Trouble Getting Going

Started by ChrisK, March 10, 2014, 03:19:06 PM

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koko64

The electrodes are a worry. It's leaning out and getting worse as the revs rise if I understand the white porcelain deep in the plug (unseen to us) as well as the white electrodes. If that's because of lean jetting or a dodgey pump we'll see. The bypass test will at least sort the pump from the equation.
You're right about the bike not being run enough yet to get a definitive indication of jetting. If the pumps alright I think too lean though. At least we know the soot on the plugs isn't from a choke system, so I'm guessing fat slow jets. ;D

An open airbox usually needs more fuel via the needle and main jets, but I don't know what a W motor might want, maybe a little less at a guess. It's often a dodgey vacuum petcock that starves a motor (how many of those bloody things have failed on this forum). Clagged fuel filters too. I've seen a bronze gauze filter glued shut by fuel additives, even after being soaked in carb cleaner. I had Honda's with the same petcock problem and on race bikes we removed perfectly good petcocks that couldn't keep up with race jetting.
2015 Scrambler 800

ChrisK

Here's a video I took of how it's running. Hopefully you guys can hear it alright over the plates.

1998 M900
2007 CBR600RR Track Bike
1982 Virago 920 Cafe/Fighter Project
1980 Lambretta Moped
Supra Boats enthusiast

"There is no minimum."  - some guy.

koko64

#107
Was the bike started cold with no squirts of the accelerator pump, or was it warm already? If that motor was cold, then it started way too easy (even more so if it's cold there and you didn't prime with the accelerator pumps). That would mean too fat slow jets. If the motor was warm then disregard that.

Sounded pretty normal at idle. Couldn't judge at higher revs due to the clutch clatter. [evil] The sound may be clearer on others' computers.

I think bypassing the fuel pump as Howie suggested is a good idea, just to tick that off the list. You will need a full tank with gravity feed. See if it starves for fuel or clears up. If no difference, then you need to order a range of slow and main jets. If it's jetting related, then I would go out on a limb and say order 160, 162.5 and 165 main jets x2, and 50, 52 and 55 slow jets x2. The unused jets are worth keeping as you plan to go to V heads or other mods so you may well have to tune again. The jets aren't expensive.
I would guess the mild W heads don't need as much jetting, so say start with 160 mains and 50 slow jets, but that's a guess. There is every chance the logic works opposite. I hope someone who has tuned a W 900 motor will chime in as I'm guessing for a reasonable baseline. See what speeddog says, because maybe the mild cams and small W valves don't let much A/F mixture in meaning you really need to start with 165s and 55s! Ah the joys of tuning! [laugh]

IIRC you already changed to a manual fuel tap and have a fresh filter. But do the pump bypass test first.
2015 Scrambler 800

koko64

Just so you know, I pmed speeddog about this thread. I think he can help you.
(Mild post whore post) ;D
2015 Scrambler 800

Speeddog

I've not done FCR's on a W-head 900.

Try this as a starting point, worked well on a V-head 900:

air screws  1t    
fuel screws 2t   
slow jets 52
Needle clips at -5th groove from the top
Mains 160   


- - - - - Valley Desmo Service - - - - -
Reseda, CA

(951) 640-8908


~~~ "We've rearranged the deck chairs, refilled the champagne glasses, and the band sounds great. This is fine." - Alberto Puig ~~~

Speeddog

I searched through this thread, and didn't find it...

Can you describe mods and configuration of the motor?

pods, stock filter, cut lid, stock lid, 39's, 41's, stock mid-pipe, aftermarket mid-pipe, stock cans, no cans, X-box.....
- - - - - Valley Desmo Service - - - - -
Reseda, CA

(951) 640-8908


~~~ "We've rearranged the deck chairs, refilled the champagne glasses, and the band sounds great. This is fine." - Alberto Puig ~~~

koko64

#111
Pretty sure its a 98 M900 W heads, FCR41s, Exactfit coils, open airbox (not sure if chopped or drilled), lightened flywheel, K&N filter and free flowing cans (dunno which type).
2015 Scrambler 800

ChrisK

#112
Koko, the motor was pretty well warm when I made that video.

You were pretty spot on with the mods:

98 900W
Lightened Flywheel
FCR41
Wide open air box with K&N
ExactFit Coils
OEM Headers
Danmoto Slipons


I still have the vacuum petcock and OEM fuel pump. So sometime today I will run a fuel line straight from the tank to the carbs and see what happens. If the situation improves I will do a manual petcock and new pump. If it doesn't improve I will order a range of slow and main jets and drop the needle clip position down.

Sound right?
1998 M900
2007 CBR600RR Track Bike
1982 Virago 920 Cafe/Fighter Project
1980 Lambretta Moped
Supra Boats enthusiast

"There is no minimum."  - some guy.

koko64

You may have  to rejet anyway, but bypass the petcock to the pump first off, as your pump may be fine. Reports of pumps failing do sometimes occur here, but  petcock failures are common.
Manual petcocks are a good mod and cheaper than oem pumps. Mikuni pump rebuild kits are available however, but my money is on the notorious petcock.
2015 Scrambler 800

ChrisK

A question I just thought about sitting here: The FCR's came with a small fuel filter at the end of about 6 inches of fuel line. You take your existing fuel line and hook it up to the upstream end of that filter. Is it necessary to have both your original filter and that smaller filter? Could that be problematic? I don't know much about fuel filters.

I'm still going to investigate the petcock first, then the pump. Just thinking out loud I suppose.
1998 M900
2007 CBR600RR Track Bike
1982 Virago 920 Cafe/Fighter Project
1980 Lambretta Moped
Supra Boats enthusiast

"There is no minimum."  - some guy.

Speeddog

Bypass the vacuum petcock, install a manual valve.

FCR's will occasionally hang a float valve, then you'll get fuel in the crankcase.
Best to always have a valve.

For no airbox top, 55 PJ may be a better start.
- - - - - Valley Desmo Service - - - - -
Reseda, CA

(951) 640-8908


~~~ "We've rearranged the deck chairs, refilled the champagne glasses, and the band sounds great. This is fine." - Alberto Puig ~~~

ChrisK

Quote from: Speeddog on March 13, 2014, 09:48:30 AM
Bypass the vacuum petcock, install a manual valve.

Doing this after work. Where do you guys normally mount these, for easy, firm access?
1998 M900
2007 CBR600RR Track Bike
1982 Virago 920 Cafe/Fighter Project
1980 Lambretta Moped
Supra Boats enthusiast

"There is no minimum."  - some guy.

silas

Chris, fyi, I have the fuel filter that came w/ the fcrs on my bike as well as a napa one under the tank w/ no problems. I have an aftermarket mikuni fuel pump w/ a Pingel fuel tap, both inline on the outside / left side of frame.

My W headed '98 has 165 mains in the 41's thanks to koko and brad's advice. Pulls harder & accellerates better at freeway speeds than the stock 155's. 

I added the W heads...small difference mostly up top..slightly more vibrations too...
Ride fast, ride safe
'98 M900, '92 Yamaha TDM850

Howie

Install the manual petcock anyway.  My experience is they often fail in the open position.  This is how mine is mounted, not pretty, but easy access and the fuel line is moved away from the hot engine a bit.  You want it to be 5/16.


ChrisK

Eliminated the petcock and the pump from the equation. No better. On to jetting?
1998 M900
2007 CBR600RR Track Bike
1982 Virago 920 Cafe/Fighter Project
1980 Lambretta Moped
Supra Boats enthusiast

"There is no minimum."  - some guy.