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Discussion Starter #1
This is on a BC750k5.

I synched the carbs and adjusted the floats. Now that it is back together, I have no power when I go WOT ( i did before). once i twist the throttle all the way, it boggs and loses speed/power. If I let the throttle up to 2/3's it will gain power again and speed up.

can synching the carbs make me lose power at WOT? The power was there before, but not now.

One other thing I did was to reroute the fuel line throught one of the holes in the carb rack. now the fuel line goes down slightly and then back up before it hits the split to each carb? Is fuel gravity fed or sucked from the tank, or both?

Any ideas would be great.
 

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Mut
The gas is gravity feed from the tank to the carbs - try re-routing the gas lines again. Sounds like your sucking your gas lines dry.
 

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Discussion Starter #3
I re routed the gas line back to how they were. It didn't help.

I am still bogging at full throttle.

Does synching the carbs have anything to do with performace at WOT? Is it possible that by seting the floats and synching carbs it would become apparent that my main jet is too small?

As a reminder, it ran great at WOT before i set the floats and synched the carbs.

When synching the carbs, i left only one thread visable above the lock nuts. There had been 2-3 threads viable before i fuct with it.
 

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Sounds to me like you're losing a cylinder or two at full throttle. And no, it's not really possible - that is to say, you may or may not get that impression, but unbalanced carbs won't operate better than balanced carbs under any reasonable circumstance (barring, say, dramatic weather or elevation changes).

If it were my machine, I'd ride it wide open til it bogs, turn off the fuel tap, grab the clutch, kill the engine and coast to a stop. Then I'd drop the float bowls and see if any of them are empty. If so, you've proved the fuel-starvation theory. Then I'd check the plugs - if one of the cylinders is cutting out at WOT because your carbs are unbalanced, it'll in all likelihood have wet gas on it, or at least some fresh fluffy carbon deposits from a really inefficient burn. If it's cutting out because of fuel starvation, it'll look like it was running lean (white, etc).

Re-reading your post, I have a suspicion that you've set at least one of your float levels too low (tang too far bent). Try this: open your fuel tap, let the bike sit for a few minutes (off), then close the tap and pull your float bowls. The levels should be the same, and in most cases, 1/2 - 2/3 up the bowl.
 

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Discussion Starter #5
Xander,
Thanks, I'll try it all.

Would poorly adjusted floats effect WOT?

Also, a stranger walked up to me and said he thought I was missing on a cylinder. If I am missing at WOT, i am guessing that is a timing issue.

On an electric ignition, where would you set the timing? If I am looking at the plate, would you have the slot where the screw secure the plate centeres, adjusted clockwise slightly (or a lot) or counterclockwise?

Thanks
 

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mut -
I have a similar bike (cb750), your float level on these bikes is a critical tuning operation. You also need to also take a look at the jet size and the needle position on the sliders. You didn't mention if you have headers, big motor or other mods to the bike. I'll finish this posting a little later.

To Finish this reply;
The main jet is where the fuel travels during WOT operation - so if there is not enough fuel in the carb bowl then the motor will stumble much like your describing. Don't overlook the filter screen in the petcock of the gas tank. If that gets clogged with stuff from the gas tank, and the filter is slightly clogged, that would lead to less fuel going to the carbs also.

Finally - the needle setting on the slider will dictate how much fuel is allowed to the engine during various throttle operations. So if you have mods done to the engine or exhaust - the needles may need to be moved and/or a bigger jet installed.

hope this helps - keep us posted
 

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quote:Originally posted by mut

Xander,
Thanks, I'll try it all.

Would poorly adjusted floats effect WOT?

Also, a stranger walked up to me and said he thought I was missing on a cylinder. If I am missing at WOT, i am guessing that is a timing issue.

On an electric ignition, where would you set the timing? If I am looking at the plate, would you have the slot where the screw secure the plate centeres, adjusted clockwise slightly (or a lot) or counterclockwise?

Thanks
Yes, poorly adjust floats would affect running throughout the range, especially if they were off in the direction of less fuel. Also, there's no reason to think missing at WOT would be timing as opposed to carburetion - throughout the range both are critical.

If you think your timing is off, check that before you proceed with carbs, it'll only make carb tuning harder. However, given that your bike ran well at WOT BEFORE you worked on them, I fail to see why you'd think that timing is the issue now, as opposed to maladjusted carbs.

If a cylinder is being dragged by the others, it has a tendency to shut off - you might find that by adjusting the cylinder that's missing to pull a bit more, it will want to stay on at high revs. But do check your float levels.
 

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Discussion Starter #8
OK. I turned the petcock on, waited a minute, turned it off and then pulled each of the bowls to see if they were getting gas. One was not. I tapped the needle and it freed up.

I also adjusted the floats as good as I could. They really are mangled. I have new ones on the way.

I think that I have them adjusted fairly close. But, the bike is still acting fuel starved at high rmps. It bogs down until I let off the throttle some. Once I let off the throttle a little, the bike starts to run smooth and can still pick up speed.

I have a good spark. I have the timing adjusted per the specs in the manual.

It does have emgo pod filters and a kerker 4-1 with a new race baffle.
It does have a keyster carb rebuild kit in it.

