Backfiring----Valves???????

1493 Views 7 Replies 6 Participants Last post by Kenny4, Feb 11, 2010

Kenny4

Discussion Starter · Feb 7, 2010

Ever since I put the Yoshi duals on, it's been backfiring on decel under load in all ranges---Have played with a/f screw changed jetting up and down---Have never been able to fix it---It starts good and runs strong---I did find some leaks in the exhaust connections but way back by muffler.

Can't get to the leaks so I just pulled off the whole system and put on another brand new set of duals---Pro Circuits---And crap---It backfires worse with them on and there is no exhaust leak anywhere.

The only 2 things I haven't looked at is the pilots to see if they are dirty or clogged or checked valve clearance---I've held off on the valves as so many have posted up what a bucket of worms they opened---Actually R&R'ing the the air filter box is for some reason more intimidating to me than the valves.

If you guys have any other suggestions please post up---I'm sure if I mess with the valves I'll be back on here whining about something

Kenny

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Camo

· #2 · Feb 7, 2010

How many turns out are your fuel screws?

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Kenny4

Discussion Starter · #3 · Feb 7, 2010

Camo said:
How many turns out are your fuel screws?

They are 3 turns out

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Toyotadude

· #4 · Feb 7, 2010

I'd check the valves anyway if you feel you can just to eliminate one more thing.

04 KFX785, FST Stage3 cams, HMF Duals, Dynatek CDI, 210 mains, #42 pilots, James'(05-BF-750) cross-overs, 12 hole mod, polished slides, Twin air filter, 1 shim on needles, VFJ's stage3 clutch, American Star Racing 2" extended A-arms, Firestick adjustable rear axle, Honda 400EX throttle, Venforcer 4" swingarm extension and billet dipstick, brake reservoir cover and throttle cover, Jordan's(KFX Hellraiser) shorty shifter, Elka shocks, Denton steering stabilizer, 22-7-10 Sand Stars in front, 26-12-12 9 paddle Extremes in Rear, HID conversion, Trailtech bars and clamp, AC Nerfs, Bumper & Six pack rack, thecarboncartel tank guard & stator cover

04 KFX700, Lava Red plastics, Yoshimura duals, AC Nerfs, 24-11-10 8 paddle Extremes, HID conversion (coming soon)

86 Toyota 4X4, 4.3L Chevy V-6, 700R-4 trans, Marlin Crawler dual transfer case, limited-slip front diff, ARB rear diff, custom flatbed w/aluminum diamond plate insert, Super Swampers for trails & Desert Trac paddles for sand

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Nathan

· #5 · Feb 7, 2010

I had the same issue I got 42 pilots and was able to tune it out now I never have any popping.

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lambosr82

· #6 · Feb 8, 2010

Had same issue when I put my HMF's on changed out the pilots to 42's fixed the issue

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NovaKaw650

· #7 · Feb 9, 2010

It's probably lean and needs bigger pilots as others have pointed out, but check the valve clearance anyway. It's part of scheduled maintenance and needs to be done.

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Kenny4

Discussion Starter · #8 · Feb 11, 2010

Appreciate the posts---If I change out the pilots from #40's to #42's, (most of the threads recommend this when UPP's are added but not for stock), if it's too much/too rich how will I know in the seat---What should be a good indicator that it needs to go back to #40's.

Today is Wedn. and I might be leaving tomorrow nite to do about 150 miles of riding---I don't want to do anything that will screw it up---As it starts fine and runs well except for constantly backing off on decel---I love the rumbling sound of it but can't be any good for it to run this way---Also the rear exhaust has been showing black carbon/soot lately, (at 182/185)--I don't have any other jets, but was thinking of trying to change the front to the rear, (185/182), just to see if it does anything noticable.

When I get back will definitely look at valve clearance too---Thanks

Kenny

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