Starter Valve synch revisited.

So I'm trying to resolve an intermittent misfire on cold start (#3 cyl.) on my '01 VFR. I checked the #3 plug and wire, ok, nice fat spark. I thought it might be a good idea to do a Starter Valve synch. It appears my 1998-2001 Honda VFR800FI service manual has an omission on page 5-82 where it outlines the procedure. It doesn't mention starter valve #2. I did a Starter Valve synch. about 5 years ago, and don't remember dealing with this. In the past when I've found errors, I've written in corrections, but no such luck here. Checked all of my notes, nothing.

I did a forum search and found a lot of stuff about S.V. synch. and some of it conflicting with respect to #2. I saw one reference to setting #2 to match #1 (the baseline). Is this correct? Does anyone have a corrected '98-'01 manual who can verify this? I scanned in an image of the paragraph from my manual where the omission was made. Thank you.

 

Yes, from the viewpoint of an Anglo-type (American, English, etc) it seems like an omission but from the viewpoint of a Japanese vehicle engineer or Japanese technical writer it's plain-as-day that the "omission" of #2 cylinder means it gets set so that its vacuum exactly matches that of the #1 cylinder (the fixed, non-adjustable, "reference" cylinder).

So, to be perfectly clear: #1 cylinder is the non-adjustable "reference" cylinder. #2 cylinder gets set exactly to the same vacuum setting as #1 cylinder is showing. #3 cylinder is adjusted to "drop" the vacuum to indicate 20+-mm hg less than #1 cylinder. #4 cylinder is adjusted to "drop" the vacuum to indicate 10+-mm hg less than #1 cylinder.

WARNING: the following may be "Too much information"

The explanation for these settings is in Chapter 21, "Technical Features" on page 21-10. On this page Honda shows the Manifold Absolute Pressure (a.k.a. "MAP") profile for each individual cylinder. The MAP profile is what the VFR's Honda PGM-FI Electronic Control Module (the black-box located in the bike's tail) uses to control idle and part-throttle fueling.

You can see from the individual graphs that cylinder #1 and cylinder #2 have roughly the same MAP vacuum profile (that's why you set the starter valves the same on those cylinders). You can see that cylinder #3 has the lowest MAP vacuum profile of all the cylinders (that's why its starter valve is adjusted to "drop" the vacuum substantially from the cylinder #1 value). Cylinder #4 has a MAP vacuum profile that falls in between the profiles, less than cylinders #1 & #2 and more than cylinder #3, so it gets adjusted slightly lower than #1 & #2 but slightly higher than #3.

Chapter 21 stops a little short of a full explanation of exactly why the cylinders have different MAP vacuum profiles. Maybe the Honda guys felt that was plainly obvious, but not everybody lives and breathes motorcycles or engines. The differences in MAP vacuum profiles from one cylinder are mainly due to the Firing Order of the cylinders which greatly affects both the gas scavenging effects/ability of the exhaust and the moment-to-moment velocity of air in the airbox and intake trumpets.

Hope that helps.

 

It's actually very reasonable for your VFR to misfire on cylinder #3 rather than any of the others, because #3 is the one with the worst intake performance at idle (it's the one with the lowest MAP vacuum profile). Adjusting #3's starter valve vacuum to 20+- mm Hg less than #1 has the effect of opening the throttle body butterfly wider which allows more air into that cylinder.

Your cylinder #3 is probably misfiring due to over-rich fuel ratio (not enough air for the amount of fuel).

 

Wow! Thanks for the detailed reply Greg. I'll have to check out chapter 21.

The odd thing is that normally it starts cold and hits on all four right off just fine. Just recently, when started cold it lights up on three cylinders and within 15 seconds or so #3 wakes up and starts firing. It did this once before, about five years ago at 37,800ish miles. I don't remember if it was #3 slacking then too. That was when I did the S.V. synch the first time. Warm weather then as now, makes your idea of rich a/f ratio seem likely.

