Coughing and spitting on tripples

[vipergts]

Running like a pig on tripple webers

Is there anything obvious here?

Car runs very rough and lumpy between 1500 to 3000 revs if I squeeze the throttle too far.

If I accelerate gently it seems ok but anything more and it coughs and spits back through the carbs

Over 3000 revs and especially over 4000 it absolutely flies

Any help greatly appreciated as I'm starting to get bored with spending dough on this donkey

 

[amocrace]

where would you like to start? idle jets too small (they also control progression). progression holes blocked.wrong emulsion tubes. pump jets too small. pump stroke too short.air leaks carbs to manifold/ manifold to head.thats without thinking about electrics. needs setting up properly on rollers or if it has been 'tuned' take it back and tell them to correct it

 

[zedhead260]

...or simply out of balance.

 

[SeanDezart]

needs setting up properly on rollers or if it has been 'tuned' take it back and tell them to correct it

Ditto !

 

[pmac]

where would you like to start? idle jets too small (they also control progression). progression holes blocked.wrong emulsion tubes. pump jets too small. pump stroke too short.air leaks carbs to manifold/ manifold to head.thats without thinking about electrics. needs setting up properly on rollers or if it has been 'tuned' take it back and tell them to correct it

Wot he said +1

 

[Wyn]

Was it running ok before with the carbs newly fitted?
If so then it sounds like blocked jets in one or more of the carbs
Carefully remove each jet and clean them out one by one.
Loads of detail on the net on how them carbs tick

 

[Rob Gaskin]

I can see the problems - too much Blue in the engine bay and you are insulting it by calling it a Donkey all the time

Has it ever run properly on these carbs?

If not are you expecting it to be right first time without tuning - that's a big ask?

Yep agree with the other posts. It sounds weak mid-range but check for air leaks before taking it to a rolling road. It's well worth spending a few quid on getting this sorted by someone who knows what they are doing - best go by recommendations if you can.

It would be wise to get some air filters on it too.

 

[vipergts]

Thanks guys.

Its never run completely right on these carbs but I give it to the "experts" and things don't really change.

Feels to me like its weak hence the spitting.

Its since had the pump repositioned and a PRV fitted along with proper fuel lines and clips etc.Oh and filters

There is a good Guy in Essex who is supposed to be mustard and with a rolling road so I'll take a trip

Help is very much appreciated.

 

[SeanDezart]

Its never run completely right on these carbs but I give it to the "experts" and things don't really change.

The guys that fitted them aren't qualified as far as I'm concerned.

Its since had the pump repositioned and a PRV fitted along with proper fuel lines and clips etc.Oh and filters

Experts not qualified ? Through which criteria where they chosen to tinker with your beloved ?

By curiosity - where/how was the fuel pump ?

 

[SKiddell]

I don't mean to be patronising but..
A carburetor is a very accurate and in most cases quiet complex fuel metering device which requires a number of criteria in order to work correctly some of which are

To be in excellent working order, to be jetted correctly, all linkages to be in A1 condition, to be correctly sized for the application (cam, exhaust, compression etc), fitted to the manifold correctly......thie list goes on.

With triples (one p) this effect is multiplied 3 times, the most common fault being that the linkages are not fit for purpose and are best left in the bin along with the wrapping for some new ones, 75% of the triple setups I have seen, have linkages that I wouldnt use in a mechano set never mind a performance car

Balancing triples alone requires a good understanding of how they work plus access to things like a carb snail (device to measure the air flow for balancing).

Find a reputable rolling road with someone who knows what they are doing (as opposed to someone who says they know what they are doing) and who can demostrate it by the work they have done.

 

[Rob Gaskin]

The problem with triples is that on a Z you are setting-up 6 carbs and 3 sets of linkages. This arrangement is ok for the racing/rally guy who has his car professionally tuned and kept in good order but for many Z owners this is not the case. When I had a 4 cylinder bike I had a set of 4 flow-guages to set the throttle position - that was bad enough.

I suspect most people fit these carbs for the looks, induction roar and the hope that a big step in performance will result. Yes they do look lovely (especially yours) and they do make a nice noise (too loud perhaps for track-days without filters) but very often the performance improvement is not there and in fact I reckon there are members in the club whose cars would run better on the well set-up standard carbs.

The other issue is fuel consumption, 'big' triples tend to be very thirsty from what I gather.

Anyway I hope you get them sorted and they give the driving experience you were hoping for. Lets hope it goes from being a donkey to a race-horse.

 

[Albrecht]

Its never run completely right on these carbs but I give it to the "experts" and things don't really change.

Feels to me like its weak hence the spitting.

