IainB
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| posted on 3/5/06 at 10:04 AM |
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Bike Carbs
This is really doing my head in now, i dont get time with the car during the week and at the weekend I just end up getting nowhere with these bl**dy
carbs.
The carbs in question are zx6r Mikunis, bogg bros manifold and zx6r electric pump. 1st set of carbs were rejetted to 160 (main jets?) and 2nd set are
identical but standerd jets. All fitted to 1498cc sohc fiat unit - new plugs, leads, etc.
Started off 6 months ago running fine on old weber datr. Ignition fine, etc.
Been fiddling with both sets of carbs for months now and the best i can get is rough firing and fuel spraying out from the trumpets. Yes im using the
choke.
Started with idle screws fully in (no firing at all on cranking) gradually unscrew them (now about 8 turns out) get regular firing but never seems to
pick up and go. The idle speed screw is half turn in after contact with throttle linkage. If throttle is opened too much the engine will not fire at
all (running lean?)
There seems to be rather a lot of fuel squirting out from the trumpets while cranking, i think its coming from the hole to the right of the brass
screw:
Spoke to bogg bros and they suggested the carbs might be dud as they should run pretty dry on trumpet end (mate had Tiger with zx7rs and yes they run
very dry and no spraying fuel!) Hence me gettin 2nd set of carbs but still no joy.. Unfortunatly Im up in Glasgow so bogg bros expertise is out of the
question and i dont know anywhere else who would have the knowhow.
Please help! i know bike carbs are the way to go but these ones just dont like me... 
Regards, Iain
http://s43.photobucket.com/albums/e365/IainB1986/
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andyharding
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| posted on 3/5/06 at 10:12 AM |
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My R1 carbs spat back until I cured the leaky manifold.
Take the carbs off and turn the engine so that #1 intake is closed. Then stick your mouth over the manifold pipe and blow. There should be no air
blowing out around the manifold flange. Washing up water helps find small leaks. If there is a leak you may have the manifold over tight or not tight
enough. Get a new gasket and soak it in light oil overnight to make it swell up then re-fit. If this doesn't seal things try some silly-cone.
Other possability is ignition timing. I'd gues you want about 10-12 degrees at idle. Check with a timing light.
Also, make sure the carbs are balanced. If you don't have the right tool take them off and align all the butterflys with one of the air
drillings. This should get them pretty close.
Jetting isn't critical. They should rund reasonably smoothly on 160 mains I would have thought.
Do you have the hoses connected up correctly?
Is the fuel pressure correct?
[Edited on 3/5/06 by andyharding]
Are you a Mac user or a retard?
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mookaloid
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| posted on 3/5/06 at 10:21 AM |
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Really stupid suggestion - I know nothing about bike carbs 
But the brass screw looks like a jet to me and this would suggest that that side should be be pointing towards the engine.
So are you sure that the carbs are fitted the right way round?
As I said - probably a stupid suggestion so feel free to tell me to go away.
Cheers
Mark
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andyharding
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| posted on 3/5/06 at 10:26 AM |
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Yes, they are right. Slider is away from the engine butterfly towards.
Are you a Mac user or a retard?
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DarrenW
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| posted on 3/5/06 at 10:30 AM |
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My old fashioned downdraught used to spit back. It was a combination of fuel pressure too high and timing a mile out.
Id check ignition timing again first with a strobe. If you are running the bike pump that normally fed those carbs then i cant see pressure being your
problem. Are the sliders nice and free? What needles are you using. Ithink a lot pf people go for dynojet needles sothey have some adjustment on
height - dont go spending tho until you are sure you need them.
i assume the engine is healthy and valves are sealing fully etc.
ive heard of people using easy start to check for manifold leaks - if engine picks up its drawing easy start thro a hole.
To be honest sounds like a call to Boggs and pressure them into an answer is the way to go. Did they supply the carbs?
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Surrey Dave
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| posted on 3/5/06 at 12:35 PM |
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8 turns out on the idle screws is crazy should be between 1-3 , have you checked the float hieght? this can be crucial, have you got any giant air
leaks where blanking plugs should be i.e in plastic tops , they are connections that are used for balancing, do the pistons lift OK and drop with some
kind of damping? , if not check the rubber diaphrams, fuel pressure should be around 1 -2 pounds.
Getting desperate now , are the fuel connections on the bottom (float bowls) not on top (overlows)
Thats all I can think of at the mo , even without any rejetting my bike carbs started easily and ticked over smoothly..
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oliwb
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| posted on 3/5/06 at 05:27 PM |
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Gotta agree 8 turns out is crazy! think mine are 2.5 - 3.....Maybe you should start lookin for some cheap ZX7r carbs as they're simpler and
crucialy we know they work! Might even fit the spacing on the manifold if ur lucky! Still check your ignition timing...I know you think its right
but I also know that you don't know its right.......(not sure that makes sense but ahwell!).....Good luck....Oli.
