| Author | Message | ||
     Elmono |
I've read the tuning manual and I do not understand the terms "detonation" and "flat spots." When I come off of the throttle I have backfiring, but I do not know where it is. The exhaust could be the problem as the D&D set up allows for air in the bended pipe between the header and the muffler. I replaced the intake seal and gaskets and the exhaust gaskets 2 weeks ago and I retightened the exhaust. Also, is there a safe way to tune the main jet? Riding at full throttle seems kinda crazy. Yes, I AM A WEENEE. FYI: I'm at sea level, it's about 105 degrees in the shade, 100% humidity, and I've got a K&N Forcewinder-type air cleaner and a D&D slip-on exhaust. Stock ignition and stock M2 cams. Thanks, Chad. | ||
| Aesquire |
Tradition dictates that you tune the main jet first, so that you don't run too lean & melt pistons. Then the rest of the powerband get's attention, without so much worry. The best way, ( and I've spent countless hours on my GS750, bombing down expressways, cutting the throttle, pulling onto the shoulder, yanking plugs & putting in fresh, new ones.....sigh, & I still suck at reading plugs. ) is to find a good Dyno guru with a dyno that has an exhaust sniffer. He can quickly set you up properly, & I'll bet for less money than that ticket you get for doing 120 plus. IMHO | ||
| Eboos |
I am running #25 pilot and 165 main. I didn't mess with the needle. The bike seems happy. Check my profile for mods. The popping out the exhaust when down shifting is normal, I wouldn't sweat it (I think it has to do with valve overlap). | ||
| Bluzm2 |
Eboos. Popping out of the exhaust is not normal. If you have popping, either your A/F ratio is off or you have an air leak. Maybe in the intake or the exhaust. Check the header flanges, they should be about 8 foot pounds or so. Make sure the slip on joint is sealed with high temp silicon. Check you intake seals. I've had 4 different exhausts on my M2 with an HSR42 I've never had popping unless there was a leak somewhere. Keep looking, you will find it. Brad | ||
| Elmono |
96 needle + e-ring in the middle + 32.5 pilot + 170 main = no popping. But now the air screw is useless... I can screw it in and stall the bike, but I can remove it before I affect the idle. Smaller pilot maybe? Also, replacing jets and needles on this carb is easy as pie. But I think that I'll wait until November until messing with it again. It's like 110 degrees here. | ||
| Eboos |
"If the engine speed does not slow after two-and-a-half turns out, the pilot jet is too large and should be exchanged for a smaller one." From Mikuni's tuning manual page 4. | ||
| Xldevil |
Popping out of the exhaust is not normal Mikuni is telling another story: 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. http://www.mikuni.com/fs-tuning_guide.html (Message edited by xldevil on September 04, 2006) | ||
| Elmono |
This site is awesome. Info at your fingertips. Yeah, Eboos, I need to exchange for a smaller pilot but I think I'll wait a few months. I figure for now, too rich is safer than too lean. And the bike runs better now than it did before. I shouldv'e never sold my first Mikuni, these things are great. Not that I claim to know what I'm doing, but it's a pleasure to be able to tweak a carb. And I figure if I screw up, someone here will be able to bail me out. I think I now know what flat is, but what's detonation and how do I detect it? Thanks, Chad. | ||
| Smokinjryan |
25 pilot and 165 main is the same as me in Jersey pretty much sea level. I have CF can-ham with k&n with a supertrapp pipe with 13 disks. I went 30 Pilot bur didnt get much response out of A-F screw. So went back to 25 with only about 1-1/2 turns out and it likes it and popping has stopped out tail pipe. |
