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Author Topic: Gosh Darnit - It was all going too well!  (Read 1871 times)

Suitor_Stu

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Gosh Darnit - It was all going too well!
« on: April 11, 2008, 06:23:57 PM »
Okay guys, bear with me here while is spin you a tale...

Basically, after getting my bike (2002 Bullet 500 classic 4speed no ES) back working again after doing my service everything was fine.  I swapped out the original air filter for a S&B pancake one, did the duckbill breather mod, removed PAV, have kept the stock silencer for the time being and re-jetted the carb (120main, 27.5pilot and kept the standard needle - with clip in the centre position) and stuck a fresh spark plug in.  All was going well except for needing some throttle on starting (still doesen't like the choke being used) but I put that down to the fact I still hadn't properly adjusted the idle mix.  Probably did close to 50 miles with this setting and nothing majorly wrong.  Anyway, carb started leaking gas from the float overfill tube, so I dismantled it and low and behold, the float circuit was jammed open, so I sorted that and gave the bowl a wee clean.

Then I re-installed the carb.  This was when the problem started.  The bike pulls fine from idle to about 1/4 or so throttle opening, but then is very eratic inbetween - not wanting to hold a steady speed, and popping too.  If i open the throttle to 3/4+ then the bike pulls like a train and doesn't falter, but when I back off the throttle into the 'cruise' position (around 1/2 or so) the same problems occur again.  It is also fine if I'm just above Idle, but that's not much use on modern roads!  Just spent the best part of 2-3 hrs fiddling with the idle settings trying to make absolutely sure it's nothing to do with that (since this was the only thing I have adjusted since re-installing the carb), so the bike now idles fine but is still having problems in the midrange.  Which brings me neatly to the needle.  If I move the clip one or 2 spaces down on the needle (to richen things up) does this sound like it will rectify the problem?  I'm mainly asking because I am hesitant to do this because things seemed to be working fine before the idle mix was sorted...do you think it could be something more complicated?  I've checked all the connections in the carb and as far as I'm aware, its airtight, so I'm fairly sure it's not leaking at all.  And I haven't adjusted the tappets or points, but as far as i'm aware there is no adjustment needed (or at least there wasn't when I was doing the service).

Sorry for another long post guys, but I've just been so stumped as to what has happened that I'm just a wee bit frustrated - so taking it out on the computer!  Any help will be really appreciated!

Cheers, Stu

dogbone

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Re: Gosh Darnit - It was all going too well!
« Reply #1 on: April 11, 2008, 07:01:26 PM »
Stu 120 may be still too little. when my engine was stock, I used a 125 w/ the needle max rich. work with the needle position.
 
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geoffbaker

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Re: Gosh Darnit - It was all going too well!
« Reply #2 on: April 11, 2008, 07:32:37 PM »
Make sure your throttle cable isn't sticking and you can turn the throttle handle easily. You should be able to hear the slide "clink" when you let go of the throttle as it closes.

I've had no trouble with the factory setting for the needle. I had it higher but it turned out I didn't need it once I got the idle properly adjusted.

Also, did you check the pilot jet to make sure it wasn't gummed up too?

LotusSevenMan

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Re: Gosh Darnit - It was all going too well!
« Reply #3 on: April 11, 2008, 07:47:21 PM »
When you removed the PAV you did block up the hole left in the intake manifold from the removal of that metal tube did you? It's still blocked OK? If not it'll run lean giving symptoms you advise.
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deejay

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Re: Gosh Darnit - It was all going too well!
« Reply #4 on: April 11, 2008, 08:37:35 PM »
Stu, I'm running a similar set-up to you, I am running a 127.5 main. I would richen that sucker up, then its all needle adjustment and air mixture screw adjustment.

Thumper

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Re: Gosh Darnit - It was all going too well!
« Reply #5 on: April 11, 2008, 09:47:05 PM »
Stu,

I agree with your assessment that you're looking at a needle position issue.

(BTW, you might look at this if you have not already: http://www.enfieldmotorcycles.com/forum/index.php/topic,190.0.html)

So is it a rich or lean issue?

You have retained the stock exhaust therefore your mixture could very well be rich since you increased the jet sizes. A person can run with no air filtration at all and still have the spent gases bottle-necked at the exhaust.

It should be easy enough for you to determine. Lower the needle *one* position and see if the problem worsens. If it does, raise it two positions and see if that cures it. If you feel strongly that it's a lean condition, then reverse the movement as I've described them.

You can also look for the most common symptoms prior to fiddling with the needle in order to get a better indication of which direction to go:

Run the bike (fully warmed) at that nasty throttle position and pay close attention. Do you get a pop or backfire? Do you get a stumble? (These are hard to describe, but my experience is that the former are lean while the latter is rich).

More obvious and a better measure is: At a constant speed, do you see any white smoke coming out of the exhaust? If so, it is likely rich.

Another good measure is to run for about a minute at that throttle position and then chop the throttle and ignition to examine the plug. Is it wet, black? Again, if so, it's rich.

Save your idle adjustment for last. It contributes least to the overall mixture and you spend less time there than anywhere else (although I'm not saying to just let it idle poorly).

