beqa16v
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| posted on 8/4/12 at 05:48 PM |
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Bike carbs issues on a Lada engine
First of all hello everybody.
I am from Georgia, Tbilisi, rebuilding the Estona 21 single seater which was originally designed in 80s.
They came with Lada 1600cc heavily modified engines. The engine which I have built has:
Lada 1600cc 8v
bike carbs from ZX750. 160 main jets
Estonia 21 exhaust 4-1
intake and exhaust channes ported
T-shaped lightened valves
3 angle valve seats
2mm shaved from the head (compression 10.5)
BMW M20 valve springs
weight leveled pistons
lightened and weight leveled connecting rods
lightweight flywheel
crankshaft balanced together with the flywheel
The video of the first warmup is here: http://www.youtube.com/watch?v=GL_UAJEoD68
Dont judge from this video as things have changed since then
Carbs are 38mm Keihins from Kawasaki ZX750R, not the latest model, i think they are pre 2003.
I am using a standard Lada mechanical fuel pump with a return valve which maintains constant 1.5psi pressure. I am monitoring the pressure live having
the gauge hooked up.
Took carbs to a friend of mine who works on bikes. He checked the bowls, diaphragms etc and confirmed that carbs are in a good shape. He also set a
float height. All jets are clean, i have carefully drilled the mains out with a 1.6mm drill. They should be around 162-165 now. Idle screws are 3.5
turns out.
How it worked in the begining, all observations are made on neutral:
The engine starts fine but needs a choke while cold
when worm, it does not idle properly and returns slowly to idle sometimes.
struggles at around 4000 and refuses to go further on neutral. Bogs by staying at that rpm
sometimes struggles to respond to throttle input.
used to backfire from carbs
After working on elimination of potential air leaks I have removed the spark plugs today and they were very black with some black gunk on them.
Cleaned them and put back on. On cold it was perfect. Under choke the engine was working at around 1200rpm very well without backfires from carbs (I
did not rev it though). But after it warmed up it started to struggle. Tweaked the dizzy a little bit and got a good throttle response from idle but
could not go past 4000 again. After around 10-15 minutes of working i turned the engine off, removed the plugs and they were already black. Cant
understand whats causing this. The return seems to be doing its job. I have tested it by pumping the fuel by a lever on the pump. I hear the fuel
flowing back to the tank as the gauge reaches 0.1 bar.
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will121
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| posted on 8/4/12 at 06:05 PM |
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posilbly running to rich from plugs, need some sort of lamba mixture sencing to check, may be main jets to large as aroung 4000 rpm may be where the
main jets start to effect mixture, as for tick over mixture try adjusting air screws 1/2 turn at a time to see what gives best idle running
[Edited on 8/4/12 by will121]
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r1_pete
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| posted on 8/4/12 at 06:20 PM |
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Also check the carb tops for leakage, I used to run the same carbs, to ensure a seal I filled the groove in the carb lip with rubber lube before
seating the diaphragm.
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beqa16v
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| posted on 8/4/12 at 06:30 PM |
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quote:
Originally posted by r1_pete
Also check the carb tops for leakage, I used to run the same carbs, to ensure a seal I filled the groove in the carb lip with rubber lube before
seating the diaphragm.
They dont have adjustable needles do they? What kind of washers should i put under them when tuning? How many mm?
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snapper
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| posted on 8/4/12 at 06:36 PM |
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Mikunies have white washers on the ends of the needle you can move them up to reduce mixture down to increase.
The needles have a profile and different profiles can increase ordecrease mixture at different revs.
There are also some good set ups available if you google Mikunie and Bike carbs
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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beqa16v
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| posted on 8/4/12 at 06:39 PM |
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quote:
Originally posted by snapper
Mikunies have white washers on the ends of the needle you can move them up to reduce mixture down to increase.
The needles have a profile and different profiles can increase ordecrease mixture at different revs.
