Valtech Jet Blocks for Holley carbs

so you think you can meter it better and deal with 2 power valves ? .....it's a jeep the secondarys will hardly ever be used enough to see a benefit of a slight jet change. mehh.

 

Double pumper use secondary power valves...vacuum secondary carbs generally don't.
I agree that for this application it probably isn't nessecary.

 

I agree. But I love to tinker...

 

Doug -- I spoke with Holley tech guy this AM and after I described what I had (225, fresh build, 10;5:1 CR, Offy 360 Dual Plane intake, high lift short duration cam, Sanderson headers, etc.) he shuffled a bit, hemmed and hawed and said that a 470 TA would work.

The 470 TA has some stuff that the 4160 390 does not - second metering block with replaceable jets, annular boosters, spring loaded valves, etc. and all for about the same price as a 4160 390. If it will work, I'll get one… BUT...

I would like to know what 'drivability issues; you have. What is the problem, what is your set-up? What have you tried?

I appreciate your experience with this carb.

 

my 390 is going on tomorrow stay tuned

 

Holley's product literature says that only the 670 and 770 TA have annular boosters. Just FYI.

https://www.holley.com/products/fue.../avenger/off-road_truck_avenger/parts/0-90470

I have read about a specific off-road change that the TA carbs have that causes drivability issues. But I don't remember the specifics ... I think it was on IFSJA. If your google-foo is strong, you could search there. IIRC Ristow at IFSJA knows a lot about these and the other Holleys.

 

The carb has a part throttle stumble...initial acceleration is great, then it'll sputter for a second or two before picking up again. The same thing occurs if you're driving along at a steady slow speed and try to accelerate. The stumble occurs right at the power valve opening point...I did quite a bit of experimenting with different power valves to confirm this. It's simply getting too much fuel when the power valve opens. Going to a different squirter helped some but the biggest improvement came from the old carb tuners trick of putting a piece of thin copper wire in the power valve channel in the metering block to reduce the fuel flow. It's improved enough that it's more of an annoyance than a serious problem.
As Tim mentioned, the TA carb uses a different design in the metering block to improve off road function, but it seems this came at the expense of driveability.
BTW, mine is an all original (except carb & intake) 225 with 160K miles on it, & I live at 6500 ft elevation. It would be interesting to see how this setup would perform on a fresh engine at sea level.

 

Thanks, Doug -- so this stumble happens when the secondary opens and the power valve squirts? What intake manifold are your running? Does it happen when the engine both cold and hot? What power valve did you end up using?

Sorry for all the questions, but you have been a great help.

Mike

 

Tim - The product sheet on the 470 TA says annular boosters… but then says that only on the 670 and 770 in the 'small print'… bummer.



Mybe this is a new addition to the product?

Mike

 

Look at the part numbers. The 470 is not there.

 

last time I started my 390 it had a slight off idle stumble . switched from the orange pump cam on #2 to #1 and it helped ... then I switched squirters ,,,,I need to run it now ...keep you posted

 

Warlock, you need to post some pictures in another thread. I may have missed some from previous posts. Would be interesting seeing some from your neck of the woods.

 

LOL!
I grew up Jeeping in Colorado, & so have my kids.
The list of trails I haven't been on is pretty short...

 

I've been doing the 4X4 thing here in CO for something like 45 years. Trust me, there is still some trails to be explored.
The thing that saddens me is that several of them seem to be getting closed.
Still lot's of trails in surrounding states to hit.

 

Thanks, Chuck. Helpful as usual.

 

That looks like a problem solver for my jet boat. Sputters when hitting deep holes going up the river.