I think you are right. I remember reading about someone sanding down a small ridge on the pump cam. Might of been you.
I'm going to eliminate the choke.
Originally Posted by fc-Pilot
I have had the same issue with the 4781. The 50cc squirter on the secondary side hits a "flat spot" of sorts and due to the friction it sticks just a little. I did a little "custom" work on the plastic pump cam as well as gave it a touch of moly grease and it was not a problem after that. If you have a choke on that thing it very well could be the fast idle cam in the choke mechanism that is holding the primaries open as that is what it is designed to do. Take a close look under the choke mechanism and I bet you will see how it works and that it is your culprit. Just my un-educated guess anyway.
I wouldn't worry too much about the secondary transfer slot not showing. My 4781-3 idles/runs best with the front slot squared and the rear covered. I also have the front mixture screws 1.5 turns out with the rears just barely cracked out after seating them. No flat spots at all.
I sanded the pump cam, slightly, added some grease and the sticking is all but gone.
I removed the choke and filled the choke control arm opening with JB weld. After removing the choke, I don't see the inconsistency with the butterfly opening.
I adjusted the primary transfer slot to .022.
I removed the float bowls and check the power valve. It was a 6.5. Since my engine only produces 7.5 - 8 Hg, at idle, I replaced the power valve with a 3.5. (According to Holley: engine vacuum / 2 = PV size.)
I check the installed jets and they are 80 on both sides. Seems a bit big, will see.
Now I just need to get the new inlet fitting I ordered from Summit and test it out.
Thanks again for all your help.
Carbs I have been getting have been wet with solvent for 10 yrs easy. Just needs a little grease like you have done on the pump cam. Will get better with use. The secondaries are normaly almost shut. May need to be opened or closed for best snappy throttle. The holley vac/by 2 is a guideline only. I would run the boat at cruise and you will probably see a higher value, making the 6.5s just fine. Dont mess with the jets until you have a dyno/lake session with AFR meter, or a plug read on a fresh set of plugs. Holleys are very close out of the box these days.
The boat ran a lot better. It did have a bit of hesitation when nailing it from idle. Seem to be at about 1800 RPM.
I check the vacuum at cruising speed and it is around 5Hg. I am currently running 6.5 power valve. I'm going to put a 3.5 in it and see what happens.
I did find my secondary float level was low. I'll set it up and do another test run, before I change the power valve.
Thanks for all the help.
Just an update and comment about Holleys being right out of the box
I took the boat out for test and tune. It ran pretty good, but has a very slight hesitation at about 1800 RPM when mashing the throttle.
I checked the float levels and the secondary side was very low. I adjusted the level up, but still had the hesitation.
The boat ran very good, besides the hesitation. Mind you, this hesitation seem like less then a second.
I checked the plugs and they look a bit lean, but not bad.
When I got the boat back home, I decided to change the power valves to the 3.5s, to see if that would help with the hesitation. When I removed the secondary float bowl, I placed it in a bucket and I heard something hit the bucket before I got the bowl in. I looked and it was a jet! I did not change the secondary jets or remove them.
I believe the jet was in when I was testing. Or, at least, part way in. I would imagine it would of run poorly with only 1 jet.
When I replaced the jet I noticed that the threads were slightly bunged up right at the start. I lightly screwed the jet back in, making sure not to cross thread, by hand. Then tightened it with a screw driver.
I checked the rest of the jets and they were all tight.
Next test and tune, I'l check out how the 3.5 power valves work. If no change, I will change the secondary squirters +2 and see if that helps.
If you have any suggestions on tuning, I would appreciate it.