Well
I’m trying to follow in Indy’s footsteps here, I won’t be able to hold a candle to his TH400 documentary… however, this is an attempt at a little tech article on how to rebuild a holley carb. This is part one - since the parts are literally soaking in carb cleaner as I type - and - since I only have a one gallon can of carb cleaner - the parts have to be cleaned “in shifts”.
This carb is a 4777 650 mechanical secondary - lovingly referred to as the “double pumper”. This carb is in pretty good shape over all - judging from the outside appearance. However - once opened up - you can see what leaving gasoline in a carb for long periods can do.
I’ve probably not taken enough pictures to detail each step, but I hope at least some of you will find this helpful. I realize many of you have probably rebuilt more of these things than I have - and I welcome your additions here.
The first few shots are of the carb as I started with it - swap meet fresh, and stored for untold months in my shop…
Below you can see what makes a double pumper a double pumper - two accelerator pumps - one primary, one secondary, these are both standard volume pumps - larger pumps - 50cc I believe are available.
Looking down the venturi’s - you’ll notice this carb has no choke currently installed, and it has the standard booster venturi’s and air bleeds - some higher end carbs have downleg boosters, removable air bleeds, etc, this one is a pretty standard issue unit.
Here’s the first dis assembly - remove the four bowl retaining bolts, and with a firm whack from the handle of a screwdriver against the needle/seat fasteners and the bowl gasket will let loose - revealing the primary jets and power valve in the metering block, and the center hung brass float and needle / seat assembly:
Here you can see some of the nasties left over from leaving who knows what kind of fuel in this carb for who knows how long… I hope that wherever else this stuff has settled that I can’t see - the carb cleaner solution will remove.
More shots of the nastiness - this shot also shows the bowl vent extensions (white plastic things) that came on this carb.
After removing both bowls, I removed the throttle plate assembly from the main body of the carb. This allows access to the bottom of the metering blocks to remove them - as the old gaskets really like to stick these things hard to the main body…
This shot shows the “power valve saver” check ball between the two primary throttle blades, this was a standard on this carb - all the older carbs (not sure what model year they made the change) you’ll have to drill and install this check valve yourself to keep your power valve from being blown out if you get a back fire…
Here is an example of how I try to keep the parts organized while I’m taking the carb apart - even if you’re doing this on your picnic table like I was - keeping the parts organized and labeled - along with taking pictures during the tear down can really save you some time and frustration at re-assembly time.
Notice in the above shot - the small silver “needles” these must go in the main body under the accelerator pump squirters - shown above them on the cardboard - which are held in with phillips head screws - and have a gasket between the squirter and main, and screw and squirter.
This shot shows both bowls, needle and seat assemblies, and standard inlet fittings for flare nuts
(5/8" nuts adjust the float height - slotted screws lock down the adjustment - like the squirters - gasket under screw, and nut)
Here’s more nasty - inside the bowl:
Below is an accelerator pump assembly removed from the bottom of the bowl, the little orange rubber thing is an umbrella check valve seal - during assembly - these seals need to be pulled through the bowl bottom carefully with pliers, don’t forget the spring - and don’t mix springs between pump sizes - they are different
(no worries here - pri and sec pumps are the same)
The next shot is my probably somewhat unconventional method of removing stubborn metering blocks… I have clamped the main body CAREFULLY upside down in a vice - then - using the extra portion of casting that protrudes from the bottom of the metering block as a point of impact - I give it a couple taps with hammer - and the metering block gasket finally gives up and I can seperate the blocks from the main body.
Below you see both metering blocks removed from the main body - the secondary block on this carb does not have a power valve. This carb has the most common factory installed power valve - market with a stamp 6 5 - which means it opens for enrichment when the manifold vacuum drops to 6.5"Hg. For most carbs - this power valve works well, if you have a really nasty cam with very little idle vacuum - you may need to change to a lower number valve to keep it from opening at idle.
Close up of the power valve - hard to see the faint stamping - but there is a 6 and a 5 in there along with a couple other characters.
Here is the power valve removed from the metering block - which requires a 1" wrench.
Below is a close up of the pin that holds in the plastic vent tubes - simply push those up with a screwdriver, then pull the pin out the top with pliers, then wiggle and remove the tubes - ALL plastic parts must come out of a carb before putting it in the chemical dip cleaner.
Here’s the vent and pin removed:
Here’s the gallon dip tank I have - originally purchased to clean the three one barrels on the 90hp merc outboard…- with a little creative packing - I’ve got both metering blocks, both accelerator pump housings, and both bowls in the can together. The main body and throttle plate won’t fit in there, so - cleaning them with carb clean spray and blowing everything out with compressed air will have to suffice. I miss my old 5 gallon can of hydroseal!
Don’t sweat it if you can’t get all the gasket material off the castings before putting them in the carb dip - that’s OK - they’ll come off easily after soaking a while. Cleaning the gasket surfaces is tedious - I generally use a razor blade and a pick set - you have to be careful not to damage the sealing area, these carbs are aluminum pretty soft.
Source : Forums - The BangShift.com Forums