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4th gen -94 Another OKI replica :), carb set-up?


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Hello! New forum member, first post!

Have almost completed the building of a budget OKI 91-93 replica. 94 VFR+RC45 farings. Have a slip-on and is also planning to run just the connection pipe for sound of it :).

Would like to remove airbox lid, but have heard that calls for major re-set of needles and jets. Searched but did not find any thread about it?

And some pitcures to make it a bit more interesting!

Looking fwd to hear the visdom from the croud!

BR /Per from Sweden.

Snett framifrån.jpg

Min hoj sida.jpg

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Hej Per!

 

Stunning looking bike.

 

 

Why would you want to remove the airbox lid?

More induction sound? Remove the rubber snorkel at the front. That will have no ill effect on performance imho.

Removing the lid or drilling holes WILL require dyno time abd rejetting.

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3 hours ago, PerH said:

Hello! New forum member, first post!

Have almost completed the building of a budget OKI 91-93 replica. 94 VFR+RC45 farings. Have a slip-on and is also planning to run just the connection pipe for sound of it :).

Would like to remove airbox lid, but have heard that calls for major re-set of needles and jets. Searched but did not find any thread about it?

And some pitcures to make it a bit more interesting!

Looking fwd to hear the visdom from the croud!

BR /Per from Sweden.

Snett framifrån.jpg

Min hoj sida.jpg

Very nice!

 

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Great looking bike, thanks for sharing. 
 

Regarding removing the air box lid, doing that would *greatly* increase the amount of air coming to the carburetors so to keep the air/fuel ratio correct you would also have to increase the amount of fuel coming in by installing larger jets and/or changing the needle settings. But, there is a limit to what any engine needs as far as air and fuel, without things like larger intake runners, camshafts, exhaust, you can overwhelm the engine. Plus, if you removed the air box lid I’m not sure how you would secure the filter. Overall what others have said, about all you would want to do is remove the snorkel and then add extra fuel by re-jetting.  Most Japanese bikes with carburetors are on the edge of running lean (too much air) from the factory anyway, you definitely do *not* want to add more air without adding more fuel.

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Thanks for the kind feedback on looks. Think it turned out as good as garage(rattle can) paint job can do :).

About fueling. SO it's ok to remove snorkel for more noise but not lid. Thought that snorkel was also leaning out to much and causing a flat spot if not re.jetted or other needles was used.

I was hoping that somebody had done the maximum air, std system with slip-on + dyno with altered jetting that I could use as base point. Working with access to the carbs on these bikes are challenging hehe. You get a bit spoiled when having been use to injection type of bikes. But it's a special feeling with carbs, starting, heating up... Takes you back to first 4 stroke bike that was a CBR 900 RR -92. I think I will Keep as is for time being as it did run great after cleaning of carbs and I have only done  a couple of miles on it before painting, last autumn.  Spring is hopefully here in some weeks time. Thanks everybody! Will add some more pictures that I have and than with indicators and final stickers on it.

/Per 

Aft_side.jpg

fwd.jpg

instruments.jpg

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22 minutes ago, PerH said:

Thanks for the kind feedback on looks. Think it turned out as good as garage(rattle can) paint job can do :).

About fueling. SO it's ok to remove snorkel for more noise but not lid. Thought that snorkel was also leaning out to much and causing a flat spot if not re.jetted or other needles was used.

I was hoping that somebody had done the maximum air, std system with slip-on + dyno with altered jetting that I could use as base point. Working with access to the carbs on these bikes are challenging hehe. You get a bit spoiled when having been use to injection type of bikes. But it's a special feeling with carbs, starting, heating up... Takes you back to first 4 stroke bike that was a CBR 900 RR -92. I think I will Keep as is for time being as it did run great after cleaning of carbs and I have only done  a couple of miles on it before painting, last autumn.  Spring is hopefully here in some weeks time. Thanks everybody! Will add some more pictures that I have and than with indicators and final stickers on it.

/Per 

Aft_side.jpg

fwd.jpg

instruments.jpg

 

Tinkering with the airbox will yield no performance (hp or torque) improvements to the engine's output and as mentioned above can result in flat spots and other undesirable rideability issues.   The airbox is tuned to the engine to give it the optimum air / fuel mix for any given rpm / load.  The thread below has a great explanation of the airbox's purpose and function (you may have to scroll up to see BusyLittleShop's explanation).  Even though you're working with carbs vs FI, the principles of airflow volume and speed remain the same.  Honda got all the performance out of the engine that it can give by tuning the airbox - best practice is leave it factory stock.  If there were gains to be had, Honda would not have left that on the table.   If desired, removing the PAIR system from it will shed a few pounds and won't affect performance or smoothness of delivery. 

 

https://www.vfrdiscussion.com/index.php?/forums/topic/97395-full-exhaust/&tab=comments#comment-1122398

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No question about honda knowing how to design engines. But they have been very conservative from time to time. It might very well be what you state and for sure, the thread about rc45 you passed on shows just how sensitive it can be. I thought that snorkel was to limit induction noise. Having said that, reaching +10% of filling efficiency sound very much. I though that main focus was to keep velocity right in runner as well as length right for getting convergating pressure pulse at intake valve closing. Anyway. Have experince as well just how much can be lost by fitting an aftermaket exhaust. Bought an aftermarket Muzzy 4-1 race exhaust for my 96 zx7. Was back in 97 when I did not know what I do today. Have a master in mech engineering where we had some corses in engine theory and have been working with hydrodynamics for 15 years. Neither did I understand why the std exhaust looked so funny from the visual 4-1. It was actually a 4-2-1 org. So result? Bike run like absolut crap between 3500-9500rpm, farting and popping like crasy. Ended up putting on the std pipe again.

 

anyways. I would die for learning what hrc did to the rc45 engine to reach 180+bhp. Just imagen if one could get a hold of the building spec of such motor... that’s same as getting 240bhp from a 1000cc engine.

Thanks for the very interesting stuff everybody! Made my day! All the best!

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13 hours ago, Cogswell said:

 

 If desired, removing the PAIR system from it will shed a few pounds and won't affect performance or smoothness of delivery. 

 

 

 

EU 750's never got this PAIR crap :laugh:

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Aye, to compensate for their gas guzzling V6 and v8 cars maybe?  :laugh:

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S4?  Sold mine when I moved to Europe, always thought I'd buy another one and go all Devek on it... Er, never happened!

 

Ciao,

 

JZH

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