Carb question

[skokie]

Holley 4175 spreadbore vs a qjet. What are some of the pros and cons? Also vehicle is a daily driver. Stock 350.


Thanks

[jimfulco]

I put a brand new Holley spread-bore on a brand new stock 350 in 1972 and it never ran too well. I put the Q-jet back on it & it's still there. The Q-jet had much better throttle response, slightly better fuel economy, a much better idle, and seemed to make just as much power, and it didn't sputter and pop (think lighting a small pack of firecrackers) when you floored it from mid-range RPM.

[68speedalert]

Generally speaking, for an everyday driver, Q-Jet EVERY time.

Holleys have power valves that go bad often, idle circuits tend to clog easily. If you like working on your carb, get a Holley.

Q-Jets can be hard to overhaul for some. Lot of rods and stuff to keep and get in place. But....once you do have it set up right, it can run good for a long time. Parts are very available form most parts stores.

JMHO

[Billla]

For a stock engine, it's hard to beat a Q-jet. Small primaries for economy around town, BIG secondaries for the occasional heavy right foot. They're also usually tuned pretty close to the right settings out of the box, and with the vac. secondaries it's kind of self-tuning.

Holleys are great performance carbs, but in my experience they take a ton of tuning to get them right on - my carb was *6 sizes rich* and *3 secondary springs light* out of the box. Additionally, people generally get ones that are just way too big - an 850 double vs. a 600 vac.

I don't agree with the observation regarding power valves, etc. - I hear about it all the time but I've never actually seen one blown.

I completely agree with the overhaul comment; there are a few tricks (accel pump, etc.) but it's pretty straightforward if you take it slow and careful.

[68speedalert]

Originally Posted by Billla

I don't agree with the observation regarding power valves, etc. - I hear about it all the time but I've never actually seen one blown.

I didn't say 'blow'. I'm sure if you've been thru a lot of carbs that Holleys are just like Motorcraft 2 bbls, the valve diaphram goes bad. When it does, it will run pig rich fronm fuel running straight from the bottom of the bowl into the manifold.

I've ever seen any of them that I thought were 'blown' as well. The ones I see are from being old and attacked by something in the fuel.

I agree with all your observations.