A little hesitation

bbf
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A little hesitation

Post by bbf »

Ok, so I've been a member for some time and have read a lot of the carb threads. But I have a question regarding carbs and where to start. I just double checked the sync and it's dead on. Plugs look really good as well. So my I'm wondering why when the bike gets under load( me riding) it wants to spit and sputter at half throttle for a few seconds before clearing. It doesn't matter what gear either. The bike is a 1400 with k&n drop in filters and a stage 1 jet kit from factory pro. The exhaust is straight piped but has lollipops set about 4" from the end. Just wondering if anyone else has had this issue and what worked for you... or am I gonna have to go through air/fuel tweaks, needle height adjustments and etc....

Thanks
Lee

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Herb
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Re: A little hesitation

Post by Herb »

Does giving it a little more throttle clear it up?

If so, it is probably the needle set a little too low.
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Re: A little hesitation

Post by bbf »

Herb wrote:Does giving it a little more throttle clear it up?

If so, it is probably the needle set a little too low.
Thanks for the reply Herb!
Once I hit 3/4 to full throttle its good. When the throttle is held steady it's good. But to get to 3/4 to f/t it starts to pop/backfire and hesitates for about 3 seconds. Then its hold on cause she's movin!

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BRONX INTRUDER
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Re: A little hesitation

Post by BRONX INTRUDER »

bbf wrote:
Herb wrote:Does giving it a little more throttle clear it up?

If so, it is probably the needle set a little too low.
Thanks for the reply Herb!
Once I hit 3/4 to full throttle its good. When the throttle is held steady it's good. But to get to 3/4 to f/t it starts to pop/backfire and hesitates for about 3 seconds. Then its hold on cause she's movin!
Kinda lost me there.
1st sentence says 3/4 - full it's good.
3rd sentence says get to 3/4 - full starts to pop/ backfire and hesitate for 3 seconds.
So she's acting-up for only about 3 seconds after you just hit 3/4 and only at that point; regardless of gear?

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Re: A little hesitation

Post by bbf »

BRONX INTRUDER wrote:
bbf wrote:
Herb wrote:Does giving it a little more throttle clear it up?

If so, it is probably the needle set a little too low.
Thanks for the reply Herb!
Once I hit 3/4 to full throttle its good. When the throttle is held steady it's good. But to get to 3/4 to f/t it starts to pop/backfire and hesitates for about 3 seconds. Then its hold on cause she's movin!
Kinda lost me there.
1st sentence says 3/4 - full it's good.
3rd sentence says get to 3/4 - full starts to pop/ backfire and hesitate for 3 seconds.
So she's acting-up for only about 3 seconds after you just hit 3/4 and only at that point; regardless of gear?
Sorry Bronx, brain goin faster than I type or brain lapse. Lol. It's the mid throttle range where it starts the hesitation. So starting out easy on the throttle it's fine... once I hit the mid throttle range it starts to act up. Then if I get the throttle to the 3/4 to wide open it gets through the hesitation and takes off. Hope this clears up what I'm talking about and not more confusing. Hahaha. So basically I have to putt through the gears or start to putt then bust on the throttle to get through the mid range hesitation.

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Re: A little hesitation

Post by m2h »

bbf wrote:Ok, so I've been a member for some time and have read a lot of the carb threads. But I have a question regarding carbs and where to start. I just double checked the sync and it's dead on. Plugs look really good as well. So my I'm wondering why when the bike gets under load( me riding) it wants to spit and sputter at half throttle for a few seconds before clearing. It doesn't matter what gear either. The bike is a 1400 with k&n drop in filters and a stage 1 jet kit from factory pro. The exhaust is straight piped but has lollipops set about 4" from the end. Just wondering if anyone else has had this issue and what worked for you... or am I gonna have to go through air/fuel tweaks, needle height adjustments and etc....

Thanks
Lee
Hi Lee, could be a number of things going on here. If synch is good have you tried A/F adjust to get best idle? Idle at 1000rpm.? You say it has a stage one kit so am not sure if they give you new pilot jets with that kit. I say that because your issue with steady revs and it playing up can be related to the pilot jets which are in use at that stage. If they are too small the bike tends to surge on and off and the popping sounds like a lean mixture. The other thing, the position of the lollipops can have an effect on mid range performance. When i ftted QQ- baffles on mine they said to set them 6" from the end. Slant cuts can affect where they go also. If they have locknuts externally you could try loosening them and twist the lollipop more in line with the pipe and see if that makes a difference by reducing back pressure. More than likely it will make your issue worse but it could mean you might need to move them deeper. Dont know if that is an easy thing for you. Just my 2 c worth buddy. Good luck :cheers:
M2H
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Re: A little hesitation

Post by bbf »

Thanks m2h for the reply. My schedule has been so crazy lately I haven't had time to really check back on the forum board or tinker on the bike. I did however ride the bike to work on Friday. On the way to work it ran like a champ. It was around 60 degrees. But on the way home it started acting up again and the temp was mid 80's. Not sure why it ran ok at a cooler temp. Hopefully I can tinker with it this weekend. Thanks again for the input.

