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Author: Subject: Bike Carb question
rm0rgan

posted on 21/7/18 at 03:26 PM Reply With Quote
Bike Carb question

Afternoon!

I have bought a Danst manifold and ZX6 carb kit to fit to my Blacktop Zetec (running MegaJolt).

I see the manifold has a take off installed to the left which I'm assuming is for a vacuum or servo take off - do I need this? If not I'm guessing I can just block it off?

Danst Bike Carb Manifold
Danst Bike Carb Manifold


Also, at the bottom of the carbs there is a connector that I'm unsure of - I know the one at the top is for fuel but what is the bottom one for? Do I need to connect it to something?

ZX6 Carbs
ZX6 Carbs


Thanks for any pointers - much appreciated :-)





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kingster996

posted on 21/7/18 at 03:53 PM Reply With Quote
Blank off the manifold vac pipe.

Difficult to see from you pics but on bike carbs you often get a water feed from cooling circuit that helps with carb icing. So could be that. Or you can also get a breather to the float bowls. So could be that too.






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Angel Acevedo

posted on 21/7/18 at 03:53 PM Reply With Quote
May the bottom be to pressurize fuel bowls in case of forced induction??





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rm0rgan

posted on 21/7/18 at 04:03 PM Reply With Quote
quote:
Originally posted by kingster996
Blank off the manifold vac pipe.

Difficult to see from you pics but on bike carbs you often get a water feed from cooling circuit that helps with carb icing. So could be that. Or you can also get a breather to the float bowls. So could be that too.


That would make sense. In my head all I need is to connect up the fuel as they are gravity fed - I'll run a pipe to mt catch tank for the bottom ones just in case they vent something somewhere!

Just waiting for my bike fuel pump to turn up and then I can fit em!





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chris

posted on 21/7/18 at 09:14 PM Reply With Quote
Bottom connection is fuel in top connection leave to atmosphere or pipe into back plate of air filter
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Davedew

posted on 21/7/18 at 09:27 PM Reply With Quote
Bottom one is fuel feed to carbs.
Top one is breather for the diaphragms under the plastic caps. This one is left to atmosphere on my setup.





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rm0rgan

posted on 22/7/18 at 08:31 AM Reply With Quote
Perfect - had just seen a photo of a set up on the MK facebook page and saw fuel in at the bottom :-)

Can't wait now to get them on there!

Thanks for all the help, much appreciated





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posted on 22/7/18 at 08:26 PM Reply With Quote
I run R1 carbs on a DanST manifold on a Black top using Megajolt with MAP sensor . It is always considered better to have a vac pipe to all the inlets to flatten out the pulses...

[Edited on 22/7/18 by redturner]

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rm0rgan

posted on 30/7/18 at 08:09 AM Reply With Quote
So, I have been having a few challenges that presented itself like I had an air leak between the carbs and the manifold but have checked, resealed, checked and rechecked again but cannot detect one, so don't think this is it....

Fitted
Fitted


I'm told the carbs had been run and checked on a test rig prior to dispatch for balance, idle and free RPM pickup and so took the carbs off again yesterday just to check/count how many turns each pilot air screw was set at (most websites indicate 3 and 3 and half turns as being pretty normal as a base setting). I found carb 1 (the one I seem to have an issue with) was right out at 6 or seven turns - whereas all the others were at 3 turns.

Other observations:

Carb 1 is pulling much more air than the others

Carb 1
Carb 1


Carb 2
Carb 2


Carb 3
Carb 3


Carb 4
Carb 4


If I put my hand over carb 1, the engine idle will drop/die, but doesn't over carbs 2,3, & 4.
Pick up is actually quite good, but the revs hang occasionally (although not always) which would typically indicate an air leak somewhere but I know it's not from the manifold or carb interface. Cylinder/Carb 1 is popping occasionally on tick over and in general the engine is really smokey/oily/rich, however Cylinder 1's plug is clean/dry, whereas 2,3 & 4 are all black and oily - anyone any other ideas on what else I should check ?





