Author Topic: why is my 750 boggin 1/16 -3/4?  (Read 3026 times)

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Offline Artf0rm

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why is my 750 boggin 1/16 -3/4?
« on: March 18, 2012, 06:20:19 PM »
So I got a really nice idle going with my CR-specials on my 750 tonight but every time I twist open the throttle sharply it tries to die.  If I twist it open super, super slow it will make it through that bogging and really rev up nicely.  Falling back down to idle just like it should when I snap the throttle closed.  Whats going on?

Offline BobbyR

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #1 on: March 18, 2012, 06:34:07 PM »
What year and model is it?
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Offline Artf0rm

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #2 on: March 18, 2012, 06:39:56 PM »
1976 Cb750.

Offline dfoxengr

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #3 on: March 18, 2012, 07:36:34 PM »
is there a booster on those that isn't functioning?

Offline Artf0rm

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #4 on: March 18, 2012, 08:32:19 PM »
no booster.

Offline Stev-o

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #5 on: March 18, 2012, 09:11:49 PM »
Stock exhaust?  Air box installed?? Any mods???
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Offline andrewk

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #6 on: March 18, 2012, 10:09:06 PM »
CR-specials as in race carbs?  (http://www.sudco.com/cr.html)

Offline heffay

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #7 on: March 18, 2012, 10:17:18 PM »
Sounds rich, what does adding choke do to that bad range?
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Offline Retro Rocket

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #8 on: March 18, 2012, 10:41:34 PM »
CR-specials as in race carbs?  (http://www.sudco.com/cr.html)

Yep, CR race carbs,  i haven't seen the build but they are race carbs and are meant for wot operation, they are not the best carb for the street, if they are on a stock engine i am not surprised it bogs down low, even on a warmer engine they will do the same thing. They don't have much of an idle circuit and aren't meant to work well at low revs....

Heffay, if its running rich at low revs the choke will just kill it completely....

I prefer RS Mikuni's or the older Mikuni smoothbores off the old Kawasaki's, infinitely more tunable..
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Offline heffay

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #9 on: March 18, 2012, 10:48:25 PM »
CR-specials as in race carbs?  (http://www.sudco.com/cr.html)


Heffay, if its running rich at low revs the choke will just kill it completely....



And this is how you troubleshoot
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Offline Retro Rocket

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #10 on: March 18, 2012, 11:09:13 PM »
10 points Mr obvious.... :P
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Offline heffay

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #11 on: March 18, 2012, 11:17:07 PM »
Don't act like you weren't goading for a response
Today: '73 cb350f, '96 Ducati 900 Supersport
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Offline Retro Rocket

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #12 on: March 19, 2012, 02:40:51 AM »
Don't act like you weren't goading for a response

I thought i was pointing out the obvious....  Whatever
750 K2 1000cc
750 F1 970cc
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If You can't fix it with a hammer, You've got an electrical problem.

Offline DJ_AX

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #13 on: March 19, 2012, 05:29:18 AM »
I thought the obvious answer would simply be... replace the carbs with the right ones.

(somebody had to say it :-)
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Offline Artf0rm

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #14 on: March 19, 2012, 06:57:15 AM »
Ok, so I'm in a better place to provide some additional information now.  The engine is stock with Carpy's Yoshi replica 4-1 and CR-special Carbs with pod filters.  I was having an issue where the bike would idle fine but occasionally randomly rev really high and slowly return to idle.  I checked for air leaks and everything looked fine so I raised the needle position by 1 clip and the idle smoothed out and it is now even easier to start, even cold.  I also checked all the fuel lines to make sure they are not clogged, everything looks good.  I checked the jets and they all looked clean.  (I am running 120 mains).  Today at lunch I am going to reset the needle positions an start over.   

When I turn the

Offline Duke McDukiedook

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #15 on: March 19, 2012, 09:54:44 AM »
So lemme get this straight- you put on ze podz, Crapy's pipes AND race carbs that pretty much only run well at WOT and you are wondering why you get poor throttle response. Hmmmmm.  ::)

Did you get it running properly with the stock airbox on first to get a baseline- I mean to see if the bike runs properly at all?

