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Return to: LT500R - Engine
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#Post#: 53180--------------------------------------------------
Problems Starting and idle Quadzilla
By: My90quadzilla Date: May 11, 2018, 4:36 pm
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My90Quadzilla
online
Suzuki ATVer
Join: about 24 hours ago
Posts: 1
Oregon
about 23 hours ago � #1
Only starts with throttle wide open.
I have a 1987 Quadzilla LT500. It has a Keihin 39mm carb (stock
Pilot Jet) with V-Force 3 Reeds, upgraded to 7-bolt late model
head, ported and polished, bored over one time with Wiseco
Piston, FMF TurbineCore 1 exhaust, K&N filter. Running 40:1 fuel
mix (Castor 927) with 110 racing fuel. I usually go through the
regular routine on starting it (new Spark plug) put boots on,
Turn on Gas/Choke Off, Kick over slowly 5 times, Throttle
closed, Bring Piston up to TDC and go just pass TDC, return Kick
starter to the top and kick hard all the way through with 1/4
throttle, Choke on if cold starting. I�ve found that if I hold
the throttle wide open it starts better but I Cain�t keep it to
idle by adjusting the idle/pilot screw! Since then I�ve
purchased a new Mikuni 38 flat slide carb. I haven�t tried
starting it yet with the new carb. I have read that I need to go
up 1-2 pilot jet settings from the stock one which should help
on the starting. Any other suggestions.... thank you
#Post#: 53182--------------------------------------------------
Re: Problems Starting and idle Quadzilla
By: supernutt Date: May 13, 2018, 7:21 am
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My zillas are the best starting quads I have. But I use the
stock carb bored out on them. My Hondas with the Keihin carbs
don't start nearly as easily. When its below 40 in the winter
the Keihin carbs on the big bores don't start without a space
heater aimed at them. The zillas fire right up.
#Post#: 53183--------------------------------------------------
Re: Problems Starting and idle Quadzilla
By: Rainman56 Date: May 15, 2018, 2:22 am
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What is the current jetting in the carb???Most new carbs come
with generic jetting that insn't ideal.
#Post#: 53824--------------------------------------------------
Re: Problems Starting and idle Quadzilla
By: Beerside Date: April 10, 2019, 12:36 am
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You say you use 110 race gas and castor oil? See above topic
about that. That might be your problem.
#Post#: 53825--------------------------------------------------
Re: Problems Starting and idle Quadzilla
By: Motorgeek Date: April 10, 2019, 1:26 pm
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[quote author=My90quadzilla link=topic=4957.msg53180#msg53180
date=1526074575]
My90Quadzilla
online
Suzuki ATVer
Join: about 24 hours ago
Posts: 1
Oregon
about 23 hours ago � #1
Only starts with throttle wide open.
I have a 1987 Quadzilla LT500. It has a Keihin 39mm carb (stock
Pilot Jet) with V-Force 3 Reeds, upgraded to 7-bolt late model
head, ported and polished, bored over one time with Wiseco
Piston, FMF TurbineCore 1 exhaust, K&N filter. Running 40:1 fuel
mix (Castor 927) with 110 racing fuel. I usually go through the
regular routine on starting it (new Spark plug) put boots on,
Turn on Gas/Choke Off, Kick over slowly 5 times, Throttle
closed, Bring Piston up to TDC and go just pass TDC, return Kick
starter to the top and kick hard all the way through with 1/4
throttle, Choke on if cold starting. I�ve found that if I hold
the throttle wide open it starts better but I Cain�t keep it to
idle by adjusting the idle/pilot screw! Since then I�ve
purchased a new Mikuni 38 flat slide carb. I haven�t tried
starting it yet with the new carb. I have read that I need to go
up 1-2 pilot jet settings from the stock one which should help
on the starting. Any other suggestions.... thank you
[/quote]
I see multiple problems:
Something or many things are not right. You should not have to
install a new spark plug for every cold start. Your carburetor
is a mile off or your riding style is not keeping the spark plug
clean.
If the engine starts more quickly holding the throttle wide
open.....this is usually a sign that the engine is flooded.
The choke (enriching circuit) functions best when the throttle
is completely closed. As the throttle is opened the effect of
the choke diminishes. By the time the throttle is 1/4 open the
choke is not functioning at kick starting RPMs. A common tuning
error on the Keihin carbs is having too large of a pilot jet.
When the pilot jet is too large, the idle-slide-stop screw,
usually requires the slide to to be open more than 2 mm, making
the choke barely functional at closed throttle and choke
activated.
Some brands of race fuel have poor vaporization characteristics
at cold temperatures making starting at cold temperatures
difficult.
Castor oil also has problems staying dissolved in some fuels at
cold temperatures.
What temperature are you having starting problems?
What brand of fuel are you using?
What jets, needle and slide do you have in the carb?
What heat range spark plug are you using?
When the slide is in the idle position, what is the distance
between the bottom of the slide and the floor of the airflow
passageway under the slide?
95% of the starting problems is one of or a combination of the
following: type of carburetor, carb jetting, and throttle
positioning and knowing when to or when not to activate the
choke.
#Post#: 54699--------------------------------------------------
Re: Problems Starting and idle Quadzilla
By: Gaz Date: August 17, 2023, 9:58 am
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Jerry, is 2mm the recommended idle slide height on the Mikuni?.
At 38mm venturi, assuming 6DK3 @ 3rd clip, 3mm slide height and
lower puts the needle's straight portion (2.6mm widest part)
into the needle jet minimizing the needle jet's influence. Is
that the correct part of the needle that should be in the needle
jet at idle or should the start of the first taper (2.5mm) be in
the needle jet at idle? Would it be correct to say anything
under 3mm (minimized needle jet influence) that maintains a
decent idle is a suitable slide height setting? Cheers.
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