Why Wait for Fuel Injection


15 replies to this topic
  • arel451

Posted July 07, 2007 - 02:58 PM

#1

I know it isn't the real thing, but it is interesting nonetheless...http://racerxcanada....r-the-fcr-carb/ hopefully this link works

  • Ga426owner

Posted July 07, 2007 - 03:08 PM

#2

That is interesting....a leakjet on the diaphram....probably cheaper than the R&D Floatbowl...I wonder how well it works

here is another link about it
http://www.mxnewsfee...e.php?artid=942

or put a deposit on one of these exotics

http://www.motorcycl...y07_benelli.htm

  • cowboyona426

Posted July 07, 2007 - 05:27 PM

#3

Very interesting indeed, I'll be keeping my eyes peeled for more info on this mod.

  • grayracer513

Posted July 07, 2007 - 05:27 PM

#4

And after you find out where the leak jet should be set, why would you ever want to change it? Seems like waste.

  • cowboyona426

Posted July 07, 2007 - 05:31 PM

#5

grayracer, if you ride trails and change elevation quite a bit, wouldn't being able to adjust the leak jet help keep your jetting spot on?

  • grayracer513

Posted July 07, 2007 - 05:37 PM

#6

The leak jet is not something that affects jetting, per se, only accelerator pump performance, so I will say, no.

  • cowboyona426

Posted July 07, 2007 - 05:38 PM

#7

Hmm... good info.

  • ben_suhard

Posted July 07, 2007 - 08:21 PM

#8

Interesting.

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  • WB450

Posted July 08, 2007 - 11:03 AM

#9

ProMed posted a ad for this last week, it's been moved for some reason.

  • Ga426owner

Posted July 08, 2007 - 01:01 PM

#10

And after you find out where the leak jet should be set, why would you ever want to change it? Seems like waste.
and
The leak jet is not something that affects jetting, per se, only accelerator pump performance, so I will say, no



:thumbsup: for me the answer is very simple ... the 2003 YZF450 has no leakjet. I am dumbfounded as to why.........and never has a good reason been given to me

Even though on my 03 the AP has been modded by zipty - I want more instantaneous power like my 2006 with the zipty mod and the ability to fine tune it...yes once it is set,,,,it is set. But right now you and I and everone else with a 03 have no LJ on our 03 dragster MXers. :busted:

I have been pondering the R&D floatbowl..but it is 250.00. Now there may be another less costly way....to achieve my goal. :thumbsup:

  • grayracer513

Posted July 08, 2007 - 07:41 PM

#11

... the 2003 YZF450 has no leakjet. I am dumbfounded as to why.........

Maybe because it isn't really necessary. The throttle response on my own '03 could hardly be any more instantaneous than it is, for practical purposes.

  • Ga426owner

Posted July 09, 2007 - 05:36 AM

#12

Maybe because it isn't really necessary. The throttle response on my own '03 could hardly be any more instantaneous than it is, for practical purposes.



maybe...but I respectfully and totally disagree :thumbsup:
I have emailed Merge to see what info they can give me on this product. I will post their answers

  • grayracer513

Posted July 09, 2007 - 08:53 AM

#13

But, Dave! But, Dave! You've never ridden mine. :thumbsup:

Here's the thing about leak jets in the first place, and why the 250F got one before the big bikes did:

When the throttle is opened from idle, there is a temporary drop in the vacuum over the discharge nozzle in the carb throat, which is what pulls gas up and into the intake air stream, and a resulting drop in intake air velocity. If the throttle is opened gradually enough, this drop in the vacuum signal is of no consequence. An increased amount of air flows through the carb, and additional fuel is delivered by it to accelerate the engine.

But if the throttle opens too quickly, the drop in intake vacuum is too great, and fuel delivery basically stops for the moment; the engine stumbles in response. Air begins to flow in larger quantities through the carb, and in most cases, it restarts the fuel delivery in time to keep the engine from dying.

A carb can be designed to richen the mix as the throttle transitions from idle to partly opened. This is effective, but the downside is that it is sometimes difficult to do that and also have it run cleanly at low throttle openings under light loads. Enter the accelerator pump.

This is a simple mechanical pump operated by the carb linkage that physically pumps gas into the air stream to cover the drop in the intake signal. Fuel is only delivered while the throttle is actually being moved, so if the right amount is sprayed in, it covers for the bog, and the jetting takes back over when the the engine catches up. The engine is now able to respond to sudden throttle opening, and still cruise cleanly just off idle.

How much gas the engine needs from the accelerator pump depends somewhat on what state of tune the engine is in. Smaller, high-strung engines with aggressive cam profiles and relatively large carbs for their displacement need more help than bigger, mellower ones with relatively smaller carbs (the 450's, as strong as they are, are not as wild an engine as a YZ250F for their size). The simple cure is to increase the amount of fuel dumped in by the accelerator pump. But here, we run into another little problem.

The accelerator pump is a positive displacement pump. It will discharge the same amount of fuel with the same amount of linkage travel regardless of how fast the throttle is opened. This means that the pump will also deliver some extra, unnecessary fuel during small, partial openings, like when the rider is trying to work through a a corner or a tricky woods section. Bigger or milder engines will tolerate this better because the pump shot isn't that big to start with. But, if we take a highly tuned engine and set it up so the pump delivers a big enough shot to prevent a bog, the pump may drool enough fuel into the engine during such small changes in throttle to cause the engine to perform poorly in those situations.

For that, we use the leak jet. The leak jet's purpose is to eliminate the accelerator pump discharge during slower openings of the throttle when it isn't needed. Picture a squirt gun. If you pull the trigger hard, you get a long hard stream, of course, but if you pull it slowly, it squirts the same amount of water, just not as far. But let's drill a hole in the barrel half way down, and point the squirt gun upward. Now, if we pull the trigger hard, we get two streams, one out the front, and one out the side. But pulling the trigger slowly only causes water to run out the side hole, and not at all out the main discharge.

That's exactly how the leak jet works. The bigger the jet, the less the pump discharges during slower throttle openings. So, having a leak jet in and of itself does not improve the performance of the accelerator pump in any way as far as response to sudden throttle openings. They are only useful if the amount of fuel required to prevent a bog is so great that it causes excess richness during low power operation, and also to improve fuel economy and reduce emissions.

Leak jets do, of course, leak during quick throttle flips too, and so they bleed off some of what would have gone into the engine. From this standpoint, it does make it possible to use them as a way to adjust the volume of fuel delivered by the pump stroke, but that is not it's primary function. The carb has other ways of doing that built into it with or without a leak jet, such as the pump timing and stroke adjustments, and the length of the button on the pump diaphragm.

Now consider that during most of the popular pump mods, the pump is modified to produce a more positive, larger shot, and then a larger leak jet is installed to reduce it again. Does that seem contradictory to anyone else? It obviously works, but it seems like it could be accomplished by tuning within the design as is, too, although that might be more difficult in some ways, and possibly more expensive in total.

  • Ga426owner

Posted July 10, 2007 - 10:33 AM

#14

But, Dave! But, Dave! You've never ridden mine. :thumbsup:

Here's the thing about leak jets in the first place, and why the 250F got one before the big bikes did:

When the throttle is opened from idle, there is a temporary drop in the vacuum over the discharge nozzle in the carb throat, which is what pulls gas up and into the intake air stream, and a resulting drop in intake air velocity. If the throttle is opened gradually enough, this drop in the vacuum signal is of no consequence. An increased amount of air flows through the carb, and additional fuel is delivered by it to accelerate the engine.

But if the throttle opens too quickly, the drop in intake vacuum is too great, and fuel delivery basically stops for the moment; the engine stumbles in response. Air begins to flow in larger quantities through the carb, and in most cases, it restarts the fuel delivery in time to keep the engine from dying.

A carb can be designed to richen the mix as the throttle transitions from idle to partly opened. This is effective, but the downside is that it is sometimes difficult to do that and also have it run cleanly at low throttle openings under light loads. Enter the accelerator pump.

This is a simple mechanical pump operated by the carb linkage that physically pumps gas into the air stream to cover the drop in the intake signal. Fuel is only delivered while the throttle is actually being moved, so if the right amount is sprayed in, it covers for the bog, and the jetting takes back over when the the engine catches up. The engine is now able to respond to sudden throttle opening, and still cruise cleanly just off idle.

How much gas the engine needs from the accelerator pump depends somewhat on what state of tune the engine is in. Smaller, high-strung engines with aggressive cam profiles and relatively large carbs for their displacement need more help than bigger, mellower ones with relatively smaller carbs (the 450's, as strong as they are, are not as wild an engine as a YZ250F for their size). The simple cure is to increase the amount of fuel dumped in by the accelerator pump. But here, we run into another little problem.

The accelerator pump is a positive displacement pump. It will discharge the same amount of fuel with the same amount of linkage travel regardless of how fast the throttle is opened. This means that the pump will also deliver some extra, unnecessary fuel during small, partial openings, like when the rider is trying to work through a a corner or a tricky woods section. Bigger or milder engines will tolerate this better because the pump shot isn't that big to start with. But, if we take a highly tuned engine and set it up so the pump delivers a big enough shot to prevent a bog, the pump may drool enough fuel into the engine during such small changes in throttle to cause the engine to perform poorly in those situations.

For that, we use the leak jet. The leak jet's purpose is to eliminate the accelerator pump discharge during slower openings of the throttle when it isn't needed. Picture a squirt gun. If you pull the trigger hard, you get a long hard stream, of course, but if you pull it slowly, it squirts the same amount of water, just not as far. But let's drill a hole in the barrel half way down, and point the squirt gun upward. Now, if we pull the trigger hard, we get two streams, one out the front, and one out the side. But pulling the trigger slowly only causes water to run out the side hole, and not at all out the main discharge.

That's exactly how the leak jet works. The bigger the jet, the less the pump discharges during slower throttle openings. So, having a leak jet in and of itself does not improve the performance of the accelerator pump in any way as far as response to sudden throttle openings. They are only useful if the amount of fuel required to prevent a bog is so great that it causes excess richness during low power operation, and also to improve fuel economy and reduce emissions.

Leak jets do, of course, leak during quick throttle flips too, and so they bleed off some of what would have gone into the engine. From this standpoint, it does make it possible to use them as a way to adjust the volume of fuel delivered by the pump stroke, but that is not it's primary function. The carb has other ways of doing that built into it with or without a leak jet, such as the pump timing and stroke adjustments, and the length of the button on the pump diaphragm.

Now consider that during most of the popular pump mods, the pump is modified to produce a more positive, larger shot, and then a larger leak jet is installed to reduce it again. Does that seem contradictory to anyone else? It obviously works, but it seems like it could be accomplished by tuning within the design as is, too, although that might be more difficult in some ways, and possibly more expensive in total.


Greyracer...very nice read (great explanation to Carb characteristics and function)and I see the point of the contradiction....squirt amt vs leak jet size.....I had almost determined 60/40 rule that my carb (Remember my bike has a bigbore 470kit)quite possibly has not enough fuel flow....hence the need for a adj LJ(equivalent to a smaller LJ)as in the R&D Racing ADJ LJ bowl. The verdict is still out....I am curious as to what settings your carb has (AP Timing etc).....to eleviate this. I also desire more fine tuning....probably because I am a idiot....for as close to 100% perfected performance regarding fuel/carb & flow......more testing/info is needed for me to make up my mind.......so the challenge continues....
Very curious what our carbs have to compensate for no LJ.....:thumbsup: This is the confusing part to me...must be pump timing, TPS setting...I feel like the infamous bog,,,is prevalent on 03s when throttle is whacked open quickly.....tricks like the Quickshot....help but do not totally get rid of it...

Here is Jerry's reponse to my inquiry...and he seems to indicate some of your points:

Hi David, Sorry for the delay getting back to you. We have been overwhelmed with interest which is always a good thing, we should have probably waited another week and then we would have the web site up which has some nice instruction videos that explain most of the technical stuff.

The kit plugs off the leak jet (when you have one) and you then drill a bypass hole through the bottom of the float bowl. This new hole aligns with the leak passage in the diaphragm cover which of course is adjustable by means of a fuel screw type needle.

The kit comes with -

*
New Adjustable diaphragm cover.
*
Leak jet plug.
*
Allen wrench for installing the leak jet plug.
*
Drill bit for boring the new bypass hole.
*
Drill fixture that you attach to the float bowl (so you get the hole in the correct place).
*
Instructions

If someone has their carburetion spot on the only difference they are going to feel is a change in "hit" (low to middle accelerating power) when they adjust the screw. However it's very unlikely that it's already correct because most carb settings that people run are too rich on jetting and lean on the accelerator pump.

As far as the wiring the arm is concerned, that works well as long as you have a short diaphragm if you have a long diaphragm the arm has more travel and that puts a lot of stress on the linkage.

This kit works on fuel volume so it allows you to utilize the full flow the pump is capable of pushing out and consequently works in conjunction with many of the modifications that play with duration and timing.

What you need in your case is to be able to pump too much fuel through your closed system then use the adjustability to back it off so you have lean and rich adjustability. I believe that the main fuel volume limitation of the early models is diaphragm length.

As far as the R&D float bowl is concerned, we have taken a different approach to the same issues and I can only say that R&D makes some nice stuff and I am not going to knock a competitors product.

Hope you find this useful

Sincerely

Jim Lewis
Merge Racing

PS, If you decide to get the Merge kit and you want to send it in, we will mount it up for you and make sure you have enough fuel flow for +/- adjustability. I am interested to see why you don't already get too much fuel with all the modifications that you have had done

  • WB450

Posted July 10, 2007 - 10:51 AM

#15

Well, are you sending it in?

  • Ga426owner

Posted July 10, 2007 - 11:48 AM

#16

Well, are you sending it in?



not quite ready yet to make that decision. Still waiting for what this thing cost....avail end of the month.....I like the fact that he will set it up and test....great customer service.....:thumbsup:
got new shockbearings and rear brake work/fluid changes to do first.....going on right now.....





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