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Discussion Starter · #182 ·
sprayed the insulators with brake cleaner and the bike stalled. replaced the boots with new ones and all seemed ok...until i took it out on a test ride. idle at stop is ok. mid range and WOT absolutely dog slow. lots of sputtering and very low power. sprayed the new boots and bike stalled again.

is there a logical step by step for checking the circuits. i tried re-jetting, but didn't seem to change things. carbs were rebuilt 500 miles ago and i'm hesitant to break them apart again. but i'm getting a little frustrated and trying to make sense of the issues. i've got good compression, good spark and clean fuel.

I wrapped the exhaust. and i'm using a non-stock air box. i know these things require changing things from stock, but...
 

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you could always just get yourself a set of Keihin CR or FCR carbs and join the cool kid club...
 

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Discussion Starter · #186 ·
thanks. usually go thru Dynoman Performance. I do have a webike account. good stuff there.
 

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thanks. usually go thru Dynoman Performance. I do have a webike account. good stuff there.
I've purchased a lot from dynoman too. Theres a lot of backordered stuff right now, I'm on their waiting list for a CR29 rebuild kit.

Webike is super reliable and reasonably priced. The $30 DHL shipping is very fast too.
The only downside is all the instructions you get are in Japanese, so you'll want to download the Google translate app on your phone.
 

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Discussion Starter · #188 ·
thanks. I'm going to try to get this CV to work. put permatex sealant on to account for anything that is breaking the vacuum. also, i'm going back to the drawing board on jetting. if it's cutting out mid range, i'm running too lean.

btw, love the quote from alwhite00 you have on your response.
 

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Discussion Starter · #189 ·
went back to basics, starting with the stock jet sizes and A/F setting. idle is solid, steady and adjustable. nothing weird with the idle circuit. going from idle to 1/4 throttle causes the engine to stall consistently. no leaks with new intake boots. looking for ways to diagnose if this is a too lean or too rich situation. or if this is strictly something with the pilot jetting...

just playing with this carb rack until my CR31 rack arrives.
 

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Will it rev in neutral?
check your float height recently?
engine Idling on all cylinders? Exhaust pipes all getting hot equally?
I mean 4 cylinder engines will run (not well, but at least run) on such a HUGE range of a/f ratios that for it to die, something drastic must be wrong.
 

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went back to basics, starting with the stock jet sizes and A/F setting. idle is solid, steady and adjustable. nothing weird with the idle circuit. going from idle to 1/4 throttle causes the engine to stall consistently. no leaks with new intake boots. looking for ways to diagnose if this is a too lean or too rich situation. or if this is strictly something with the pilot jetting...

just playing with this carb rack until my CR31 rack arrives.
Get four washers of equal thickness and put them under the needles to shim the needles up. That will slightly richen the low to low-mid throttle.
104894
 

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the engine die-ing at just off idle, I bet there is still an issue with the idle circuit/pilot and not even getting to the needle and needle jet part of the fueling...

it sounds like a throttle cutaway issue, but more likely probably an issue in the carbs itself with that initial vacuum signal?
 

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Discussion Starter · #193 ·
fffff
Will it rev in neutral?
check your float height recently?
engine Idling on all cylinders? Exhaust pipes all getting hot equally?
I mean 4 cylinder engines will run (not well, but at least run) on such a HUGE range of a/f ratios that for it to die, something drastic must be wrong.
will not rev in neutral. floats are all new (non-adjustable, like original), sync'd and checked all cylinders engaged when idling. exhausts are wrapped, which means i need to adjust jetting, i believe. also, have a custom air box from Steel Dragon Performance (www.steeldragonperformance.com). designer of this product said it was designed to work at stock setup.
104898


pilot jet too small? primary? Secondary? needle set (forgot about the washer idea...thanks 8Ball)? Are there cross reference guides to jets based on, say, vacuum pressure readings? tried a lot of different combinations so far, but idle to mid-range continues to be an issue.
 

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Polished off my Honda DOHC carb cleaning manual from Mike Nixon...

According to my info, the early dohc models used metal tangs on float. 81 and later used non adjustable float. But whatever...

Who did the carb cleaning? These carbs have more holes than... (you fill in the blank)

One of these holes is called the bypass outlet. Transition holes are another name used. Just off idle, as you crack the throttle plate, you expose the bypass hole and fuel is drawn in. On the schematics, this is not controlled by the idle mix screw and like the idle circuit piggybacks off the primary main jet.

Depending who cleaned the carbs, they may or may not have made sure this opening was cleared. And could contribute the off idle stalling...

Apparently the US cb750 carbs were jetted extremely lean at idle and off idle. An accelerator pump was added to keep the bike running. This might also be an issue if clogged or not functional. But less likely given the small throttle openings you are having trouble with.

Your slow jet (or idle jet) is pressed in (at least it should be on a 3 jet carb) and cannot be replaced. If for some reason they are replaceable (some places say some models post 81 had removeable slow jets. the cb1100f had removeable slow jets and only 1 main), you are in luck! definitely bigger might cure some of your problems.

fffff

will not rev in neutral. floats are all new (non-adjustable, like original), sync'd and checked all cylinders engaged when idling. exhausts are wrapped, which means i need to adjust jetting, i believe. also, have a custom air box from Steel Dragon Performance (www.steeldragonperformance.com). designer of this product said it was designed to work at stock setup.
View attachment 104898

pilot jet too small? primary? Secondary? needle set (forgot about the washer idea...thanks 8Ball)? Are there cross reference guides to jets based on, say, vacuum pressure readings? tried a lot of different combinations so far, but idle to mid-range continues to be an issue.
 

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went back to basics, starting with the stock jet sizes and A/F setting. idle is solid, steady and adjustable. nothing weird with the idle circuit. going from idle to 1/4 throttle causes the engine to stall consistently. no leaks with new intake boots. looking for ways to diagnose if this is a too lean or too rich situation. or if this is strictly something with the pilot jetting...

just playing with this carb rack until my CR31 rack arrives.
turn the air screws... that's one way.
blipping the throttle is another...
typically if lean at idle, the bike rpms hang and is slow to come back down.
if rich, the bike bogs and can drop below idle rpms and even stall.
 

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Discussion Starter · #197 ·
hhhh
turn the air screws... that's one way.
blipping the throttle is another...
typically if lean at idle, the bike rpms hang and is slow to come back down.
if rich, the bike bogs and can drop below idle rpms and even stall.
thanks!
 

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Make sure your bike is up to operating temp.
So that's a good way to know what a lean condition is like. When the bike is cold, more of the fuel not in a combustible form (droplets and condensed fuel on the walls) and the bike is relatively lean. If you blip the throttle when warming up, you get that lean rev hang.
Other things you could try is to pull the choke a little. see if it runs better or worse. Look at the plugs. exhaust smell...
 

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if it won't rev off idle i'd start with pilot jets. but if you can't change pilot jets, you're a bit screwed.

can you put the std airbox back in and see if it fixes it? or std pipe? at least then you'll way which way you've fucked it. cv can be a real pita, and anything you do upstream (airbox side) generally generates more issue than downstream.

fcr seem real expensive until you've disappeared up your own arse in confusion trying to make the unworkable work. or some cv from a later thing you can get a jet kit for - 600 of some variant?
 

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... and if all else fails, money and time is apparently no object so get rid of those BS CV carbs and put something simple on there that can work :cool:
 
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