howdy all, i just pulled my fcr 39s off of my m900 for a good scrubbing and blowing out of the passageways. i had a sticking high idle and suspected sync was needed. didn't look bad, but figured i should go ahead and clean them up while they were off.
threw them back on the bike tonight and damn near killed the battery trying to get her to crank. if f twisted throttle several times, i could get it to fire, but would die very quickly. stock fuel pump and petcock (which i'm about to rebuild and replace) so i was wondering if maybe they need to be "primed" by filling the float bowls or something so it'll run and build up vacuum and get the pump going. Is this just a ridiculous thought and there is obviously something else wrong? Just seems like it doesn't have enough fuel to maintain running.
are there any general difficulties in starting! after a carb rebuild? i remember after a rebuild of an old CV carb on my old zuk 650 i had similar problems and it had a vacuum petcock too. can't remember, but i think a bunch of starter fluid straight to the intake finally got it going.
thanks for any help! now i need a [drink].
steven
Any takers? Feel free to speculate...
Quote from: svr on February 26, 2010, 12:12:08 PM
Any takers? Feel free to speculate...
It's possible the pump hadn't filled the bowls, or the petcock stuck.
The petcocks usually fail by dumping fuel into the horizontal manifold.
I've had good success starting bikes using the method you described; starting fluid sprayed in as you crank the engine.
Contact cleaner works too.
Of course, if the engine backfires, it may be a bit exciting.
Safer method is only spray when the engine isn't turning.
Quote from: Speeddog on February 27, 2010, 07:19:33 AM
I've had good success starting bikes using the method you described; starting fluid sprayed in as you crank the engine.
Contact cleaner works too.
Of course, if the engine backfires, it may be a bit exciting.
Safer method is only spray when the engine isn't turning.
I like the cranking method better.
Ether can lock up a motor too easy.
I was assuming that he wouldn't go overboard on the spraying. [laugh]
But we are dispensing advice on the internet, so anything could happen.
<No disrespect intended to the OP>
Quote from: Speeddog on February 27, 2010, 07:26:02 AM
I was assuming that he wouldn't go overboard on the spraying. [laugh]
But we are dispensing advice on the internet, so anything could happen.
<No disrespect intended to the OP>
Yeah...
it seems the OP has the process down.
Ether is hard on rings no matter how you use it, but worse if you static spray IMO.
I etherized a lawnmower once, it was not pretty.
Quote from: howie on February 27, 2010, 01:07:52 PM
I etherized a lawnmower once, it was not pretty.
That poor Briggs/Tecumseh didn't stand a chance... [laugh]
Thanks for the tips eveybody. I dd Luke u guys suggested an filled each cylinder with ether, and fired her up. Is it ok for 30 ft blueflames to shoot out the exhaust and air cleaners? Kidding. I think IM onto what's up but illwait til IM sure to expose my idiocy.
Loosen fuel line at bowls and crank a few secs.
Does it fump freely? If so, pump & petcock probably OK.
Plugs don`t get wet?
Well, i haven't solved this issue. Here's what I've done:
Cleaned carb multiple times, adjusted sync.
Replaced vacuum petcock with manual valve.
Installed an adjustable mixture pilot thumbscrew for easy adjustments.
Carb has the adjustable slow air jet. I've got it at 1 turn out right now.
Carb is getting fuel to float bowl and the accelerator pumps are working.
I've rebuilt the vac fuel pump and I've also tried bypassing it as well and doing a gravity feed.
Replaced all fuel lines and vacuum lines.
All this and it will fire up if i dump several squirts of fuel via accel pump before cranking. It will run for a few seconds then die. Won't start again until I twist throttle several times and dump more fuel in. I can continue this ad infinitum or until the battery finally dies.
It almost seems as if the carb will not pull fuel from the float bowl since its starting with excess fuel dumped to the cylinders. Is there any condition that would cause this? If you can help, i will [bow_down]
When it dies, plugs are dry?
Where did you buy the FCR`s, do you know your jettings?
If so, please share.
You sure of no tank vent problemos?
pretty sure its not a vent issue. same deal with the gas cap open. i also blew air through the vent and overflow tubes and they appear clear.
the carbs came on the bike when i bought it. i'll try to recall all the jetting and once i pull the carbs again, i'll update this. i know the pilot is a 60 and i think 155 main. can't recall the main air size so once i pull them again i'll derby.
as far as plug condition, i'm dumping so much fuel in that they are wet to my recollection, but i need to go start it and then pull them immediately to be sure. i know they have come out wet previously, but can't recall if i had pulled the throttle before that so i'll get back to you on that.
any chance this could be an ignition/coil or related problem?
