"Flat Spot" in Aisan Carburetor

[Tham]

Thanks, Todd, Hurricane and Love KE.

The problem problem seems to be more pronounced
on acceleration from start on a colder engine, it doesn't
appear to bad after the engine has warmed up. It is
particularly bad when the airconditioning compressor cuts
in. I'm using the lightest possible compressor already,
the Sankyo 505, normally meant for 600 - 1,000 cc engines.

There also seems to be a kind of constant "tugging"
or "pulling" at slower speeds in second gear or so. I'm
wondering if maybe it is the primary jet rather than the
accelerator pump that is giving problems.

when you were playing with it. when you turned the
throttle just a little bit, did u notice the lever arm move
and pump in a shot of fuel then the main stream comes
and continues as u open the throttle more

[quote=Toddw]
It should start squirting as soon as you move the throttle.
Check the linkages as some of them thad some small
amount of adjustment.

The lever pump does move and squirts in a single shot
of fuel, but if the throttle linkage is turned too little (like
maybe 3 mm), there doesn't seem to be any squirt. There
doesn't seem to be any bends to the linkages for the pump.

try playing with the other mixture screws and see
wat happens

Er.....there seems to be only one mixture screw at the
base on the Aisan carb ?

what ya can do it just pull the carby apart (not that hard)
just make a note of were every thing came from then
clean all the jets out and make shore that there not block
and that

Looks like I'll have to take it to the mechanic to do
that. I've been a bit hesitant to do this so far, because
I've been told that once the carb is taken apart, there
tends to be problems later on, such as fuel and vacuum
leakages, tuning difficulties, etc. No ordinary car user in
Malaysia knows how to take apart a precision, complex
and sensitive device like a carburettor,assemble it back
and get it in good running order again (including even
some mechanics here). Wished I had the expertise and
guts like you younger guys over there.

This carb had been lying idle for a year in my house.
My usual mechanic told me that once this happens,
there tends to be oxidation in the internals of the
aluminium housing which might well cause blockages
in the circuit. I've poured two bottles of carb cleaner
into the tank, but doesn't seem to do much.

Wished Nikki had direct replacement carburettors
for the 4K. Even the Nikki's mixture screw is easier
to access and adjust, being angulated at 45 degrees
rather than flat down like the Aisan.

[oldcorollas]

This carb had been lying idle for a year in my house.
My usual mechanic told me that once this happens,
there tends to be oxidation in the internals of the
aluminium housing which might well cause blockages
in the circuit. I've poured two bottles of carb cleaner
into the tank, but doesn't seem to do much.

Wished Nikki had direct replacement carburettors
for the 4K. Even the Nikki's mixture screw is easier
to access and adjust, being angulated at 45 degrees
rather than flat down like the Aisan.

yup, and also if you have crap fuel, the additives can form hard deposits and block the passages...

carb cleaner will do little for oxidation and dirt.

get an adaptor plate. the should be common.
or just make one.
then use webber or nikki...

or just learn to pull apart the carby.. there is really nothing to it.. just need to look at the parts diagram and not get things mixed up.

[love ke70]

3mm before it squirts, ill have to check mine but i think that couidl well be the issue
the 4k doesnt have the torque for aircon just so gutless lol

[mike1980ra40]

Sometimes a flat spot can be caused by a dizzy's dwell angle being a bit out.
I had a flat spot and theres were i found mine.

[Tham]

Sometimes a flat spot can be caused by a dizzy's dwell angle being a bit out.
I had a flat spot and theres were i found mine.

Thanks, will try to check that out too.

I'm using an electronic distributor, taken from a 5K.

Wished I had my old dwell-tach meter with me.

Must say you take superb aviation photos too, particularly
those of the F-111C.

[Tham]

This 4K Aisan carb had a built-in idle stop solenoid,
which I've taken out, because if it malfunctions with
the probe in the extended position, the engine won't start.

The older carb (3K) had a bolt covering the hole
meant for this solenoid, so I took it from there and
used it to cover the hole left vacant in the above carb
after taking out the solenoid.

I wonder if any possible vacuum leaks around that
bolt might cause this flat spot problem.

[mike1980ra40]

Thanks, will try to check that out too.
.....
Must say you take superb aviation photos too, particularly
those of the F-111C.

thanks for that, nice to know people out there like them makes me wanna go take
some more

cheers

[love ke70]

wtf mike lol

tham are you talking about the fuel solenoid?

id say it may be related to the dizzy, seeings as it hasnt been regraphed or anything...

[Tham]

wtf mike lol

tham are you talking about the fuel solenoid?

