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Holley 50cc Pump Geometry Issue


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Anyone else running a 50cc pump have this issue? I'm not super find of where the pump arm sits on the bolt head. It's just barely making contact. Does it work? Yes. Could I bend the linkage? Probably. Just curious if others have run into this and if so, if they just chose to run it, or if the decided to bend the linkage to make the bolt line up better with the pump arm. I've got one photo representing idle, 1 at WOT and one from above and below. 

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Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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It looks to me like the problem is with the pump, the outside ear that the pivot axle is attached to appears to be bent in towards the carburetor, forcing the arm in. If you try to adjust (bend) the arm the adjustment screw is attached to the adjustment screw will rotate in and off the pump arm. The bolt head that pushes on the pump arm needs to stay perpendicular to the arm, so you can't bend the section it is attached to, either. Is there enough space around the screws that attach the pump to be able to rotate the pump a little?

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1 hour ago, Don C said:

It looks to me like the problem is with the pump, the outside ear that the pivot axle is attached to appears to be bent in towards the carburetor, forcing the arm in. If you try to adjust (bend) the arm the adjustment screw is attached to the adjustment screw will rotate in and off the pump arm. The bolt head that pushes on the pump arm needs to stay perpendicular to the arm, so you can't bend the section it is attached to, either. Is there enough space around the screws that attach the pump to be able to rotate the pump a little?

Good eyeballs Don. I'll try it the next time I take the carb off. I didn't feel much wiggle room, but it probably would not take tons to make a difference at the contact point. 

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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1 hour ago, Don C said:

It looks to me like the problem is with the pump, the outside ear that the pivot axle is attached to appears to be bent in towards the carburetor, forcing the arm in. If you try to adjust (bend) the arm the adjustment screw is attached to the adjustment screw will rotate in and off the pump arm. The bolt head that pushes on the pump arm needs to stay perpendicular to the arm, so you can't bend the section it is attached to, either. Is there enough space around the screws that attach the pump to be able to rotate the pump a little?

I'll be pulling it again to go from the .37 Nozzle to the .40 with the hollow screw as soon as it comes. I didn't think I'd need to go that high, but the .37 didn't fully cure my hesitation, so I guess .40 it is. Anyway, when I put it back together, I'll see if there is enough wiggle room to get it to line up better. 

Edited by Big Red Mach 1

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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That pump arm ought to be slap bang in the middle of the adjustment bolt head. Can you compare the old 30cc one to the new one, even from your pictures? You can't set up the .015" clearance as it is.

 

Edited by Stanglover
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Geoff.

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3 minutes ago, Big Red Mach 1 said:

I'll be pulling it again to go from the .37 Nozzle to the .40 with the hollow screw as soon as it comes. I didn't think I'd need to go that high, but the .37 didn't fully cure my hesitation, so I guess .40 it is. Anyway, when I put it back together, I'll see if there is enough wiggle room to get it to line up better. 

 I know your cam and vacuum are way different to mine, but that seems to be a big jump on the squirter to me. As I've said before, I fixed mine bogg/hesitation with just going from a 31 to a 35. Don't chase more than one thing at a time.

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Geoff.

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7 minutes ago, Stanglover said:

 I know your cam and vacuum are way different to mine, but that seems to be a big jump on the squirter to me. As I've said before, I fixed mine bogg/hesitation with just going from a 31 to a 35. Don't chase more than one thing at a time.

31 to 35 helped a lot but by no means cured it. 35 w/ 30cc to 37 w/ 50cc helped just a tiny bit. A lot less than I was hoping it would honestly. I'm not sure if the 35 to 37 just wasn't enough, or what. I thought I'd throw the 40 on with the hollow screw to see. $25 is worth the price of admission in my mind to know. I know stall speed on the torque converter can play into this as well, but I didn't test launching at different RPMs, and now it's raining and is supposed to for the next few days. I was hammering it from 35ish mph. It still falls flat very briefly and then goes. Maybe I can post a video from my dash cam. Maybe I'll pull the SD card and see. 

Edited by Big Red Mach 1

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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 Thanks Chris, I misspoke where I wrote "clearance". I know you know what I meant, but some might not. That should refer to a .015" feeler gauge inserted between the arm and adjuster "nut" when throttle is fully open to ensure the diaphragm is not overly extended. In other words there is potentially .015" more travel on the diaphragm, if that makes any sense. There's probably a better description that doesn't come to mind right now. 

As I don't have any experience with automatics, I think that too could be an issue. Annoying isn't it!

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Geoff.

