Seems off - one side of accelerator pump jet is blocked off

[tdskip]

Hi guys - detailed enough question I wanted to put it out of another thread.

On my 1968 DHSA carb the accelerator pump jet (has two nozzles that are shaped like a Y) has one of the blocked off, looks like it was blocked with metal on purpose or someone did a gorrilla move on it and damaged it. Effectively only one side is open, meaning one carb will get flow and the other will not.

I check the diagrams and new replacement parts and it looks like this is the same as the new ones.

Is there any reason this would be like this correctly? In other words, have I found a real problem or is this expected?

Seems odd - I'm used to and expecting everything to be symmetrical.

Thanks!

https://www.piercemanifolds.com/product_p/76211.htm

[18Fiatsandcounting]

... have I found a real problem or is this expected?

It is to be expected. I just checked on my "spare" 26/34 DHSA that I have on the shelf, and it only has an opening for the primary bore. I believe that is true for my 28/36 DHSA that is on my '71 spider, but I'm going by memory on that one.

My guess is that the reasoning is thus: the accelerator pump is meant to provide an extra squirt of fuel when you first open the throttle, otherwise the engine would go lean and stumble from the sudden inrush of air. However, on carbs like the DHSA where the second barrel kicks in only when the first barrel is almost wide open (vacuum operated secondary), there's already enough fuel rushing in from the main jets of the primary barrel, and so that little squirt from an accelerator pump on the second barrel ain't gonna do squat. In other words, any fuel from the accelerator jet at that point is trivial compared to the fuel coming from the primary's main jet circuit.

I'm also guessing that for carbs that have both primary and secondary barrels open in unison, there is indeed a need for a primary and secondary accelerator pump jet. My 38 DGAS is one example.

-Bryan

[tdskip]

Thanks Bryan.

Got it all back together and turns out one of the primary jets wasn’t fully flowing due to crud. Cleaned the heck of of every and soaked all the jets and tubes in cleaner and HOKY COW. Drives like a whole different car now.

Thanks again for all of the help.

Hope you are having good Sunday.

[18Fiatsandcounting]

Awesome, tdskip! Say, did you ever see if your secondary is opening up like it should? I'm not aware of a good way to test this, as I seem to recall that it would only open up if the engine was under load and at almost full throttle. You might see it begin to open if you're in neutral and work the throttle by hand, but again, my recollection is that the engine isn't pulling enough vacuum as it revs too freely while in neutral.

One way to test this for sure is to take off the hood, find a quiet road, put it in 5th gear, floor it, and watch to see if the secondary opens. In my younger and more foolish days, this was how I did it, but there must be an easier way...

-Bryan

[tdskip]

Good morning Bryan - I have to check that still. Honestly the carb is so smooth and she runs so nicely I assume it is happy but not going to poke at it.

(I will check soon).

Have a new issue to deal with first, starting a new thread. Ugh.

Thanks!