I have a McCulloch SC and a Holley 4150 blow through that I modified following this link, https://www.hangar18fabrication.com/blowthru.html. I'm getting leakage from around the green accelerator pump gasket/flange and a bit out the right side throttle shaft.

#ad


Have any of you had this issue and found a fix like maybe RTV over both sides of the green gasket/flange?

I've heard reference to O-rings for the throttle shaft but the leak there is very small so wish to avoid machining for an O-ring.

Glenn

 

Is it leaking from throttle shaft just sitting at idle , not running , or is it wet after driving and making boost??


As far as the accel pump leak, make sure its not leaking from a screw gasket and misleading you. If you havent , replaced the pump diapram and make sure the screws arent too long. Ive had some pretty rough surfaces on the accel pump mount and never a leak.
I dont think rtv will work. Fuel will eat it.

 

Hi tbird,

The leak from the throttle shaft, I can deal with. It's the leakage from the accel pump after boosting it that I'm trying to get rid of. If I just drive around without getting into boost (but what fun is that ), where I'll get 1/2 to a teaspoon full of gas on the back pump and less on the front.

I just changed my search string and found that it may also be to a bent accel pump housing along with the too long screws that you mention. The post from a chevelle site, https://www.chevelles.com/posts/7334777/is helpful but not sure about the stiff battery cable wire that's mentioned. I may try gaskets from old pumpers, placed on the bottom and then make up some backer plates under the accel housing. These would be like the SBC valve cover plates under the screws to better distribute the load.

"how much did you take off those pieces when you surfaced them? I've been doing that for 30 years without running into this with the bottomed out screws. You can cut the gasket part of an old diaphragm of and use it to double the gasket, but be careful not to over tighten it with the gasket stack. It will warp the pump housing and start leaking between the screws. Hard to fix then.

when surfacing this stuff it's good to be careful. you're trying to cut down the high spots to match the low spots. Sometimes guys get to watching the process, see the high spots getting shiny and end up trying to get the low spots to look like that without completely machining down the high spots. You only need to sand it till the first scratches start showing in the low spots, the gaskets will take up some of the slack. Another thing I learned to do was to use one strand of clean battery cable, cut it to length about 3/4 the way between the screws on the long side. dab a little grease or glue and stick it to the pump housing. This will add pressure to the gasket sealing area in thew area where it leaks worst. There's always more then one way to skin a cat.....

Did you put the extra gasket above or below the diaphragm? We used to put them between the bowl and diaphragm to increase the capacity a little, but they always leaked. If you're just using it for a spacer to make the screws seem shorter put it below the diaphragm."

Also dumb of me on using RTV. I do have duel resistant sealer that I could use though.

Glenn

 

I meant to say bowl screw gasket.

Maybe take the bowl off and inspect the pump accel area. IMO , stacking an extra section of gasket on the accel diaphragm is masking the main issue.

If its been awhile , replace the bowl and metering block gaskets. Pull the carb, make sure the base plate screws are tight, and the base plate gasket is good. Check for vacuum leaks around the carb. Any vacuum leak will spit fuel under boost.

I guess what im saying is, take the carb off and look everything over. You might find the obvious.

 

Thanks tbird, that's my plan for today. I'm also thinking that the wire idea is worth considering depending on what I find. I have some solid copper wire from garage door sensors and old TV antenna wire that could be used.

Glenn

 

the gasket area on the diaphragms is pretty thick. That flange would have to be hit by a truck to be so far out that it wont seal. So im not feeling the wire idea.

 

curious what you might find.

 

I found both accel covers were bent on all sides. I had not over tightened them but also didn't check or know to. Also going to check screw length now.

I just ordered a new pair of Holley covers on ebay

#ad

#ad

 

Machine screw lengths are JUST okay and the bent housings prove it. I have small washers that I'll also be using.

I tried carefully to straighten one out, no problem on the sides perpendicular to the pump arm but not on the others. It cracked.

Glenn

 

Yeh those are whooped. Looks like they where both bottomed out.
When you get it back together, adjust the spring adjusters on the arm until there is slop, then adjust back until there is no slop and go an extra 1/4 turn or so. Then operate the arm with the throttle lever to wot and make sure the accel pump still has some room to go yet. This will guarantee they arent bottomed out.

Some will set them by bottoming the accel pump by hand, and then adjust it to fit a shim between the pump arm and the lever to guarantee its never bottomed.

 

Yes, thanks for that. I adjust them the second way

 

Success! I got the new housings yesterday. I sanded them a bit with 600 paper on a flat table then cleaned up the bottom mating surfaces on the carb and accel housings, then assembled it. Note the thin embossed Holley plate.It puts a perimeter load on the gasket. I don't know what the part number of the plate is.

I tightened by hand only, then brought the screws into snug, and finally gave each about an 1/8 of a turn with one of those tiny handled screwdrivers that I got at HF.

Tested it this morning with full boost a half dozen times and ZERO leaks!!

#ad