Qjet

[SONNY G]

I have been having issues with my Holley 500 2 barrel running rough and stalling while offroading (not just on incline/declines but also driving through ruts).

I know everyone has a very strong opinion on this subject, so while you read this just remember I am just learning so I just go off what I hear. I am looking for some opinions as I need to decide which way I will go.

So I think the carb I talked to someone about was a Qjet (think it's a Rochester). I know a lot of people are running throttle bodies .

I have a pretty stock 302 (I have had her for 23 years) i haven't really done anything to it. Just like everyone, I want it all (good on the street as well as offroading) , she is mostly a daily driver but want to get her out more.

One place I talked to said he will build a Qjet , engine tested ready to install with an adapter for just under $600 delivered.

I also looked up throttle bodies but those are minimum 2 to 3x more. I just had a couple guys just tell me that they are experiencing issues with their throttle bodies and are going back to a carb. But I have also talked to people That LOVE their throttle bodies.

Does anyone have experience with a Rochester Qjet 4 barrel? Is the price of just under $600 a good deal?

Thank you in advance for your time/help,

Sonny

 

[ntsqd]

I don't know how much you know about Rochester Quadra-Jets, but for off-road use their primary advantage is that they have a small footprint, centrally located fuel bowl. No matter how you tilt the carb it is hard to uncover the jets in the fuel bowl. For street use their primary venturis are small giving good throttle response and their secondaries are large.
They do not like a lot of fuel pressure and prefer to run at less pressure than what a Holley typically wants, so you may need to add a regulator if you don't already have one.

MISF has one on each of his drivers except for his latest DD which is EFI. He dialed them in and they ran very, very well, but he was frequently having to fiddle with them to keep them right at the peak of their tuning. If you go down this path you'll need to learn enough to be your local expert because they do not tune like a Holley, and most who would try to help you will be lost. They're not hard to tune, but they are different. From what I recall when I was looking at this option ~25 years ago this book was the best available on the topic: https://www.carburetion.com/Products/ProductDetails.aspx?part=BK-HP14 There's a new book out and it may be better and may not. I've not looked it over.

No idea how well developed your Holley is, but there are some tricks. Some folks extend the bowl vents on a Holley up as high as the air filter will allow to help with keeping slosh in the fuel bowl from getting into the venturis. Using the "vent whistle" insert can also help with this.
A trick that used to be used in the rear bowls of drag race cars were little tubes that fit into the jets (some were thread-in spacers that moved the jets themselves). These moved the point of fuel pick-up back towards the rear so that when the car launched hard and fuel moved to the rear of the bowl the jets wouldn't be uncovered. Either of these methods requires notching of the float for clearance. I've not read much about these being used off-road, but it seems to me that set to the middle of the bowl would be the best possible location for the jet's fuel pick-up.
Then there's a so-called "Dry-Sump" Carb mod, but unless you're forced into using a carb specifically this is a really complex undertaking.

I would venture that most of the troubles folks have had with throttle bodies has been fuel tank and fuel delivery related, not the throttle bodies themselves. A well baffled tank or a very well thought out fuel pick-up will eliminate these problems. Some, no doubt, had trouble with tuning the system. Pays to go with a system that has excellent support or a system that your local dyno tuner has a lot of experience with, or be prepared to learn enough and acquire the various tools needed to tune it yourself.

 

[ntsqd]

What is the name of the shop quoting you $600 for the carb? I know that there is at least one shop more or less down your way that specializes in off-road racing carbs and if it is they who are quoting you $600 I'd jump on that.

 

[SONNY G]

I ended up purchasing my Qjet from (Bruce) Carburetors Unlimited in Arizona. He said it's about a 2 week build time so I am still waiting for it. While talking with Bruce I found out that there are a couple different options, such as one has only (02) adjustable screws and another carb has (03). I'm still learning s not sure if it's really necessary to have the 3rd one but I figured for a little extra money I can just get it now instead of "wishing " I had bought it the first time.

I am excited/anxious about this purchase as it is not cheap but hopefully a GOOD BUY. I have done a lot of research and read a lot of good things about Bruce. I just wish I could have purchased the Offenhauser manifold people have recommended but out of my price range/budget. I will be using an old Edlebrock manifold.

I will post an update when I get everything installed.

If your in the LA/OC and have experience installing a Qjet I would love some assistance, BBQ and Beverages will be provided.

 

[SONNY G]

Anyone know the tightening sequence and torque specs for the manifold and carb?

While I am asking questions, what spark plugs (and what gap are you running) and what spark plug wires (size)? I read people like the ford performance 9, but looking into it , it looks like those are for EFI engines ??

Thank you in advance for your time/help,

Sonny