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Flat Tops vs Round Tops


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#1 Hunter

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Posted 10 June 2008 - 12:23 PM

I am buying a 260Z L28 that has triple manikus (how ever it is spelt or pronounced??)
I am going to get the triples removed and get SU's put on it.
I have a L28 Fuel injected turbo I am going to put in the car, hence I will not need the triples.
The bloke I am buying off has round tops and flat tops he could install.

I need some feedback on the following so I can make a choice:

Which is the best?

What are the technical differences between the two?

Are they different sizes?


P.S. I have flat tops in my 1974 260Z 2+2,

#2 Scoota G

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Posted 10 June 2008 - 12:52 PM

Round tops are SU type and the flat tops are Hitachi. If i were you i would keep the Triples and then buy a set of Round tops off Ebay as i have seen quite a few on there latley. I have a set of SU round tops that i was going to donate to the Drag car project if it went through.

#3 JP240z

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Posted 10 June 2008 - 01:17 PM

Hitachi make both round tops and flat tops actually.
The hitachi round tops are pretty good and can be jetted to run almost as well as tripples, but the flat tops are dirt.
Get the tripples and sell them, or get him to put the round tops on.
Oh and also the round tops are 240, whilst the flat tops are 260.

#4 Hunter

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Posted 10 June 2008 - 02:09 PM

I am getting the car for $2000 less without the triples.

All I need is the twins to drive the car home and around.

are the 240Z round tops big enough for a L28? Would it run lean?

The car has a L28 installed.

The Hitachi round tops would have "HITACHI" written on them somewhere wouldn't they?

#5 JP240z

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Posted 10 June 2008 - 02:55 PM

You should be able to richen it sufficiently for a stock L28 using the mixture screws.
In the long run of you were going to stick with it you would probably re-jet them.
Yeah that guy is dreaming with the tripples so go with the round tops.

#6 Hunter

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Posted 10 June 2008 - 03:16 PM

Cheers round tops it is unless someone else can convince me otherwise.

Has anyone run Round Tops on a standard L28 before?

#7 dalee

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Posted 10 June 2008 - 03:32 PM

i am running the rounds on a bog standard l28, runs great and pulls well from low rpm. 

previous owner ditched the efi set up in favour of 240z carbs

#8 Hunter

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Posted 10 June 2008 - 03:42 PM

i am running the rounds on a bog standard l28, runs great and pulls well from low rpm. 

previous owner ditched the efi set up in favour of 240z carbs


Cheers

Sounds good, do you know if there is any modifications to the carbs?

#9 Scoota G

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Posted 10 June 2008 - 04:03 PM

$2000 less yea take the twins ;D

#10 dalee

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Posted 10 June 2008 - 04:44 PM

I just have the standard 240z (round) carbs as far as i can tell, my 3 sets are all the same - no fiddling with the needles.  Just adjust the mixture until you have it running well.  EG Mine starts after sitting for 3 weeks after 2-3 cranks with no choke, starts to loose power above 5,500rpm but with a stock cam all you are going to do at that rpm is make more noise. I just give the old girl a breather and find another gear.

#11 Toecutter

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Posted 11 June 2008 - 01:32 AM

Round tops are the goods. Flat tops are boat anchors people throw out with the rubbish.

Sulio

#12 Hunter

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Posted 12 June 2008 - 10:44 PM

sulio what are the reasons behind them being rubbish, one I can mention from experience is that the floats soak up fuel and sink in the float bowls.

Are they the same diameter? Is it easier to tune/balance one over the other?
Is one more responsive than the other?

#13 PZG302

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Posted 13 June 2008 - 07:59 AM

The flat top Hitachis were used on the 260's when stricter emission controls came in in California. They are basically a pollution carbie that lost a lot of power because of the new emission controls. Because of the market size in California the rest of world pretty much had to suffer as well.

Similar situation for Australian cars in 74 with ADR 27, the pollution one that crippled power outputs of the Holden, Ford and Vliant motors at the time.

#14 Hunter

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Posted 13 June 2008 - 08:12 AM

Thankyou.... ;D

Clear as Crystal now

#15 Zedman240®

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Posted 13 June 2008 - 08:38 AM

It might be a bit late but the reason flat tops are good boat anchors is because internaly they have alot more plastic parts that degrade with time and replacements arent available. So when you have a set running badly...nothing can be done that would be worth their value.

#16 Hunter

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Posted 13 June 2008 - 09:28 AM

Cheers Zedman ..............yeah one of my floats in an existing pair is soaked with fuel and sinks in the float bowl

#17 blue fairlady

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Posted 19 June 2008 - 12:04 PM

Hi I am new here , I have a hitachi with round tops on my 240Z 73, after money spend to a carbi specialist tuning, the plugs were fouled quickly, he then recommended reconditioning. That done again and paid, the same fouling my god what's wrong and what should I do , some one mentioned above round top hitachi are good if well tuned, , Should I not loss faith and carry on with this Hitachi, How do you adjust the mixture?  Or should I go for SU, if so which model?? and do I need mod to linkages and the rest
Thanks for helping!!

#18 JP240z

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Posted 19 June 2008 - 04:37 PM

Stick with hitachi, but not with your carb "specialist".

#19 Scoota G

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Posted 19 June 2008 - 06:16 PM

My car was doing exactly the same thing. Check your Valve gap and adjust. The problem was caused by broken rings on mine.
All the first set of rings were broken and good mate told me that this is common with japanese engines, older japanese engines

#20 pauly_adams

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Posted 19 June 2008 - 06:34 PM

check your spark plugs if there ngk bp6es change them to ngk bp5es i think your problem will vanish as mine did.

cheers pauly




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