Author Topic: Carb Help (Read 3717 times)

Asphalt · « **on:** November 28, 2006, 10:59:07 AM »

I have recently Synced my Carbs, and although it helped it seems to have developed another problem. My idle is eratic. When I blip the throttle, or turn the throttle at all, the engine hovers and slowly falls. Very slowly. When I adjusted the A/F mixture screw it didn't help. I also have had a slight loss of power. Any ideas?

pmackie · « **Reply #1 on:** November 28, 2006, 11:15:46 PM »

Possibly an air leak. It sounds suspiciously like an overly lean condition at idle. Firstly adjust your air screws again. Start at factory settings and then go richer.

Make sure you haven't pulled off a vacuum hose when you adjusted the carbs, that would let air in as well. Check the carb boots and make sure everything is tight. You can spray a little WD40 around the boots while the engine is running. If it slows down, it is sucking air somewhere.

Check your air filter, etc. - start with the easy stuff first.

Was it acting up before you started the carb sync?

99er · « **Reply #2 on:** November 29, 2006, 10:40:36 AM »

Yeah, anything that you toyed with since it ran fine ar enow suspect. That includes the mix screws, vacuum taps, and idle RPM. Of course, this is a classic symptom of a throttle cable that is too tight. Make sure there is slack on both sides and that the throttle snaps back to the stop.
Marc/Atlanta

Asphalt · « **Reply #3 on:** November 29, 2006, 09:34:12 PM »

Alrighty....well I actually fixed, it. I went back inspected all the vaccuum caps, hoses ect, then I checked all my cables and went ahead and oiled them while I had them off, and readjusted them. Seems I was running WAY too lean. I didn't know running that lean would make your idle like that but apparently it does. I went ahead and adjusted the A/F miture screws, until the idle could hold on for itself. then smoothed it out. Problem now is the slight power loss on the bottom end.

The bike runs smooth, it idles nicely and I spend a lot less time with the choke on at 6 am in the morning. It seems very smooth, but just not as responsive at the bottom end. I had a very long lecture about shimming and changing jets. BUT it seems that doing the SYNC messed with the fuel stages, because it was adjusted to the way the carbs were synced. Changing the Sync, changed the A/F Mixture (or so I am told) and thus the issues I ran into. I am already 3 and a quarter turns out already, so I think I am going to try and put the snorkel in to see what happens. I have been told that since I went one step smaller on the pilot jets, this very well could be my problem.

SO, here is what I have done. K&N Filter, Yosh R3 exhaust, then I put in the larger main jets (127.5), and went one step down on the pilot jets (35) , 2 shims each needle (.05"), just under 3 and a quarter turns on A/F screw, and removed the snorkle. It is a 99 Bandit 1200s. Right now, I have no flat spots, and this is the first time the idle has been smooth. I get a tiny bit of vibration at 5000 RPMs and a little past, but no where near as bad as before. So before i commit to trying the bigger pilots, does anyone have any suggestions? For the power loss? I know this sounds strange, but I use to have no problem pulling power wheelies, and now--it almost seems like the bike cant do one.

Thank you 99er and pmackie for the advise....

CWO4GUNNER · « **Reply #4 on:** November 29, 2006, 10:53:02 PM »

I am surprised you went one step down (leaner) on the pilot jets which runs the carb until almost 1/4 throttle at which point your main jets really do their job. Also remember opening up the intake and the exhaust with a stock needle jet designed for a lean EPA mixture is not best. A smother tapered needle jet i.e. Ivan dyno tested needle jet & pilot kit with airbox mod instructions (21 holes) is well worth $100 as it is Dyno tested perfect when applied to specific parameters with the after market exhaust you have already installed. You need to trust the research work and recipe that someone else has spent months testing on a dyno for your B12 model year (91). My (05) Ivan stage 2 jet kit recipe mod worked wonderful from day one, and so very well its like it was custom made for my bike, and in a way it is as this kit has already been tested from scratch, all I had to do was follow the recipe to a tee and performance perfection was the result.
Conclusion. If your going to patch your own tire, at least buy a tire patch kit as having all the ingrediance (rubber, glue, and time) isn’t exactly the same thing but rather re-inventing something already painstakingly invented and available at less cost in time, frustration, and money then you should afford to spend….

