Slight backfire and hesititation

[Diablotin]

it's time to tell to my gf, since i'm saving money I can get already a radial setup and pay back the money haha

I will try reducing the octane to see how it runs, I don't like wasting money anyway
Thanks for the info guys

 

[tugla]

4.55L to 1 imp gal
3.78L to 1 us gal

 

[bagherra]

Well, I did the Seafoam, gave it a fresh tank of 87 gas, and checked the carbs. Did a synch just to bring everything up to spec. It's a little better but still stutters. Usually between 3500-5000. WOT stutters a little and idle is perfect. Pops when decelerating.

After looking around the site it seems my symptoms suggest that's a bit lean. Might be the weather change...you got me. I'll tweak the AF a little to see if I can richen it up a bit.

 

[naughtyG]

After looking around the site it seems my symptoms suggest that's a bit lean. Might be the weather change...you got me. I'll tweak the AF a little to see if I can richen it up a bit.

Considering the rpm range it's happening in, I don't think your A/F screw will help.

You might want to get some small shims (thin washers) and put them under your needle clips to raise them slightly. That should do the trick.

 

[Diablotin]

Btw can I use any replacement for the Seafoam ? I don't find seafoam here but maybe other furl additive for carb engine.

 

[naughtyG]

Get some BG44K - can get it on eBay at a decent price.

 

[bagherra]

Thanks for the shim idea. I'll get some of those.

 

[4gasem]

Btw can I use any replacement for the Seafoam ? I don't find seafoam here but maybe other furl additive for carb engine.

Chevron Techron is another great one.

 

[[email protected]]

I'd run it with some seafoam or BG or whatever for a bit and get some fresh fuel in there and some miles on it before you assume it is a tuning issue.

 

[98Redlne]

Exhaust Gas Technologies has shim kits that fit our carbs. Fairly inexpensive and quick shipping.

EGT Shim Kits

 

[naughtyG]

I had .040 shims on my needles.

That EGT kit could be good - just get one twin kit then use the .030 on two carbs and the .010 and .020 together on the other two. That raises all 4 needles by .030, which should be well enough..

 

[bagherra]

Ok gang, I shimmed the needles and cleaned out the carbs. I forgot that Sean's kit came with some shims ready to use. The 4-5K rpm stumble/pop is gone but it now has an off idle stumble (1.5-3K). It was there before but hard to determine where it happened in RPMs. Now that 4-5K has solidified, the lower rpm stumble is more obvious.

I'll resynch the carbs for good measure, adjust the AF on the carbs, do another synch and give it a go. I'll finish up tomorrow since it's night now. The 4-2 Mark's pipes will anger the neighbors.

As an extra step I've added some Seafoam to the tank. I really think I'm close. I appreciate all your help.

This brings back "good" memories of playing with the carb on my old Roadrunner when dialing it in.

 

[naughtyG]

Sounds like you're getting there, great! Off idle this should mostly be to do with the A/F screw settings, if the carbs are in good sync, I think.
I would maybe try to back off on the Seafoam now and see what straight gas does. Remember Seafoam has alcohol in it too, which may just add to ethanol-induced crapness..

 

[98Redlne]

Another thing to thing about is if your carbs are gummed up now, running seafoam may cause that crap to be blown out.

A couple of tanks from now the bike may need some carb attention again.

 

[gleno]

Well, I did the Seafoam, gave it a fresh tank of 87 gas, and checked the carbs. Did a synch just to bring everything up to spec. It's a little better but still stutters. Usually between 3500-5000. WOT stutters a little and idle is perfect. Pops when decelerating.

After looking around the site it seems my symptoms suggest that's a bit lean. Might be the weather change...you got me. I'll tweak the AF a little to see if I can richen it up a bit.

Sounds like you have a vacuum/air leak in the intake manifolds somewhere.

1) check to see that the carbs are correctly seated in the rubber intake hoses and that all the hose clamps are tight. Don't forget to check the connectors on the V-boost hoses as well.

2) Make sure that the rubber caps on the intake manifold vacuum ports are tight and that the spring clamps are doing their job.

3) Make sure the intake manifolds are tightly secured to the heads and the O-ring seals are sealing properly.

4) Make sure the air box is correctly fitted.

There are some other leak points that can cause deceleration popping but I'd try this first.

 

[mavgrab302]

87 ignites quicker than your higher fuels aswell, messing with spark curve V8s could have some detonation with lower fuels but wouldn't worry about it too much with a bike, high fuels burn slower.

 

[bagherra]

Yeah! I tweaked the AF and it is much better. The low-rpm stumble is 98% gone. I'm going to tweak a little more tomorrow but I think I have it now. Thanks a lot guys! This site rocks!

 

[naughtyG]

Good stuff. Just out of interest, what setting did you end up with on the A/F?

 

[bagherra]

Good stuff. Just out of interest, what setting did you end up with on the A/F?

I added an 1/8 of a turn to what it was originally set at. I didn't count the existing turns.