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5th gen starter valves sync INCORRECT for last 22 years


Jkson

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On 17 September 2020 at 11:16 AM, bog said:

Just curious, are these settings relevant to a 6th generation, i synched my 2003 the other day and set all 4 cylinders the same, but i still have what i call a stutter just off idle, the motor acts lean at low rpm to me, i am used to carbureated engines, i had an 1987 vfr 700, which was a super  machine, very friendly to work on and tune, does anyone know the exact reason for setting 5th generation engines with different vacuum readings, im wondering if 6th gen. would benefit from a different setting,  anyone have any input?

Hi Bog. Jkson the original poster goes into good detail regarding the reason for offset vacuum for the fifth gen with his very first post! Note the non adjustable reference starter valve for a fifth gen in No.1 on a sixth gen it's No.4.

 

My own personal experience with setting a 6gen to all equal to No.4 has provided good results, with none of the "stutter" you mentioned. Many others which I've read about have also achieve good results for a 6gen. Perhaps the mapping for a 6gen is very different to a 5gen thus the reason for equal vacuum on a 6gen.

 

Your "stutter just off idle" is commonly caused by starter valve unbalance, however in your case it appears to be something else. I've found that setting the throttle cable slack to a minimum helps, just in operator smoothness (check after adjusting, that swinging the steering from lock to lock there is no increase in idle rpm). 

Things like spark plugs, air filter, fuel quality and type, fuel filter, tank condensation, vacuum leaks, modifications  etc. might have an effect on your "stutter just off idle" Assumming also your warm engine idle rpm is correctly set to 1200. Even overheated and high resistance wiring or joints for Main Fuse B 30amp (All the EFI and sensor power) and of course poor grounds and connectors, can cause poor rideability issues.      

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Grum, thanks for the answer, my experience with engines and mechanical items has been lifelong, rode motorcycles for 40 years, ran a mc shop for 5 years, bsa norton triumph, 25 year aircraft mechanic, the engine on my bike definetly acts lean, never the less, this winter i will strip the bike and perform all the mods i can, electrical etc.  i will also go through the fuel system, fuel inj.  filter, regulator, plugs..  i have set the throttle cable freeplay to min, my bike is a 2003, with 5400 miles, has been well taken care of, my idle is 1300, at low throttle settings you can feel the bike is hunting so to speak, i think i will also replace all the vacuum lines, do you have any info on remapping ? is that the only way to enrichen the system at low rpm?  all help is appreciated....bog

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17 minutes ago, bog said:

Grum, thanks for the answer, my experience with engines and mechanical items has been lifelong, rode motorcycles for 40 years, ran a mc shop for 5 years, bsa norton triumph, 25 year aircraft mechanic, the engine on my bike definetly acts lean, never the less, this winter i will strip the bike and perform all the mods i can, electrical etc.  i will also go through the fuel system, fuel inj.  filter, regulator, plugs..  i have set the throttle cable freeplay to min, my bike is a 2003, with 5400 miles, has been well taken care of, my idle is 1300, at low throttle settings you can feel the bike is hunting so to speak, i think i will also replace all the vacuum lines, do you have any info on remapping ? is that the only way to enrichen the system at low rpm?  all help is appreciated....bog

Check this out, it might be what you're looking for if you feel the need for richer fuelling.

https://www.boosterplug.com/shop/honda-800-series-51c1.html

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Re 5th gen differential vacuum & 6th gen  equal Vacuum.

 

its all to do with the headers length NOTHING else. If you look at the right side of both bikes with the riders leg heat shield removed, you  can see that on a 5th gen #1 cylinder header is the rear most of the C shaped headers that run down & under the right foot rest. With #3 cylinder header being the forward one. You can easily see that #1 is significantly longer. 
 

On the 6th gen Honda fixed this by making #1 & 3 headers swap over & thus #1 header is the forward one. This also explains why the 6th gen front headers cross over  to keep the merges the same. Thus all 6th gen headers are within a couple of inches of each other in length. So they can run the same vacuum settings.
 

