Carb tuning. Flat spot

srt44116kfx400 · 01-14-2012, 11:13 PM

Ok guys im pulling my hair out. I cant seem to get my FCR39 dialed in the way i want it. ( its not me i swear)

My quad is a z400 with Ported head, KW valves, Drz springs, 12.5 comp piston with Drz base ( 13.0 comp???) Open Air box, -16 oz flywheel, full Wisco clutch kit with billet inner and outer hubs. Full Hmf exhaust and a Fcr 39. with quickshot 2, wired AP, and adjustabel fuel screw. Im at sea level and its abouth 20-30 deg. Main is a 160

It runs fine and goes like hell but there is a DEAD spot that i can feel. ( i leat others ride it and they cant feel it) Its starts fine, Revs perfect and pulls like hell with a nice crisp exhaust tone 1-3. When i hit 4 and 5 it has a sluggish feel to it, like its being restricked and the exhaust is more if a lower lugging sound thand crisp.

Best way to decribe it is it ( think a heart beat up and down then she flatlines in 4,5 )

I have checked the plug and it is perfict tan color with a hint of black. ( more than once) Im lost as to mabe its to rich or lean?

Deffently sounds like a fuel issue to me. ( mabe pepcock clogged????)

z455 · 01-14-2012, 11:28 PM

Start by checking your fuel flow and float height. Also why do you have the AP wired when you have the quickshot?

srt44116kfx400 · 01-14-2012, 11:36 PM

I will have to check the fuel flow. Its is the stock petcock. And I had it wired before i got the Quickshot, never unwired it. ( Do u think its a problem?) I have very little bog at all ( even if i stab throttle from idle )

If the fuel flow was the issiue woulnt that be leaning out up top?

jasmf24 · 01-14-2012, 11:41 PM

Quote:

Originally Posted by srt44116kfx400

I will have to check the fuel flow. Its is the stock petcock. And I had it wired before i got the Quickshot, never unwired it. ( Do u think its a problem?) I have very little bog at all ( even if i stab throttle from idle )

If the fuel flow was the issiue woulnt that be leaning out up top?

Look into getting the raptor petcock.

beaverclever02 · 01-15-2012, 01:05 AM

I was under the understanding that you don't want the AP wired with the quickshot, the quick shot was supposed to fix that. I would look toward the Petcock, sounds like a flow issue. Make sure all your vent tubes are clean and clear, and change that petcock.

711streetfighter · 01-15-2012, 03:47 AM

The quickshot doesn't fix anything with the bog , keep it wired. I would say change to a raptor petcock. I had a similar problem. I was fine with the stock motor but when I built my motor the stock petcock didn't cut it. I was going full out in 4th/5th and it would fall on it's face after a few pulls. If anything you might want to get it to a dyno to measure your fuel/air mixture.

biggiej42 · 01-15-2012, 08:12 AM

How about a bigger set of cams too? Do you have new or old style hot cams? I'm at sea level also, running a 175 main.

cataway · 01-15-2012, 12:47 PM

i'd say a 170-172 mj anyway

CFM-Z440 · 01-15-2012, 01:14 PM

I would start with the petcock since it's a higher gear problem. The reason is that if the carb is using fuel faster than it's filling, by the time you're in 4th the bowl is probably lower than it should be, and you spend longer periods of time at wide open throttle in the higher gears.

Un-related, but I would also throw away the stock carb to air box boot and find something better. The 400EX boot is a common mod that is cheap and works great. This will likely require larger main jetting also. The stock boot is restrictive.

cataway · 01-15-2012, 01:36 PM

if he's still using the stock air boot I'd hardly call it un-related

CFM-Z440 · 01-15-2012, 01:50 PM

They can run properly through all 5 gears with a stock boot. It's not the cause of his problem, therefore it's un-related. Maybe semi-related would be a better term if we're going to split hairs.

