Zetec on zx9r carbs

[helinelly]

Hi guys I’ve running zx9r carbs on zetec but it’s running hot i have the right jets do I need. Block anything off ect

[Graham]

how do you know its running hot and not just an iffy gauge reading?

what do the plugs look like?

the main jets usually want drilling out to something like 1.6 mm.

retarded ignition timing can also make an engine run hot.

[katana]

FYI the Zetec as std. was designed as a 'hot run / lean burn engine' so what would be hot for a pinto could be normal for a zetec.

Also, have the carbs been set up by someone who KNOWS how to do it - many sets supplied with generic tune ie. drilled main, blocked air bleeds and f**k all else!
Bike carbs are quite sophisticated to get REALLY right and not many people are willing or able to spend the time to do it!

Its a pet peeve of mine - using bike CV carbs are no different than to using 4No 1.5" HS SU carbs - they function exactly the same but no one chooses
the latter as they're regarded as ancient and not 'sporty' enough! And they'd take a similar amount of time / tuning to optimise . . . . . . Rant over

[Graham]

ive just run up an engine fitted with 38mm bike cv carbs, yeah they worked ok,

A back to back test against my 45's, it was a real eye opener, alas i cant say any more for a bit, but lets just say i wont be rushing out to buy a set myself unless they are still attached to a bike!

[onecamohv]

ive just run up an engine fitted with 38mm bike cv carbs, yeah they worked ok,

A back to back test against my 45's, it was a real eye opener, alas i cant say any more for a bit, but lets just say i wont be rushing out to buy a set myself unless they are still attached to a bike!

This will be interesting.... !

[katana]

ive just run up an engine fitted with 38mm bike cv carbs, yeah they worked ok,

A back to back test against my 45's, it was a real eye opener, alas i cant say any more for a bit, but lets just say i wont be rushing out to buy a set myself unless they are still attached to a bike!

I can imagine what the result will be . . . . . . . but its comparing apples to eggs. Race derived, smoothe bore carbs against road going, general purpose CV carbs. I wonder if the Weber's would be tractable from 1,500 rpm through to 11,000+ rpm?
I'll still be interested in the result and look forward to seeing a rack of 1.5" SU's on the DD purely for reference LOL!

[Graham]

I can imagine what the result will be . . . . . . . but its comparing apples to eggs. Race derived, smoothe bore carbs against road going, general purpose CV carbs.

absolutely, i totally agree, we are not comparing like to like, but if you want to go fast just bunging a set of bike carbs on isnt all win win, like some suggest. Neither is it such a cheap option, ok a set of used bike carbs is a lot cheaper than new webers, but thats also comparing apples to eggs.

The set i just tested is the second set of carbs, the first set which came as a package with manifold from a well know supplier, supposedly plug and play cost quite a bit, but literally did not work! the engine started and ran, but under load simply would not work, 7bhp @3000 was best i could get from them! rich as hell and the slides would not lift under load. i basically wasted a day trying to get them to work. Out of desperation incase it was the engine or dyno at fault i put the webers back on, bang 175bhp as expected. i still dont know why, but my guess is in there previous life on a bike something had been done to them which meant they didnt not work, second hand carbs come with risks whether from a car or bike.

on the subject of Su's one quick look at the damper piston probably is all you need to know as to why they dont run them one per cylinder, that piston weighs a ton, if you had a plastic piston weighing bugger all like a bike carb....

[fingersnfumbs]

So..
Could twin SU's i.e 1 carb sharing two cylinders. Surely thast would be a great set-up.?
Strange you rarely see SU's on Fords given how simple and tunable they are.

[Graham]

So..
Could twin SU's i.e 1 carb sharing two cylinders. Surely thast would e a great set-up.?
Strange you rarely see SU's on Fords given how simple and tunable they are.

1 SU for two cylinders was common, mgb, Rover P6 2000tc, triumph spitfire, E type jag, mini cooper/1275 gt and loads of Austins.

twin and triple su carb conversions for ford Zephyr/Zodiac's from the 1950's used to be common, and not that rare on 1500 pre x/flow. teh thing is with newer Fords is su's dont hold much advantage if any over a twinchoke weber, and anyone wanting real performance is going to fit twin webers not a pair of su's

[onecamohv]

1 SU for two cylinders was common, mgb, Rover P6 2000tc, triumph spitfire, E type jag, mini cooper/1275 gt and loads of Austins.

twin and triple su carb conversions for ford Zephyr/Zodiac's from the 1950's used to be common, and not that rare on 1500 pre x/flow. teh thing is with newer Fords is su's dont hold much advantage if any over a twinchoke weber, and anyone wanting real performance is going to fit twin webers not a pair of su's

i often thought it would be a pretty good cost effective alternative to split 48's on road rally cars to run twin SU's? Obviously, its not going to be as good, but i wonder why no one has tried twin SU's on a pinto for UK road rally regs... ? do you reckon it would work?