On a 5th gen #1 & 3 are very different lengths, thus they need the differential vacuum. 
 

I've said this many times in the past, so please pay attention at the back 😂

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2 hours ago, Mohawk said:

Re 5th gen differential vacuum & 6th gen  equal Vacuum.

 

its all to do with the headers length NOTHING else. If you look at the right side of both bikes with the riders leg heat shield removed, you  can see that on a 5th gen #1 cylinder header is the rear most of the C shaped headers that run down & under the right foot rest. With #3 cylinder header being the forward one. You can easily see that #1 is significantly longer. 
 

On the 6th gen Honda fixed this by making #1 & 3 headers swap over & thus #1 header is the forward one. This also explains why the 6th gen front headers cross over  to keep the merges the same. Thus all 6th gen headers are within a couple of inches of each other in length. So they can run the same vacuum settings.
 

On a 5th gen #1 & 3 are very different lengths, thus they need the differential vacuum. 
 

I've said this many times in the past, so please pay attention at the back 😂

 

Yes, I agree that the length of the headers (relative to one another) is very nearly the complete solution (something around a 90% solution) and as a result constitutes the majority explanation for the odd-seeming instructions for the Starter Valve Sync procedure.

 

But the design element that keeps header length from being a pure, complete, 100% solution is the VFR's irregular V-4 cylinder firing order, because it (the VFR's irregular firing order) causes localized, cylinder to cylinder changes/differences in gas velocities and resultant "scavenging" and flow of gases from individual cylinders.

 

The VFR headers (whether 5th Gen or 6th Gen) are a "tri-Y" design, so you have to consider the gases from each of the 4 cylinders, the order in which they are fired, the lengths of the individual headers from each cylinder, and the order in which the exhaust pulses arrive at the "Y" merges within the header system. 

 

I'm not college-trained in Fluid Dynamics (as high speeds gases act like fluids), so I can't give an absolute fact analysis of the situation.  But maybe we could get to a better understanding with a side conversation, I'm open to hearing opinion and analysis that dissects/examines the timing and effect of the VFR's 1-0-3-0-0-2-0-4- firing order and how that timing interacts with the two different versions (5th Gen vs. 6th Gen) of the VFR "Tri-Y" header system.

 

Right off the bat I'm reminded of the 2 choices of header that were available for a motorcycle I have some experience with, the Suzuki GSF400.  There was a "four-into-one" header and there was a "Tri-Y" (or call it a 4-into-2-into-one).  The "four-into-one" was (supposedly) optimized for high-rpm operation but not so great in the mid-range RPMs, while the "Tri-Y" was (said to be) better in the mid-range RPMs but gave away a bit in the high-rpm.  

 

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  • 1 month later...
On 9/20/2020 at 10:40 AM, Mohawk said:

Re 5th gen differential vacuum & 6th gen  equal Vacuum.

 

its all to do with the headers length NOTHING else. If you look at the right side of both bikes with the riders leg heat shield removed, you  can see that on a 5th gen #1 cylinder header is the rear most of the C shaped headers that run down & under the right foot rest. With #3 cylinder header being the forward one. You can easily see that #1 is significantly longer. 
 

On the 6th gen Honda fixed this by making #1 & 3 headers swap over & thus #1 header is the forward one. This also explains why the 6th gen front headers cross over  to keep the merges the same. Thus all 6th gen headers are within a couple of inches of each other in length. So they can run the same vacuum settings.
 

On a 5th gen #1 & 3 are very different lengths, thus they need the differential vacuum. 
 

I've said this many times in the past, so please pay attention at the back 😂

Follow up question,

If one replaced their 5th gen headers with equal length headers and set the vacuum equal across all 4, how would that affect the fuel/air ratio? It looks like some cylinders are getting more fuel than others and if air flow is now the same(in theory) would that cause some cylinders to run lean at idle and/or other rpm? or are those fuel maps different just for idle?

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