Fuelling issue advice needed

[PaulR]

I would like to resolve a long term fuelling problem on my '98 M900 and will be getting a dyno and help from Rosso Corse when time permits. I have (obviously....) got non-standard stuff which complicates things, but I want to eliminate as many factors as possible beforehand. I'm using K&N pod filters and a RoadRacing under engine exhaust and have what seems to be lean running/fuel starvation troubles. I already have new needles and needle jets (Factory Pro) set to highest setting, 42.5 Pilot jets and 170 Main jets. Carbs have new gaskets and the diaphragms appear ok. I was planning to overhaul the vacuum pump and change the fuel filter too (I've already had the fuel tank breather thing which is now cured)
Does anyone have any advice or suggestions for anything else? Other things to watch out for or check/replace? Obviously changing to EFI would be ideal, but that's not going to happen....

[DrD]

Is the fuel starvation throughout the throttle response/RPM range or would bigger mains again sort it?
I run DynoJet stage 2 with K&N, modded air box lid and SILs and have not run out of needle settings yet.
But see what happens when running with new fuel filter first.

[PaulR]

Starvation shows up at part throttle/highish revs - typically trying to cruise on a steady throttle (hah! not often...) at about 80 in top, or coming back onto throttle after shutting off (making mid-corner throttle control very tricky) Also if accelerated hard then shut off, a blank spot before coming back again. Seems maybe like low fuel level in float bowls, although I have checked and set float height to the best of my limited ability. Maybe the fuel pump is not keeping up? I had it dyno'd a few years ago and they put in the 170 mains which gave an increase in overall bhp, but I am more interested in rideability and throttle response than flat out power, which is why I want a dyno looking more at air/fuel ratio throughout the range than just full throttle results. I don't want to be changing carb settings if the problem lies elsewhere in the fuel delivery chain. I've already had a problem where the fuel line gets kinked when the tank is lowered!

[Mr Gremlin]

put the airbox back on !!
you have lost inlet tract length and gas flow velocity , the best way to fck up fueling is to fit pods.
:)

[Flip]

...Pod filters don't work with the standard CV carbs. You'll never be able to set them up properly so it's either put the airbox back on or buy a set of FCR's and talk to the lovely people at PDQ if you really want to keep the pod filters.

[gary tompkins]

put the airbox back on !!
you have lost inlet tract length and gas flow velocity , the best way to fck up fueling is to fit pods.
:)

Yeah that

Several others have fitted pods and failed to get bike to run properly on CV carbs

Flat slides will run ok without airbox - if you can stump up the £700 to purchase a set

[Dirty]

They look nice though :)

[gary tompkins]

I would rather have a monster that runs right than one that looks great and runs like a pig

[Dirty]

You are 100% right Gary. There is a limit to looking good. I guess you could equate cone filters to high heels. I know I look great in them but they severely impair my walking efficiency :)

[DrD]

Missed the pod fitted.
Yep - air box with modded lid and free flow air filter not pods unless you want to stump up for FCR's

[Saint aka ML]

I have not needed fcr's.... Railed setup not split.

[Nickj]

I guess you could equate cone filters to high heels. I know I look great in them but ..... )

More information there than we needed I think LOL

[PaulR]

Thanks all! I'm certainly not willing to put appearance over useability - I like the less-is-more approach and the see through the frame look, but if I have to put the airbox back on I shall. Don't know where I'll put the Stebel horn though.... I like the idea of FCRs (old school and I've never much liked CVs) but not sure about the cost. How much, Saint?
Still not sure if I should go for a dyno, or would I just be wasting money? I went for a 130 mile tootle last night and it was great on acceleration, but steady throttle always leaves it hunting and surging, and I can see that riding with the throttle pinned open is only going to end in trouble (specially as I'm at least 30 minutes away from an open road...) and while leaving the choke on a bit helps, it's a primitive solution even for me!
I'll dig out the airbox and research what to cut - if anything...