Yes, Love KE, I meant the anti-dieselling or fuel cut-off
solenoid, similar to this :

http://www.nardek.com.au/aisanidlesolenoid.htm

Id say it may be related to the dizzy, seeings as
it hasnt been regraphed or anything...

Yes, it might well be related to the distributor . But this
flat spot problem wasn't there with the older 3K carb then.
Is the dwell/advance curve of the electronic dizzy
supposed to match the carb ?

Is the dwell of an electronic distributor adjustable ?

Regraph the dizzy ..... you mean the advance curve ?
How does one adjust it ?

Thanks.

[love ke70]

one doesnt, dizzy shops do...
if it was running properly before then maybe it isnt an issue with that....

http://www.rollaclub.com/faq/index.p...Series/4kstall
something interesting about the fuel solenoid..

as its likely a carb related thing, consider...making that squirt of fuel come in as soon as the throttle moves a tiny way, (by bending the rod) as ive had an inkling from the start thats what it is. if nothing else you will please my curiosity

[Tham]

http://www.rollaclub.com/faq/index.p...Series/4kstall
something interesting about the fuel solenoid.

Should one wrap some of those white insulation
tape, the type normally used for plumbing pipes,
around the threaded base of the blanking bolt,
to seal off any possible vacuum leaks ?

as its likely a carb related thing, consider...making that squirt of fuel come in as soon as the throttle moves a tiny way, (by bending the rod) as ive had an inkling from the start thats what it is. if nothing else you will please my curiosity

Wow, bending the rod ..... will have to be done
real carefully. You mean kind of straighten out
the bend a little ? Might well make it worse if
I overdo it.

How about cutting the spring on the rod like this
guy did here ? Wonder how much it should be cut.

http://www.rollaclub.com/board/index.php?showtopic=5582


Furthermore, thhis electronic dizzy which I've installed,
also appears to have some major problems with the
centrifugal and two-stage vacuum advance. It's actually
salvaged from a 5K, and doesn't seem to be really
compatible with the 4K.

To experiment if the vacuum advance was the cause of
the flat spot problem, since you mentioned it hadn't been
regraphed, I tried disconnecting it. I expected the car to
run more sluggishly, but at least more smoothly.

The car ran like the Incredible Hulk ! It was not only
more sluggish, it was tugging and surging heavily like a
camel as it tried to pick up speed, making me nauseated.
Seems to be problems with the circuit or the centrifugal
advance. Wonder if it's a faulty unit.

I've connected the two-stage vacuum advance with a
T-joint to the carb's single inlet, but the advance doesn't
seem to be sufficient - worse than the single-stage vacuum
pump on the old points dizzy. To check it out, I tried
advancing the timing as far as I could, probably close
to 30 degrees at idle. I expected the engine to knock
as it accelerated, but I could hear none.

[oldcorollas]

you seem to misunderstand what you are trying to do?

30 degrees at idle??

the solenoid MUST have metla on metal contact with the carby, or it will nto work, since the current flows through to the engine..

perhaps by using a bolt to fill the "hole" you have left open the internal passages and it now doesn't work how it should?

you should check the operation of the vaccum pots on the dizzy, and then set as per normal.. check where the vacuum source is on the carby too.... manifold or ported vacuum?

start by ACTUALLY checking the advance and vacuum mechanisms of the dizzy... then clean the carby properly.. if you don't know how to, then it's time to learn
if the carbvy has been sitting around for too long, it might be stuffed.
you should at least open it up and check the main jets are not blocked, and the power valve works correctly...
etc

[Toycrash]

Sorry, but didnt bother to read all this thru...

I went to have a look down the carb's throat
just now. It did squirt fuel when the throttle
was opened, but the stream seems extremely
small and thin.

If this is still the situation, you have to clean the accelerator pump jet! When it works, the squirt is wery noticeable.

As for the idle solenoid, you sure can use that bolt or even shotened valve will do. Nothing gets mesed up or gets any leaks by there.

Intake leaks are main reason for K engines not to work properly.

pvc valve should be tested and make sure your carbie hasnt got a worn axle, it tends to leak there.

[derekjay]

I have exactly this problem on my Celica with a carburetted 21R-C. When cold it has a really unreliable idle. Essentially I need to keep my foot on the gas and make sure the revs dont go below 500rpm or it will stall.
Now the cause of this problem I have been told is leaky seals and diaphragms in the old carburettor which need to be replaced. For my particular carbie I have been quoted $50 for a reconditioning kit, or about $200 for a mechanic to do it for me.

[Toycrash]

derekjay Is your carbie with electrical choke? If so they tend to "loosen" a bit by age, so you might be fine with little adjustment there.