Bizzare starting issue on 86 700F

Recently, I've been having some real trouble starting (and idling) my VFR700.

I have an impossibly hard time starting it with all 4 cylinders wired up, but when I disable the front-left cylinder (pull the plug wire, or unplug the coil) it starts up much easier (??) sounding a bit off because 3/4 of the cylinders are going, no surprise there. When I plug the FL coil back in, depending on the engine speed, it'll either speed up and sound more or less normal, or die within about 10 seconds if the speed is below around 1500 rpm. It used to be that the engine would run fine when I would futz around with the idle screw, down to well below 1000rpm, maybe 600 or so (since you can reach it while sitting on the bike ) The engine dies a lot easier when cold so I've got to idle around 2500rpm or so (!)

When I try to start it with all 4 cylinders firing, it sometimes sounds like its getting pushed backwards during the cranking (a loud sound and the oil pressure light goes on for a sec, and the lights dim very momentarily.) So I'd guess that the cylinder is firing at the wrong time...

Thing's I've done: carb sync, choke check, running all sorts of unholy petro products through the engine, checked the pickup resistances (OK) ...

I'm not actually that sure it's just the one cylinder, it might be the two linked cylinders because I got the same kind of reaction on 3 cylinders when I did a crank with the engine super-cold (10f or so).

The only things left seem like they'd be timing related, i.e. black box is funny, but has anyone else heard of something like that? I'd rather have another opinion before buying another black box.

 

Hmmm...
Mysterious...

The first thing that comes to mind is most likely a bad coil or coil pack (if 2 cylinders share paired coils).
Some Auto Tune-Up places and parts stores can test coils for free.
Might as well have them check all 4.

If the coils check out, then it may indeed be a bad brain.

Interesting symptoms...

 

That sounds like a simple case of fuel varnished carbs. Pull them off and give them a really good cleaning, especially through the idle passages as they are the smallest diameter and plug up first (hint hint).

 

I'm guessing that it would be just about impossible for a cylinder on VFR to fire at wrong time if plug wire is correct.

Don't think anyone has ever seen case where CDI is still working but changed timing, although factory manual recommends a check.

Time to dig out that timing light and pop off timing hole cover??

It's easy to swap coils around to test them.....and sparkplugs too.

Note: Your bike may have 3 pick up coils, so test them all.......

count yourself fortunate if you have riding weather, most don't.

 

That would explain the dying-at-idle, but I don't think that would explain the easier-start-on-3-cylinders...

I'll do another clean on the carbs (tore them down half a year ago or so and cleaned them out with gumout carb cleaner; good stuff!) but I can certainly try it again. (By the way, why does the manual say to not reuse the metal lock plate? I can't figure that one out...)

I've tried replacing that coil with another one that I've bought, as well as moving the coils around (there are 4 individual coils), it didn't really change anything...

 

SOOOOOOOooooo

This starting issue sounds like an authentic unsolved mystery!

can't come up with another guess now,
let us know your results....

 

I don't have a timing light, although I have a friend that has an (old) one, or maybe I'll just pick one up on the cheap on eBay (recommendations?)

I don't actually have riding weather (Boston area) but that doesn't mean I won't ride!

There are 3 pickups on the 86 F model (two for crankshaft position sensor, one for cam shaft sensor (?)) The cam shaft sensor disappeared from later models (86FII/87 all) although it is indeed used as unplugging it while the bike's running causes instant shutdown.

 

New plugs & plug wires?

Maybe it's as simple as a badly fouled plug - maybe your prior carb cleaning knocked something out of whack and that cylinder is now drowning, which makes me think:
Inspect the carb diaphragms CLOSELY for rips/tears/holes, and also the float levels, float bowl needles & seats (badly worn; not fully closing), and possibly that float may be bad - fuel soaked/not floating.
Fuel could be overflowing that float bowl and drowning the cylinder - that can be erratic & unpredictable.

Your comment about "pushing backwards / oil press. lite / lights dimming" makes me think vapor-lock, again suggesting flooding cylinder.

Maybe also check the enrichener circuit for that carb, and throttle plates & linkages.

What are the cranking symptoms w/all 4 connected?
Cranking a long time?
Almost catching/starting but not quite?
Need a lot of choke (enrichener)? - Make any difference?
Pops/backfires?
Fuel smell? - From near carbs, or from tailpipe?
Any cranking/starting difference when only 3? (easier/harder/quicker/no pops etc)

How many miles on it?

Install fresh plugs - try it.
If still same, swap a couple plug wires around.
If still same, look at carbs again, carefully measure float level, consider testing #1 (LF is #1 cyl, correct?) float.

*ps - where you from near Boston?
I was born & raised (& escaped from) Lynn "City of Sin".

 

How do you define vapor lock? I guess I don't understand what you mean when you say vapor lock..