[Saint aka ML]

All parts are included but throttle assembly is cracked with piece missing (working) after off.

Will add my current K&N filter that should go on air-box with open lid cover. FCR's are 41 twin railed so for air-box use.

Need setup anyhow but frankly you can apparently make fcr's work without air-box (I would not as you loose torque).

Price 600 for lot? The way I explained it to my self is you save on petrol ;) I gained 20 miles to tank in town.

[J.P]

PaulR,
I've had all my Ducati's re-mapped and would HIGHLY recommend it if you have the time and an extra £500. Make a big difference to my 1200 Multistrada and my 1100 EVO, and would definitely make a difference to older bikes.
I would automatically factor it into a purchase in the future.
Manufacturers have regulations to adhere to and that's where all the problems come from.
You can change this and change that but you will not achieve the full potential of the engine without a remapping. You may get some of the way there but not the full potential.

[gary tompkins]

This bike has carbs and not fuel injection J.P

No ECU to remap

[J.P]

ignore everything I said then :)

[Mr Gremlin]

Thanks all! I'm certainly not willing to put appearance over useability - I like the less-is-more approach and the see through the frame look, but if I have to put the airbox back on I shall. Don't know where I'll put the Stebel horn though.... I like the idea of FCRs (old school and I've never much liked CVs) but not sure about the cost. How much, Saint?
Still not sure if I should go for a dyno, or would I just be wasting money? I went for a 130 mile tootle last night and it was great on acceleration, but steady throttle always leaves it hunting and surging, and I can see that riding with the throttle pinned open is only going to end in trouble (specially as I'm at least 30 minutes away from an open road...) and while leaving the choke on a bit helps, it's a primitive solution even for me!
I'll dig out the airbox and research what to cut - if anything...

if you put velocity stacks on , then fit the pods over the top then you can set up the fueling ok, Search "AT power throttle bodies " they can make you some that will work :)

[PaulR]

Thanks all! (I was quietly ignoring J.P, trying not to draw attention......) Funds (well, children really) won't permit FCRs, but thanks for the offer Saint. Mr G, I'm intrigued by the velocity stacks - does this mean it's just (as if it were that simple!) a resonance thing to do with inlet tract length? I'm not that hung up on the pods so I'm tending towards going back to the stock airbox, as I'd rather have smooth rideability than flatout power - and I can see the pods are no magic route to that anyway. They do make an impressive noise, but that just gets painful after a while, and the exhaust takes care of noise duties without being right in my face. Maybe just a K&N filter in the stock airbox will do for the summer....

[DrD]

You could put the velocity stacks into the std airbox (but I would still remove most of the top of that) if you could seal the air box to stack interface - hummed about doing that but just cut the top off my spare air box and kept the not so nice rubber inlets from the airbox to carbs.

[Dirty]

It's your exhaust causing all the trouble. I'll volunteer to remove and dispose of it for you :)

[PaulR]

Cheers D! Maybe you could take care of the lack of FCRs too...:chuckle::chuckle:

[PaulR]

So, following the general consensus that CVs will never work properly without the airbox, I put it back on this morning. I'd forgotten what a pain that is, and had to undo all my previous cable tidying and lose the Nautilus, but since the new air filter arrived yesterday (super quick delivery from jjcraceandrally on ebay) I got on with it, used the Factory Pro recommended jets - 42.5 pilot and 145 mains with needle on 3rd slot, went for a test.... and.....
and it still runs like s*** - different kind of s***, but still s***, surging away at low speed like it's going from 1 to 2 cylinders or running out of fuel. Better on bigger throttle openings, but still a real flat spot if you accelerate, shut off then open up again.
Rosso Corse gave me a couple of o-rings for the main jets (which I thought I had but obviously didn't...) so I'm thinking that I'll just take it to them.