If your not living life on the edge you're taking up too much room!
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Surrey Dave
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| posted on 3/5/06 at 05:40 PM |
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I cant see from the photo, what angle are these carbs mounted at?
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rusty nuts
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| posted on 3/5/06 at 05:41 PM |
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Don't know a great deal about bike carbs but I would suggest perhaps disconnecting power supply to fuel pump and then get someone to crank
engine on starter while you spray eezistart or brake cleaner into manifold (just a second or so) If the problem is fuel based engine will fire up and
perhaps run for a second or two . If it does'nt fire properly then I would check the static timing . You will be unable to check timing with a
strobe until engine is running
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givemethebighammer
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| posted on 3/5/06 at 09:19 PM |
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My blackbird keihin carbs on my 2.0L zetec (with Kent FZ2001 cams) are as follows:
42 pilots - 1.5 turns out on mixture screws
170 mains
standard needles (J5FZ) with washer as oem
vacuum hole in slide drilled to 2.5mm
Dynojet springs (weaker than standard ones)
AFR at idle is 14.7 - 15. everywhere else AFR is 12-13 (with a few slightly richer and weaker spikes here and there).
It sounds like either your float level is too high or your fuel pressure is too high (the later could affect the former). Which fuel pump are you
running ?
Just read you are using a bike pump, when you turn the ignition on can you hear the pump tick then stop as the needle valves close in the carbs or
does it just keep ticking ?
If it stops ticking I'd check your float level and perhaps lower it 1mm to see if it makes a difference.
[Edited on 3/5/06 by givemethebighammer]
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TangoMan
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| posted on 3/5/06 at 09:40 PM |
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More info needed
It does sound like too much fuel pressure or float level too high. I can't see any other reason or fuel squirting out, unless you have connected
the fuel pipe to a breather and not the fuel inlet.
Have you checked the plugs after cranking. I guess they will be soaked. This would confirm one of the above.
Try disconnecting the fuel pump power and then try starting with just the fuel left in the float chambers. If it starts and runs for a while this
would again indicate one of the above. If not then perhaps it may be something else.
I would also try to get a look at a bike with the carbs fitted as the fitted angle can be critical. Don't assume they should be level as on many
bikes they are designed to fit at an angle.
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IainB
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| posted on 3/5/06 at 10:42 PM |
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Cheers for all the feedback guys! much appriciated 
"have you got any giant air leaks where blanking plugs should be i.e in plastic tops , they are connections that are used for balancing, do the
pistons lift OK and drop with some kind of damping? , if not check the rubber diaphrams, fuel pressure should be around 1 -2 pounds."
Where would these balancing plugs be? Pistons lift fine and free and yes drop with damping.
The bike pump seems to run fine, clicks up to pressure then stops. Its from a zx6r so should be matched to carbs.
I rebuilt the head last winter so the valves should be fine and seating properly, valve timing hasnt changed and there is no way that the spark timing
has changed either. Megajolt will be running soon so that will clear up any issues there!
The carbs are mounted so the float bowls are level, bogg bros said they have mounted carbs at all sorts of angles with no problem. Here is a link to
a ZX6R carb removal webpage, seem to be mounted in slightly more of a downdraft position...
Carb Removal
Here is my setup...
Fuel inlet is on the bottom between carbs 2 and 3, you can see it in the following pic (green):
The plugs are pretty wet after cranking so im presure i have got the right fuel inlet!
There is several small diameter rubber hoses that run between the float bowls, what are these? are these balancing thingys? carbs 1 and 4 have no
where to join up to so I have left them open?. Pretty sure they are not fuel lines. Oh, and the breather hose on the top has been left as seem in the
pics.
I now have a list for the morning:
1. Check Manifold/Carbs are sealing onto head.
2. Experiment with blanking off small rubber hoses on float bowls.
3. Run pump up to pressure, crank, then disconnect power, crank again and see if we have any (more) life. Iv done this before and IIRC it gets worse.
Would this suggest lean idle mixture? I once had an outboard motor that reved it nuts off before finally dying when u turned off fuel. so i see what
ur getting at..
Will report back in the morn'
Bit of fiddling and the mouse will roar again yet....
Iain
[Edited on 3/5/06 by IainB]
http://s43.photobucket.com/albums/e365/IainB1986/
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IainB
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| posted on 4/5/06 at 10:34 AM |
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Right, checked manifolds - sealing fine.
rubbers and carbs have also been checked and they seal. No leaks.
sprayed some easystart directly into manifolds with no carbs and the engine would fire so im assuming ignition is OK?