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Re: A little hesitation

Post by Herb »

you have a midrange lean condition. Lean conditions get worse with heat. The main jets may be a size or 2 too small.
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Re: A little hesitation

Post by WintrSol »

Herb wrote:you have a midrange lean condition. Lean conditions get worse with heat. The main jets may be a size or 2 too small.
Or, the needle is set too low; the needle (mostly) controls the mixture from about 1/4 to 3/4 throttle (depends on the CV piston position, which depends on air flow), and adding a spacer to lift it *could* improve it. Of course, the source for the needle jet is the main jet, so that is also a factor.
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Herb
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Re: A little hesitation

Post by Herb »

WintrSol wrote:
Herb wrote:you have a midrange lean condition. Lean conditions get worse with heat. The main jets may be a size or 2 too small.
Or, the needle is set too low; the needle (mostly) controls the mixture from about 1/4 to 3/4 throttle (depends on the CV piston position, which depends on air flow), and adding a spacer to lift it *could* improve it. Of course, the source for the needle jet is the main jet, so that is also a factor.
you are right, probably easiest to start with raising the needle. I didn't think about the fact that he said he has a jet kit in it, so the needles that came with it may be adjustable. If so, lower the circlip one notch and see if it helps
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Fred
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Re: A little hesitation

Post by Fred »

Herb wrote:you have a midrange lean condition. Lean conditions get worse with heat. The main jets may be a size or 2 too small.
You are not on main jet at mid range. You are needle jet but mostly Idle jet transitions.

You need to check your idle transition jets in the throat just behind the butterfly.

If you raise the needle you are also enriching the top end which you say is ok.

You need to check for tiny holes in your Diaphragm which means your needle is not operating on mid range but will when you give it the gas.

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Re: A little hesitation

Post by Herb »

Fred wrote:
Herb wrote:you have a midrange lean condition. Lean conditions get worse with heat. The main jets may be a size or 2 too small.
You are not on main jet at mid range. You are needle jet but mostly Idle jet transitions.

You need to check your idle transition jets in the throat just behind the butterfly.

If you raise the needle you are also enriching the top end which you say is ok.

You need to check for tiny holes in your Diaphragm which means your needle is not operating on mid range but will when you give it the gas.
By half throttle you are on the needle jet, which gets it's fuel from the main jet, either raise the needle or increase the main jet.

As far as WOT goes, the needle should already be all the way up, and would have no effect on the fuel flow, Unless, there is a problem with the diaphragms or slides, but here again, that would impact WOT also.

One other thing is the float level. If it is set on the low side, it can cause a lean condition.

http://www.dansmc.com/carbs2.htm

Pilot or idle jet system.

Pilot Group The idle jet controls the idle and on up to quarter throttle, give or take a bit. On some carbs, like Mikuni there is an air jet too. In conjunction with the idle jet there is an idle jet air screw. This screw leans or richens the fuel mixture for a smooth idle and on up to one quarter throttle. From the idle jet, there are little passages cast into the carb that lead to holes just in front of the throttle valve or plate. There can be just one hole or there can be several, depending on the carb design. They effect the mixture as long as the vacuum, in the venturi, is over them. As the throttle opens further, the vacuum moves to the needle jet and jet needle.
The Throttle Valve.

SlideThe throttle Valve is the big slide that opens and closes your throttle has a bevel angle cut in one side of the big round (can be flat, too) slide, toward the air cleaner. This angle comes in several sizes and helps control the fuel mixture from idle to about 35% open throttle.

Needle Jet.

Needle Jet

This jet doesn't really even look like a jet, but it is! It controls the fuel mixture from 15% to 60% open throttle. It sets in the center of the carb, right over the Main Jet.

Jet Needle.

Jet Needle This is the needle that rides in the throttle slide and goes into the needle jet. This Jet Needle controls the fuel mixture from 20% to 80% open throttle. It can come in many different sized tapers. Sometimes, one needle can have several tapers on it. The top end of the Jet Needle has grooves cut in it, usually five, and you can move the little clip up (which moves the Jet Needle down in relation to the Throttle Valve and Needle Jet) to lean the mixture or down (moving the Jet Needle up in relation to the Throttle Valve and Needle Jet) to richen the mixture. Most late model bikes have needles with only one groove cut in them. This is so you can't richen the mixture, thereby keeping the EPA happy.

Main Jet.

Main Jet
This jet controls the fuel mixture from 60% to 100% open throttle.
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Re: A little hesitation

Post by Fred »

Thats Mikuni slide--we have Mikuni BS 36 CV with transition jets.

The main does feed the needle jet it is also called the metering jet because it meters the max flo the carb can handle --it is not doing that at mid range is it. So the flow into the engine at that point is the needle jet which is coming in to help out the the transitions.