You do have good spark on both?
Got spark using a spark tester. I assume plugs are ok since both cylinders fire if I dump fuel in there. Any thoughts? Thanks
Don't assume the plugs are OK. You want to pull and inspect them anyway.
Will do. Is it possible they could fire the bike for a few seconds but still be bad?
They are great carbs.
How far out is your Idle Mixture Screw turned? (You fitted the fancy ones, so that will be easier than getting the right size screwdriver up there). Have you set your Idle speed adjuster (knob on a cable, wish they were all that easy) back to where it was before you pulled the carbs apart? No offence intended if you have already reset these adjustments to where they were before the rebuild.
I would have the idle mixture on the rich side (maybe 2-2 1/2 or even 3 turns) and your idle speed set at a higher speed, say 1300-1400 rpm. Since you cant adjust your idle since it wont idle , wind the Idle Speed Knob in quite a bit and give the carb a few squirts if that wont flood it. Try starting with that. I needed a fast, rich idle to get the thing going more than a few seconds.
I would put that slow air screw back to 1 1/2 turns. By bike dropped idle speed substantially with it one turn out.
A set of standard plugs is cheap as has been suggested and you got spares if thats not it.
Sorry had to go to work, I'm back on. The reason I suggest a fast idle and rich Idle Mixture Screw setting is because I found that necessary to get the motor started before I could tune it after installing the carbs. The bike displayed the same symptoms as yours, run for a second or so and die. Theres no choke/enrichener so the accelerator pump is it. Therefore an idle mixtire on the rich side is important. Even more so the case if the weather is cold. Normally you would expect the IMS to be 1-2 turns out for highest/strongest idle speed with the correct slow jet. That 60 slow jet will help if it's cold. Its on the rich side as a baseline setting for a reason.
Another thing, your float level should be 9mm. I hope the floats weren't disturbed too much with the clean/rebuild. They can mess things up if they are out. Patrick Burns site has great tuning info on this. You can access it via Cal Cycleworks site.
Tell us how you go.
thanks for the tips. i've tried the high idle speed and that does help keep it running for a couple more seconds, but still dies. I've tried anywhere from closed to 3 turns out on the idle mix. i'll screw it way out to see if it helps keep it running, but with a 60 pilot i'm sure it will need to be turned in after i get it running. i'll play with the slow air screw a bit too and see how that goes.
on another note, i'm beginning to suspect something else, so let me give you some back story. few weeks ago, the bike just fired up like a champ. easier to start than my efi bikes i've had. after getting warm, i noticed a sticking high idle though and wanted to take care of that. i checked carb sync via manometer and all appeared ok. i go out for a long ride and after fully warmed up, the bike lost power and was sputtering like out of gas. stopped, got gas, still sputtering. stumbled my way back home. pulled plugs, and they looked ok. so the hanging high idle and this sputtering, i thought ok i've got carb issues maybe air leak and clogged jets or something. pulled carbs, cleaned, replaced, no start. i've repeated carb cleaning a few times, changed fuel lines, filter, petcock, pump, tried gravity feed. Still no dice. So, getting back to my new suspect: the regulator/rectifier. I had begun to notice tach twitching before this all went to hell, so perhaps its related. coils ohm out good. I've got good spark on both cylinders for as long as i hold the starter (much longer than it will run), so i'm thinking ignition is all good. I've done a bit of research and when regulators are failing, these are some possible symptoms. i've got a cheap one coming in off ebay just to see. other thougts are maybe stator (?) but i don't know symptoms there.
I've also got seals forthe vacuum release plate on the fcrs coming in as well, but its getting to the point where i'm just throwing parts at it.
lemme know what u guys think.
A carbed bike with a mechanical fuel pump should be able to run as long as there is enough power in the battery to crank and enough reserve to run the ignition. Want to give the ignition a little more power? Pull the headlight fuse. I assume you went through the base settings after doing the carbs?
