| Author | Message | ||
     Randy_spann |
I've tuned the carb, repacked the vance & hines, new intake seals, new exhaust seals. Still get popping in exhaust upon deceleration. 2000 M2. Anybody solved this problem? | ||
| Dave_02_1200 |
Sounds like it might be an exhaust leak further upstream. Have you checked the exhaust port gaskets and the nuts on the header flanges? | ||
| Randy_spann |
Yes, new exhaust port gaskets, new nuts torqued to spec. | ||
| Daveswan |
This is from Mikuni's site: It is normal for many high performance exhaust systems to moderately backfire or pop when the throttle is closed from mid-to-high rpm. In fact, one should expect a well-tuned high performance engine to "pop" and "crackle" when the throttle is closed at high rpm. The popping is a result of the air/fuel mixture becoming very lean when the throttle is closed and the engine is rotating well above idle speed. It is also necessary that the exhaust system have rather open mufflers. Why This (normally) Happens: 1) When the throttle valve is in the idle position, fuel does not flow out of the main system (needle, needle jet, main jet). Fuel is only delivered to the engine by the pilot (idle) system. 2) The combined effect of the closed throttle and elevated engine rpm is to create a fairly strong vacuum in the intake manifold. This vacuum, in turn, causes a high air flow rate through the small gap formed by the throttle valve and carburetor throat. 3) Under these conditions the pilot (idle) system cannot deliver enough fuel to create a normal, combustible air/fuel ratio. The mixture becomes too lean to burn reliably in the combustion chamber. It gets sent into the exhaust system unburned and collects there. 4) When the odd firing of the lean mixture does occur, it is sent, still burning, into the exhaust system where it sometimes ignites the raw mixture that has collected ---- the exhaust then pops or backfires. | ||
| Buell_bert |
Excellent posting Daveswan. | ||
| Harold |
I stopped mine from popping with a larger pilot jet, which also helped cold starts. | ||
| Randy_spann |
Harold - Do you know what size pilot jet you went to? | ||
| Harold |
I can't remember, but it was one size larger than was in there. How many turns do you have your adjustment screw out? I think after 2-3 turns to get it to idle the best, one size larger jet is needed. | ||
| Terrycoxusa |
I hold my throttle slightly open when decelerating, it stops the backfiring. 99S3 | ||
| Skntpig |
Stock carb try a 45 pilot. 2.5-2.75 turns out from lightly seated A/F screw | ||
| Langperf |
I have a 98 M2 with the Keihin CV carb, Buell race header with a D&D canister, Zippers HPCV Carb mods which consist of a modified slide, different needle, and the accelerator pump destroked about 80%, a carb intake velocity stack air cleaner adapter I fabricated myself, and a Dyna programmable ignition. I spent a bunch of time dialing in this setup about 7yrs ago. Ended up with a 48 pilot, idle mixture screw out approx 2-1/2 turns with a 195 main. The thing ran perfect, easy starts no popping on decel. At the beginning of the riding season last year out of the blue it started to become hard to start and wouldn't idle off choke until almost completely up to operating temperature.(65+Deg ambient temp) Then it would occasionally do the lean cough through the carb upon acceleration, heavy popping on decel, and it started pinging on the top end WOT. None of this had ever happened in the 5yrs since I tuned it. At first I attributed it to maybe a bad tank of gas. Tried several different fuels, no change. Changed plugs, checked for vacuum leaks, no luck. Still running like a outta tune sportster. Took the carb off disassembled and cleaned everything in my carb tank (no signs of gum up when I disassembled it) everything looked like new. No change same problems. Just for good measure replaced all the intake and exhaust seals. Same thing. So I'm scratching my head like "What the hell" This thing ran perfect for 5yrs. So I thought (and the only logical conclusion) I wonder if they changed something in the fuel, some oxygenating additive or alcohol to decrease emissions.(Wouldn't make a difference on a fuel injected motor because it would automatically compensate) So I went up to Zippers to get a #50 pilot and a #200 main. Alas, Zippers was out of #50 pilot jets (A clue) but had all others in stock. Swung by the local H-D dealer which had some #50 pilots in stock. Came back, installed the #50 pilot and #200 main, warmed it up, did an idle drop and went for a test ride. All problems solved. starts good, idles good, no lean cough on accel, no popping on decel, no pinging on top end WOT. Back to her good ole wheeling hooligan self.   | ||
| Buell_bert |
Hey where can I get a hand full of different high and low speed jets so I can play around a bit. | ||
| Buell_bert |
I ordered 3 high speed and 4 low speed. What happens if you put to high of a low speed in??? | ||
| Fahren |
Rich idle. Jets can be had over the counter at HD dealer. | ||
| Randy_spann |
Fixed the problem with a 45 idle jet. (thought I had done the idle jet a couple of years ago!). 200 main jet. Now runs perrrfect! |