When the piston " not slide is fully open then the metering jet will be on play.

This would be when pulling a caravan uphill at 4000 rpm.

You could take the main jet out and still not notice any improvement at mid range.

The BS is not like others. I have posted this information more than once.

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Re: A little hesitation

Post by Herb »

Fred wrote:Thats Mikuni slide--we have Mikuni BS 36 CV with transition jets.

The main does feed the needle jet it is also called the metering jet because it meters the max flo the carb can handle --it is not doing that at mid range is it. So the flow into the engine at that point is the needle jet which is coming in to help out the the transitions.

When the piston " not slide is fully open then the metering jet will be on play.

This would be when pulling a caravan uphill at 4000 rpm.

You could take the main jet out and still not notice any improvement at mid range.

The BS is not like others. I have posted this information more than once.
What the hell are you talking about a transition circuit? There is no such thing.

These have a TRANSIENT ENRICHMENT SYSTEM, not transition, that ONLY works when the throttle is suddenly closed at high speed.

These work EXACTLY as the link says they do, except for the addition of the slide diaphragm.

Page 5-9 of the VS1400 manual that is pinned at the top of the 1400 forum.

First and last sentences.

TRANSIENT ENRICHMENT SYSTEM

This transient enrichment system is a device which keeps fuel/air mixture ratio constant in order not to generate unstable combustion when the throttle grip is returned suddenly during high speed driving...

This system to keep the combustion condition constant by varying the fuel/air mixture ratio by controlling air flow in the pilot circuit.

If you REALLY want to know how these carbs work, the manual is really useful...
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Re: A little hesitation

Post by Fred »

You dont know about the transition jets do you. I thought you knew all bout the 1400.

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Re: A little hesitation

Post by Herb »

Fred wrote:You dont know about the transition jets do you. I thought you knew all bout the 1400.
I know there is NO SUCH THING.

There are 4 fuel metering circuits on the BS carbs.

If anyone wants to know and understand them the information about the carb operation starts on page 5-8 of the manual. You can download the manual from a post at the top of the VS1400 forum.

If you have questions, I am more than willing to answer them. if I don't know the answer I will tell you so.

I am done going around in circles with this idiot.
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Fred
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Re: A little hesitation

Post by Fred »

Herb wrote:
Fred wrote:You dont know about the transition jets do you. I thought you knew all bout the 1400.
I know there is NO SUCH THING.

There are 4 fuel metering circuits on the BS carbs.

If anyone wants to know and understand them the information about the carb operation starts on page 5-8 of the manual. You can download the manual from a post at the top of the VS1400 forum.

If you have questions, I am more than willing to answer them. if I don't know the answer I will tell you so.

I am done going around in circles with this idiot.
So you don't know about the 3 transition jest in the throat ok well if you don't know then you dont know.

I have given you this information before . I can not be held responsible if you don't read it.

A big 1400 cc V twin needs quite a bit of fuel . Harleys use pumps or accelerator jets that squirt it in.

Ever wondered why Suziz dont-- Transition jets------ just because you do'nt know does not mean they do'nt exist.

You got one outside get off your fat arse and have a look.

In the mean time I will look at the manual and explain it to you.

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Re: A little hesitation

Post by Fred »

Ok ive looked in the manual and it does not talk about them but strangely shows a picture of them.

Now I give my knowledge for free 50 years of it as all kinds of engineering and race bike preparations for castrol.

If some one has no gratitude and calls me an Idiot then ....................

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Re: A little hesitation

Post by Lechy »

Fucking hilarious you 2 are, arguing over 2 words that describe the same effect.
:lmao:
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Re: A little hesitation

Post by WintrSol »

Looking closely at the diagram on page 5-9, you will see a port controlled by the pilot screw, which is on the downstream side of the throttle plate when it is closed. To the right of that port are three open ports that are covered (mostly) when the throttle is closed, and are fed directly with the pilot fuel and air jet mixture, and as the throttle plate is opened begin adding to the mixture, the 'transition' point, if you will. The transient enrichment valve normally allows a metered amount of air into these ports, but reduces the air when the valve closes, when the vacuum rises enough, enriching the mixture to improve what would be a lean condition, and is not active under most conditions.

As the throttle is opened more, the contribution of the pilot circuit through the ports near the throttle is reduced as the needle jet takes over, thus the mixture control transitions from the pilot circuit to the main/needle circuit; at some point, the contribution of the pilot circuit is negligible, and the needle jet is in full control until the CV piston rises enough to turn control over to the main jet. If the pilot fuel jet is too small, you will have a brief lean condition as you move the throttle off idle, until the needle jet takes over. If the needle jet/jet needle is effectively too small, you will have a lean condition in the region above where the pilot circuit is less effective, but before the main jet takes over; if the taper of needle is wrong, or the needle is set too low in the jet, you can get the lean mixture somewhere between ~1/4 throttle and ~3/4 throttle, but just where it occurs depends on a lot of variables.
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