Well, I got her running! Biggest issue was the slow air screw. Very sensitive little beast that is. I was trying running it between .5 and 1.5 turns out. Turned to to about .25 out and she fired right up. So, now I want to do a bit of optimization and perhaps some of you carb gurus can help me out. The .25 turns out on the slow air screw seems a bit restrictive. Any thought on this with 39's on a M900? Also, my slow fuel jet is a 60 which seems to be a bit rich, correct? This also jives with the fact that fully closing my mixture screws won't kill the bike (idle slows a bit, but won't die). Also, my needle is on the bottom clip (closest to the taper), which seems non-ideal.
Here's what i'm thinking as possibilities: 1. 58 slow fuel so that i can run the mixture screw at about .75 turns out. 2. slightly richer needle so that i can run it a few clip spaces up. But what to do about that slow air screw. Go to a smaller main air jet so that the slow air screw can be run at 1-1.5 turns?
FWIW, plugs looked a bit rich after idling for a while yesterday. I'm running pods, but do the air screw adjustment with the filters off and bike running. Are pods just so much less restrictive than an open airbox that they could account for needing a much smaller air screw setting? Alsok, she'll chug and die if i blip the throttle too quick (worse than before i tore into the carbs).
thanks for everyones help so far!
Quote from: svr on March 22, 2010, 10:12:55 AM
Well, I got her running! Biggest issue was the slow air screw. Very sensitive little beast that is. I was trying running it between .5 and 1.5 turns out. Turned to to about .25 out and she fired right up. So, now I want to do a bit of optimization and perhaps some of you carb gurus can help me out. The .25 turns out on the slow air screw seems a bit restrictive. Any thought on this with 39's on a M900? Also, my slow fuel jet is a 60 which seems to be a bit rich, correct? This also jives with the fact that fully closing my mixture screws won't kill the bike (idle slows a bit, but won't die). Also, my needle is on the bottom clip (closest to the taper), which seems non-ideal.
Here's what i'm thinking as possibilities: 1. 58 slow fuel so that i can run the mixture screw at about .75 turns out. 2. slightly richer needle so that i can run it a few clip spaces up. But what to do about that slow air screw. Go to a smaller main air jet so that the slow air screw can be run at 1-1.5 turns?
FWIW, plugs looked a bit rich after idling for a while yesterday. I'm running pods, but do the air screw adjustment with the filters off and bike running. Are pods just so much less restrictive than an open airbox that they could account for needing a much smaller air screw setting? Alsok, she'll chug and die if i blip the throttle too quick (worse than before i tore into the carbs).
thanks for everyones help so far!
Hi Steve
Great to here that it's running.
They come delivered with 155 mains and EMT needle on pos-n#3. That right? Those settings are for a pretty stock set up. Main jet and needle pos-n will have to be affected by open air box/pods in my experience.
What needle is it? EMT or other size/taper?
Since the needle root diameter, slow jet and slow air jet overlap off idle a bit, your slow air jet tuning may not be true untill you sort your slow fuel jet (or float level for that matter).
You shouldn't have to buy other slow air jets, being adjustable and worth their weight, although that's a long way turned in. You would just be buying a small one anyway. Save your dough. That chugging is possibly symptomatic of the slow air jet being turned way in as it effects how the bike comes off a closed throttle. Is it a
rich chug, or a
lean spit and miss? I would have thought that a small slow air setting was indicative of lean slow fueling. I'm still fiddling with that one between 1 and 1 1/2 turns out.
Since slow fuel jets are cheap in your part of the world (Cal Cycleworks has good deals), I'd buy a few sizes with the money saved on having an adjustable slow air jet, say 50-58 to save on freight. I tried 58s but they were too rich. I'm running 52s on advice from your part of the world. They are still on the rich side but hey there's winter to come. My Idle mixture screw is out 1 turn as a consequence. It might go out to 1 1/2 turns in the middle of winter. It has been suggested to me that differences in fuel in different parts of the world means tuning advice doesn't always travel well.
I'm running 165 main jets (pretty big I reckon) and needle pos-n #6 out of #7. The same as my old Superlight with 39s and very similar mods to my current bike: pistons, porting, open air box, advanced cams.
From what I've read and been advised, I would not touch the main air jet if it is the common as delivered 200 size. Sometimes a high needle pos-n is indicative of a too small main jet. Main jet tuning first could save you money on an uneccessary needle purchase.
How are the float levels, if they are out they will give you hell on most carbs I've played with. Bad float levels can corrupt your other adjustments. 9mm for FCRs is the figure most mentioned to me, (I've talked to a few people, you can PM me about that if you like).
Just some stuff to consider.
Good luck.