BTW, after I increased the pilot jet size on the idle circuit of my Ural, it preferred to be started without choke on all but the very coldest days. I wonder if you're experiencing a similar condition with yours...

Good luck and let us know what you find out.

Matt
« Last Edit: April 11, 2008, 09:57:21 PM by Thumper »

Suitor_Stu

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Re: Gosh Darnit - It was all going too well!
« Reply #6 on: April 17, 2008, 01:41:13 PM »
***WARNING LONG POST***

Right guys, time for an update.  There has been some nice weather here recently, so I gave myself a break from studying for my uni exams and decided to tinker a bit.  Thanks for all your help, I think I may have fixed the problem (for the time being at least).

@LSM, that was the first thing I checked to be honest.  I did the prescribed 'self tapping screw and silicone sealant' job on it, so just checked to make sure it still is fitted properly, and it didn't appear to be leaking or anything.  I also replaced the rubber intake manifold as suggested by pretty much everyone at the service too so that ruled out that link.

@geoffbaker, throttle was fine too - was a bit paranoid about that one since I'm still not pro. at removing/refitting carb and throttle bodies - esp with the tank in place!  But it dis indeed clunk, and I observed it through the air intake side as I turned the bars and made sure that the throttle body did not lift at all.

@Thumper, it was definately popping (so lean midrange? but see my findings below, they may contradict this, so maybe it wasn't a 'pop' as you describe it)!  Infact when I was on my way home that last time I passed a few cyclists (the pedal kind) and damn near killed them cause i had a backfire right beside one of them.  I put my hand up to apologise, but I felt like a right twit!

With regard to jetting, thanks to all who pitched in, here are my findings.

Before service, jets were stock and needle clip was in 2nd from bottom position.  Got quite a few problems with misfiring before I did the service, and low and behold the plug was covered in soot when I took it out.  So I kinda knew my bike wasn't gona like big jets just quite yet (waiting for new exhaust for that!)

First off (after service), the carb was fitted with 120main and needle clip in middle.  About 30miles after service (it was a fresh plug at service) this was plug colour;


Brown, but looking quite dark.  Anyway, after I started having all the problems I described earlier, I had to use a bit more of the throttle to get around since it wasn't liking the midrange.  After my last trip just before I posted on here, with the same settings as before, but with about 50 more miles on it, started to look a lot more black


I stuck a new plug in and decided to drop the main jet to a 117.5 ( i thought the 120 was maybe causing the whole mixture to become rich and fouling the plug with more miles) but richen the needle up (1 clip down).  I know I should have probably done them one at a time, but basically this was my decided treatment and I was sticking to it!  Anyway, after going for a nice 50 mile jaunt yesterday (where I was using all of the rev range, but mainly cruising at 50-60mph).  Had a wee peek at the plug after some midrange riding and this was the result (very good light cause it was so sunny!)


That looks like a nice chocolate brown/cafe au lait colour there.  Would you all agree, or do you think it's too light and I should richen up a bit more?  It's a bit more difficult to start now, got to give it a bit of throttle, but seems spot on after it's warmed up.  My only concern is that even though it's a bit more difficult to start, it still refuses to start at all with the choke on!  I though that this indicates a rich runner, but i've always had that problem even from bog stock day1...

Anyway, thanks again for your help!

Cheers, Stu

Thumper

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Re: Gosh Darnit - It was all going too well!
« Reply #7 on: April 17, 2008, 03:34:15 PM »
SS,

Good job!

As for the new chocolate color: looks good to me. More important than plug color is performance. I assume that an acceptable level of performance accompanies that color? I never change carb settings based on plug color. I check plug conditions as a result poor performance.

Regarding the choke: If your idle circuit A/F mixture is rich enough it will negate the need for choke. Note that I am not saying this is correct - just saying that if you fatten-up that A/F mix to be overly rich you won't need a choke. (As I indicated previously, this was the case with a Ural I had after I enlarged the pilot jet). If your idle circuit A/F mixture is so rich that it negates the need for a choke - then there's a good chance that it's too rich to have a smooth idle.

If your idle is smooth and you can start the bike (allowing for the slightly more difficult start and slight throttle opening that you've mentioned) - I wouldn't worry about it! No one says you have to use the choke. If it's running too lean at idle as it warms up, you'll know it.

Since you indicate this happened when it was stock ("it still refuses to start at all with the choke on!  I though that this indicates a rich runner, but i've always had that problem even from bog stock day1...") I'd suggest that if you feel it needs further investigating:
1) Meticulously verify that the choke mechanism is working the way you think it should - from lever to inside the carb. If it is adjustable, examine that as well.
2) Ensure that the idle circuit in the carb is not blocked. Visual inspection, compressed air and an ultra-thin beading needle can help. (many people recommend against any metal wire or needle being used to probe passages. I've found that it works as long as you take care not to deform soft brass or break the wire itself off in the passage).
3) Ensure that the idle adjustment mechanisms mechanically work as expected (idle speed screw and idle A/F mixture screw).
4) You have found the main jet to be too rich and addressed that. I'd suggest you put back in the stock pilot jet.

Matt