more rpm last year with same prop, so you still have something that is limiting your top end.  The hesitation when the secondaries open does provide a clue that something in the fueling is amiss.  When rebuilt, were the shaft bushings checked / replaced, that is area for an air leak.  Also, anytime there is a hesitation on a carb that uses an accelerator pump setup when opening the throttle or actuation the accelerator pump, that can be the culprit.

[Michigan boarder]

Specific to the accel pump, @Woodski and I think a couple of others pointed out to me that my linkage was off by 1 hole.  I was complaining about a hesitation, and after viewing my pic they determined I could move it a hole and sure enough that fixed the hesitation.

Pic:

[cgsmakaveli]

to confirm, the accelerator pump shouldn't have anything to do with the back barrels, just my primary which i feel is fine on a hole shot. 

[Woodski]

@cgsmakaveli:  Normally no, the secondaries open past the prime point on the linkage, but not knowing your exact setup can't rule anything out.  Another clue is your comment on calibration, sounds like you changed the calibration from last year so you might go back to the calibration that worked last year at least as a baseline test.  Note - compared to an automotive calibration, boats tend to be setup on the rich side, mainly as a conservative measure as they run under load pretty much all the time.  Your cool weather calibration might have been pretty rich hence it ran better when you adjusted for warmer weather.  What specific calibration changes did you make from last year and what indicators are you using to calibrate the mixture?

[cgsmakaveli]

just spoke to holley and the universal kit 37-1541 doesn't come with a spring for the diaphragm so it must be the same as last year. They also mentioned checking to make sure the right power valve was put in and whether this particular valve came with a check ball or restrictor (some did some didn't). 

[drh]

If the fuel level in the secondary bowls was too low like you suspected would that be causing it to lean out momentarily when they open?

[cgsmakaveli]

1 hour ago, drh said:

If the fuel level in the secondary bowls was too low like you suspected would that be causing it to lean out momentarily when they open?

no, i played with this. I will eventually start to lose power after a few seconds if the fuel level is too low. However, it did not impact the slight hesitation as i raised the float and lowered the float to both extremes. 

[cgsmakaveli]

I am told the back barrels shouldn't open until 4,000 rpm. 

Would this isolate the issue to the front barrels then? Something else? 

[drh]

Use the paper clip trick and run it up to the hesitation point - not past - to see if they are even opening. Put the clip at the top of the actuator rod next to the diaphragm body and see if it moves. If not then you know it's not the secondaries causing the issue.

[cgsmakaveli]

have confirmed they are opening in the past but didnt check at RPM as we were still just starting to tune the carb this spring.