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daviep

posted on 30/7/18 at 10:21 AM Reply With Quote
You need to start off by balancing them.

Make sure there is not something sticking number 1 open to begin with, if everything seems OK mechanically then balance them as normal.

Do you know how to balance them?

Cheers
Davie





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rm0rgan

posted on 30/7/18 at 10:34 AM Reply With Quote
quote:
Originally posted by daviep
You need to start off by balancing them.

Make sure there is not something sticking number 1 open to begin with, if everything seems OK mechanically then balance them as normal.

Do you know how to balance them?

Cheers
Davie


I can't see anything sticking number 1 open but haven't opened them up internally yet. They were supposed to have been balanced before they were shipped to me but either this was not the case or something happened in transit which I cannot rule out, only the package seemed intact and well wrapped.

I have vacuum gauges in the garage but there are no take offs on the carbs or the silicon rubbers that came with it (nor on the manifold) to connect to, so will need to buy some bike ones with vacuum pipes on and use those, then switch back to the silicon rubbers. Even if it was out of balance, would it present symptoms like this though?

I understand logically going through each step to rule things out though, just frustrating and time consuming.





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David Jenkins

posted on 30/7/18 at 01:52 PM Reply With Quote
quote:
Originally posted by rm0rgan
I have vacuum gauges in the garage but there are no take offs on the carbs or the silicon rubbers that came with it (nor on the manifold) to connect to, so will need to buy some bike ones with vacuum pipes on and use those, then switch back to the silicon rubbers. Even if it was out of balance, would it present symptoms like this though?




You have a perfectly good balancer in one of your earlier pictures:



It's what I used to balance my carbs.

And yes - the engine will run like an absolute dog if the carbs are out of balance.





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daviep

posted on 30/7/18 at 02:01 PM Reply With Quote
There is no reason not to use your air flow meter to balance the carbs, it may not be quite as simple as having 4 manometer's connected at once but it shouldn'the present any great problems.

Out of sync carbs can cause rough running. Rev''s hanging on the over run can be caused by weak mixture, I would reset the #1 air screw to the same as the rest once you have balanced the cars.

Davie

Edit: like DJ says

[Edited on 30/7/18 by daviep]

[Edited on 30/7/18 by daviep]





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Davedew

posted on 30/7/18 at 02:30 PM Reply With Quote
My rolling road guy used exactly the same flow meter as you have to balance my bike carbs.

The way mine were balanced was like below:-
Get a base reading from carb 1 (carb closest to throttle cable attachment). Then balance carb 2 to carb 1, then carb 4 to carb 3, then carb 3 to carb 2.

You might need to increase the idle speed to 1500 rpm ish to make sure the engine doesn't die when adjusting them.
Make sure then carbs are all closed when checking the flow. When we were adjusting the screws on mine sometimes we found the throttle would open slightly causing the reading to be out.

hth

Dave





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rm0rgan

posted on 30/7/18 at 02:43 PM Reply With Quote
quote:
Originally posted by daviep
There is no reason not to use your air flow meter to balance the carbs, it may not be quite as simple as having 4 manometer's connected at once but it shouldn'the present any great problems.

Out of sync carbs can cause rough running. Rev''s hanging on the over run can be caused by weak mixture, I would reset the #1 air screw to the same as the rest once you have balanced the cars.

Davie

Edit: like DJ says

[Edited on 30/7/18 by daviep]

[Edited on 30/7/18 by daviep]


Cheers Davie - I may need to do it the other way around though and get all the air screws to the same setting and then have a go at balancing them. Carb 1 is definitely running weak and very lean :-)





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rm0rgan

posted on 30/7/18 at 02:43 PM Reply With Quote
quote:
Originally posted by Davedew
My rolling road guy used exactly the same flow meter as you have to balance my bike carbs.

The way mine were balanced was like below:-
Get a base reading from carb 1 (carb closest to throttle cable attachment). Then balance carb 2 to carb 1, then carb 4 to carb 3, then carb 3 to carb 2.

