Holley 4160 set up questions.....

[Lou C]

Hello all,
I didn't want to rebuild my 30 year old Q-Jet again so started thinking about possible alternatives. There's Holley and Edelbrock. On this engine (OMC rigged 4.3) I do not think the Edelbrock would have fit because of the OMC shift linkage bracket and relays on the starboard side. The Edlelbrock just seems to wide to fit esp on the V6 models. So I went with the Holley and OMC/Volvo used this same carb when they stopped using the QJet in 1990. I was able to get the factory fuel line and throttle bracket from BRP, who still sells OMC parts. I was not able to get the adapter plate they used, but found that the Mr Gasket one sold on the Holley website was about the same size. All I had to do to make it fit was relocate the down relay for the trim system.

OK on to the question:
it seems to idle excessively rich and the idle mix screws have little or no effect till they are screwed in all the way. Then the idle rpm increases to about 900 from 600 and if I try to adjust it down with the idle speed screw the engine dies. I called Holley and the tech suggested that too much of the idle transfer ports are exposed, which greatly enriches the mix. In fact the plugs are black whereas before even with the old QJet they were not. Should I adjust it with the throttle cable disconnected? It may be the adjustment on the throttle cable is too tight pulling the throttle plates open a bit.

Thoughts?

 

[Bondo]

It may be the adjustment on the throttle cable is too tight pulling the throttle plates open a bit.

Ayuh,..... I know, Nothin' 'bout Holleys,..... could be idle jets or needles, or adjustments,... donno,...

But,.... To properly adjust a throttle cable, the carb linkage is pushed tight against the idle adjustment screw, 'n the cable is attached With Tension, Pushin' on the idle stop screw,....

Don't need alot, but the cable must Push against the screw,....

 

[Lou C]

Yep that makes sense!

 

[Scott Danforth]

what jet and power valve do you have?

should be a #25 or #35 power valve and maybe #58 or #60 primary jets for the V6

 

[Lou C]

https://www.holley.com/products/fuel_systems/carburetors/marine_carburetors/parts/0-80492

 

[jimmbo]

If the primary throttle plates have to be open so much that too much of the off idle slot is exposed(often occurs when a street/emissions carb is paired with a high lift long duration cam, or the timing is so far retarded the carb has to oppened up far greater than normal, the off idle response will be poor. Some tuners will resort to changing the the Accelerator Pump cam to try to compensate. However, there is a way to have the primary throttle plates in the correct postion and still get enough air for a good idle. On a lot of carbs that meant drilling holes in the throttle plates, however on a 4 bbl Holley, there is a little known secondary throttle shaft idle stop, that is adjustable from the bottom of the carb. All 4bbl Holleys have a functioning idle circuit, to keep fresh fuel in the secondary fuel bowl, and to reduce flooding if the inlet needle-seat does not close properly. With the primary throttle valves proper positioned with regards to the off idle fuel slots, the secondaries are opened a bit, the carb installed and what the result is. It may take several adjustments to get it right. As always keep a written record of any and all tweaks and adjustments, you there is not confusion as to what was done, how much, and what order

This is a Holley 4175, but every Holley 4bbl I've looked at has this adjustment screw

 

[Lou C]

Thanks, I have seen this referenced in some of the articles I have read about this issue. Hopefully the idle will be close to right when I have the primary throttle plates adjusted to the right point in relation to the idle transfer slot.

 

[Lou C]

OK disconnected the throttle cable, and lowered the idle so it was running off of the idle circuit with just a bit of the transfer slot exposed. This way I was able to adjust the idle mixture as it should be done and the rpms responded to the adjustment just as they should. Now I just have to get the throttle cable hooked up so it does not push on the throttle lever and allows it to return to curb idle with the throttle plates closed (or nearly closed). Idle quality was much better than first run.

 

[Lou C]

Figured out the other part of teh problem, throttle cable keeping the throttle open. On the OMC Cobra system, you are supposed to shift the remote into fwd, then pull it halfway back to neutral to adjust the trunnion on the throttle cable to take out the slack. Found this in my OMC factory shop manual. I was trying to do it after pulling lever (OE OMC control box) out to disengage the shift system. I believe that is what was throwing me off....will try again to get it right tomorrow.

