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dynojet question, still running lean

  • Thread starter Thread starter jordraatt
  • Start date Start date
jordraatt said:
... yes the carbs were fully stripped and cleaned, many times. ...
Click to expand...
That tells me that they still might not be clean. Done properly, it only takes one time.


jordraatt said:
... the valves were not adjusted, as it ran just perfectly before installing the pods. ...
Click to expand...
All the more reason to suspect the valves. They can run "perfectly", right up until the point where the valves get burnt.



EvilEnfield said:
..., if that doesn't help then get yourself some of these;

http://www.ebay.com/itm/20-PC-MICRO...ultDomain_0&hash=item2a1e14285b#ht_500wt_1180

http://www.ebay.com/itm/4PC-Hollow-...delKits_JN&hash=item5d33b3fb62#ht_5191wt_1163

Then you can drill out the jets which you know are too small to see if it helps.
Click to expand...
Please don't drill out any jets. Starting with the fact that you have NO idea what the starting diameter of the jets is now (you have a number, but not a size), you also don't have any idea how much bigger to make them. Then, if you do ever get the bike running and sell it, the new owner is going to say, "wow, how did he ever get it to run with these little (numbered) jets?" New jets are only a couple bucks a piece.



jordraatt said:
to drill the holes bigger or change the main jets will probably work if the problem is in the upper rpm area.. but both of us are struggling with lower/mid rpm area.. that means changing needle position and/or adjusting float height
Click to expand...
The float height should be set to the STOCK height, as it affects ALL circuits in the carbs. Give them all a proper baseline from which to work.

Believe it or not, the main jets can be a problem at 2000 rpm. :eek:
Yep. The circuit that is being used is more dependant on throttle position than engine speed. Open the throttle at 2000, the mains are called to duty.


MisterCinders said:
The jet circuits affect different throttle positions. That's why you see everyone ask about throttle instead of RPMs for carb issues. RPMs mean nothing.

The jets and throttle relationships are:

Pilot = idle to 1/4 throttle
Needle = 1/4 to 3/4 throttle
Main = 3/4 to WoT
Click to expand...
Also note that there is some overlap on these settings. For example, the pilot will still be adding a bit of fuel through most of the range, bit it is such a small amount compared to what the main will be adding when at full throttle. The main is actually providing the fuel that is regulated by the needle circuit, differences in its metering ability only show up when the needle is fully open.



NeyborDayfid said:
On the VM carbs, IIRC, you have 2 mixture screws.

On the CV carbs, IIRC, you only have the one mixture screw right at
the front on top of the carb right before the intake boot. (to the engine)
Doesn't taking this out make it leaner, while turning it in makes it richer?
I thought opening this up allowed more air. I could surely be wrong though.
Click to expand...
Yep, it's another one of those times. :rolleyes:

On the CV-type carbs (the Mikuni BS-series carbs in our GS bikes), that screw is the "idle mixture adjustment screw". The mixture is pre-set by the pilot air jet and the pilot fuel jet, then run through some passages inside the carb to the top of the throat. There are three small holes, one is always open, right at the throttle plate, a second that is opened just as soon as the throttle plate moves, and a third one that is a bit downstream. The one that is always open can not supply as much mixture as the engine needs at idle. The two at the throttle plate can not supply what the engine needs at low throttle openings. That is why the third hole is adjustable with the "mixture screw". Turning the screw OUT will add mixture, richening up what gets to the cylinder. A good starting point to start your tuning is with the screws three turns out, then slowly tweak them from there, listening for highest engine idle speed (best running).

.
 
Hi,

Steve said:
On the CV-type carbs (the Mikuni BS-series carbs in our GS bikes), that screw is the "idle mixture adjustment screw". The mixture is pre-set by the pilot air jet and the pilot fuel jet, then run through some passages inside the carb to the top of the throat. There are three small holes, one is always open, right at the throttle plate, a second that is opened just as soon as the throttle plate moves, and a third one that is a bit downstream. The one that is always open can not supply as much mixture as the engine needs at idle. The two at the throttle plate can not supply what the engine needs at low throttle openings. That is why the third hole is adjustable with the "mixture screw". Turning the screw OUT will add mixture, richening up what gets to the cylinder. A good starting point to start your tuning is with the screws three turns out, then slowly tweak them from there, listening for highest engine idle speed (best running).
Click to expand...