[katana]

Unfortunately SU's suffer from the usual CV carb malady when racing - throttle response. This can be tuned but as Graham said the slides do weigh a bit, but for a road car this would be less of a problem.

But if an alternative to split 48's was needed - I'd steer you straight to a pair of Mikuni HSR 42's / 45's or 48's. These are the dogs danglies and single ones often get fitted to turbo'd bikes and flow well enough
to exceed 400 rwhp - not bad from one throat LOL!
http://www.hammerperf.com/images/mikunihsr424548.jpg

[lowscorts]

absolutely, i totally agree, we are not comparing like to like, but if you want to go fast just bunging a set of bike carbs on isnt all win win, like some suggest. Neither is it such a cheap option, ok a set of used bike carbs is a lot cheaper than new webers, but thats also comparing apples to eggs.

The set i just tested is the second set of carbs, the first set which came as a package with manifold from a well know supplier, supposedly plug and play cost quite a bit, but literally did not work! the engine started and ran, but under load simply would not work, 7bhp @3000 was best i could get from them! rich as hell and the slides would not lift under load. i basically wasted a day trying to get them to work. Out of desperation incase it was the engine or dyno at fault i put the webers back on, bang 175bhp as expected. i still dont know why, but my guess is in there previous life on a bike something had been done to them which meant they didnt not work, second hand carbs come with risks whether from a car or bike.

on the subject of Su's one quick look at the damper piston probably is all you need to know as to why they dont run them one per cylinder, that piston weighs a ton, if you had a plastic piston weighing bugger all like a bike carb....

I can Prob guess who's kit, i see a lot of bike conversions and some of the 'kits' are horrendous, with no understanding of how the carbs are supposed to work and the drilling jets just costs the customer more labour in the long run, having to guess a base size as a starting point (especially as no two installations are the same)

[Graham]

i often thought it would be a pretty good cost effective alternative to split 48's on road rally cars to run twin SU's? Obviously, its not going to be as good, but i wonder why no one has tried twin SU's on a pinto for UK road rally regs... ? do you reckon it would work?

from what ive seen from the bike carbs you will loose a big chunk of midrange compared to sidedrafts

[onecamohv]

from what ive seen from the bike carbs you will loose a big chunk of midrange compared to sidedrafts

interesting for sure - especially when its a common comment in the MGB world that a DCOE conversion on a B-series has the same effect.. My brothers MGB still runs twin Su's and its a nice spec engine. the general consensus from the MG community i believe is that a DCOE conversion is good for circuit racing but terrible for midrange. never driven one with a DCOE myself but the engine in is current form goes very well

[onecamohv]

Theres alot more to bike carbs than magazine articles and other sources would lead you to believe. I put alot of work into developing bike carbs for a good few different engines, and got very good results. a CV carb working on vacuum is never ever going to have the throttle response of a DCOE with pump jets, but for a fast road application they are super smooth and reliable when setup right.
my bog standard C20XE made 164bhp from memory on bike carbs, and the RR operator who is a weber man, was impressed at the time.
They have their place i think depending on the application...a great option for a regularly driven fast road car/weekend car that needs to start and run smoothly on a cold sunday morning

[Graham]

interesting for sure - especially when its a common comment in the MGB world that a DCOE conversion on a B-series has the same effect.. My brothers MGB still runs twin Su's and its a nice spec engine. the general consensus from the MG community i believe is that a DCOE conversion is good for circuit racing but terrible for midrange. never driven one with a DCOE myself but the engine in is current form goes very well

i guess you also have to take into account what midrange actually is, midrange on an Rl31 equipped pinto is a lot higher up the rev range than on an asthmatic B series

[Graham]

Theres alot more to bike carbs than magazine articles and other sources would lead you to believe. I put alot of work into developing bike carbs for a good few different engines, and got very good results. a CV carb working on vacuum is never ever going to have the throttle response of a DCOE with pump jets, but for a fast road application they are super smooth and reliable when setup right.
my bog standard C20XE made 164bhp from memory on bike carbs, and the RR operator who is a weber man, was impressed at the time.
They have their place i think depending on the application...a great option for a regularly driven fast road car/weekend car that needs to start and run smoothly on a cold sunday morning

absolutely, in terms of peak power the bike carbs got close to the webers. 164 from carbs on a standard xe isnt bad but from what i understand some way short of a big pair of webers,

[onecamohv]

absolutely, in terms of peak power the bike carbs got close to the webers. 164 from carbs on a standard xe isnt bad but from what i understand some way short of a big pair of webers,

just checked, 167.9bhp. 38mm CBR900RR Keihn carbs. still probably short of a pair of 45's, bear in mind totally standard unrebuilt engine, no porting or anything.
like i said i think they have their place, for what i needed for autotests which was smooth power delivery from a standing start on mashing the throttle wide open, it never hesitated, stumbled or anything that would cost time. so, hard to say what costs more time, rolling road numbers or reliable delivery of smooth power.... food for thought if nothing else