Help me Leon! (and everybody) RESOLVED!!!

[Jethro]

First off, this is a continuation of this post:
http://www.thegsresources.com/_forum/viewtopic.php?t=32912

It got to be a technical post when I didn't mean it to be.

Leon, can you explain to me the difference between the needle circuit and the main circuit? I'm only familiar with the way the manual explains slow speed circuit (which I understand as the pilot circuit) and main system.

Thanks man. The good news is I finally figured out my starting problem!!! It seemed I neglected to clean the float bowl covers, the starter jet port in the bowl itself was clogged in two carbs. Starts in an instant! Still a little cold blooded, but starts nice and choke works as it should. All and all normal.

 

[pano]

Just as a reference with about the same bike

I have got K&N pods filters, dynojet kit with the dj138 mains and the needles on the fifth notch from the top. Everthing else on the carbs are the stock parts. I do need full choke on start and then reduce it slowly while it warms up which takes about 5 minutes. Last year I put 140 Mikuni mains in because I thought they were just slightly larger than the dj138's and on one trip to the mountains I bogged big time in fifth gear climbing the mountain. Too rich. With the dj138's my plugs are not clean and white but have a sooty used appearance. When warmed up it pulls well all around and has no flat spots. Oh Yeah, mixture screws are about 3-4 out with one carb 4-5 out.

 

[daveo]

Re: Help me Leon! (and everybody)

Re: Help me Leon! (and everybody)

can you explain to me the difference between the needle circuit and the main circuit?

glad to hear you got your carbs right :lol: the needle has a taper and varying thickness to it, these are used to control fuel flow,(taper becomes narrower as needle raises, allowing more fuel) with the size of the main jet, below the WOT position, which is the main circuit only. On dynojet kits they give you a set of their needles with the mains also, the needles are of different thickness and taper than the stock. So the needle circuit is always effected by the main circuit, but not vice-a-versa

 

[Jethro]

Thanks Pano. Do the mixture screws affect slow and main cirucits on the carbs?

I'm confused becuase I have 145 Mikunis in there, needles at the highest notch and I'm still getting wicked lean reading on the plugs. I seem to have the pilot circut running nice, good plug reads there, but at WOT the bike is really cuttin out now, almost sounds like I threw a rod (but didn't) with a nasty knocking. The plugs at 3800rpms is ok, still leaner than I'd like, but if the mixture screws affect the entire range, they might need more attention. I thought they just affected the pilot circut.

 

[pano]

I am pretty sure the mixture screws work the idle circuit mainly. Unlike computerized fuel injection where the computer can change the mixture as needed the carb works as a series of overlapping fuel circuits that if tuned properly are seamless.

Mixture screws - idle
needles - off idle and mid range
mains - WOT


Just be careful with that lean condition you dont want to cook anything. Did you say you had K&N's? If you don't maybe your filters allow more air in than mine.

Are you sure the bowls are getting plent of gas? Maybe the vent line from the tank is pinched and although you have plenty of pipe the air can't get back in the tank fast enough.

 

[focus frenzy]

sorry for the delay, the needles are part of the mains, they regulate how much fuel flows from the main jets as they move in and out of the mains.
raising the needle will richen up the mid range of the throotle positions but normaly has little effect on wide open throttle as the taper of the average needle drops off to nearly straight towards the end of the needle.

what do you have your float level set at? (important and will have a effect on tune)
is your petcock (lol) flowing enough fuel?
if you are using a inline fuel filter, is it flowing enough fuel? (not all filters work with gravity flow fuel systems)
could there be a kink in the fuel line restricting flow?

if not enough fuel is getting to the carbs, it will start, idle, and run around town slowly just fine, but rear its ugly head when you get up to highway speeds or get on it as the restricted flow will not be able to keep up with the demand of the carbs, and the fuel level in the bowls will drop and the bike will lean out.

plenty of people have gone nuts messing with carbs trying to figure out a lean run condition when the real problem was not enough gas getting to the carbs.

 

[Jethro]

The petcock is working perfectly, the fuel line is not kinked and I don't use an inline fuel filter. I have set the floats as the manual suggests, but tonight I am going to ensure the float level is correct with a hose connected to the float bowl drain. Just made an adapter last night by drilling through an old float bowl drain screw. I don't know what else to do, how can 145 mains and my needles at the max height still be be too lean?

How long do I have to run the bike to get a good plug read? I basically drove down the road about 1/2 mile and turned around, keeping the bike at 3800 on the tach on the 1/2 mile back. Is that long enough to give a proper plug read?

 

[Hoomgar]

Jethro, sorry to say this but your plight is educating me so I am watching here. I hope you get it soon.