 

[Lou C]

OK fooled around with this thing most of the summer, tried everything the Holley tech guys said to try. This particular application of the 4160 does not use a power valve but bigger jets to compensate (68 primaries). I checked the floats and they were a bit off but even setting them level, it still idles too rich and surges on acceleration and higher rpms. I think there is some internal defect and I am going to send it back to Holley to see what they say, I did not want to disassemble it further to check.
Sooo….I pulled out the 30 year old Q-Jet and carefully took it apart and cleaned it, paying attention to those idle air tubes. Rebuilt it with a standard marine rebuild kit. Float and accel pump were fine and the carb was really not dirty inside. Well, it fired right up and ran better than the Holley ever did! Do I feel foolish not doing this in the first place! I was led to believe that rebuilding Q-Jets was complex and difficult, it really is not. You just have to pay attention when replacing the air horn to get the metering rods and air tubes lined up right.

Live and learn....

 

[jimmbo]

The Q-jet is my favorite carb, probably the best engineered carb ever made. It can also be one of the most complicated carbs to recalibrate, and also the most versatile too.
As for the Holley 4160... I have never seen one that didn't have a power valve on the primary side, they never have on on the secondary side. With squarebore carbs I prefer the 4150 as it has a metering block with jets and often a power valve on the secondary side. However I much prefer the 4175 as it, like the Q-jet is a Spreadbore carb. While the Holleys can be tuned for either best power or best fuel economy, it takes a bit of effort to tune it for both. Drilling out, or filling and redrilling, the power circuit orifices in the metering block will be needed to get both the best power and best economy.
Your Holley may have been hindered by one of those very poorly engineered/designed Squarebore to Spreadbore adapters. I have only ever seen one, about 40 yrs ago that didn't reduce/restrict the flow of the primaries
Was it a Marine Holley carb? Or an auto/truck carb?

 

[Lou C]

The 4160 I used is a brand new Marine carb that is specifically calibrated for the OMC/Volvo 4.3 V6 Holley part number 80492. I used the exact same OE factory adapter plate that was used on these engines (still available from Volvo Penta). I thought of using the spread bore 4175 (I believe they both used this carb on the V8s, since no adapter shows up in the parts diagrams) but I don’t think it will fit due to the fuel inlet being on the front of the bowl vs the side on the 4160. The front fuel line connection would likely hit the thermostat housing on the shorter V6. I did wonder if one could use the side entry bowl on the 4175 though. I still think there is a basic defect in this carb causing the rich running. The floats are set right, the needle valves hold when you blow thru the inlet with the bowl inverted, the idle transfer slot is not over exposed and the idle needles are set 1/2 turn out. What else can cause this bad/rich running?

 

[Lou C]

Here is the plate I used, first I used an aftermarket Mr. Gasket plate because OMC/BRP did not sell the OE one any longer but I was able to source it from Volvo/Penta right here on iboats. It did not make a difference, ran equally bad with both.

 

[Lou C]

Here is the exact Holley carb I used:
https://www.holley.com/products/fuel_systems/carburetors/marine_carburetors/parts/0-80492
68 main jets and no power valve

 

[jimmbo]

Fuel bowls will not interchange between a 4175 and a 4160.
A ruptued/leaking Power Valve diaphragm will result in an often hard to diagnose ‘Rich’ condition

edit: looking at the Holley Spec sheet it does appear to have no power valve. Might have something to do with the V6 uneven firing order and the resulting reverberations in the induction system. Weird, but I will assume the Holley engineers knew what they were doing.

 

[Lou C]

true but this carb does not use one. Since I have no warrantee on the carb any longer I may just take it apart myself and see if anything obvious jumps out at me but if not I may send it back to Holley and see what they want to make it work right. I'd like to have it as a back up to the Q-Jet.

 

[jimmbo]

I saw the spec sheet and it showed no power valve. Weird.

The 4175 is a good carb as it retains the small primaries of the Q-jet. It doesn’t have the sophisticated booster venturi of the Q-jet, but it can flow more CFMs on the primaries.

 

[Lou C]

I spoke with a Holley tech and he said the main jets were made bigger on this carb due to the lack of a power valve. I was amazed how much better the Quadrajet ran, even being 30 years old.

It does make sense that the uneven firing pulses of the V6 may have some influence on their choice, since all the other carbs that have power valves are for V8 applications.

 

[Lou C]

Well dragging this up from the past. I took that Holley apart and have a question....I took the front float bowl and metering block off blew out all the passages, air bleeds etc, nothing seemed clogged. Then removed the rear float bowl and found..that all the clutch bolts on the metering plate were loose but one. Yet the gasket & plate were stuck on good. Not sure if most of the clutch bolts not even being finger tight could have caused my difficulty. I left the Q-Jet on and don't have any plans of taking it off because it still runs fine with it, for now.....

Any thoughts Holley gurus?