Hi Robert,
At 22:22 12-06-97 +0200, robert ylitalo wrote:
>Eric Kieboom wrote:
>>
>> At 16:42 12-06-97 +0200, robert ylitalo <robert.ylitalo@kiruna.se> wrote:
>> >i have installed kn air filters in my car
>> >The cars runs perfect on idle and up to 3000rpm.
>> >But if i increase the rpm th rpm starts jumping between2500 and upto
>> >3500. Why is this?
>>
>> When you say 'jumping', do you mean the engine starts missing? Does it feel
>> like it's running out of breath?
>>
>> In that case, your problem may be similar to what I experienced on
>> installing K&N's and a free-flow exhaust: lean running. My car didn't want
>> to rev over 4000 rpm if it was under any sort of load.
>> The 'problem' is, K&N filters admit a lot more air to the carbs compared to
>> the orginal system, upsetting the mixture. Now may be the time to start
>> experimenting with richer needles. You may also need stiffer damper
springs...
>>
>Your description is exactlly correct
>is it not possible to set the carbs?? Must i buy new needles and damper
>springs. Someone told me that i could use some thicker oil in the carbs
>What is your experience?
My experience is that in this case, no amount of adjustment will get you a
proper mixture, unless you go for richer needles. Thicker oil may help
improve acceleration, but the engine will still run lean. This can be
disastrous in the long run if not properly taken care of (think of burned
pistons, valves and such).
When I had my badly worn carbs overhauled, rebushed, hardened, polished,
etc. by a specialised firm, I told them what had been done to free the
intake and exhaust systems of restrictions, so they could figure out what I
needed in the way of needles and damper springs. All this didn't come cheap,
but worked very well -> peace of mind.
>From the Moss/Triumphtune catalogue: "When [K&N] filters are fitted it is
necessary to change damper springs to the 8 oz. type (yellow). These are
stronger and improve the low speed/idle mixture." Be careful you specify HS2
when ordering new springs.
There's a rudimentary needle chart in the same catalogue. It says there are
'AAN' needles in standard HS2's (presuming you have the original HS2's in
your '65 Mk.II). I think it would be safe to go up to 'AAU' type needles.
These are recommended for 'pluskit A', part of which are K&N filters.
If you really want to find out what makes SU's tick, you could try and find
a copy of 'SU carburettors' which is in the workshop manual series by
Haynes. It lists *hundreds* of different needles for all types of SU's. One
of my favourite bedside books.... ;-)
Although you mailed me directly, I would be interested to hear more from
others on the list, so I've cc'd to the list. Hope you don't mind.
Eric 'treat yer carbs right' Kieboom
The Netherlands
('77 Spit 1500)
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