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40 minutes ago, Stanglover said:

 Thanks Chris, I misspoke where I wrote "clearance". I know you know what I meant, but some might not. That should refer to a .015" feeler gauge inserted between the arm and adjuster "nut" when throttle is fully open to ensure the diaphragm is not overly extended. In other words there is potentially .015" more travel on the diaphragm, if that makes any sense. There's probably a better description that doesn't come to mind right now. 

As I don't have any experience with automatics, I think that too could be an issue. Annoying isn't it!

I did know what you meant for sure. I actually was able to get a feeler gauge in there believe it or not. LOL 

I'll have a driving video of her up shortly. 

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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It's a few minutes longer than it needs to be. I didn't want to take an eternity to crop the video. You will see/hear me hit it a few times from 35/40ish MPH. And once from the light. I didn't load up the torque converter or try to do a burnout at the light. Just good solid acceleration. Anyway, I'm sure you will hear the drop when I mash it. Feel free to give any thoughts or input. Carb came with a 31. I upped to a 35 and it helped a lot. This 37 didn't help much. Considering going 40. Power Valve is a 8.5. I believe I'm jetted properly. Thanks!

 

 

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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Double check the idle speed setting on the secondary throttle. It should be open 1/4 turn on the adjusting screw. If it's open too much it can cause a bog on acceleration. Make sure the secondary throttle spring is correct, if the secondary throttle opens too soon it will also cause a bog.

Make sure the pump cam is in the #2 position.

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“If you can't explain it simply, you don't understand it well enough.”

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14 minutes ago, Don C said:

Double check the idle speed setting on the secondary throttle. It should be open 1/4 turn on the adjusting screw. If it's open too much it can cause a bog on acceleration. Make sure the secondary throttle spring is correct, if the secondary throttle opens too soon it will also cause a bog.

Make sure the pump cam is in the #2 position.

Great stuff as always Don.

I'll double check that setting, but I'm 99% certain that the secondary blades are fully closed or darn near. Cracked a hair if at all. I'm running the stock spring, but do have a spring kit. The QF735 does have the nice little easy access screw that allows me to open them faster or slower. I'll adjust toward slower and see if that helps. Of the two cams that come with the 50cc kit I used the yellow, as that one was said to be the most aggressive. There was only 1 hole in it (Brown cam has two). But I know I put it in hole #1 on the linkage. I'll rotate it around to hole #2. 

Thanks!!!

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Edited by Big Red Mach 1

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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I have a QF 735 VS on my 351C and it runs very strong, no bogs at any speed. I have a 6.5 power jet with the stock squirters and upped the jets a few sizes. It spins the tires easily from a dead start with no brake and if I floor it from a 35-40 roll it breaks the tires no problem. I have to be careful not to go sideways cause of the posi. 

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John - 72 Q Code

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24 minutes ago, jpaz said:

I have a QF 735 VS on my 351C and it runs very strong, no bogs at any speed. I have a 6.5 power jet with the stock squirters and upped the jets a few sizes. It spins the tires easily from a dead start with no brake and if I floor it from a 35-40 roll it breaks the tires no problem. I have to be careful not to go sideways cause of the posi. 

That's interesting. So the squirter these came with was a 31. The PV installed was the 6.5 you still have. Stock main jets were 68's. Do you know which ones you are running now? Are you fairly stock or highly modified? I'm .030 over. Flat Top Pistons, Blue Thunder intake. D0AE Closed chamber heads. Cam is a Comp Cams 270H. Every engine is going to be different. That's for sure. 

 

Edited by Big Red Mach 1

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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I have a QF 735 VS on my 351C and it runs very strong, no bogs at any speed. I have a 6.5 power jet with the stock squirters and upped the jets a few sizes. It spins the tires easily from a dead start with no brake and if I floor it from a 35-40 roll it breaks the tires no problem. I have to be careful not to go sideways cause of the posi. 

2 hours ago, Big Red Mach 1 said:

That's interesting. So the squirter these came with was a 31. The PV installed was the 6.5 you still have. Stock main jets were 68's. Do you know which ones you are running now? Are you fairly stock or highly modified? I'm .030 over. Flat Top Pistons, Blue Thunder intake. D0AE Closed chamber heads. Cam is a Comp Cams 270H. Every engine is going to be different. That's for sure. 

 

I’m .040 over with flat top pistons, blue thunder intake, 71 closed chamber heads with 10.3:1 compression. Cam is Crower Power Beast 292/302. Pretty close but I guess I have a little more cam than yours. I have a c6 auto with Trans-Go shift kit, 2500-2800 stall converter and 3.50 gears. 
l’ll have to get back with you tomorrow and I can tell you exactly what jets I have in, my notes are out in garage. I think I have 74s in the front and 78s in the rear? I’ll let you know for sure tomorrow.