It could be a fuel problem, as you say, as when I tried to figure it out a couple weeks ago I had it to the point where I could look down the throats and see what happened. I did get the telltale white mist from that cylinder a few times while I played with it but I just chalked that up to "didn't get a chance to fire since I stopped cranking." However, this cylinder had far more intake fires/pops than the rest of them, so, ... could be.

I checked the choke, it's definitely disengaged when I've got it closed (although the pin seat could be going, I guess.)

The linkage is good, plates... look ok, I guess (what would I see?)

Also, maybe important, a while back (months, before I did the carb clean) the needle in this cylinder's carb broke off (??) but it got run for a bit before I was able to replace it. Since the cleanout, and up until about a month ago, it would run/start fine (the plugs were replaced after I installed the new needles). Also, there's always been a small amount of popping with closed throttle/high rpm (engine braking at 6k+ rpm).

With 4 cylinders, the cranking sounds normal-ish about half the time, a quarter it sounds a bit off, and the rest is loud thunks from the starter, the oil pressure light on momentarily, dimming lights, etc. It mostly won't start at all, although occasionally (after running for a bit.. sound like a fuel issue?) it'll start right up with 4. With three, it sounds a bit muted and a bit unhappy, but it definitely catches easier from cold or from hot.

It's got about 29K miles, I bought it with about 24K. If (when) I try the new plugs I guess I can't really reuse the crush washer, can I... at least they're cheap.

I was born and live in the Boston area, but at the moment I'm in "sunny" San Diego. (Both times I've gone to San Diego this year, it rained, so I remain unconvinced that it's actually sunny here. :wink: ) I'll be here for another week before being able to work on my bike but I did think I'd be able to pick up some stuff from salvage shops easier here than in MA.

 

Hmmm, boy...

"Curiouser and curiouser", said Alice...

I really think it's a fuel problem now.
It really appears to be richness/flooding.

"there's always been a small amount of popping with closed throttle/high rpm (engine braking at 6k+ rpm)." - This is definitely a sign of rich fueling - excess fuel in the exhaust tract on overrun causes exhaust popping.
It would seem it's been re-jetted; Who knows how correctly?

An incorrect Pilot jet might cause problems, but it seems very unlikely.
Check the metering/diaphragm needles - be sure they're all at the same height/groove.
I suppose it's possible that whoever re-jetted the bike may have drilled out the Idle jet and/or slide or throttle plate hole too big on that carb (depending on what was called for) - again unlikely, but who knows...

Are you running separate pod filters, or OE airbox?
"intake fires/pops" - Actual backfires through the carbs/airbox?
Or pops out the exhaust?

Everything you said is really making me think float / float-needle & seat.
May also be insufficient vacuum to the diaphragm not raising the slide properly, which may be causing some of the popping & rough starting, although I believe you said you had recently Synch'ed the carbs.
Inspect the vacuum lines - any cracking or loose connection, replace them.
Hell, plan on just replacing them - a 20-some-odd year old bike with 30k miles, and the vacuum hoses very likely have age, heat and ozone induced hardening and cracks, even if you can't see it easily.

I gotta say, the strained starter is a little odd - doesn't really seem to jibe with the rest of the symptoms.
Could be coincidental and not really related, or due to backfires causing momentary very high cylinder pressure (vapor-lock).
Do the popping and starter lock-up symptoms seem related / occurring simultaneously?
Less starter issues if you keep the throttle cracked open slightly?

My gut is telling me the #1 carb has issues, but probably nothing a careful rebuild wouldn't cure.
Although I may be completely off-base!
(but that's my hunch)

Be sure to check vacuum hoses and the diaphragm very closely, also that needle & seat, and the float level.

** Big Question: Any excessive fuel smell when it's hard starting??

Another thought: IF the carbs all check out OK, a Compression test and Leak-Down test may help determine if an Intake or Exhaust valve is not seating, or possibly other mechanical cause.

*ps - new spark plugs always come with new crush washers.
If for some reason there are now 2 washers stacked on top of each other in that cylinder, then the plug is not fully in the combustion chamber, which would cause all sorts of running issues, especially starting problems.
Be sure that there is only one washer per spark plug.
(now I just got a thought in my head that I hope the cylinder head is not cracked, possibly from over-tightening a plug, not likely tho')

 

Well, it probably is jetted a bit rich (I figured somewhat rich is probably safer than somewhat lean.) When the needle broke off, I couldn't get an OE replacement, so I got a dynojet kit and replaced all the needles/main jets. I think I selected the freeer-flowing-exhaust main jet, since I have a non-OEM exhaust system as well (although to be honest it's probably not freeer flowing than the OEM, it's a supertrapp 4-to-1 into a screwdriver'd GSXR muffler... the supertrapp fell off on the highway )

I'm close to 100% sure that the needle settings are all the same groove. It could very well be that the vacuum volume in the diagraphm isn't sealed properly, I'll have to take that apart and check. There aren't any vacuum hoses on this bike, since it's not a CA model (cheers to Honda), instead there's just the 4 carbs sitting right on the cyls. Maybe the seal between the two is iffy...

