Carb Question

[Bottom Line]

I have 340 hp Mercruisers with Rochester Q-Jets. I'm thinking of getting the carbs rebuilt but have seen some good comments on new Edelbrock 1409/1410 carbs. Anybody have any thoughts/experience on switching to the Edelbrocks? Thanks.
Mike Ford

[MikeP]

IF the carbs will bolt on with no changes - linkage fits, fuel lines fit, auto choke works, etc etc. Then it might be worth doing. Otherwise, I'd rebuild the Q jets.

NOTE: I am NOT a fan of Qjets and in many years of engine building, replaced them every time it was "legal." But properly rebuilt they are satisfactory and if carefully rebuilt/adjusted, they are actually pretty good - but don't expect that sort of adjustment to happen anywhere but at some sort of automotive machine shop that works on such carbs regularly. Any place that does a lot of work on NHRA "Stock" class engines will be good at rebuilding a Qjet for best operation. One of the main problems is that if it's an old Qjet, you have no idea what a previous owner did to them and wrong jets, wrong metering rods, STUPID air valve settings, etc are common.

So...if you do a rebuild, be sure that you or whoever's doing KNOWS to look for this sort of stuff. Also, Qjets were known for leaking at their casting plugs and for floats that would absorb gas and not float so well. Any qjet rebuild should include new floats, which are NOT part of a rebuild kit and a check to be sure that the casting plugs have been epoxied or, if not done, that it be done at this time. The epoxy on the casting plugs was a standard Qjet fix virtually since they came out in the '60's. If you do a search on "Quadrajet + epoxy" I'd bet money you will end up with MANY explanations of how to do it so I won't go into it here. Again, a good shop would do this automatically.

[Bob Bradley]

I replaced the carbs on my old Chris Craft 327's with the Edelbrocks and was very happy with them. I go them from Parts Automotive Warehouse (see: http://www.pawinc.com/). Do a search on Marine Carb and the 600CFM Edelbrock will come up at $337.95, and the 750 CFM is priced at $339.95. These are new in box, not rebuilt, carburators. They also have other makes, but these worked with my 1965 square bore intake manifolds.
Bob

[krush]

I like Q-jets. They aren't to hard to rebuild.

[Trojan]

You can't go wrong with the Edelbrock marine carbs. I put them on my last 2 boats what a carb. Make sure you buy the jet kit. There real easy to tune with the jet kit everything you need is in it. No new gaskets required when jetting. Antique Q-jets are junk compared to the Edelbrock. Q-jets were junk from the day one and are notorious for wasting fuel. They might be good for a drag car when all you doing is squirting gas into the motor for 3 seconds. They have no use on a boat motor. They could anchor your trout-line down or anchor a channel marker.

BILL

[Beckytek]

I must be missing something. I bought my boat in 2004 and use it every week and have yet to have a problem with my Q-jets. Maybe I'm just lucky. Ron

[MikeP]

I don't think you are missing anything. As I noted previously, the Qjets work fine if they are properly set up. I'd guess that some of the issues they have were addressed. Though the casting leaks are common, it would probably be incorrect to say they ALL leak. And if they were epoxied in the past, the problem no longer exists anyway.

I had Crusaders in my previous boat and despite my inherent dislike for the Qjet, I did the rebuilds on them and they did a fine job. It was a lot cheaper than buying new carbs. BUT there is no doubt in my mind that a bad-running Qjet is much worse than a bad running carb of just about any other design. They are very complex compared to a standard Holley and it is easy to get them totally out of whack. If someone has replaced the metering rods you are hosed until you correct that and it's not one of those things one normally thinks about when doing a rebuild.

I have to admit that I always thought of them as being part of the "How can we make something that is inherently simple be as complicated as possible" school. But it's worth remembering that they were designed to provide reduced emissions while, at the same time, providing the performance expected in the muscle car era at WOT. Some would argue that they did neither job very well.

[krush]

The beauty of a Q-jet is that it is almost "auto-sensing" like modern fuel injection. It's truly a masterpiece of engineering.

And because of this complexity, people misunderstand and don't like it!

[MikeP]

As far as it being a masterpiece of engineering...well, it has a LOT more moving parts than other carbs of its era, that's for sure! So if more parts make it a masterpiece, then perhaps it is!

What the Qjet did with it's nest of metering rods, etc, was an attempt to fine tune the mixture FOR EMISSIONS PURPOSES throughout the range of throttle opening. You have to remember again, that this was a carb SPECIFICALLY designed to meet ever-tightening emissions requirements when engines were not electronically controlled in any way. So the stepped metering rods were there to keep the metering adjusted to the leanest fuel delivery possible that would keep the engine running. Once at WOT, all the rods are clear and they have no effect on the mixture.

Of course, this lean setting that was good for emissions was not so good for midrange operation and led to complaints among the performance crowd about poor off-idle performance and general midrange operation though most folks in 4 door Oldsmobiles/whatever didn't really notice or care. SO...performance oriented owners changed the metering rods to aftermarket ones that would allegedly "correct" the problem. But often, as is frequently the case, owners figured if richening a little was good, richening a LOT was much better! So sometimes they are running very rich, especially when combined with floats that don't and leaky casting plugs. Folks also commonly changed the air valve adjustment so that the secondaries would open earlier - usually much too early - putting a huge "hole" in the power curve though giving the "feel" of "WOW" when the engine finally got enough RPM to actually use the airflow and "kicked it.". It felt "wow" but the car went substantially slower on the track.

But again, the most important thing to remember about it is that it was a first generation EMISSIONS carburetor; that was its reason for being. The fact that it also came on GM performance cars was due to emissions, not due to GM's performance divisions wanting to use it. And, like many "first generation" emissions items, like Cat converters, airpumps, etc it met the Fed emissions requirements with the sacrifice of some driveability.

Marine Q jets have (at least they are SUPPOSED to have) different metering rods than automotive Qjets to provide a richer low/mid fuel mixture - this was essentially what the performance folks did with their car carbs though, of course, it was "illegal."

As I said before, they can be just fine but they do take some fiddling. It's not complex in the sense that "normal" folks can't work on them but someone who is not familiar with the quirks, "fixes" and the frequently-changed metering rods and who just slaps a NAPA "rebuild kit" in one may be quite disappointed if the stars didn't align (no leaking casting plugs, no non-floating floats, no wrong metering rods, etc)

[67hat34c]

If you rebuild the q jets do not use National Carburators in Jacksonville FL. I use to support them but their quality has gone to crap.