Author Topic: Are these lean symptoms? (Read 6162 times)

sirdarkheart · « **on:** June 12, 2006, 11:58:29 PM »

Hi Everyone,
3 year MC rider, 1st time B4 owner (and LOVING IT!). So my newly bought B4 as jetting issues, it was recently tuned-up by a professional (carb clean, carb synch, plugs, oil&filter, air filter clean and oil, coolant flush and refill, brake fluid refill and flush). Evidently, this mechanic diagnosed the bike as having jetting issues, but he doesn't do jetting. IT has a full V&H exhaust on it, K&N filter (to fit OEM airbox), and supposedly a jet kit. It has 6 quarter size holes in the airbox top that someone did. THere is a flat spot anywhere under 8K rpm and when you try and whack the throttle open 3/4 to full under 8K rpm the bike does not respond and kind of stutters. Above 7.5-8K rpm, the bike pulls like it should. I read threads on this forum and random ones on jetting and carburetion tuning. It seems like I have lean symptoms (or too large a main jet according to one of the articles).
Symptoms:
-Flat spot under 8K rpm when 3/4 to full throttle is applied (in any gear).
-Popping sound when rolling to a stop with throttle rolled off (I think this is a classic symptom of being too lean).
-Power if throttle is 1/4 open

So I duct taped the 6 holes in the airbox and it didn't seem to help all that much. Should I go ahead and occlude the main intake for the airbox located in the rear of the airbox top? Or would that be bad? I'm just trying to locate what the problem is before I go into the shop and get charged a bunch of $$$.

2nd question:
If I try and move the needle position higher in the carbs (to richen the mixture), does that mean I have to carb sync everytime? Or can I just unscrew the tops put some shims on each needle, button the carbs up and go?
BTW, what shims do you guys use (size and type)?
Thank you for any input you can offer!
D

interfuse · « **Reply #1 on:** June 13, 2006, 09:19:27 AM »

Sounds lean. Start by raising your needles a notch.

You don't have to do a carb sync after every adjustment... I usually test ride it before I bother syncing the carbs.

sirdarkheart · « **Reply #2 on:** June 14, 2006, 12:24:52 AM »

So,
I raised the needle height by putting the clip on the needle down notch by notch until I reached the bottom. It was the highest I could raise it. Still low end to mid range flat spots. So I decided to go the opposite direction, I went leaner and raised the clip on the needle up so that the needle would be lower in the needle jet. This seemed to have worked. The bike now runs great on the low end and when I blip it, it does not drop rpm from the idle position! SO I took it out for a spin. Full throttle worked great for 1, 2, and 3rd gear. However, if I try and do it for 4th gear there is still a flat spot between 6-8 K rpm. I don't know what the deal with that is, but I suspect that I actually do need to change the jets. I can still drop the needle one more position, but it seems that is really too lean.
Any comments?

gsxr400 racer · « **Reply #3 on:** June 14, 2006, 11:09:55 PM »

once again , i know i said this once before or a million times if you get 2-1 positions on your needle from the top or bottom you have to choose a new main jet! Ya hear! cheers lol

sirdarkheart · « **Reply #4 on:** June 15, 2006, 12:16:45 AM »

Thx for the tip! Would it be harmful for the engine if I did not change it though, and just ride around with a 6-8k rpm flat spot? Just curious... Do you think I need a larger main jet or a smaller one based on my bike running better when I moved the clip position 2nd from the top (leaned it out)?
Thank you a bunch! BTW, I bought the bike from Steve W. from Sacramento, CA he said he knows you (or knows of you).

gsxr400 racer · « **Reply #5 on:** June 15, 2006, 05:49:51 PM »

smaller

sirdarkheart · « **Reply #6 on:** June 16, 2006, 06:32:28 PM »

thank u !