Also blocked off small rubber hoses at carbs 1 and 4. they dont appear to be letting air into carbs anyway.
as you can see carb 1 0r 4 has no where to join on to - its blocked off now...
Still no joy with carbs on and connected up - fires and splutters and sounds like its going to burst into life but never quite does. No change.
Tried disconnecting fuel pump but it just seems to do the same til it runs out of pressure and dies - no noticable improvement.
Cheers for ur call Oli, i think i may have to get some zx7r carbs as you suggested, at least we know that they work! Jus hope they are the same
spacing - il try to find out on some bike forums...
Im all out of ideas now in afraid, what a f*cking waste of hard earned.
Iain out,
http://s43.photobucket.com/albums/e365/IainB1986/
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andyharding
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| posted on 4/5/06 at 10:42 AM |
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OK sounds like you need to go right back to basics.
Can you put the old carb on and see if the engine runs fine then? If you've been messing with it for 6 months there is a chance that something
other than the carbs is wrong (ie stale fuel) and testing with the old carb would eliminate this for sure.
If the above proves it's the bike carbs then they need to be checked over to make sure all the critical bits are working and set up correctly.
All butterflys needed to be in sync the idle screws all need to be about right and the same and then it should at least run on choke and with the idle
speed turned up.
If you can find out if they have the same spacing as R1 carbs you can post them here and I'll try them on my 1600 Pinto which is currently
running perfectly.
Are you a Mac user or a retard?
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andyharding
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| posted on 4/5/06 at 10:44 AM |
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P.S. when cold I do get a little bit of spitting back.
See here (100MB):
http://www.inetc.co.uk/download/MVI_7763.AVI
Are you a Mac user or a retard?
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IainB
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| posted on 4/5/06 at 11:16 AM |
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unfortunatly i no longer have my old manifold as bogg bros cut the flanges off to make the new one! Doh. Been trying to find another one for ages so i
can prove that everything else works ok, kinda rare part to find...
the spitting back is more of a mist that actual droplets, il try to post a vid or something later this evening, got work to go to now.
Cheers, IAin
http://s43.photobucket.com/albums/e365/IainB1986/
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IainB
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| posted on 7/5/06 at 04:37 PM |
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Right, had another go today and got some video for you.
Sorry about quality of vid, sound and camera crew! but it was filmed by my flatmate with webcam with shitty mic...
Video
From watching the carbs with someone else turning the key i can now see that the mist of fuel is coming the the small brass screw below
Is this the idle air screw?
Anyway, have a look see and tell me what u think..
Oh, and i know the top hose on the carbs looks like its going to the fuel pump but i really isnt, jus restin on it
My Best, Iain
http://s43.photobucket.com/albums/e365/IainB1986/
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Mike7
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| posted on 7/5/06 at 06:18 PM |
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Hi Ian,
It's a long time since I worked on 'bike carbs, but that looks like a jet ... I think ;-)
This site here:
http://www.drpiston.com/Cvcarbs.html
has some useful info about 'bike carbs.
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Mike7
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| posted on 7/5/06 at 06:41 PM |
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Have a look at this:
http://www.drpiston.com/Mikuni.jpg
Main jet? The last time I worked on a Jap carb was on my Suzuki 550.
In 1984.
So where did 22 years go? 
Idle airscrew should be on the side of the carb, probably fitted with a spring.
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MikeRJ
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| posted on 7/5/06 at 09:19 PM |
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quote:
Originally posted by IainB
Also blocked off small rubber hoses at carbs 1 and 4. they dont appear to be letting air into carbs anyway.
as you can see carb 1 0r 4 has no where to join on to - its blocked off now...
They may be float chamber vents or simmilar, they probably shouldn't be blocked off unless someone knows better? I take it you've tried
with them unblocked?
Does the fuel only spray out of the jet when you are cranking, or all the time?
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IainB
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| posted on 7/5/06 at 10:21 PM |
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Yeah tried with them unblocked at first with no luck. they are blocked up now and are so in the vid above...
Iain
http://s43.photobucket.com/albums/e365/IainB1986/
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Mike7
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| posted on 7/5/06 at 10:22 PM |
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Are these the carbs:
http://www.sudco.com/keihin.html#FCR
If so, it looks like there's two types, downdraft and sidedraft.
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robbydee
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| posted on 8/5/06 at 05:11 PM |
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deffinatly the fuel pump off a carbed bike?
cause injection bikes run alot higher pressure. could be too much for the floats..
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TangoMan
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| posted on 8/5/06 at 11:31 PM |
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Video
Although the video is not the best quality it does sound like you are getting some firing.
Are you sure that fuel is getting to all 4 carbs. Are all plugs wet if you take them out.
Don't be mislead by the easystart as I think that fires from compression without a spark plug.
Sounds to me like poor fueling or very retarded ignition.
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