Now that I think about it, I had that same cam in my engine before I had it rebuilt. It seemed to fall flat on its face at 5000 rpms, just had nothing up top. Even had the same 770 carb for awhile, then I switched to the Quick Fuel. The QFT definitely was better than the Street Avenger, but it still died off fast. The Comp 270h cam is a single pattern cam and Cleveland’s like a dual pattern. 

Edited by jpaz
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John - 72 Q Code

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8 hours ago, jpaz said:

I have a QF 735 VS on my 351C and it runs very strong, no bogs at any speed. I have a 6.5 power jet with the stock squirters and upped the jets a few sizes. It spins the tires easily from a dead start with no brake and if I floor it from a 35-40 roll it breaks the tires no problem. I have to be careful not to go sideways cause of the posi. 

I’m .040 over with flat top pistons, blue thunder intake, 71 closed chamber heads with 10.3:1 compression. Cam is Crower Power Beast 292/302. Pretty close but I guess I have a little more cam than yours. I have a c6 auto with Trans-Go shift kit, 2500-2800 stall converter and 3.50 gears. 
l’ll have to get back with you tomorrow and I can tell you exactly what jets I have in, my notes are out in garage. I think I have 74s in the front and 78s in the rear? I’ll let you know for sure tomorrow.

Now that I think about it, I had that same cam in my engine before I had it rebuilt. It seemed to fall flat on its face at 5000 rpms, just had nothing up top. Even had the same 770 carb for awhile, then I switched to the Quick Fuel. The QFT definitely was better than the Street Avenger, but it still died off fast. The Comp 270h cam is a single pattern cam and Cleveland’s like a dual pattern. 

Very cool. I also have a C6 with a B&M Shift Kit, Deep pan and the R Code Servo. 2500-2800 stall converter and 3.50's out back. So we're slightly different in cam, and you are .010 larger bore than me. Other than that, really close. 

In my case I went lower with my jets in the front, and kept the stock jetting in the back. Thought being to run the leanest jets you can in the front so that at cruise you are most fuel efficient. Use the power valve and squirter combo in order to make power when you want it/need it. Having said that, it's not like I take the car on long trips. So does that really matter? Maybe not.

I'm still going to take Don's suggestions about re-positioning the cam and having the secondaries open slower. Takes 10 minutes and I don't need more parts. But I would definitely love to have you conform your jetting for me in case I want to go that route. Thanks!

On the cam, you are correct, not much going on above 5k. Definitely the wrong cam for the car. It will definitely get swapped in the future. I see a rebuild coming in the next 18-24 months.

Edited by Big Red Mach 1

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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Ok I was wrong on a couple things, of course lol. Anyway I have 72s in the primaries and 81s w/ jet extensions in the secondaries. Went up a few sizes from the way it was new. I have a 6.0 power valve, not 6.5. It was originally supposed to be set up with a 6.0, but whoever set my carb up wasn’t wearing their glasses and put in a 5.0! The pump cam is pink and I have it in position #1. I have the secondary opening spring 7/8 open from seated. 

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John - 72 Q Code

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Thanks John. I'll take note of all of that. Again, I'm going to make the minor tweaks Don suggested based on where I currently am. If I'm not happy with those results, I may head toward where you are as you seem happy with it and our cars are very similar. 

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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1 hour ago, jpaz said:

Ok I was wrong on a couple things, of course lol. Anyway I have 72s in the primaries and 81s w/ jet extensions in the secondaries. Went up a few sizes from the way it was new. I have a 6.0 power valve, not 6.5. It was originally supposed to be set up with a 6.0, but whoever set my carb up wasn’t wearing their glasses and put in a 5.0! The pump cam is pink and I have it in position #1. I have the secondary opening spring 7/8 open from seated. 

Are you launching hard enough that you needed the jet extensions, or do you just like to add those in the secondary fuel bowl for good measure? 

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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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. 

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John - 72 Q Code

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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. ;-)

 

Edited by Big Red Mach 1

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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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

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2 hours ago, B229218 said:

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. 

Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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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.

 

 

Holley_Carb_Tuning.pdf

Black 1971 Mach 1

351C/FMX/TrickFlow Heads/Lunati Retro Roller Conversion

Classic Auto AC, Manual Front Discs, Upgraded Springs/Shocks/Close-Ratio Steering

 

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24 minutes ago, 71coop said:

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.

 

 

Holley_Carb_Tuning.pdf 202.92 kB · 2 downloads

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. 

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Chris -  Born in '73 - Drive a '73 / Former U.S. Army 63B10-H8 / 1st Infantry Division - The Big Red One

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