Mr. Steve, I've seen you explain this hundreds of times. It gets better and more eloquent with each telling. I just wanted to say "thanks". ;)

All the best to you and yours,

Cliff
 
Thanks Mr. Steve.
I now see how that works. An eloquent telling indeed.
Regards. :o
 
Steve said:
That tells me that they still might not be clean. Done properly, it only takes one time.



All the more reason to suspect the valves. They can run "perfectly", right up until the point where the valves get burnt.




Please don't drill out any jets. Starting with the fact that you have NO idea what the starting diameter of the jets is now (you have a number, but not a size), you also don't have any idea how much bigger to make them. Then, if you do ever get the bike running and sell it, the new owner is going to say, "wow, how did he ever get it to run with these little (numbered) jets?" New jets are only a couple bucks a piece.




The float height should be set to the STOCK height, as it affects ALL circuits in the carbs. Give them all a proper baseline from which to work.

Believe it or not, the main jets can be a problem at 2000 rpm. :eek:
Yep. The circuit that is being used is more dependant on throttle position than engine speed. Open the throttle at 2000, the mains are called to duty.



Also note that there is some overlap on these settings. For example, the pilot will still be adding a bit of fuel through most of the range, bit it is such a small amount compared to what the main will be adding when at full throttle. The main is actually providing the fuel that is regulated by the needle circuit, differences in its metering ability only show up when the needle is fully open.




Yep, it's another one of those times. :rolleyes:

On the CV-type carbs (the Mikuni BS-series carbs in our GS bikes), that screw is the "idle mixture adjustment screw". The mixture is pre-set by the pilot air jet and the pilot fuel jet, then run through some passages inside the carb to the top of the throat. There are three small holes, one is always open, right at the throttle plate, a second that is opened just as soon as the throttle plate moves, and a third one that is a bit downstream. The one that is always open can not supply as much mixture as the engine needs at idle. The two at the throttle plate can not supply what the engine needs at low throttle openings. That is why the third hole is adjustable with the "mixture screw". Turning the screw OUT will add mixture, richening up what gets to the cylinder. A good starting point to start your tuning is with the screws three turns out, then slowly tweak them from there, listening for highest engine idle speed (best running).

.
Click to expand...
Steve,

Do I understand your explanation correctly:

The mixture screw isn't changing the RATIO of air/fuel going into the cylinder, but just adding more air/fuel of the same ratio to the carb throat so there is a greater mass of gasoline in the cylinder? i.e. more gasoline mass in the same volume in the cylinder under compression = richer?

I will delete this comment if it unnecessarily confuses the issue.
 
http://www.drpiston.com/MikuniA.html

Here's a picture that cleared it up for me. It shows that it's actually allowing more fuel in through a passage up the side of the carb. I had mistakenly thought that it allowed more air in as it's on the top of the carb but it does indeed open up the bypass port and allow more metered *MIXTURE* to be pulled into the venturi.
I'm glad to have this straight.
My humble thanks. :)
 
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My understanding was that it was more fuel added as well, therefore changing the air/fuel ratio. I'm just checking to make sure that I'm not misunderstanding, too.

EDIT- that diagram you have linked shows that the screw adds more mixed fuel...
 