[PaulR]

Put in new plugs, checked mixture screws - still useless on small throttle openings, surging away like a surging thing on its way to the festival of surging. I tried putting the snorkels back on - still the same. Removed airbox lid and filter - still exactly the same. Off to Rosso Corse tomorrow!

[DrD]

Hmmm...Sounds a bit like air leak affecting partial throttle.
Couple of basic checks

Is hose to vacuum pump (from inlet tract) ok?
Any cracks in the carb hoses?

[PaulR]

Thanks - I'll check those out. Off out with the children now, then the Tour de France, so it may be in the morning...... I don't really want to give up yet!

[PaulR]

Did a sneaky check while the pre-going out faffing about was on - no sign of any problems with hoses....
Dalston house was fun though!

[PaulR]

So, I took it to Rosso Corse and..... they were shut! Hands up who knew they were closed on Mondays and left me to it. I decided to check thoroughly once more before giving up, so having removed the feckin' airbox once more (the only good thing about pods is the easy access to the carbs) I took them apart and discovered that one of the rubber seals between the jet carrier block and carb body was damaged - maybe this was allowing too much fuel through? Both plugs looked like it was running rich, but one was as black as Newgate's knocker and sootier than Sweep's mate. I replaced both jet block seals, along with the mixture screw o-rings and the float assembly o-rings (both of which looked ok, but I don't ever want to take the little canutes apart again) Needle valves still looked fine, as did float levels, diaphragms, springs and needles. Went for a quick test and........ everything appeared to be ok! No more surging at least, but I'll have to wait to do a higher speed test as I'm at least 30 minutes from the nearest road without traffic lights every 15 metres and 30 mph limits (also the billowing clouds of smoke by the end of the road alerted me to the oil leak from the carb heater oil line union which is now , of course, almost inaccessible because of the aforementioned feckin' airbox, and which will have to be addressed before any more testing - it's like having a BSA again....)
But hey ho, things look better!

[Dirty]

Aha, glad to hear you may have got it sorted at last

[PaulR]

Thanks! All seems fine (airbox off again and oil line banjo washers replaced...) Still no higher speed test, but I went to Rosso Corse (where I met Slob - very good to meet you!) and it ran very well. So far the conclusion I'm drawing is : don't bother with pod filters on a bike with cv carbs. Also that Rosso Corse are extremely kind and helpful, and Allen's Performance are as good and reliable as ever for Mikuni carb bits.
D - sorry the exhausts didn't turn out to be the cause of all the trouble.......

[PaulR]

Finally got in a faster test on Saturday - 160 miles down the Highway to the Sun (A303) to Somerset. Fantastic! Smooth and responsive through town, then smooth and fast on motorway. Much quieter too, which is actually a bonus on longer runs, and fuel consumption averaged 42 mpg over getting out of London and then some higher speed cruising (I'm not admitting to any speeds here...)
The conclusions I'm drawing here are - if pod filters were an improvement for CV carbs, Ducati would probably have used them in the first place; thorough checking of everything pays off (the tiny seal on the jet carrier block)
I can now recommend the Factory Pro jet kit with 42.5 pilot, 145 Main and needles on 3rd notch for a M900 with standard airbox, snorkels removed and K&N air filter.
Now, if only I hadn't given away my other airbox lid, I could try a bit of cutting.......
Thanks for all advice and support!

[Dirty]

Excellent news. So are you not wondering what it might be like with the pods on now the jet block seal issue is fixed? :devil:

I'll get my coat...

[PaulR]

Ha ha! I'm not taking the airbox off again - I'd like to find space to put the Stebel back on though....... I'm off for a few weeks, so I'm just going to ride as much as I can (but a certain amount of tinkering is inevitable) Pod intake noise was cool around town, but a pain in the ears on open roads.... See you at a london meet after the summer?

[Dirty]

Fair enough, I don't blame you. Now it's sorted best left alone. But I wonder.........:scratch::mand:

Yes, see you at a meet. Or if you fancy a 2 man tunnel run one evening let me know! :flag: