Bike Carb problem on BMW M10 engine 518 E28 Bogging

[Neil]

Finally got the ZZR1100 carbs fitted yesterday and got it idling okayish today! Problem now is when the throttle is opened quickly it bogs down / cuts out / farts loads of fuel out of the carbs and tries to set on fire haha, here's a link to a vid I made early, hope you can help.

Cheers Neil.

[Waxoyling Lyrical]

Are you feeding them with the correct fuel pressure? I notice you don't have the fuel pressure regulator connected.

[Neil]

Hi sorry, I'm using the fuel pump off the bike that the carbs came off, cheers.

[Clamity]

Have you tried it with the trumpets on to see if it make any difference?

My zzr1100 runs a bit like that when cold at low revs because I have an air leak back there somewhere. Once it's warmed up a bit it's fine though I have an entertaining step in the torque curve about 3500 rpm.

[retrowrongun]

Sounds like its too lean or pump not supplying enough on demand

[barrytrotter]

over fueling surely,try a fuel regulator.and also the manifold looks very long is it home made that looks quite along way for the fuel and air to travel befor it gets to the cylinder

[barrytrotter]

if long is good how come on the bike there about half an inch away and the manifolds you can buy look half the lenght of what that 1 is

[cesarbarbosa]

I think the carbs are not tilted enough as the fuel bols aren't leveled making it a bit dificult to fuel proper...
But thats me saying...

[Neil]

I have the feeling it's over fueling, badly. But I'm far from an expert on carbs! I'm gonna try some smaller jets because the ones fitted at the minute are 156 and 160s but I can slide a 6mm drill bit through them like a d*ck in a shirt sleeve so have the feeling they may have been drilled out or am I being a sausage? Regarding the carb angle I don't understand what the problem would be? They are sat with the floats open and when the fuel pump is switched on they close off and then does the pump. Thanks for the helpful replies so far guys.

[Kieran]

Bogging and spitting back is classic lean symptoms.

I'd richen the pilot mixture screw to about 2.5 turns from seated.

It won't be the mains because you are not on them at that stage. Have you lifted the needles too?

If fuel isn't dribbling out if the overflow pipes, angle is fine.

[Bolf]

Mixture and timing is the items i'd be looking at , as long as the jets are right!

[Neil]

Fuel isn't dribbling out anymore it was when I first fitted them but I removed them and found the floats weren't moving freely so I cleaned them out and that fixed that. With the carbs off I turned all the idle screws all the way in and back out three full turns each, I haven't touched the needles. I wonder if I should try another half a turn on each?

[Kieran]

What's it like with the choke on? If the engine is cold, spitting back is 'normal'.

[Neil]

Went back out earlier for 5 mins, all I did was twist the idle mixture screws on the front two carbs out half a turn each (easiest ones to get to) so they are now out 3.5 turns each now and the difference was very noticeable! Chuffed, I'll have a proper play tomorrow after work. Kieran I see you have put a wanted thread up for a hydrolastic pump, I don't have one for sale but I do part own a Churchill pump with a mate you're welcome to use. Thanks for all your help guys, I'll keep you updated!

[Neil]

Ok I'm four turns out now on each screw and it idles absolutely spot on but when driving it's running on for a while after I put my foot down a tad and I have gradually increase the throttle to get it moving if I press it too quick / hard it just bogs and drops down. Could this be main jets being too small? Only thing I can think of now! Cheers.

[avengertec]

I had to block off a hole on zx6 carbs as they did the same thing that sorted it
It was the small hole on the right looking on your pics just try temp covering them up nothing to loose

[Neil]

Cheers I'll give that a go, I must add that it revs up no bother with the choke on, this is what's got me thinking the jets are too small? Or am I miles away?

[avengertec]

1.6mm main jets should be a good base

[retrowrongun]

I would also be wanting to run a fuel swirl pot to aid with on demand fuel delivery as you now have 4 float bowls to fill instead of one ,and would also fit a fuel pressure regulator and gauge too ,if nothing else this may help with a diagnosis as you could be suffering with not enough pressure or fuel delivery when throttle snapped open possibly

[Neil]

Blocked off the holes and it's did go a tad better, drilled out the jets to 1.7mm, tons better! Only problem now is it runs on quite a bit when revved up slowly then let off, got it booked in at Bogg Bros on Saturday to get it tuned now I can drive it.