Quick question:

WOT = wide open throttle?

 

[daveo]

Thanks Pano. Do the mixture screws affect slow and main cirucits on the carbs?

I'm confused becuase I have 145 Mikunis in there, needles at the highest notch and I'm still getting wicked lean reading on the plugs.

If the needles clips are in their highest slot, that would be why you're too lean, higher slot=lower needle=leaner mix, unless I'm misunderstanding.... and you're rich at the top, I'd go down 2 sizes on the main, and down to the middle slot on the needles, the mixture screws only affect idle and a very little above, the way to check plugs is hold it at whatever RPM you're trying to adjust and then shut off engine using kill switch, with throttle held open at given RPM, don't let it ramp down...kill the ignition and pull a plug

 

[Jethro]

Yup, WOT= wide open throttle.

Man, Mark. This jetting thing has just about got me beat down. It a damn good thing I sloved the starting issue, though. If I didn't have some encouraging progress, y'all might have seen a new "Road Ready Bike For Sale". Even though it's only road ready to 6000 rpms. Anything beyond that and it's nothing but sputtering, banging and poping. Sounds bad. I did elimninate the popping at deceleration though, the big boy jets and needles at the max, must have gotten rid of the leaness enough to at least stop that. I'm about to order a 150 and a 160 main- 160 being the largest Mikuni main jet made! I just don't understand how I can be so freakin' lean with the setting I have right now!

I'm about 1 week away from making a call to my credit union. A new bike is getting to be more attractive each and every day, payment and all...

 

[Jethro]

If the needles clips are in their highest slot, that would be why you're too lean, higher slot=lower needle=leaner mix, unless I'm misunderstanding....

Sorry, my logic and choice of words is confusing to many, and sometimes myself. Whan I say highest setting I actually mean highest fuel flow- lowest notch on the needles. With the lowest notch on the needles and 145 mains, I am still getting plugs that look like they have been painted with off-white glossy paint. The center ceramic is as clean as it was when it came off the shelf.

 

[Hoomgar]

Man Jethro, don't hole a piston trying to get there buddy. There is one evil element in the mix here. You just need to find it. There is no way a bore of your size and carbs your size require the largest mains made. That alone has to tell you that the main jet sizes and maybe even the needle adjustments are not your issue. Start looking elsewhere, really hard. Go back and check the stuff you say you already checked. Your missing something.

I know jack crap about jetting but am smart enough to know that from what I am reading your problem does not seem to be the mains or the needles.

You know the saying, if what your doing isn't working after several tries, stop doing it and try something else.

Dig deeper man. Something else is wrong I fear.

 

[daveo]

What type of air filters are you using? K&N/Dynojets flow more than a generic pod filter, that's why they replace the stock needles and jets with DJ parts (they don't mix and match either, must use DJ needles with DJ jets)....also the slide lift hole is drilled larger, which if not done will cause leanness, as the slide (and needle) doesn't lift as well. The carb overflow vent lines should also be removed from the overflow vents, those can also cause leanness....

 

[Mr. Jiggles]

That's what I'm a bit unclear on - are you using dynojets or mikuni's? BTW, you can order 5 sets of dynojet mains (5x4) for $30 directly from dynojet - http://www.dynojet.com/jetkits/jetassortment.php (I actually did that last week).

 

[Jethro]

daveo Posted: Wed Mar 23, 2005 7:46 am Post subject:

--------------------------------------------------------------------------------

What type of air filters are you using? K&N/Dynojets flow more than a generic pod filter, that's why they replace the stock needles and jets with DJ parts (they don't mix and match either, must use DJ needles with DJ jets)....also the slide lift hole is drilled larger, which if not done will cause leanness, as the slide (and needle) doesn't lift as well. The carb overflow vent lines should also be removed from the overflow vents, those can also cause leanness....

I have K&N filters and what I believe is a DJ kit. The holes in the slides have been drilled out by the previous owner, I checked them out. I've heard people say that Mikuni jets don't match well with DJ needles, but I don't belive it. I just think the sizes can differ for the same number. The carb vent lines are removed.

I had 4 problems when I started this jetting nightmare:

1. off the line hesitation
2. popping at 1/3 throttle
3. lack of top end power
4. lean reading on plugs

I have solved the first two. It runs great off the line without hesitiation. It no longer pops at all, on decel or anything. It still has a lack of top end power, with a new problem that arose when I put the 145 mains in- it sounds like I have snapped a piston rod when I'm at WOT above 7000 rpm! Bang, pop, bang, bang bang!!! Really loud, and still no ability to go any faster. And the plugs still read way lean at all rpms.

