Author Topic: Slight backfire or misfire on small throttle openings (Read 7893 times)

rider123 · « **on:** September 20, 2006, 03:20:32 PM »

Hello I'm having some small backfire or misfires on a Holeshot stage1 kit. For those of you who don't know, my #4 cylinder is crazily richer than the other 3 cylinders which are fine. I turned the mixture screw on #4 cylinder to 2.5(I'm at 3.5 on other 3 cylinders) and it seemed to slightly help the problem so I turned it to 2 turns to see if that helps as well. The deposits on the spark plugs on the other 3 cylinders are what you expect, sooty but can wipe off fairly well. On #4 cylinder the deposits are different. They are hard and shiney as well as being obviously more due to more fuel getting in there. When I drive at small throttle openings I get backfiring or misfiring, at large throttle openings it's fine. Could it be that #4 cylinder is so rich it's "loading up" and misfiring? I've tried taking a shim or two off of #4 and it seemed to help a bit but not as much as turning in the mixture screw. I know the bike is still rich because when I rev the throttle some black smoke comes out and the idle goes below the set idle for a half second and then jumps back up. What does backfiring or misfiring mean at small throttle openings? It seems to get worse when heated up but it may just that I notice it more. It does not pop at all on deaceleration.

Settings:

2nd gen Bandit
110 mains, 5 shims 1.5" hole
cylinders 1-3 3.5 turns out
cylinder 4 2 turns out (2.5 turns and it was still crazy rich.)
Float height on all 4 cylinders: 13mm

Red01 · « **Reply #1 on:** September 21, 2006, 08:54:51 AM »

Call Dale at Holeshot.

But I'm thinking something is wrong with your #4 carb . . .

rider123 · « **Reply #2 on:** September 21, 2006, 08:09:55 PM »

Ok well I fixed the backfiring problem, it turned out I was too lean on the pilots. I dropped the needle 2 shims and it seemed to help. But overall I think the bike a little rich so I'm going to drop 1 shim on the other needles tomorrow. I just don't understand it. I dropped the float bowl, checked the float height, I can see when the needle stop the fuel flow. At first I thought it was a stuck float but it wasn't. I'll have to get a second opinion because the shop I went to refuses/can't fix it. It was perfectly fine before the jets went in. At least I narrowed it down to the main jet. When I give it some throttle some black smoke comes out so I know it's rich.

I have a feeling it may be the needle valve or something because when I take the cap off it smells heavily of fuel in the slide. But the needle valve seems to be working. I'll try taking off the float bowl again but I don't know what's going on. I don't understand why the bike shop refuses to drop the bowl. For fun I might stick the 100 back in there. If it doesn't work phuck it I'll sell it in the spring. It's never really run 100% and it seems fincky as phuck to get it going. I'll take a loss and buy something else.

chupacabra · « **Reply #3 on:** September 22, 2006, 06:52:30 AM »

Take the jet out and use a magnifying glass to read the # stamped on it and make sure it matchs the others, also use the magnifying glass to look at the needle valve (needle hooked to the float) and check the seat closely. Then put and jet and needle valve in diffrent carbs. Take a look at the pilot also. Check the shims and make sure their not getting stuck holding the needle (the needle in the slide) to high. Look into throttle body and look for cracks or holes that aren't suppose to be there.

rider123 · « **Reply #4 on:** September 22, 2006, 01:04:55 PM »

Well I dropped the float bowl and everything seems fine. I put the bike on prime and held the floats up manually and it doesn't leak. I checked the float height and its right on 13mm. I can't find anything pyhsically wrong with the carbuerator. Maybe raising the floats to 14mm might help? I'm going to get a second opinion at another shop and if I can't fix it I'll either put it back to stock which is crap, or sell the bike at a loss and get something else this thing is the most finicky bike I've owned.

Snubnose · « **Reply #5 on:** September 24, 2006, 10:45:22 PM »

Quote

this thing is the most finicky bike I've owned.

I hear you loud and clear! Had similar issues with mine too, however, We (Bazza and I) found that with the removal of the timing advancer(stock one back in) and removing dales main jets(stockers back in), shims back to 3 or 4 from 5 and covering up the hole I made in the box up top, she runs great, perhaps mildly better "springier?" than with dales full stage 1 system.(I'm actually considering putting the 2 remaining shims back in which will bring back to 5 shims) but leave everything else stock minus the comp 1 holeshot exhaust.

A word of advice, BE PATIENT with her, I understand your frustration, BOY , do I ever!, these annoyances can soon mount up and cause you to do something you might regret!. Be patient, and perhaps give "OUR" solution a try?

Eventually because of the decreased mileage, poor idle and smelliness of the bike (rich) I figured it wasnt worth it and reduced my pleasure riding the bike (enough said). I figured the only way to re-kindle my love affair with sylvia (Silver B12) was to start enjoying her again, so went back to "Sudo stock" but better off for it.

http://forums.banditalley.net/viewtopic.php?p=18912&highlight=#18912

rider123 · « **Reply #6 on:** September 25, 2006, 01:23:36 PM »

Did you leave the 17.5 pilots in there or go back to 15's? Mine idles fine with the advancer in there.

Snubnose · « **Reply #7 on:** September 25, 2006, 04:56:21 PM »

Quote

Did you leave the 17.5 pilots in there or go back to 15's? Mine idles fine with the advancer in there.

I went back to the 15's (If thats what stock was, Been so long now I forgot what the stockers were). Perhaps your timing was ok from the factory, mine wasnt.

rider123 · « **Reply #8 on:** October 04, 2006, 06:34:17 PM »

I'm going to try the 15's in there just to eliminate that possiblity but I think the shop phucked the carb up royally. I have the stock mains in there and the plugs still are black and wet with fuel. What the phuck did they do? Hello we're just screwing in jets here, anyway I'll pop the 15's in there then I know it's not the jetting which I never though it was anyway. The thing was fine before they touched it. What the phuck. Maybe they wacked out the floats or something? They seem fine at 13mm.

Dave 02 1200 · « **Reply #9 on:** October 06, 2006, 11:57:12 PM »

What did Dale say? I have a 2002 B12 with a HS stage 1 and stock exhaust. 5 degree advancer is in place. Bike runs absolutely great. It was lean and ran hot when stock but now it runs cooler and has super throttle response. Mileage is 42 to 47 depending on how I ride. I suspect that something is not quite right, like an o ring out of place. Maybe a plug reading could help see what might be happening. There is even a possability that, with the pipe's increased flow, you could be running on the lean side at certain throttle positions. Be patient, check the small stuff, and then call Dale. Good luck.

rider123 · « **Reply #10 on:** October 10, 2006, 08:38:02 PM »

I cant do anything or talk to Dale untill #4 cylinder works properly again. Im seriuosly considering selling this thing and I've only had it 8 months. It's never run right from day one and no one can seem to get it together to fix it(shops or dealer). So if it can't be fixed in the next week it's going on the chopping block and I'll buy something else. I'm giving it one last shot. If I'm lucky it may get stolen and at least I'll get the insurance for it. I think I got a Lemon.