01-14-2012, 11:13 PM	#1 (permalink)
srt44116kfx400 :::Mini LT50 Rider::: Join Date: Mar 2008 Location: Cape cod Posts: 79	Carb tuning. Flat spot Ok guys im pulling my hair out. I cant seem to get my FCR39 dialed in the way i want it. ( its not me i swear) My quad is a z400 with Ported head, KW valves, Drz springs, 12.5 comp piston with Drz base ( 13.0 comp???) Open Air box, -16 oz flywheel, full Wisco clutch kit with billet inner and outer hubs. Full Hmf exhaust and a Fcr 39. with quickshot 2, wired AP, and adjustabel fuel screw. Im at sea level and its abouth 20-30 deg. Main is a 160 It runs fine and goes like hell but there is a DEAD spot that i can feel. ( i leat others ride it and they cant feel it) Its starts fine, Revs perfect and pulls like hell with a nice crisp exhaust tone 1-3. When i hit 4 and 5 it has a sluggish feel to it, like its being restricked and the exhaust is more if a lower lugging sound thand crisp. Best way to decribe it is it ( think a heart beat up and down then she flatlines in 4,5 ) I have checked the plug and it is perfict tan color with a hint of black. ( more than once) Im lost as to mabe its to rich or lean? Deffently sounds like a fuel issue to me. ( mabe pepcock clogged????) __________________ 2004 ltz 400 Wisco 12.1 Drz base gasket Hotcams Cams Hotcams shims DID timing chain Ported+polished head. Kb Stainless Valves DRZ Valve sprigs Fcr 39, Boysen 3, adjustable fuel screw. Full Hmf sport series Uni air-filter { no Lid } Trail tech -16 flywheel Stock cdi Amr monster coil Renthal big bar Handel bars Pro taper Clamps MSR levers Power Madd handguards Lonestar +2 +1 A-Arms G-force +2 axle Works suspension All around Houser Swing arm + droplink Houser +2 steering stem Gpr steering stabilizer

01-14-2012, 11:28 PM	#2 (permalink)
z455 :::LT500 Rider::: Join Date: Jan 2010 Location: North Carolina Posts: 1,231	Start by checking your fuel flow and float height. Also why do you have the AP wired when you have the quickshot? __________________ 04 LTZ 445 95mm CP 12.78:1************ Elka stage3 front & rear Web 540-539************* JRD +3 LT A-arms 42mm Kehin*************** Burguard +1.75 swingarm Full HMF shorty *********** Hiper tech3's in Kenda klaws Dyna programable********* Lonestar axle, carrier & stem

01-14-2012, 11:36 PM	#3 (permalink)
srt44116kfx400 :::Mini LT50 Rider::: Join Date: Mar 2008 Location: Cape cod Posts: 79	I will have to check the fuel flow. Its is the stock petcock. And I had it wired before i got the Quickshot, never unwired it. ( Do u think its a problem?) I have very little bog at all ( even if i stab throttle from idle ) If the fuel flow was the issiue woulnt that be leaning out up top? __________________ 2004 ltz 400 Wisco 12.1 Drz base gasket Hotcams Cams Hotcams shims DID timing chain Ported+polished head. Kb Stainless Valves DRZ Valve sprigs Fcr 39, Boysen 3, adjustable fuel screw. Full Hmf sport series Uni air-filter { no Lid } Trail tech -16 flywheel Stock cdi Amr monster coil Renthal big bar Handel bars Pro taper Clamps MSR levers Power Madd handguards Lonestar +2 +1 A-Arms G-force +2 axle Works suspension All around Houser Swing arm + droplink Houser +2 steering stem Gpr steering stabilizer

01-15-2012, 01:05 AM	#5 (permalink)
beaverclever02 :::LT500 Rider::: Join Date: Feb 2011 Location: Holt, Mo Posts: 1,742	I was under the understanding that you don't want the AP wired with the quickshot, the quick shot was supposed to fix that. I would look toward the Petcock, sounds like a flow issue. Make sure all your vent tubes are clean and clear, and change that petcock. __________________ 03 Z400, Fly Aluma Steel Bars, Blob removed, fly kill switch, ASV levers, Power Madd hand gaurds, MQ park brake block, DG O-series pipe with Curtis sparks header, Pro Armor full nerfs with heel gaurd, CST Ambush Front and Rears, GBC Sand shark and shark fins on douglas blue label, No lid,pro design air filter, no snorkel, 6000k HID conversion, procom cdi, 06 ressie shocks, FCR39 tuned.

01-15-2012, 03:47 AM	#6 (permalink)
711streetfighter :::LT500 Rider::: Join Date: Dec 2009 Location: OK Posts: 1,208	The quickshot doesn't fix anything with the bog , keep it wired. I would say change to a raptor petcock. I had a similar problem. I was fine with the stock motor but when I built my motor the stock petcock didn't cut it. I was going full out in 4th/5th and it would fall on it's face after a few pulls. If anything you might want to get it to a dyno to measure your fuel/air mixture. __________________ LRD Attitude Aluminum Frame, 462cc Stroker, 41mm FCR, 540/539cams, Curtis Sparks Exhaust, Dyna Prog, Fox Float EVOL DSC up front, +2 Burgard A-arms, Janssen Outlaw Rear Suspension Kit with Elka stage 3 shock, Team Industries +3 Axle, Hipers, Flexx Bars, Laker Plastics, intake by me, front mounted battery, Rekluse EXP clutch, Trailtech flywheel, and a few other goodies .

