need help with stock mikuni carb for 88 2,6l

[robertson5347]

I'm trying to rebuild the stock carb. and need some help. 1st. trying to locate the proper hole for the ball pump check valves. The carb. diagram is not specific enough to show this. Saw this once on utube but cannot find it. Also how do you remove the diaphram vent valve? Have tried to pry out the diaphragm but the valve is stuck tight. Does abyone know of a way to manufacture the valve since you can't find one to buy

[xboxrox]

My 1986 carb not same as yours but check my photo albums & this thread: http://www.mightyram50.net/vbulletin/showthread.php/8131-Mikuni-carburetor

[FMS88]

There are three check balls in the plastic mixing body: two for the main accelerator pump and one for the auxiliary accelerator pump (AAP). If you haven’t already, separate the top, air horn from the mixing body and remove the gasket. In the body near the accelerator pump are three plugs.
http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=26394&stc=1

The one on the right in the picture is to the pump inlet, the one on the left is the outlet. The center plug is to the AAP. The left plug will fall or lift out easily, but use a fine screw driver of the right plug and a small wood screw to catch and lift out the center plug. The plugs are all different and each has a spring and ball underneath. Don’t mix the plugs, springs or balls.
By the “diaphragm vent valve” I’m assuming you mean the bowl vent valve. The diaphragm between the plastic housing and the metal air horn has a shaft that extends into the air horn and passes through a rubber disk that opens or closes off the bowl vent openings. This disk is probably what's preventing you from removing the diaphragm/shaft. Remove the cover next to the fuel solenoid to view and access the diaphragm’s shaft and the rubber disk shown in the center of this pic. The solenoid is removed so you can see the end of the shaft through small round hole to the right of the rectangular disk access.
http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=26392&stc=1
Try lubricating the disk and shaft then work the diaphragm/shaft out separating it from the disk. Here’s a couple diaphragm/shafts and disks to show how they look like after removal. The disk sits at the narrowest point of the diaphragm shaft.
http://www.mightyram50.net/vbulletin/attachment.php?attachmentid=26393&stc=1
If the disk is hard and brittle, it may get destroyed in the removal process. Replacement diaphragms are available but new disks are really hard to find so expect to have to make your own if ruined. In that event use the original as a guide and try modifying a faucet washer of similar diameter. They seem to be of comparable dimensions and hardness. Or got a 3D printer?

[SubGothius]

That diaphragm+shaft part is often mis-listed as a "choke pull-off" (maybe the same part is used for that purpose in another application?).

I have one barely-used I could provide, that I'd obtained before realizing the middle disc was perished on my old one, installed it anyway and capped off the vent hose barb hoping that'd let me pass emissions in case the malfunctioning vapor valve was causing the rich-condition smog flunk (turned out it wasn't that after all). Soon gave up on the Mikuni altogether and swapped to a Weber, much better in every regard.

[FMS88]

Good point, SubGothius. Tomco is one supplier that calls it a choke pull-off. Their P/N is 7404. Unfortunately Tomco doesn't list the disc, but it can be acquired by purchasing an entire vent valve kit for $200-300 depending on the jobber. The current P/N is MD617185 (previously MD612742). At that price, might just as well get a Weber.

[SubGothius]

Good point, SubGothius. Tomco is one supplier that calls it a choke pull-off. Their P/N is 7404...

Yup, Tomco 7404 is the one I got.