So you throw on all this race stuff without reworking the engine at all- makes perfect sense to me.  :o
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Offline heffay

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #16 on: March 19, 2012, 10:32:23 AM »
so lemme get this straight...

a guy buys a bike that is thrashed, missing lots of stock parts... guy is supposed to buy all the stock parts, get it running, AND buy all the parts he actually wanted to put on to make it his own? 

not saying that is artform's situation... but that makes sense to me, NOT   ::) :o ::)
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Offline Artf0rm

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #17 on: March 19, 2012, 03:54:35 PM »
yeah, Dukie.  This bike came to me with 3 pod filters and spray painted rattle can flat black but I digress..

New developments!  I dropped the needles back down to where they were before, reset the air screws and fiddled with them.  I now have a full power bad and what I would describe as good throttle response.  I will need to take it to someone much more specialized to get if fine tuned.  Now I just have to figure out why my clutch is now suddenly not engaging.

Offline Rigid

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #18 on: March 19, 2012, 04:20:13 PM »
Don't let the haters turn you off.  Some of us are here to help.  Glad you got it sorted out, almost.
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Offline Artf0rm

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #19 on: March 19, 2012, 04:56:35 PM »
Don't let the haters turn you off.  Some of us are here to help.  Glad you got it sorted out, almost.

Thanks Rigid.  Small Victories!  I'm sure dukie is trying to help in his own "special" way.

Offline Duke McDukiedook

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #20 on: March 19, 2012, 10:32:10 PM »
I am. And I am not hating, I just don't understand the rationale with the build so far. I would want to make sure the bike runs in stock condition (close as possible) before I went making a bunch of changes to the intake, carburation, exhaust, etc.

Unfortunately when you go farther from stock to determine if the bike runs well at all it makes it harder for us to help you. As you probably know by now those CR carbs are pretty much poop for anything besides WOT- they are racing carbs after all meant to go full bore unlike street riding where you are mostly idling and staying in the 4-6k power band most of the time.

But each to his own I guess.
In hindsight the money you spent on the pipes and carbs could have been spent on things that actually affect performance- you could have ported the head and chucked a hot cam in for the money you spent on the crapy pipes and CR carbs- and gotten a pretty good performance boost.

Have you run the bike with the stock carbs in the beginning to see if the bike runs properly in the first place? Checked your timing, spark, fuel to rule all those gremlins out?
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Offline Retro Rocket

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Re: why is my 750 boggin 1/16 -3/4?
« Reply #21 on: March 19, 2012, 10:53:16 PM »
I am. And I am not hating, I just don't understand the rationale with the build so far. I would want to make sure the bike runs in stock condition (close as possible) before I went making a bunch of changes to the intake, carburation, exhaust, etc.

Unfortunately when you go farther from stock to determine if the bike runs well at all it makes it harder for us to help you. As you probably know by now those CR carbs are pretty much poop for anything besides WOT- they are racing carbs after all meant to go full bore unlike street riding where you are mostly idling and staying in the 4-6k power band most of the time.

But each to his own I guess.
In hindsight the money you spent on the pipes and carbs could have been spent on things that actually affect performance- you could have ported the head and chucked a hot cam in for the money you spent on the crapy pipes and CR carbs- and gotten a pretty good performance boost.

Have you run the bike with the stock carbs in the beginning to see if the bike runs properly in the first place? Checked your timing, spark, fuel to rule all those gremlins out?

Forget Rigid Dukie, he just has no idea....  I couldn't understand the rationale at all either, i agree that the money spent on carbs and pipe could have achieved far better results if used on the right applications.

What were your expectations of the CR's and pipe.? In my opinion they are the wrong parts for a stock engine, the pipe is fine with a rejet of the stock carbs but why CR's.? you will get poor fuel economy for virtually no gain. The up and down idle will be the pods, once again, these carbs are built to run velocity stacks, either use K&N pods with the built in velocity stacks or try and run them with the stock airbox and jet them down to suit.  No hating here either.... ::)
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
If You can't fix it with a hammer, You've got an electrical problem.