01-15-2012, 08:12 AM	#7 (permalink)
biggiej42 :::Official Spammer::: Join Date: Jun 2006 Posts: 3,399	How about a bigger set of cams too? Do you have new or old style hot cams? I'm at sea level also, running a 175 main. __________________ 05' Z434 12.5:1CP,Full Yosh TRC,FCR40,175/45,Rat Stack,Dyna Programmable,AMR Coil,KW Valvetrain,536/540 Web's,DID Tchain,PWR Radiator,Raptor petcock,Gunnar Kill,Elka S3 Front+Rear w/link,Roll+1 Stem,GPR Stabilizer,SL Hyd.Clutch,Tag T2,LSR+3 Arms,Burgard+1 Swinger,Quadtech Rad Shrouds,Supersprox 14/40t,UM Air Box,YFZ Calipers,SS Lines,PA Bumper,Asv's,Roll Nerfs/Heels/Pegs,LSR Axcalibar,Douglas G2 Beadlocks/Razr's,Hid,YFZTail,Pwrmadd's,TT Vapor+Dash,CV4's,RickyStator. July 2011 QOTM Last edited by biggiej42; 01-15-2012 at 08:15 AM.

01-15-2012, 12:47 PM	#8 (permalink)
cataway :::Official Spammer::: Join Date: Mar 2006 Posts: 3,062	i'd say a 170-172 mj anyway __________________ 03 ltz400,95.5bore,+5crank,P&P,13.7:1,JE piston,spacer plate,RHC +1 intakes valves,RHC #208in&187ex cams,DRZ manual decomp,DID cam chain,no air box,Sredrum TB 42mm FCR,RAT stack,WB fuel screw,EMN needle,quick shot,06 clutch 450r drive plates w/trx400 ex springs,C2HB,ex thumber,trx450r air boot, Barker Performance pipe, trailteck flywheel,dynatek,nerf bars,450r shocks, nerf bars,+4 swinger,lowered front & rear

01-15-2012, 01:14 PM	#9 (permalink)
CFM-Z440 Super Moderator Join Date: Sep 2006 Location: Southern Minnesota Posts: 6,437	I would start with the petcock since it's a higher gear problem. The reason is that if the carb is using fuel faster than it's filling, by the time you're in 4th the bowl is probably lower than it should be, and you spend longer periods of time at wide open throttle in the higher gears. Un-related, but I would also throw away the stock carb to air box boot and find something better. The 400EX boot is a common mod that is cheap and works great. This will likely require larger main jetting also. The stock boot is restrictive. __________________ 03 LT-Z 470 Max Power 12.5:1 94mm Piston, Hot Rods +5 Stroker Crank, Web Cams 539 (+6) IN / 539 EX, with Hot Cams sprockets, Ferrea +1 Valves, LTZ/DRZ springs (IN)DRZ springs (EX), DRZ Manual Decomp. Ported head, FCR 41 with Noss adaptor, Home made intake, Modified HMF Full System, Home made header, Trailtech flywheel, Dyna Programable 54hp 36ft lbs

01-15-2012, 01:36 PM	#10 (permalink)
cataway :::Official Spammer::: Join Date: Mar 2006 Posts: 3,062	if he's still using the stock air boot I'd hardly call it un-related __________________ 03 ltz400,95.5bore,+5crank,P&P,13.7:1,JE piston,spacer plate,RHC +1 intakes valves,RHC #208in&187ex cams,DRZ manual decomp,DID cam chain,no air box,Sredrum TB 42mm FCR,RAT stack,WB fuel screw,EMN needle,quick shot,06 clutch 450r drive plates w/trx400 ex springs,C2HB,ex thumber,trx450r air boot, Barker Performance pipe, trailteck flywheel,dynatek,nerf bars,450r shocks, nerf bars,+4 swinger,lowered front & rear

01-15-2012, 01:50 PM	#11 (permalink)
CFM-Z440 Super Moderator Join Date: Sep 2006 Location: Southern Minnesota Posts: 6,437	They can run properly through all 5 gears with a stock boot. It's not the cause of his problem, therefore it's un-related. Maybe semi-related would be a better term if we're going to split hairs. __________________ 03 LT-Z 470 Max Power 12.5:1 94mm Piston, Hot Rods +5 Stroker Crank, Web Cams 539 (+6) IN / 539 EX, with Hot Cams sprockets, Ferrea +1 Valves, LTZ/DRZ springs (IN)DRZ springs (EX), DRZ Manual Decomp. Ported head, FCR 41 with Noss adaptor, Home made intake, Modified HMF Full System, Home made header, Trailtech flywheel, Dyna Programable 54hp 36ft lbs

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