Tonight I have decided to do the following. Check the float height with a tube in the drain, instead of just setting them by the height measurement given in the manual. This will rule out any float problems and fuel delivery problems becasue I know the fuel tap, gas cap vent and fuel line are all perfect. I am also changing from my 180 air jet to a 170. Maybe that will richen up the pilot circuit some. Then I will shim the needles past the lowest notch, raising them even further, and put the 138DJ mains back in. I am thinking the banging I am getting at WOT is too much fuel, but I can't do a plug read becasue I haven't got the low end right.

Am I right in thinking that when I'm on the needle circuit, the size of the main makes no difference whatsoever? That would make sense, as I have a huge main jet in there now, and it runs like crap at WOT.

 

[Jethro]

Wow, by this page on the NGK site, I can honestly say that the nearest match is the first pic stating normal condition!

http://www.ngksparkplugs.com/techinfo/spark_plugs/faq/faqread2.asp?nav=31200&country=US

What seems wrong to me is that the very tip of the plug, the part you bend to gap, is totally coated in white, almost glossy. It in no way could be called tan or even grey as the NGK page says.

I'll take a pic of my plugs tonight for general comment!

 

[Mr. Jiggles]

Am I right in thinking that when I'm on the needle circuit, the size of the main makes no difference whatsoever? That would make sense, as I have a huge main jet in there now, and it runs like crap at WOT.

Over the past couple of weeks I've also been tuning my carbs, which is why I've taken such an interest in your dilemma. I've got KN pods with an aftermarket pipe of unknown origin. I had been running DJ132's with the needle in its highest position and I was getting surging (lean) at about 1/3 throttle which would be the needle circuit. I changed up to the DJ138 that comes with the kit and the 1/3 throttle surging that I had seen before went away. I don't know how correct this is but my thinking now is that the needle/needle jet meters whatever is coming through the main (afterall, the needle jet gets its fuel through the main, correct?). So, for a given needle position you'll get x% of whatever the main jet can deliver. However, like so many other things I'd bet that this relationship (if true) is linear only over a limited range of main jet sizes.

Jeff

 

[KEITH KRAUSE]

Let me put this jet needle/needle jet and main jet thing in different words.
Fuel enters through the main jet, goes up through the space between the needle jet and jet needle, and enters the carb throat.
Fuel flow will be regulated by the smallest opening along this passage. The smallest opening will be around the widest part of the tapered needle and the needle jet. The jet needle gets slimmer and slimmer towards its end.
As the tapered jet needle rises with throttle opening, much of it completely leaves the needle jet. The remaining portion, now much slimmer, allows more fuel to pass through the needle jet. The higher the needle rises, the wider the opening around the jet needle and the needle jet becomes. At about 3/4 throttle position, this opening becomes larger than the main jet opening. Since the smallest opening regulates fuel flow, the main jet now regulates the fuel flow.

 

[KEITH KRAUSE]

Jethro, I asked at your other topic about the possibility you could have jet needle spacer(s) missing or installed in the wrong order? Any spacer(s) that were used with the stock jet needle are to be re-used with a DJ needle. If a spacer is left out that goes under the e-clip, or on some carbs, the order of spacer install is incorrect, the needle can be "lean".
I gotta say the "noises" you're hearing do not sound good. Could be something beyond jetting. I hope not. I've heard "pinging" before, caused by either lean jetting and/or incorrect ignition timing. Usually, in severe cases, you'll see the plugs electrode start melting first. Pre-ignition.

 

[Jethro]

Nice. That explains it well.

Anyway, I've made some really good progress tonight. I came home and pulled the carbs to go back to the DJ138 main and put in the 170 air jet to richen up the pilot circuit. Got the carbs out and re-jetted and back in the bike in under 45 minutes. I'm getting too good at this. I left the needles at the lowest notch. Took it for a rip and this is what I have for plug reads now:

#3 cyl is still a little lean, but I'm pretty happy with the rest. A synch will probably do wonders after all this carb fiddleing. Bike rode smooth with no flat spot at all right up to 100mph. No hesitation at all off the line. Starts perfect with a little choke, nice and warmed up, ready to ride in 45 seconds to a minute. Sweet.

I still had wicked surging and cutting out at WOT though. For the first time I rigged up a clear fuel tube to the bowl drain like the shop manual shows. My freakin' float heights are way too low. I bench set them exactly like the book said, but it didn't cut it. The tube tells the tale clear as day. I'm resetting the floats now. How much you wanna bet that this fixes the problem?

Thanks everyone for the help, I may have it figured out now, I'll give you a ride report when I can (gonna snow tonight).

"And remember kids, don't trust your float heights to what you set on the bench!"