The guys that fitted them aren't qualified as far as I'm concerned.

I don't think it's fair to blame it all on somebody else unless you give the full story. Did these people recommend, supply and fit the parts? What's the spec of the engine? What's the spec of the fuel supply system? Are there any other factors that could be involved?

I've seen cases where people buy parts secondhand, or mix and match from different sources, and then complain that something's wrong. They then take this dog's dinner to somebody who they think can wave a magic wand over it all and turn it into a Michelin starred meal. On the other hand, if you were starting from scratch - with brand new parts - you could easily find yourself facing all sorts of questions as to what to buy. Huge amount of variables involved.

Sometimes customers will expect to have their engines running perfectly even when they've got the wrong size aux venturis installed, they don't want to run to the expense of changing to more suitable emulsion tubes, and they don't have a clue what pogression drillings or pump rod stroke they have. They'll even baulk at the cost of buying six new main jets and six new air correctors. They think it's just a case of twiddling the right bits to make it all work.

So what's the FULL story on these carbs? What are they, and what are they fitted to ( what's the spec of the engine etc )? You might turn up at a proper rolling road dyno finding that you need to replace half of what you've already got. On the other hand it may be something very simple indeed...

 

[Rob Gaskin]

Vipergts, I find this Thread interesting because I know more people who have issues with carbs and I have considered at times to change to triples but stuck as yet with my very good (but old - 1966) SUs.

I notice the filters on another photo of yours.

 

[Ian Patmore]

Vipergts,
All valid points made above. Triples of any brand can be fantastic but they can be expensive to get running right (new emulsion tubes/venturis etc). As asked before engine spec, what parts are in the carbs at the moment?

The other issue is fuel consumption, 'big' triples tend to be very thirsty from what I gather.

Rob, they can be, but I was surprised how good mine were (48's) on a run up to Scotland and back. Though the gauge drops when you start giving it some on very quiet roads!

And properly tuned triples will help on the fuel economy as well

 

[chef]

not just rust in the petrol tank is it? i had this problem in 2 z's , i tried alsorts the first time and it was just that. just in case, you never know,
good luck

 

[SeanDezart]

Have to agree with Ian and Skidden !

Mine was regularly giving better fuel consumption than some original spec 240Zs although I'd prefer a pair of 2"SUs up to a certain power-point anyday - lovely kit !

Never had to touch mine in 5 years but all was new, all 'mated' to the entire engine, set up properly and rolling roaded.

 

[jonbills]

I found this book very helpful.
How To Build & Power Tune Weber DCOE & Dellorto DHLA | eBay
You need to be a rich man indeed to have triples and not learn how to maintain them.

 

[vipergts]

OK Guys

The engine was supplied by a well known Z guy local to me. Very nice people, known them for ages and I'm always pestering them.

They fitted the engine together with brand new 45's.

This is how it looked and I had a fair bit of justified criticism over the set up with a Facet pump right up front with no PRV and rubber hoses. (See pic)

Now I have the pump up back with decent lines and a PRV.

Engine is a 2.8 with a cam that benefits from hi revs. Dizzy suitably pre curved etc.

Now today I went over to track and road to see Steve. These guys really know their stuff.

The problem with the car is that the chokes are 36's and cannot create enough speed to satisfy the needs due to them being too large. I really need 32 or 33's IF available...34's may have to do.

This will create more air speed. The car also runs too rich above 4000 rpm sooting out their probe..

He spent a fair bit of time setting and balancing the carbs

Driving along at a constant it spits and farts but above the 4000 revs it absolutely flies.

 

[SKiddell]

Hmmm we still don't know the spec of the engine so for them to say the chokes are too big is a little premature (but possibly true) as there are other factors that can affect gas speed.

What is the cam (lift, duration, lift on overlap etc etc) who made it (kent, Nissan, Schnieder, joe blogs)
What is the compression ratio
What exhaust manifold are you using
What head, valves etc, what are the flow characturistics of the head)

What puzzles me is who put carbs on a car without setting it up on a rolling road properly where things like oversized chokes should be ironed out.

Why on earth 45's when a set of 40's would have given better throttle response...too many people think you can bolt on a set of big carbs and hey presto instant 300 hp.....each componant must be matched to the other and must compliment each other.

 

[vipergts]

Trouble is I bought the engine off the builder aZ specialist who built it a while ago so there is little to go on I'm affraid.

Manifold was supplied by DJ

It could be that the gasses are escaping to easily through that manifold

Fact is 40's should have been used...no idea why 45's were used but I'm not that technical and just went with the flow. The guys at the rolling road said this is a macho mistake that is a common place.