There are also some good set ups available if you google Mikunie and Bike carbs
Mine are Keihins. I have removed one needle and it does not seem to have shims for adjusting washers
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jacko
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| posted on 8/4/12 at 07:18 PM |
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It sounds like your carbs are like my zx9r E carbs where you put small thin washers under the needle top .
you say it will not rev past 4000rpm is it like its on choke ?
is may be that your jets are two big for a 1.6 engine especially as the plugs are getting black
the other thing is you really need a bike fuel pump there the best for bike carbs
Jacko
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beqa16v
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| posted on 8/4/12 at 07:57 PM |
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quote:
Originally posted by jacko
It sounds like your carbs are like my zx9r E carbs where you put small thin washers under the needle top .
you say it will not rev past 4000rpm is it like its on choke ?
is may be that your jets are two big for a 1.6 engine especially as the plugs are getting black
the other thing is you really need a bike fuel pump there the best for bike carbs
Jacko
How thick the washer should be to match one step on adjustable needles?
No I was trying to rev a warm engine without a choke
I was trying to avoid the bike pump as the chassis can not accommodate an alternator (this is a formula car) but i guess there is no other way.
I tired another return valve which kept 3psi at one point and it was even worse. Went back to what I have now (1.5psi).
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austin man
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| posted on 8/4/12 at 08:06 PM |
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is the choke releasing correctly? and are you sure the butterflies are opening fully? I have ZX9 carbs fitted and the revs do seem slow to drop off
Life is like a bowl of fruit, funny how all the weird looking ones are left alone
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beqa16v
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| posted on 8/4/12 at 08:08 PM |
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quote:
Originally posted by austin man
is the choke releasing correctly? and are you sure the butterflies are opening fully? I have ZX9 carbs fitted and the revs do seem slow to drop off
choke is fine but i think the throttle spring is not enough. Will add another one
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beqa16v
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| posted on 9/4/12 at 09:56 AM |
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quote:
Originally posted by jacko
It sounds like your carbs are like my zx9r E carbs where you put small thin washers under the needle top .
you say it will not rev past 4000rpm is it like its on choke ?
is may be that your jets are two big for a 1.6 engine especially as the plugs are getting black
the other thing is you really need a bike fuel pump there the best for bike carbs
Jacko
Oh and forgot to mention that it used to do the same at 2500-3000 the day before i removed plugs and cleaned them. Tweaking ignition was helping a bit
but not much. Does this mean that the issue is spark related?
And another thing is that the engine ran rougher on a 3psi return valve compared to 1.5psi which i have now. Is it possible that even now its too
much? Therefore can we assume that a bike pump can fix this issue?
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jacko
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| posted on 9/4/12 at 01:09 PM |
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quote:
Originally posted by beqa16v
quote:
Originally posted by jacko
It sounds like your carbs are like my zx9r E carbs where you put small thin washers under the needle top .
you say it will not rev past 4000rpm is it like its on choke ?
is may be that your jets are two big for a 1.6 engine especially as the plugs are getting black
the other thing is you really need a bike fuel pump there the best for bike carbs
Jacko
Oh and forgot to mention that it used to do the same at 2500-3000 the day before i removed plugs and cleaned them. Tweaking ignition was helping a bit
but not much. Does this mean that the issue is spark related?
And another thing is that the engine ran rougher on a 3psi return valve compared to 1.5psi which i have now. Is it possible that even now its too
much? Therefore can we assume that a bike pump can fix this issue?
What i was asking is when it bogs down at 4000rpm is it as if you have put the choke on ? I think you are running to rich = to big jets if so you will
not need washers under the needle heads
I know from reading on here for years that not using a bike fuel pump that it can cause all kinds of problems can you try one to see if it helps
solve the problem you are having
This is only my opinion and the best way it get it right is to have it set up on a rolling road
Mind you don't run the engine too weak and melt pistons etc
Jacko
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matt_gsxr
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| posted on 9/4/12 at 01:34 PM |
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This page is nice for explaining the complexities of how to tune these carbs.
http://www.factorypro.com/tech/carbtune,CV,high_rpm_engines.html
One important thing to recognise is that the low speed and the high speed are controlled by completely different parts of the carb. So you must
adjust them independently.
If I were to guess then I'd say that the mains jets are far too big (or needles much too high), further you need to open up the idle screws to
help at low RPM.
It might not be the fuel pump, but a bike fuel pump draws only 2A, so you can use one on a total loss electrical system with no real problems and you
then can be sure that it isn't that.
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beqa16v
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| posted on 9/4/12 at 01:53 PM |
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Honestly I dont know how the choke bogs the engine. Never had a car with a carb. injection, turbos, rotaries - yes, but not a single carbed
vehicle.
I agree with all the above points. Its already decided to run a bike pump. I will fit it to exclude that part of the puzzle.