You might need to increase the idle speed to 1500 rpm ish to make sure the engine doesn't die when adjusting them.
Make sure then carbs are all closed when checking the flow. When we were adjusting the screws on mine sometimes we found the throttle would open slightly causing the reading to be out.

hth


Dave


Cheers Dave!





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rm0rgan

posted on 1/8/18 at 03:12 PM Reply With Quote
So the saga continues...

I've emailed DanST to check what the idle screws should have been set to and was surprised to hear that one of the idle screws was right out - they said they set them all to be 2.5 turns out as standard when balancing them which makes me think this set may somehow have missed part of their quality control, anyhow, I also mentioned to them that I can cover carbs 2,3 & 4 with no change in revs to which he thinks would suggest air is being pulled in on that cylinder somewhere - I can see the logic in that, however cannot find any trace of a leak by spraying carb cleaner and WD40 around the manifold area to see if it would change the revs at all.

The only thing I had not taken off and checked up to this point was the manifold against the head, so took it off - there was some staining on the gasket that came with the carb kit that would indicate something was leaking but it did not get to the outside edge of the gasket so assume it had remained air tight however, just to be sure I decided to fit a new original Ford inlet gasket (they are aluminium and have seals around the inlets etc rather than being just one large gasket and I think would be more up to the job). Anyhow, fired it up and exactly the same result

Increasingly I am thinking the carbs must be so out of balance that carb 1 is making the engine continue to run on even if I do cover the other 3, so think the next thing to try is balancing them.

Davedew has said which carb to balance with which (thank you), and I have set all the screws to be 2.5 turns out as DanST suggests they should have been - I will let you know how I get on!





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melly-g

posted on 2/8/18 at 06:56 AM Reply With Quote
Balance them first! mixture screws won't affect the balance. Unless bike carbs are different?

I don't think you can balance a set of carbs off the engine they are going on can you?

But balancing should be the first thing you do then start with all mixture screws the same and go from there.

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rm0rgan

posted on 2/8/18 at 07:14 AM Reply With Quote
quote:
Originally posted by melly-g
Balance them first! mixture screws won't affect the balance. Unless bike carbs are different?

I don't think you can balance a set of carbs off the engine they are going on can you?

But balancing should be the first thing you do then start with all mixture screws the same and go from there.


Not 100% sure but you should be able to them pretty close although of course there are so many variations at play on different engines I can't see how you could either.

Anyhow, made a big leap forward yesterday - I set the pilot air screws to be the same across all 4 carbs (2.5 turns out) to give me consistency across the carbs as a starting point and then had a go at balancing them using my flow meter and the method suggested above - what a difference - it started to run a lot better but was still belching out rich fumes so turned the air screws in a turn and that helped massively - tweaked the balance a bit more and then with another 1/4 of a turn in it's running much smoother and without a whole load of fumes coming out - I ended up with the idle screws turned out at 1 and 1/4 in the end.

It's at a point now where I think it's driveable to get it to the Dyno session next week where they can properly set it up - I could have done without spending a few quid trying things in the belief they were balanced but in the end I learnt a lot thanks to the help of folk on here!

Thanks folks - much appreciated!





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Davedew

posted on 2/8/18 at 10:53 AM Reply With Quote
Glad you managed to get it running a lot better. At least now you can drive it to the rolling road to get it setup properly.
I know mine runs slightly rich at idle. Initial throttle opening leans the mixture out.

I also found that I needed to richen mine slightly as when cruising at high speed with little throttle it was slightly hesitant. You could feel a slight judder. Adding an 1/8th of a turn out on the base mixture screws sorted that out.

Also if you need a map for the Megajolt let me know, and I can email a copy of mine.

[Edited on 2/8/18 by Davedew]





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rm0rgan

posted on 2/8/18 at 12:34 PM Reply With Quote
quote:
Originally posted by Davedew

Also if you need a map for the Megajolt let me know, and I can email a copy of mine.

[Edited on 2/8/18 by Davedew]


Cheers Dave - a copy of your map might be of use to compare!

If you can email it me that would be great - rob@themorgans.eu





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