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thanks for great infor guys.. thanks to you the GS lives on..

one question, andit might be a stupid one.. but what about wrapping the pods with something to block the airflow?? i know that it can't simulate the same airflow asthe stock box,but maybe it will get a little better??
 
i just don't get it! i've bought two different stage 3 kits now, and none of them worked out.. why do they even bother selling these kits, when you have to change out half the kit yourself to get it right??
 
jordraatt said:
thanks for great infor guys.. thanks to you the GS lives on..

one question, andit might be a stupid one.. but what about wrapping the pods with something to block the airflow?? i know that it can't simulate the same airflow asthe stock box,but maybe it will get a little better??
Click to expand...
I've seen this done, but may look crappy if not done well, and defeats the purpose of having the pods in the first place. Probably useful as a diagnostic tool, though. I think the worst part of doing it would be that you are changing the airflow characteristics of the pod design, and it could make getting the carbs balanced that much trickier.
 
BigD_83 said:
I've seen this done, but may look crappy if not done well, and defeats the purpose of having the pods in the first place. Probably useful as a diagnostic tool, though. I think the worst part of doing it would be that you are changing the airflow characteristics of the pod design, and it could make getting the carbs balanced that much trickier.
Click to expand...

I tried this once, then took it down the road found out I was running rich and came back with foam wrapped pods soaked with fuel. I only have pods to make access easier, because performance wise they almost take away more than they add.
 
jordraatt said:
i just don't get it! i've bought two different stage 3 kits now, and none of them worked out.. why do they even bother selling these kits, when you have to change out half the kit yourself to get it right??
Click to expand...

Don't try to re-invent the pod with a shop rag. Nail down your baselines.

ADJUST YOUR VALVES.

MAKE SURE YOU HAVE NO AIR LEAKS.

You also need to synch the carbs.

You cannot re-jet your way out of problems caused by air-leaks, tight valves or badly synched carbs. Once those things are tightened up, you have a foundation for re-jetting adventures.

Then do some plug chops and focus on getting each circuit correct. With CV carbs, I think you have to work down the circuits, starting with the main jet.
 
i fixed my problem today...everyone was telling me to move the needle clip position down towards the point so i moved it to both positions below the stock setting and it just made it worse. so instead this time i tried moving the clip one position away from the stock placement and it really cleared the problem up for me. try that if you haven't already. it really did clear it up a lot.
 
sorry i'm gonna clarify a bit...i moved it away from the needle one position.
 
now the new K&N pods arrived, and it is still running lean.. next thing to do is trying to adjust the needle height as if that works.. if not, i'll guess i have to order bigger main jets/and, or pilot jets.. this is some f****** ****!

why not sell a stage 3 kit with the pods included, so that we know it'll work out in the first place?!?! this is f****** gambling!

but thanks guys for giving me the links to sites selling jets, guess i'll order a bunch of different jets and see what will work out. anyone here who has got a setup to reccomend on this bike, with pods and 12" mufflers?? i don't even know what the original jet sizes are
 
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Jordratt,

I still do not see a response to MisterCinders about adjusting your valves. Have you?

With a 160 main in there I would not expect you to be running lean at WOT. Can you clarify at what throttle positions your problems of leanness are, and how you arrived at your diagnosis? Plug chops done under load? Revving in neutral?
 
okey, i have fixed the problem and it's running like a dream :)

first of all, i changed the pods to K&N and it got a lot better, but not allright.. so guys, stay away from cheap pods!!

it was still stumbling, but this time it sounded like it was running rich.. i did a plug diagnosis, and i was right.. so i checked the electric system, for spark problems.. i did a fully charge on the battery, and now it is sparking like a dream..

btw, those who say that pods make your bike loose hp, that's just bull****.. with the K&N pods and the 12" mufflers it's more aggressive than ever :) i hope that this thread has helped some people out :)
thanks guys!
 
Nice to hear you made sucess!
I still believe the K&N have less restriction and better cleaning than the EMGO. So in other words the K&N let moore air into the system not less as you wrote.
I have for the moment no dynajet stage 3, cheap pods, rised needles, larger main 128, stock exhoust, 1135, cv36mm. Runs very nice.. I bought K&N's, tested them, but had to put the EMGO back again..
Here is my tread on this if you are interested.
http://www.thegsresources.com/_forum/showthread.php?t=192208&page=3
Regards
Espen
 
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