Topic: Cycle X Carb Conversion decelleration problems

[bmikkalson]

Hi, looking for some ideas on whats wrong with my set up. 76 CB750 all stock sept for  Cycle X  carb conversion. Bike runs good, starts nice, idles nice MID WOT is good. The problem I am having is on deceleration the exhaust shoots big flames out.  I have tried all sorts of different pilot jets with no luck, as well as mains.  If I am cruising around with a real low load on the bike and let off the throttle to idle the bike breaths fire out the exhaust.  Any ideas on what to try??  Here is the exhaust I am running

[mlinder]

Um, where does that exhaust end?

[Shoeboxjoe]

So your bike shoots fire? I see no problem here. 

[Retro Rocket]

Um, where does that exhaust end?

Sorry guys but that would just about be the worst exhaust i have ever seen,good luck on trying to get that to run well.....

Mick

[Doctor_D]

Sorry guys but that would just about be the worst exhaust i have ever seen,good luck on trying to get that to run well.....
Mick

+1

You need about 30" of primary pipe.  What you've got won't cut it.  The "pulse" in the exhaust will return to the engine too soon from the short pipes, causing poor scavenging and confusing the carburetors.  The very unequal lengths don't help either.

[nokrome]

separated at birth 

  you just beat this guy for the most uh... unique honda 4 exhaust 

[nokrome]

oh ya, the shooting fire part
          RIGHT ON !!!!

[mlinder]

The whole length (or lack thereof) could be part of your problem

Can we see a better pic of it? The whole thing?

[lone*X]

I've built a few headers for bracket cars and sprints in my many years and you always match the header lengths from the flange to the collector so all cylinders scavenged equally.  That is the reason a "tuned" header look like a can of worms. You adjust for unequal spans by using appropriate sized curves.  The unequal and too short lengths in your header really change how each cylinder scavenges.  Don't know how you would ever get that to breath equally across all 4 cylinders.  As for flame out the exhaust, watch a NASCAR race.  Chopping the throttle at speed cuts off the air but increased vacuum on the idle jets so it pumps a lot of unburned gas through the motor until it hits oxygen in the hot exhaust.   As for the statement:  "76 CB750 all stock sept for  Cycle X  carb conversion" couldn't be further from reality.  That exhaust changes the whole dynamic of the engine.  An engine has to be balanced, intake and exhaust, and across all cylinders to run properly.  

There is some good reading on the internet for exhaust header design or theory.  You may want to get the welder out again.

[Don R]

I LIKE IT! Just stay away from the forest preserve and fuel puddles. I bet it sounds like a pro stocker.  These machines apparently are very finiky when it comes to the total airflow design.

[bmikkalson]

Thanks, guys. For the replies.  Maybe I will have to just stick with the flames.  My thoughts are many car exhaust headers are not equal. But that may be a different animal.   

[Retro Rocket]

Thanks, guys. For the replies.  Maybe I will have to just stick with the flames.  My thoughts are many car exhaust headers are not equal. But that may be a different animal.   

It is, thats why they usually produce more power and run better with extractors on them and remember, after the header on a car they have a long exhaust pipe and mufflers to give back pressure to the system.

Mick

[bmikkalson]

I hear what your saying about the length, but my original thought was based on a turbo bike where the exhaust dumps right after the turbo. The turbo may be enough of restriction in the exhaust.  I guess I could try blocking the plate a little and see if some back pressure helps.

[Retro Rocket]

I hear what your saying about the length, but my original thought was based on a turbo bike where the exhaust dumps right after the turbo. The turbo may be enough of restriction in the exhaust.  I guess I could try blocking the plate a little and see if some back pressure helps.

Yeah, i know what you are getting at but a turbo is a completely different thing all together, you can't use half a turbo system without the turbo and dump pipe and expect it to work....

Mick

[mlinder]

Pics of the whole thing, please.

[scondon]

I think that IS the whole thing, 'linder. The shadow at the bottom is the lip of the "tailpipe." 

I don't care if it runs like a dump truck, I WANT ONE! Turn it sideways so I can shoot a sonic barrage of flames at the next driver yakking away on their cell who drifts into me unawares

[bmikkalson]

Ya, thats the whole thing. The canister on the end is actually small glass pack.   

[mlinder]

Ya, then you'll never get jetting correct.

[bmikkalson]

The bike idles and runs just fine, great top end power. The only problem I cant get rid of is the flame thrower effect.   I realy get a flame when going from about 1/8 throttle to idle when crusing. Or if I am making a WOT pass and go to idle it makes lots of crackle and flames. I tried blocking off half of the muffler to see if some back pressure would help. No still shot flames.

Long story short the exhaust looks killer (my, .02) and sounds mint. But I cant have a fire breathing monster at night, attracts the fuzzz.

[gtyler5]

what conversion do you have? have you contacted cycle x? they have been pretty supportive in my experience and know their stuff. have you adjusted the valves and timing?

[mlinder]

Actual headers with some kind of muffler is what reduces flames from the back exhaust...

You don't have any mufflers, and your headers are basically too short to suppress anything either.