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| HD |
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HD
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Joined: 16 Dec 2009
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 Posted: 22:59 - 18 Feb 2011  Post subject: Possible Carb Issue? |
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I am not going to go into what has been done to this bike 
Basically if I pull away normally then it will crackle (sort of, you get what I mean ) in mid range, then after like 2 seconds it will go into the powerband. I usually give it a bit of clutch to help it  Then at the top end of the revs, it will crackle again.
However if I pull away giving it beans then it revs cleanly.
Is this anything to do with jets or something so simple as the air/fuel mixture screw?
Help
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| Paddy Blake |
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Paddy Blake
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| cb1rocket |
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cb1rocket
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Posted: 23:23 - 18 Feb 2011  Post subject: |
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mid range problem, flat spot, sounds like the needle is on the wrong clip setting.
Don't go buggering with the mixture screw, thats only for the low - idle mixture adjustment and no i don't mean the idle screw.
It revs cleanly from full wack so its got to be the clip setting. Not sure if you need to richen or lean it. Usually being in the middle setting helps.
read this from odie's post, a good guide to carb tuning:
| Odie wrote: | Follow steps in order....First, dial in:
1. Top end (full throttle / 7.5k to redline - Best Main Jet be selected before starting step 2!
Select Best Main Jet
To get the best, most even top end power (full throttle/after 7500 rpm), select the main jet that produces the highest top speed / pulls hardest at high rpm.
If the bike pulls harder at high rpm when cold and less hard when fully warmed up, the main jet is too large. Install a smaller main jet and retest until you find the main jet that pulls the hardest at high rpm when fully warmed up. This must be done first - before moving on to the other tuning ranges.
If the bike doesn't pull well at high rpm when cold and gets only slightly better when fully warmed up, the main jet is too small.
In order to properly tune the midrange and low rpm carburetion, THE MAIN JET MUST FIRST BE PROPERLY SELECTED after 10 to 15 minutes of hard use!
Do not pay too much attention to the low-end richness when you are changing main jets - you still need to be using the main jets that produce the best power at high rpm. You will deal with the low-end / cruise later - after step 2.
2. Midrange (full throttle /5k-7k)
Select best needle clip position
To get the best power at full throttle / 5k-7k rpm, after you have already selected the best main jet,
If the engine pulls better on a full throttle roll-on starting at <3k, when cool but soft when at full operating temperature, it is too rich in the midrange and the needle should be lowered.
If the engine pulls better when fully warmed up but still not great between 5k-7k, try raising the needle to richen 5k-7k.
If the engine pulls equally well between 5k-7k when cooler as compared to fully warmed up, the needle height is probably properly set.
Do not pay too much attention to the low-end richness when you are changing needle clip positions - you still need to be using the clip position that produces the best full throttle / 5k-7k power in conjunction with the main jets that produce the best power at high rpm. You will deal with the low-end / cruise next.
3. Low end (full throttle / 2k-3k)
Float height (AKA fuel level & how to..)
To get best low-end power, set float height (fuel level) so that the engine will accept full throttle, without missing or stumbling, in 2nd gear from 2.5k to 3k rpm at minimum.
Float heights, unless otherwise specified in the installation guide, are measured from the "gasket surface" of the carb body to the highest part of the top of the float - with the float tang touching but not compressing the float valve spring.
If the engine has a "wet" rhythmic, soggy area at full throttle / 3k-4k rpm, that gets worse as the engine heats up, lower the fuel level by resetting the float height 1mm greater (if the original was 13mm - go to 14mm). This will lower the fuel level, making full throttle / 2k-3k rpm leaner.
If the engine is "dry" and flat between 2k to 3k rpm, raise the fuel level.
Example: change float height from 15mm to 14mm to richen up that area.
REMEMBER, since the main jet WILL affect low speed operation, the MAIN JET has to be within 1 or 2 sizes of correct before final float setting.
Warning: If the engine is left with the fuel level too high,, the engine may foul plugs on the street and will be "soft" and boggy at part throttle operation. Adjust Floats to raise/ lower the Fuel Level.
Base settings are usually given if a particular application has a history of fuel level criticalness. The Fuel level height in the float bowl affects full throttle/low rpm and, also, richness or leanness at cruise/low rpm.
Reference: a bike that runs cleanly at small throttle openings when cold, but starts to show signs of richness as it heats up to full operating temperature, will usually be leaned out enough to be correct if the fuel level is LOWERED 1mm. Check out and RESET all: Suzuki (all), Yamaha (all) and Kawasaki (if low speed problems occur). Needless to say, FUEL LEVEL IS EXTREMELY IMPORTANT!!!