 

Chapter 21 is some good reading, I think Honda was a bit concerned about taking the VFR from its many successful years of "750 carburetor" to its new "800 FI" configuration so they pulled back the usual OEM "curtain of secrecy" in an effort to comfort people and maybe sell a few more bikes (to people who actually read things, and to others who listen to people who read things).

I think Chapter 21 goes a long way toward explaining why the VFR800 engine is so long-lasting (damn near bullet proof).

I'm particularly impressed with the "Aluminum Powder Metal Composite Cylinder Sleeves" that are made from Aluminum Oxide, Iron, Copper, Magnesium and Graphite. Apparently they are/were extremely expensive to manufacture and they do not wear down or go out-of-round or suffer from any of the other wear-related issues that normal steel/iron cylinder sleeves do.

Although it does make me laugh a bit when people (VFR800 owners) start believing that this amazing durability extends to every single part of the VFR, including items that are obviously perishable/consumable items like O-rings and rubber hoses. "yeah, these VFRs are indestructible, they last forever, you don't even have to do valve adjustments... I've got XX,XXX miles on mine (insert ungodly mileage number) and I've never done anything to it!"

 

Today i've been comparing this 4 chinese vacuometers... Only one of them match my brake bleeding vacuum tool, so i've made a table comparing what the other 3 read at different vacuum pressures... The variations where insane, but definetly ended calibrating them and adjusted starter valves acordingly...
Let's see what the bike runs like now

 

The more I read the more I learn which leads me to realize there's so much more I don't know. Is this procedure something that should be done at a certain interval? Or only when the engine becomes symptomatic?

 

I tried using these type gauges, but found them too inaccurate.
The increments are too small to adjust as needed.
I use an electronic vacuum gauge which is very accurate, but a huge pain in the arse to use as I only have one.

 

It is not in the routine maintenance schedule, but it is mentioned in troubleshooting. For example, starter valves out of synch. as a possibe cause for stalling.

 

My bike is running a bit rough at low speed, you'd think it was a bad plug or something, but it's just had new plugs fitted. could need the sync done, is it a 'big' job?

 

You may want to read this to clarify what the service manual really says. Rethink it a little bit... made a real improvement for me.
https://www.vfrdiscussion.com/index...r-last-22-years/&tab=comments#comment-1111811

Once done, it shouldn't need re-doing for quite some time, but definitely if you have re-shimmed any valve clearances.

I use an electronic VacuMate.

 

I was looking at those and they're not cheap- unless there are less expensive devices. The Digi Sync looks nice but $125.

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I am using a VacuMate, which is no cheap device, but I got it used. I have a DigiSync that didn't work so well on another bike, perhaps a little unique, but lemme hook it up to the VFR and see what I get in the next few days.... dunno if someone has tried one yet on a VFR, but I'll give you my assessment over the weekend.
I did try a Morgan Carbtune, and it's mechanical with fluctuations, but doable.

 

Thanks.

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Ok guys this could be the easiest quickest fix in history or another dumbass question, I lifted the tank and noticed that one of 4 the little vacuum hoses that plug into the airbox (the ones for setting the starter valves) was lying loose not connected, (the one furthest to the front at my left knee sitting on the bike, not that that matters)
could this be the cause of the rough running/misfire type issue? I'm hoping it is, reconnected it but it's absolutely pissing rain here tonight and I can't take her for a spin though I'm dying to to see if it's solved the problem, I let her warm up in the garage and she seems to sound/idle better, but that could just be wishful thinking, fingers crossed anyway.

 

It would be great if that is all you need to do. Still a sinc of the carbs/ or starter valves is a good thing to do, and not very difficult.

 

Are the vacuum hoses on the side of the air box numbered? and also the starter valve adjuster screws?

 

I know that on my '98 all of the vacuum hoses have a number printed on them, and the numbers are used in the factory service manual to ID them.

 

Ok I got the starter valves synced today and the difference is amazing!! I set it per the new settings on this link, the bike now pulls clean through the rev range and the idle is perfect, can't believe the difference this made, thanks to these forums I have the bike running as it should now, delighted.