Flat tops

[tanny]

I'm currently running triple webers, but at my altitude(6500 feet) they apparently(advice from a well respected z race mechanic) are doomed to always have a severe stumble at low rpm rapid accelleration unless I put a higher performance cam in to increase air flowing past jets. The jetting I have is supposedly ideal for this altitude, and the car does idle really well and performs exceptionaly well above 2500-3000 rpm.. Anyway, I have the flat top carbs(I know the bad reputation, but some people have had good luck with dumping the smog stuff) and manifold for the car and was wondering: to make them run decently, do I just seal off all smog orifices to the carb and manifold? Will the headers cause problems with using these stock carbs? Anyone with experience getting the flat tops to work without the smog system(I don't have any of the smog stuff available to me, so I couldn't put it back on if I wanted to)? Don't really want to get rid of the triples, but the stumble is really irritating and even dangerous at intersections.

[Marty Rogan]

Don't EVEN think of putting flat tops on your car. You WILL regret it. They vapor lock like crazy, which will be even worse with a header.

The Windy city Z Club used to use flat tops for a "carb toss" competion at their annual picnic.

I am not a fan of Webers either, as a malfunctioning one burned up the '73 Z that I spent 7 years restoring. Get yourself a new set of round top SU's. They are still your best bet.

Marty

[Royce]

With the time and effort put into making other carbs work with your current setup, why not get a different cam??? If you talk with a cam shop (ex. Elgin Cams in Redwood City CA) they can usualy come up with grind that will work for you. And if they can reuse your existing cam it may not be all that expensive.

You also may want to talk to a Z engine builder (ex. Rebello Racing, Pacheco CA). Maybe you can try different cam timing???

One of the problems with the flat top carbs is finding parts and anyone that knows how to set them up. Lots of people are using them with success but from what I have heard they typically change to something else when they start to have problems with them. A decent set of SU's is relatively cheap but you may find you spend as much time and money as with the new cam.

Sorry, I don't have any specific info. Hope it helps!

[N5572B]

Just an off the wall thought but...I had a similar problem with a 510, idled fine, stumbled and rough at lower Rs but ran like crazy up above...needed the valves adjusted. They were too tight and it sort of acted like a cam with lots of overlap...just a thought.

Dave

71 240

[Zedrally]

The REAL reason people knock flat tops is that they don't understand them.

When overhauled correctly, with the correct kit they will perform BETTER that round tops.

I'm running both types in different cars and the flats are definately better than round, but only after a total strip down and re-build.

Now for the bad news....

I would seriously doubt that they would work in your situation as the only way to adjust the mixture is by altering the float level. This is the biggest plus for round tops and the only solution as a SU type carb possible for you as I see it!

Why not play around with cams, possibly a rally spec cam would solve your low end power problem?

[biker]

To N5572B

You may have just solved my problem by accident. I tuned mine up last week and ever since, have had it bucking at low revs.

However, when I did the valves I was quite suprised to having adjust most of the valves which was unusual.

Have redone the carbys but still got the same problem thinking that the mixture was wrong. Will go to the valves now:ermm:

biker

[tanny]

Yes, I'll try readjusting the valves. Haven't adjusted since I rebuilt the engine(350 miles) so they could be needing an adjustment anyway. There is definitely no problem with power at low rpms once it gets over its initial stumble. However, a new wrinkle, wife had to tow me home yesterday due to very little to no gas getting to the carbs. Today will check fuel pressure, pressure regulator, fuel filter, and lines(it was the fuel pump filter. Clogged with a pinkish colored very fine powder almost like talc, so I drained the tank and cleaned the filter). I doubt that fuel supply was my original problem with stumble, since it worked really well at high rpms. As for the flat tops, I'm undecided. I think I'll take one or both apart before I decide and get a better feel for their condition. Looking on the bright side, their is no paucity of used parts at really low prices because no one wants to mess with them. That's probably a hint. Would be nice to get a mild cam and rockers, but really isn't a guarantee to solve the problem, even though it does sound logical. So that would be another $500 more or less which would be tough(read impossible) to afford right now. So I have to try the least expensive alternatives and work my way up. As for the headers heating up the carbs, I imagine the only real solution to that would be a header blanket or tape? Thanks for all the input, everybody.