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Minor backfire after jet change?
- polkat
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The only problem is when I shift down a gear to let the engine slow the bike while approaching a slow turn, or a stop. Then it mildly (almost too quite to hear-but I can) backfires through the mufflers. I figure that I must be slightly off on one of the jet sizes.
Any ideas?
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- Motor Head
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- FIX UP YOUR BIKE RIGHT AND CHEAP
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Back fire is usually a lean condition in the exhaust, do you have the air system with the reed petals on the head? It could be the valve is bad? Vacuum not hooked up properly or a bad reed petal/ carbon causing to not seat.
1982 KZ1000LTD K2 Vance & Hines 4-1 ACCEL COILS Added Vetter fairing & Bags. FOX Racing rear Shocks, Braced Swing-arm, Fork Brace, Progressive Fork Springs RT Gold Emulators, APE Valve Springs, 1166 Big Bore kit, RS34's, GPZ cams.
1980 KZ550LTD C1 Stock SOLD Miss it
1979 MAZDA RX7 in the works, 13B...
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- Old Man Rock
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What rpm when down shifting... mid range?
Little tip Larry and Plum taught me....
Seems Pilot and mains are close or spot on so get your self running ~ 5K-6Krpm then release the throttle letting her snap back to idle position...
First thing first... Carbs synced?
* If she pops and backfires, still too lean...
** On mid range acceleration, any hesitation, fall flat on it's face... still too lean...
*** Hold at a constant 4.5Krpm, is she stuttering as if running out of gas, clogged fuel line, missing etc... still too lean...
1 clip position richer and you'll feel the difference...
BTW, condition of plugs? Carbonized, sooty, oily, bright white etc...
Good luck,
OMR
1976 KZ900-A4
MTC 1075cc.
Camshafts: Kawi GPZ-1100 .375 lift
Head: P&P via Larry Cavanaugh
ZX636 suspension
MIKUNI, RS-34'S...
Kerker 4-1, 1.5" comp baffle.
Dyna-S E.I.
Earls 10 row Oil Cooler
Acewell 2802 Series Speedo/Tach
Innovate LC1 Wideband 02 AFR meter
Phoenix, Az
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- bountyhunter
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1979 KZ-750 Twin
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- polkat
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Anyway, these are Keihins from 1982, and don't have adjustable positions for the rod. Yea, carbs are cleaned, synced, etc....I've gone over it with a fine tooth comb. It idles very smoothly, and accellorates nicely with no flat spots. The backfire happens if I'm using the engine to slow down for a turn or a stop. Example is I'm doing maybe 40 in 4th gear and begin dragging it down with the engine. Then it backfires. But let me explain that better, it doesn't BACKFIRE per say, but just pops a little, so quietly that wind noise alone sometimes keeps me from hearing it unless I'm listening for it (I wear a full helmet, which doesn't help hearing much). And oddly, it seems to come a little bit more from the left side then the right.
Now, admittedly, I tried jets that were too big the first few times, and being very poor (and I mean poor), I solder filled the old ones and drilled them out. It is my guess from the drill sizes that they are closest to 68/140, and like I say, it runs great, but I guess I'm not quite there yet.
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- Old Man Rock
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Whoa .... That's a new one I never thought of... :blink:
Well clip position change is nothing but time, no $$$ required... Go one richer on the clip and take her for a spin....
Good luck, let us know how it turns out for ya...
1976 KZ900-A4
MTC 1075cc.
Camshafts: Kawi GPZ-1100 .375 lift
Head: P&P via Larry Cavanaugh
ZX636 suspension
MIKUNI, RS-34'S...
Kerker 4-1, 1.5" comp baffle.
Dyna-S E.I.
Earls 10 row Oil Cooler
Acewell 2802 Series Speedo/Tach
Innovate LC1 Wideband 02 AFR meter
Phoenix, Az
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- bountyhunter
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1979 KZ-750 Twin
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- Turtle
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Also I hear more of what the bikes noises are with a helmet on then with it off with the wind noise.
1980 KZ 1000 A4 with 750 Zephyr swing arm and ZX-9 rear wheel
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- polkat
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- TeK9iNe
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Could be a header port leak I suppose, but it sure seems to be coming from the back. As I mentioned, this year Keihin's don't have the adjustable needles. Only one setting available. Actually, I'm coming around to the drilled jets ending up a little too small (lean), and until I can afford new ones I'll have to live with it. Anyone have any real 68 and 140 jets they will sell me cheap? :laugh:
The header leak will cause the poping at the back/end of the muffler.
You can shim the needles with small washers to make things richer.
PS. Its called afterfire. Backfire is when it comes through the pods/intake.
Motorcycle Shop Owner/Operator
79 Kawie Z1000 LTD
81 Kawie Z1000 CSR
83 Honda VT750C A
85 Kawie GPZ900 A2
86 Zukie GS1150 EG
93 Yamie XV1100 E
Lucky to have rolled many old bikes through my doors
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- polkat
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Okay, I can sort of understand how a leak at the exhaust ports would cause a back....er, afterfire at the muffler ends, but if there is indeed a leak at the headers, why doesn't it afterfire more often, instead of just when slowing the engine with a load?
I have run my hand around the exhaust ports (at the head of course) feeling for blowing hot air (did this at idle) but can't feel anything. How do you check for this?
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- Motor Head
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- FIX UP YOUR BIKE RIGHT AND CHEAP
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1982 KZ1000LTD K2 Vance & Hines 4-1 ACCEL COILS Added Vetter fairing & Bags. FOX Racing rear Shocks, Braced Swing-arm, Fork Brace, Progressive Fork Springs RT Gold Emulators, APE Valve Springs, 1166 Big Bore kit, RS34's, GPZ cams.
1980 KZ550LTD C1 Stock SOLD Miss it
1979 MAZDA RX7 in the works, 13B...
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