If there are low-end richness problems, even after lowering the fuel level much more than 1.5mm from our initial settings, also check for needle wear and needle jet (part of the emulsion tube). See Worn Needle and Worn Needle Jet diagram. It is VERY common for the brass needle jets (in the top of the "emulsion tube") in 36mm, 38mm and 40mm Mikuni CV carbs to wear out in as little as 5,000 miles. Check them for "oblong" wear - the needle jet orifice starts out round! Factory Pro produces stock replacement needle jets / emulsion tubes for 36mm and 38mm Mikuni carbs.
4. Idle and low rpm cruise
Fuel Screw setting (AKA mixture screws)
There is usually a machined brass or aluminum cap over the fuel screws on all but newer Honda. It's about the diameter of a pencil. Cap removal details. Newer Honda carbs use a special "D" shaped driver, usually supplied in the carb recal kit.
Set for smoothest idle and 2nd gear, 4k rpm, steady state cruise operation. Set mixture screws at recommended settings, as a starting point. For smoothest idle, 2nd gear 4000 rpm steady state cruise , and 1/8 throttle high rpm operation.
Pilot fuel mixture screw settings, float level AND pilot jet size are the primary sources of mixture delivery during 4000 rpm steady state cruise operation.
If lean surging is encountered, richen mixture screws (turn out) in 1/2 turn increments. Alternative pilot jets are supplied when normally required.
Pilot fuel mixture screw settings, float level and pilot jet size also affect high-rpm, 0 to 1/8 throttle maneuvers. Too lean, will cause surging problems when the engine is operated at high rpm at small throttle openings! Opening the mixture screws and/or increasing pilot jet size will usually cure the problem.
NOTE: A rich problem gets worse as the engine heats up.
If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.
NOTE: A lean problem gets better as the engine heats up.
If the throttle is lightly "blipped" at idle, and the rpm "hangs up" before dropping to the set idle speed, and there are no intake leaks and the idle speed is set at less than 1000 rpm, the mixture screws are probably too lean: try 1/2 turn out, to richen mixture. Be sure there are no intake leaks and the idle speed is set at less than 1000 rpm |
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HD
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| Posted: 23:29 - 18 Feb 2011 Post subject: |
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Its a Derbi Senda, hence the sig
And it seems to be running right as the electrode is coffee ish. I mean the tip was a tad oily but I think that settled before the fucking thing decided the electrics wanted to go 
I cant for the life of me remember which clip the needle is on. I think it is 2nd? Out of 4? Manuals with the mechanics so I cant check. And the manual is shit anyway
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Paddy Blake
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reckless_b
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| cb1rocket |
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cb1rocket
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| Posted: 17:09 - 21 Feb 2011 Post subject: |
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only the OP usually bumps  He has been given a solution but nothing to report so far |
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HD
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| Posted: 17:29 - 21 Feb 2011 Post subject: |
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Correct
Just got my bike back having spent 150 on a loom and 254 on labour; thieving cnuts.
Gonna have a go at the weekend.
Would too much oil cause this? As every ride I have a nice trail or oil down my exhaust and sometimes dripped/flung onto the swingarm. Also I believe the mixture becomes leaner (oil not air) as you rev higher and if I pull away with lots of throttle, it doesn't do it...
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| N cee thirty |
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N cee thirty
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cb1rocket
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| Posted: 22:41 - 21 Feb 2011 Post subject: |
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fucking hell, 400...........jeez, thats another GP, RXS, H100 to my stable then!
whats the situation with the carb? |
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jimspeed
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| Posted: 22:56 - 21 Feb 2011 Post subject: |
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is it a premix or oil injection setup? too much oil with premix = leaner running as the same amound of fluid is going thru the carb jets but less of it is petrol
pretty much any change to anything exhaust wise with a 2 stroke means a rejet at the least tho 
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Hyosung cruise 125(passed test on, sold) Kawasaki el 252 (better than expected but sold on) Kawasaki GPZ500S first "big"bike.(sold) ZZR600 E5..Z750 2007,ER5, currently on a 2008 Enfield bullet electra x and loving it..
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HD
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| Posted: 23:00 - 21 Feb 2011 Post subject: |
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No I hate the thing. Fucking cunt is broke again! Same problem as before. The fucking electrics
It's got an oil pump.
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Rusty '02 Vito Camper + CBR600F3
Last edited by HD on 14:01 - 22 Feb 2011; edited 1 time in total |
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HD
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| Posted: 14:01 - 22 Feb 2011 Post subject: |
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They are picking up later today. Bloke sounds embarrassed according to my dad. So he fucking should be! Nice day for a ride today aswell It seems to be the same problem as before. Even before I got the loom so does that say that it isnt the loom at all? Or has something worked loose (earth?)
Oh and the exhaust is starting to rust on the front. The middle/back are fine but its where the salt and shit flicked up and stuck to the exhaust as it was hot. I dont want to spray it in VHT black paint but what are my other options.
I was going to get it chromed but that is out of the question now I have just spent £400 notes...
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Old Thread Alert!
The last post was made 14 years, 332 days ago. Instead of replying here, would creating a new thread be more useful? |
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