Acceleration delay

[knotty]

Hi I have a crossflow engine which if I try to accelerate fairly hard in second gear there appears to be a delay before the engine picks up. This doesnt happen in any other gear. The only way that I could describe it is as thought there isnt enough fuel getting through the carbs. After a few seconds the engine picks up.

There is a fuel pressure regulator fitted which is set at 2 psi which reading on previous history was a rec when the engine was dynoed.

I dont know if this is a correct setting or if anyone has any ideas as to how to cure the problem.

Gentle acceleration works fine and the problem is still there when the engine is hot.

Thanks

Knotty

[wacomuk]

carbs can do this when over throttled. also if your carbs are out of balance it wont help

what type of ignition system do you have?

carbs will never be as smooth as injection

[Hammy]

A bit more info would help- what size carbs, engine spec ( cam etc) , jetting if you know it.

Has it always done this or was it ok once ? changed anything ?

Initally I'd of thought carb tuning is out, but its worth a new set of plugs and condensor ( if you have one) becaue these are cheap and can give odd symptoms. Check the dizzy cap and leads carefully too. Then look at carbs

[Bob Green]

carbs will never be as smooth as injection

Another urban myth.

Carbs jetted correctly with a wideband meter to ensure the correct AFR are as smooth as injection.

It's not about fitting jets, more modifying the jets.

By the way Knotty, try 2.5 psi.

[stu999]

carbs will never be as smooth as injection

Another urban myth.

Carbs jetted correctly with a wideband meter to ensure the correct AFR are as smooth as injection.

As smooth, but not as efficient. Carbs are virtually impossible to get to accurately meter fuel for *all* conditions. Problem areas can be masked, but with injection it can be nigh on perfect

[Bob Green]

Stu999

I don't disagree with that but what I am saying is you don't have to spend megabucks for a fuel injection system when correctly set side drafts give the same "feel" and performance.

Most folk buy what they think are the correct jets from the local supplier.  Weber sell main jets in .05 increments.  My old car fitted with 45's needed something between 1.45 and 1.50 mains.

By soldering up the main jets and drilling to 1.47 made a night and day difference.

I quess what I am saying is don't fit stock parts, engineer your way around the problem.

[stu999]

Not disagreeing as such either Bob.

Just trying to clarify two sweeping statements (as I read them, anyway)

QUOTE

carbs will never be as smooth as injection

and

QUOTE

Carbs jetted correctly with a wideband meter to ensure the correct AFR are as smooth as injection

Both have an element of truth, and yet both are factually incorrect.

Example - There is no way on this earth that the engine in SWMBO's Astra would run as sweetly as it does with carbs thoughout the rev range - it just wouldnt happen. There is no way I could floor the throttle at little more than idle and expect it to pull away cleanly with carbs, in its present state of tune. Injection will allow it though. Yup, no doubt it would run fine on carbs once the engine revs were allowed to build before pulling such antics. And one could argue that driving like that isnt the norm anyway, so it isnt an issue. But it does highlight the weakness of carbs, in that they cannot cope with *all* scenario's, and that injection, especially on some motors, can make a marked difference to flexibility and drivability. The more highly strung the engine, the bigger the difference it is likely to make

And you will get there a lot quicker with injection too

[Hammy]

Meanwhile..... Mr Knotty hows it going ? you haven't reposted  a response.

Just to add petrol to the fire - IMO Fuel injection should give a better result in theory (after all you can't buy a car with carbs on now), the problem is that most of the systems on our cars don't measure air flow, some don't even measure manifold pressure. so the signals used are not ideal and the resulting tightness of control could be better,

Carbs are basically pressure driven devices, this is their drawback,  the flow verses pressure square law means there is virtually no pressure to drive them a low speeds if the restriction at high flow is not to be too great.  They therefore  have "offest twiddles" at low speed called idle jets and all sorts of  bypass systems to generate a low speed pressure signal ( like a second mini carburettor) .(hence hot wire flow sensors in proper fuel injection systems).  As Bob sez carbs should be able to be made to work without coughs/bangs and dead spots ( not that mine do.... but i hpoe) But its easier to twiddle fuel injection from a laptop where you have a map to play with rather than a couple of intersecting curves, which is  is effectively all you have with a carb; Setup with a handful of jets, springs, hollow tubes with more holes in and a box of drills and a need for some  real skill*

Lets also not forget the major role ignition timing has to- MY MJ installation will hopefully tackle some of the percived carb problems  I have caused by lack of part throttle advance. New cars don't have distributers either...

Agreeing with  bothsides I guess: when your x/flow has a flat spot no need to through the carbs out ,it is fixable, might not even be the carbs

* Bob...Bob....fancy a coffe sometime....bring your soldering iron..

[knotty]

Hi Sorry been away for a couple of days didnt realise I would cause an argument.

Anyway I bought the car last october and its been pretty much the same since day one.

i'm no mechanic but the engine is a 711M block with kent 244 cam the carbs are Delorto 40's but i cant tell you anything about the jetting.

I have tried the FPR at 2 2.5 and 3 psi the same thing happens.

As far as the ignition it looks like standard coil distrib etc all of which look ok but any advice on changing over to electronic would be welcome.

I have a mate close who can check the carb balancing which I might get round to at the weekend if it stops raining.

Thanks

Knotty

[Hammy]

Have a look around for air leaks too on the manifold/engine manifold/carb  connection.

[stu999]

Hi Sorry been away for a couple of days didnt realise I would cause an argument.

Anyway I bought the car last october and its been pretty much the same since day one.

i'm no mechanic but the engine is a 711M block with kent 244 cam the carbs are Delorto 40's but i cant tell you anything about the jetting.

I have tried the FPR at 2 2.5 and 3 psi the same thing happens.

As far as the ignition it looks like standard coil distrib etc all of which look ok but any advice on changing over to electronic would be welcome.

I have a mate close who can check the carb balancing which I might get round to at the weekend if it stops raining.

Thanks

Knotty

Not arguing - discussing...

Back to the problem in hand. The bit that fascinates me is that your problem does not happen in any other gear

Absolutley no symptoms in any other gear?

[wacomuk]

you could always check your carb hamsters.

Carbs have very small hamsters in them. (one hamster per choke) sometimes they can fall off there little wheels, this will cause problems!

best thing to do is push the hamster back on the wheel with a small wooden implement (e.g. a pencil) dont push to hard as they dont like it!! put a little wd40 on the hamster wheel to make sure everything moves freely and you should be good to go

[knotty]

Hi Carbs have been checked over the weekend and are now balanced. Seems to be a lot better and smoother though not perfect. But then going by what you guys say it wont with carbs.

I had a look in the carbs for the hamster wheel mine seems to have fallen off somewhere could this now be stuck in one of the cylinders. Is it small enough to get past the valves and if so is this the rattle thats now developed in the exhaust.

Also had some advice from another mate whos medical, he thinks the main problem could be a steering thrombosis.

[Hammy]

I can tell you mine have 32mm Voles if thats any help