Asphalt · « **Reply #5 on:** November 30, 2006, 05:09:47 PM »

I guess to set the story straight; (mainly because I see the crying emoticon at the end) I have no trouble trusting people who do their research at all. In fact, I have looked into it, and something that I have found is that most of the aftermarket needles have a tendency to warp the ports in the Carbs, in most cases to a point that the entire carb needs to be replaced.

Now because there is so little information about the Mikuni carbs in the 99 Bandits, or for Bandits in general I had to dig. Now I agree that the Dyno tested needles with out a doubt have a greater increase in horsepower, none of them mentioned anything about the warping. Granted someone who rides on the weekend won't see the damage mainly because the use of the bike is less than someone like me who rides on a daily basis. I was also told by 3 different mechanics who are very good, and personal friends of mine, that if I can find a way to make rejetting work without having to change to an aftermarket needle then it is an awesome idea. So that is what this is, research, not some mod junkie just rustling around and getting himself into trouble with out a clue. At the same time I am learning.

The sizes that I chose were posted on Fast Lary's website, and I was checking the validity of it. So far so good, just you end up losing some bottom end for hella top end. My mid to top works beautifully. I have absolutly no problem with smashing Gixxer 1000's after take off.

I understand that the pilots are the first line of the carbs, then the needle, then the mains. But the funny thing is, the test cost me 10 bucks for the pilots. The whole set of Jets and shims only cost a grand total of 40 bucks, and 10 dollars of it was shipping and tax. That's it, and since I am retired military, between classes all I have is time so no loss there either. I am having the bike dyno done tomorrow; I will let you know how it turns out.

99er · « **Reply #6 on:** November 30, 2006, 05:22:11 PM »

You left one thing out. Since you have a pipe and 127.5 mains, you also must have drilled a 2" hole. If only removing the snorkel and no 2", that main will be super rich. I ran a 132.5 with my K&N. 127.5 was super lean but ran like a truck with the stock filter for years. The old Krazy Ed mod of 1997...2" hole, remove snorkel, and 127.5 main/35 pilot. Good enough to become a kit sold by Dale Walker.
That modification includes the 35 pilots (makes the transitions crisp) and is super easy to install and very flat. Moving to a 37.5 stock pilot will help on the screws but make no other noticeable difference. If your throttle transitions from decel to partial throttle are smooth, the pilots are good. If you're talking power wheelies, you're in the float and needle zone. As Dale Walker used to suggest, lower the needles until she gets that wonderful stock hesitation around 4K RPM and then add one shim. Done! Anything more is wasted gas and wasted power.
I'm surprised that just a carb sync has caused such difficulty but carbs are always an adventure. Are you sure the sync was performed correctly???
Marc
'99 post crasher

CWO4GUNNER · « **Reply #7 on:** November 30, 2006, 07:09:57 PM »

FYI.
http://www.ivansperformanceproducts.com/bandit1200.htm

Asphalt · « **Reply #8 on:** November 30, 2006, 07:11:31 PM »

Ahhhhh plot thickens. No I did not do the 2 inch mod. I wasn't ready to cut into my airbox just yet, because quite a few people have posted that it wasn't effective for them.

We live and we learn and that is the idea behind what i am doing.

The first time that I did the carb sync, it wasn't done correctly, because the manual that I have has you sync from left to right. Instead of syncing 1 to 2 then 3 to 4 THEN turning the middle screw to sync each side. When I figured it out, then I did it right, then checked again 3 different times with 3 different vaccuum gauges. It is set evenly across the board. My idle and the drive is smooth now.

Thanks 99er, that is the type of info I was looking for. Like i said I am going in for a dyno tomorrow, my friend found me a comp spot in the shop and is going to let me sit in on it. I'll post the results.

Asphalt · « **Reply #9 on:** December 01, 2006, 06:43:09 PM »

Aha! The set up in Fast Larry's is good for one thing only. Smooth power curve. Had my bike dyno'd with the exact set up minus the 2 inch hole, and ended up with Max power 103.14. Plus the mains are SUPER rich. The Air fuel bottoms out just before 7000 RPM's. At idle it runs lean. So the smaller pilots do help to make this set up SMOOTH, but you have little to No power gain. So now that I know where my power went...I am going back to stock pilots, and slighty smaller mains, and only one shim. I will report back with the results. Maybe by then I will have my scanner working and I can put up the printouts..