I am thinking that either it is not getting enough air at high rpms or that the main jet is the wrong size (too small). I live at 7000ft and have a 105 (stock) jet in it.

Any ideas?

Thanks
 

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Discussion Starter #9
OK. I turned the petcock on, waited a minute, turned it off and then pulled each of the bowls to see if they were getting gas. One was not. I tapped the needle and it freed up.

I also adjusted the floats as good as I could. They really are mangled. I have new ones on the way.

I think that I have them adjusted fairly close. But, the bike is still acting fuel starved at high rmps. It bogs down until I let off the throttle some. Once I let off the throttle a little, the bike starts to run smooth and can still pick up speed.

I have a good spark. I have the timing adjusted per the specs in the manual.

It does have emgo pod filters and a kerker 4-1 with a new race baffle.
It does have a keyster carb rebuild kit in it.

I am thinking that either it is not getting enough air at high rpms or that the main jet is the wrong size (too small). I live at 7000ft and have a 105 (stock) jet in it.

Any ideas?

Thanks
 

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i would have said go up a size or two on the main jets (ie wfo jets) given your carb/exhaust mods. 7000' modifies my thinking a bit but i still suggest trying out bigger mains.
-parks
 

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i would have said go up a size or two on the main jets (ie wfo jets) given your carb/exhaust mods. 7000' modifies my thinking a bit but i still suggest trying out bigger mains.
-parks
 

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The rebuild kit you used could be your problem. I have a similar setup with my cb750 and I used the keyster carb kit also. One of my carbs pissed gas all over the ground after I got the carb back on the bike. I ended up taking out the fuel valve needle on that carb and replacing the old fuel valve needle to stop the overflow problem. I have a Kerker with pods setup and K1 carbs. My main jets are 120 with a 40 pilot jet. (stock carb jets are 110 with 40 pilots) I still think my bike is jetted too low and plan to increase the main jet to 125 (another two jet sizes). I'm also at sea level...

I'm also thinking I need to increase my pilot jet size by one size. My plugs look a little whiter than they should (reason for jet size increase) plus when hot I'm hearing a little pre-detonation at idle. Again this could be more timing issues problems vs carb problems. (Last time I checked, my timing was spot on - but it needs to be checked again...)

From everything I've read on the subject - you have to get the main jets right first before the remaining tuning of the carbs can be accomplished. The only way to tune the mains is via plug chopping. My carb tuning guide recommends two jet sizes for the kerkers and two jet sizes for the pods (2.5 increments = 1 jet size). For every three main jet size change adds one size increase in the pilot jet. The stock K1 carb main jet size is 110's - If your stock jets are 105's, try going to 115's (4-jet size increase) and see if that helps.
 

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The rebuild kit you used could be your problem. I have a similar setup with my cb750 and I used the keyster carb kit also. One of my carbs pissed gas all over the ground after I got the carb back on the bike. I ended up taking out the fuel valve needle on that carb and replacing the old fuel valve needle to stop the overflow problem. I have a Kerker with pods setup and K1 carbs. My main jets are 120 with a 40 pilot jet. (stock carb jets are 110 with 40 pilots) I still think my bike is jetted too low and plan to increase the main jet to 125 (another two jet sizes). I'm also at sea level...

I'm also thinking I need to increase my pilot jet size by one size. My plugs look a little whiter than they should (reason for jet size increase) plus when hot I'm hearing a little pre-detonation at idle. Again this could be more timing issues problems vs carb problems. (Last time I checked, my timing was spot on - but it needs to be checked again...)

From everything I've read on the subject - you have to get the main jets right first before the remaining tuning of the carbs can be accomplished. The only way to tune the mains is via plug chopping. My carb tuning guide recommends two jet sizes for the kerkers and two jet sizes for the pods (2.5 increments = 1 jet size). For every three main jet size change adds one size increase in the pilot jet. The stock K1 carb main jet size is 110's - If your stock jets are 105's, try going to 115's (4-jet size increase) and see if that helps.
 

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run some seafoam through it. If you have a sticking needle then you are dropping a cylinder when that float closes it up, some fuel cleaner will clean out any gunk that might be causing the needle to stick.

when you synch the carbs, carb #2 is your baseline, did you use that as your base or did you just adjust all carbs until they measured up?
 

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run some seafoam through it. If you have a sticking needle then you are dropping a cylinder when that float closes it up, some fuel cleaner will clean out any gunk that might be causing the needle to stick.

when you synch the carbs, carb #2 is your baseline, did you use that as your base or did you just adjust all carbs until they measured up?
 

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Geeto - baseline on #2 carb??? That's interesting - makes sense to baseline but why use #2 carb as the baseline???
 

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Geeto - baseline on #2 carb??? That's interesting - makes sense to baseline but why use #2 carb as the baseline???
 

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I had had the same problem on my cj360t, it turned out to be a torn diaphragm. A litte elmer probond glue and now it flys.
 

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I had had the same problem on my cj360t, it turned out to be a torn diaphragm. A litte elmer probond glue and now it flys.
 

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it sounds to me like you either did not sync the carbs correctly or set the float levels too low


I mean it makes sense, the only thing that changed was the float level and slide adjustments

and then it started running like crap on the top

guess next time you decide you are going to do multiple tasks, you will check the bike out after performing each individual change

I mean I'd suggest that anyhow
 
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