Holley 50cc Pump Geometry Issue

[jpaz]

Ok Chris, good luck with getting it sorted out. 
 

Well, ya I guess you can say that. It really gets up and goes! It just made sense to me to put them in. Actually it was supposed to be set up from where I bought the carb new with them but it wasn’t. 

 

[Big Red Mach 1]

A few interesting finds this weekend. 

#1. - The lower housing on the acc pump had no play in it to swing the lever to the center of the bolt head. You would have to bend it to give it a bit of a dogleg in order to sit where it should. 

#2. - My #40 Nozzles did not come with the hollow screw as it should have. So I decided to (for the fun of it), go back completely the other direction and work toward very similar spec's as John's car. Going up to a #40 squirter wasn't in the cards this weekend, and I never mind experimenting. 

#3. - I never paid attention to it before, but when I put the 30cc pump back on, guess what... The lever has a dogleg in it right from the factory. LOL. Never would have guessed that, and never paid attention to it because it came out of the box that way and everything lined up from the get-go. 

#4 - John was running 72P and 81S @ roughly 700 ft. ele. I decided to run 71P and 80S at 1,500ft. ele.  He has a 6.0PV which I did not have so I ran a 5.5PV. I'm much lower on vacuum anyway so I went 5.5 over going 6.5.

I say all of this again knowing that every car is different and that we will all get different results. Just way too many variables to expect the same results. Please don't assume I thought that I was going to match John's setup and get the exact same results. 

End result for me was that I never pulled her out of the garage. My cam just won't allow for this type of jetting without going right back to the burning eyes exhaust. That's even with my transfer slot 90% closed and my throttle blades being drilled. Even working the mixture screws I just could not get it to run well at all. Way too rich for my cam. Interesting experiment, and all good to know. Well worth the attempt because it taught me something. I guess it could have been a leaking PV, but it was brand new out of the package, so I highly doubt that. 

In the end I was super close where I was prior, and I'll pick up from that point, and I'm sure after one or two more tweaks, I'll be exactly where I need to be. I'll put a dogleg in the 50cc arm, and get that hollow screw and I should be close to good-to-go. 

Much appreciated to all involved in talking me though one of my interesting (to say the least) posts. ;-)

 

[B229218]

Does your Carb have removable idle air bleeds up above? if it does go larger this will lean it out it’s worth a shot it really solve my problem with the over rich situation You can buy a set of blank set screws from McMaster Carr very cheap and you just drove all the ones you need read up on a book Super tuning volleys By Dave vizard

 

[Big Red Mach 1]

Does your Carb have removable idle air bleeds up above? if it does go larger this will lean it out it’s worth a shot it really solve my problem with the over rich situation You can buy a set of blank set screws from McMaster Carr very cheap and you just drove all the ones you need read up on a book Super tuning volleys By Dave vizard

It does have removeable bleeds. 

 

[71coop]

Are you sure it's too rich (I'm just looking at your comment 2 posts above). Every time I had eye-burning/watering fumes, I was too lean at idle. I don't consider my self an expert, but I've solved that issue, and cleaned up idle quality more than once by richening the mixture.

I know some rich conditions can also cause that reaction, but just a thought. The document attached was written by a member of the corvette forum I used to participate in. It gets into basic carb setup and give some good guidance about the tuning and adjustments to align the carb with your engine's needs. BTW, he is well known in corvette circles as a carb/timing expert. He's helped me more than once. Not saying this is your issue, but might be worth a read for someone.

View attachment Holley_Carb_Tuning.pdf

 

[Big Red Mach 1]

Are you sure it's too rich (I'm just looking at your comment 2 posts above). Every time I had eye-burning/watering fumes, I was too lean at idle. I don't consider my self an expert, but I've solved that issue, and cleaned up idle quality more than once by richening the mixture.

I know some rich conditions can also cause that reaction, but just a thought. The document attached was written by a member of the corvette forum I used to participate in. It gets into basic carb setup and give some good guidance about the tuning and adjustments to align the carb with your engine's needs. BTW, he is well known in corvette circles as a carb/timing expert. He's helped me more than once. Not saying this is your issue, but might be worth a read for someone.

View attachment 48454

Thanks for the doc. It's a good read. In this case, I know I was rich. I went up significantly in jet size, and adjusting the idle mixture screws the RPM's just kept climbing all the way to 1,150. She was drinking like a fish. 

 

[Big Red Mach 1]

More than likely found the issue. Pulled the carb and found the high idle screw making just enough contact with the red arm/cam it rides on when engaged to keep the transfer slots exposed. Obviously could not see that with the carb on the car but immediately found it when I flipped her over. Explains the extra fuel and the high RPM leading to the burning eyes. I'll bolt her back on tomorrow and give it a try. I also took the advice of the document 71Coop provided and set the P and S plates evenly by light gap, and not transfer slot exposure, and sure enough it was quite different than the gap you get when "boxing out" both. With even gaps my Primary Transfer slot is properly "Boxed" but the Secondary side is just barely not yet exposed. I had previously read most of the other points in that document before in other places, but that advice was interesting and makes a lot of sense. Thanks!