I have an access to dyno but i want to make the car just run properly at low-mid rpms to break in the fresh rebuilt engine. After its done Ill proceed
to precise tuning on a dyno (rolling road).
[Edited on 9/4/12 by beqa16v]
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beqa16v
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| posted on 13/4/12 at 01:42 PM |
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Took the carbs to a bike carb specialist. He disassembled them and they were full with mud. Dont even know how it got there. Needle on one of the
bowls was not working and was changed. Will try to fire up the car tomorrow
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beqa16v
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| posted on 18/4/12 at 07:57 PM |
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popping and bogging at 4000 was caused by low fuel pressure (hence lean mixture). Discovered that by fitting a stronger return valve which maintains
3psi instead of 1.5. The engine improved immediately. Confirms the necessity of a bike pump. It will deliver right amount of fuel at any rpm.
But i have a lot of fuel in my oil. It smells fuel a lot.
[Edited on 18/4/12 by beqa16v]
[Edited on 18/4/12 by beqa16v]
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jacko
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| posted on 18/4/12 at 08:30 PM |
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Nice to know you found the problem let use know how you get on
Jacko
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beqa16v
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| posted on 19/4/12 at 06:04 AM |
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quote:
Originally posted by jacko
Nice to know you found the problem let use know how you get on
Jacko
Well yeah nice to find the reason at last. I think the fuel is still not enough at high rpms, the engine should be stronger still (i was only reving
it on idle). Will try to get my hands on a bike pump. They are so hard to get here
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beqa16v
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| posted on 25/4/12 at 08:05 PM |
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Just bought a ZX6 fuel pump from ebay. Does it need a relay or I can just connect the wires and forget about it? I read somewhere that it needs a
separate relay to stop pumping when unnecessary
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ReMan
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| posted on 25/4/12 at 09:08 PM |
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quote:
Originally posted by beqa16v
Just bought a ZX6 fuel pump from ebay. Does it need a relay or I can just connect the wires and forget about it? I read somewhere that it needs a
separate relay to stop pumping when unnecessary
You dont need one for normal operation.
The relays are usually used to provide forced cut off in the case of some falure or stuation
Get it running without and add in later if you really feel the need
www.plusnine.co.uk
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beqa16v
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| posted on 25/4/12 at 09:19 PM |
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quote:
Originally posted by ReMan
quote:
Originally posted by beqa16v
Just bought a ZX6 fuel pump from ebay. Does it need a relay or I can just connect the wires and forget about it? I read somewhere that it needs a
separate relay to stop pumping when unnecessary
You dont need one for normal operation.
The relays are usually used to provide forced cut off in the case of some falure or stuation
Get it running without and add in later if you really feel the need
Thanks a lot
A guy on another forum confused me by saying that I should know what kind of carbs I have to match the pump (get either electrical or vacuum pump)
My zx6 pump looks like this
Carbs are from a 750 and look like this
Hope I did everything right
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ReMan
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| posted on 25/4/12 at 09:48 PM |
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Another forum? I thought there was only one..
That should be fine. It has it's own internal regulation and only pumps as neccesary
www.plusnine.co.uk
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beqa16v
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| posted on 26/4/12 at 07:05 AM |
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quote:
Originally posted by ReMan
Another forum? I thought there was only one..
That should be fine. It has it's own internal regulation and only pumps as neccesary
Thanks a lot. I was already thinking I have missed something while researching on these.
The guy has exactly the same pump and he said it started to overflow as soon as he turned it on. Had to connect a relay etc. Cant see why this
happened if the pump was working well. If the needles had problems then the relay should not have fixed it. strange
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beqa16v
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| posted on 6/5/12 at 07:12 AM |
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The ZX6R fuel pump has arrived. will pick it up tomorrow. any instructions before I install it? Does the pup say where the negative and positive
should be connected? Will it be damaged if I mess those up? Any other tips?
PS. I have the engine in the rear so the pump will be close to both engine and the tank.
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whitestu
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| posted on 6/5/12 at 09:00 AM |
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quote:
Does the pup say where the negative and positive should be connected? Will it be damaged if I mess those up?
Hi
It should look like this:
[img]
 
Description
[/img]
The wires to the connector are black and red. Red is live.
The one with the filter on is the fuel inlet.
They are best placed under the tank so gravity primes the pump.
Stu
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