Hi all, i am in the middle of a project and need a pair of the short malossi manifolds for a two valve 900 ss / monster motor (95). there seems to be a bit of confusion on shape of these with some settling for two rears and some not, there also is a pair on ebay that are aftermarket and are completely straight, my concern is the angle of the float bowls. the carbs i have on order are split 41 keihin fcr's. So can anyone tell me who has these in stock, or even do you have any to sell me? also comments on shape welcome, thanks in advance.
Howdo! Gotta set of short malossi manifolds that I purchased (new) never used as I then went fuel injection. Will stick up pics if ya like? Cheers Pablo
The FCR carbs will run at a wide range of float bowl angles (IIRC it's about 35 deg +/- from optimum) ..... I've got a pair of downdraughts running on ST2 manifolds with the rubber part machined off, and they run as well as any other split FCR setup, even under hard braking/accelerating. The limitations in the carbs are more to do with fuel atomisation under low intake velocities than the angle of the float bowl.
Yes, i do agree but having the carb at an acute angle does not give optimum conditions for setup, particularly when you have two carbs feeding at different angles. as this is a project just for the dyno i want to keep things as simple as i possibly can for setup, only then can i start putting the carbs on a straighter tract if i need to. As for atomisation limitations, i have been running these on the long manifolds for about four years and not noticed any issues when correctly set up, on the road they are a dream. the only issue that comes to mind is when i went too light with the flywheel, that made it an absolute pig. can youn describe any other limitations you have come across, this info could be helpful, thanks.
Quick throttle opening from low revs results in the engine bogging ...... almost certainly due to fuel coming out of suspension (as it has been resolved by replacing the needle jets with ZX7R emulsion tubes to aid atomisation - unfortunately there are none left!), and exacerbated by the extra fuel being squirted into the carb by the accel. pump. If you roll the throttle on more gently from low revs, or intend to keep the engine spinning over 5k by gear changing there isn't a throttle response problem.
I have to say that i have never experienced anything quite like that, i have a 944 with fcr's on long manifolds and it will take full throttle from 3500rpm, maybe its the manifold length? if you try full gas at 1500 rpm it will bog but reasonable use of the throttle will help, on the road full gas at around 2500 rpm gets the revs up quickly to 3500 so not even noticed. interesting comment on the zx7r emulsion tubes, never heard that one, what is different with them?
Pablo, dont panic, they definately are wrong they are for a bevel carb upgrade, thanks for the offer but until i can find the proper ones i would like to hang on to them, they are very close but both carbs hit the frame tubes, if i cannot get the correct ones i will saw them off and re weld in the correct position. i am unsure of the correct part to get so if anyone knows the answer please post, bear in mind i am NOT going to saw the frame tube out to fit a sidedraft carb, i have two downdraft singles. Pablo, thanks for your help though.
The ZX7R tubes are emulsion type rather than needle jet type, so instead of the main air jet allowing air to enter the carb and blow over the top of the jet (in the carb throat), the air is channeled down the jet and through tiny holes into the fuel stream, atomising it BEFORE it enters the carb throat. This lessens the problem of fuel coming out of suspension at low revs/wide open throttle conditions ......... Kwak got Keihin to develop them to cure exactly the same problem with their WSBK 750's but once the world took to Fi, development (and production!) stopped, and now the supply of tubes has run out. Factory Pro have developed something more sophisticated (HDJ system) but along the same lines to cure bogging on carb'd Harleys & Jap cruisers (would you bother?) but when I contacted them about availability for FCR's, they acted like total pr!cks (demanding money before they'd even talk to me!), so I didn't take it any further.
Thats very interesting what you have said but why can you not tune that out with the main air jet? this does control the flow of air to the main nozzle thus doing the same thing..... i can see the problem that kawasaki had and think that it is possibly due to low gas speed at low rpm due to the cylinder size too small for the carb, this is particularly noticed on the 900 ss when using the 41 fcr on the long manifold so i am sure it will be noticed on a 750 four cylinder. (185cc per cyl!!) you tend to forget these problems in this age of fuel injection, and obviously kawasaki was after absolute max power. As i said i have run these carbs on the street for ages and have never had a problem with a 944 engine on 39's, it did take a few hours on the dyno to get it right though, i am hoping for similar results on my new engine build but i know i will loose some bottom end if i try to swamp it at 2500 with full gas pulling a trailer, but with this build its absolute top end i am after, i just wonder what is possible with the old two valve ducati engine. Whilst i am on here must say a big thanks to Sam at SPR RACING in ruddington notts, he helped me no-end setting the 944 up on the dyno. And as for jap cruisers........exactly, why bother.
The top end (>6k) on the Kwak was fine, but the low/mid response to rapid throttle openings (corner exits etc) was poor and forced riders to be constantly working the gearbox to keep revs up - the problem is specifically that when the slides are opened quickly at low revs (especially on a 450+cc/cylinder Duc) the resultant vacuum causes the fuel to come out of suspension and form large droplets of fuel (rather than the preferred mist) which don't burn efficiently, if at all.... and that causes the bogging down of the engine. It's only for a second or so. The AP chucking a squirt of fuel down the carb throat during rapid throttle opening was Keihins half-baked attempt to cure this very problem, but in itself causes the mixture to go way too rich (causing a similar but unrelated 'bogging' effect), and itself needs very careful 'tuning'. The main air jet can be sized to give the correct AF at each throttle position, but not during rapid transition from one flow rate to another. So, the emulsion tubes atomise the fuel before it enters the carb throat rather than as it enters it, minimising the chances of the fuel coming out of suspension even when entering a high vacuum area (note to physicists: is it possible to have a 'high' vacuum?). Not sure how clear it is but this image may help explain the difference in the two tube types (1 is Needle Jet, 2 is Emulsion Tube). Fuel comes in at bottom of both, but in a needle jet, air from the MAJ flows across the top as the fuel is sucked into the carb throat and there it atomises the fuel. In an emulsion tube, the air from the MAJ has to travel down the tube and mix with the fuel via small holes, giving a more atomised fuel mixture before it hits the carb throat. And yep, only reason there are needle jets and not emulsion tubes in some carbs is they are slightly cheaper to make!
Thanx for that very indepth explanation, i do think its far in exess of my poor quality riding though. might be worth a try if i can get hold of a set if nothing more than to do a back to back run. you are also quite correct about the ap needing fine adustment, with it set at the std setting the engine does just bog, mine are set up so a full throttle roll on on the dyno shows a weak gulp of air at around 16:1 closely followed by a swamp of fuel at about 9:1, this is done in miliseconds and you just get used to it, it then all levels out at about 12.5:1 flat to 10k. if you follow it from 9.5k upwards to say 11.5-12 k it does sign off weak, and nothing you do with the main makes any difference, but hey nobody is perfect. Amazing how many people buy these and fit em straight out of the box without checking or fine tuning, what a waste, thanks. ;
Pablo, defo dont panic about the refund on those manifolds, i have cut them up! it was the only way i could get anything to fit, they were the closest but no cigar, all other contenders were pants, even at £157, thanks again mate.