I don't believe the idle is drilled as the instructions didn't call for it (it did appear to have a dynojet kit in the first place. And what kind of power gains are you going to get from drilling the idle )

It's the OE airbox, single intake under the fuel tank.

When I said intake fires/pops, I meant there are actual explosions coming out the intake of that cylinder more than the others (and probably more than it should).

The float going (after 20 years) could easily be it, guess I've got to hope that it's still a purchasable part since new carbs are $$$$. If I'm lucky it's just the valve...

It's hard to say if the popping is occurring at start, it could be what's causing the thunking if it gets a double ignition. The intake pops definitely cause the engine to slow momentarily, but the exhaust pops don't seem to cause any trouble (and don't show up at low speed anyway. Well, except when I get a real backfire, that sounds like a gunshot, but that does happen very rarely, maybe once every couple months. :biggrin It's hard to say if cracking the throttle makes it work better, since I've got to do all sorts of things if I want to try and get it going on 4. I actually think that the reverse makes it a bit easier (more closed -> easier) but I'm not sure why that is.

On the hard starting, there's definitely a fuel smell from the exhaust if I'm trying to do 3 cylinders but I do recall that there sometimes seemed to be a faint fuel smell from the exhaust as well when starting normally (before I had issues.)

I'll definitely do a carb rebuild, at least on that cylinder, next chance I get. Probably easier to do them all at that point since that's the carb with the throttle cable hookup...

 

no one knew the bike was blue!! shoulda told us! anyone wanna bet the friggin voltage regulator is to blame??


if a float is leaking you can spot it (with airbox open) as fuel flowing up inside carb throat where needle goes down toward main jet. carb diaphrams have no effect on starting!

the popping could be a valve open too far or not seating, so check valve clearance on the bad cylinder.
as suggested above, it's maybe time for a compression check at least.....

 

It's not the voltage regulator (not anymore, since I replaced it in the summer with a non-OEM unit

I tore down all the carbs, cleaned and blew them out, put it back together (god, it's impossible to get those damn collars on both the carbs and engine at once). It's ... marginally better now. I can actually start it with 4 cylinders, but its still happier on 3. Also, it doesn't give me the problem that initially drove me to post (doesn't pop loudly during crank and dim the lights etc.)

I recorded a bunch of audio of the engine running (or not running) and posted them here:

http://anrp.us/vfr_sounds/

In particular, the one that seems to be the most representative of the problem I'm having (starting, running on 4 cylinders

http://anrp.us/vfr_sounds/start_normal_idle_transition_to_choked_dies.mp3

Pretend that you were looking down the throats of the carbs to position your ears.

 

I still say it sounds like clogged carbs! Maybe a good sync would help too.

 

have you centered your problem on one cylinder only??

IF you don't run your bike regularly, or bringing it back on-line from storage.....
it always helps to start up by hot wiring your fuel pump at the relay connection and FILLING CARBS until pump stops clicking .......

FRESH fuel also helps starting sometimes.

IF clicking does not stop, then probably a fuel supply problem, plugged filter, or leaking float....

 

Well, I've got the 4 dial gauge meter, I'm not sure how accurate it is (I can take it in to work and hook a vacuum pump up to it to check)

I thought I cleaned out the carb well, but it's entirely possible that I missed the idle passages. Maybe I'll try 100psi compressed air instead of XXpsi canned air. (guess I'm going to have to take out the pilots... actually, durr, I never even looked at those!) Will I break stuff if I blow compressed air down the pilot screw hole (with no gas in the carbs?)

I'm relatively sure it's just that cylinder (LF). I'm sure it's not a fuel pumping problem, the pump manages to spray me in the face quite well with gas (and even manages to fill up the chambers too).

The fuel's not all that fresh (1 month?) but I added stabil to it when I got it, so... This month was a bad one for me, I've been gone about 3/4 of the time.

 

Uh, OK, I just went and looked and made the most bizzare discovery yet... there is *NO* pilot screw in that carb (LF)... or maybe not? There's a hole about opposite where the aluminum cover is, full of dirt... not sure what that is for? breathing? see below.

 

A missing pilot screw will certainly cause it to run like crap. That's a rather large air leak.


Lane

 

Sorry, I changed my post so it's not that evident... I looked closer because it seemed like that should be impossible (missing screw?) and now I don't think it's the pilot. Whatever it is, though, its full of dirt, so that's a promising avenue to go after. It does look like it would be the right kind of hole for a screw-needle to go in...

 

Alright, after this post I'm going to stop talking until I can run it tomorrow :biggrin:

I looked again, and I realized that what I was mistaking for the anti tamper caps was actually the float chamber drain valve. So yes, I am indeed missing the pilot. At least that's settled.

Now, for a replacement, box 7 on this looks like what I need...anyone know for sure?
http://images.powersportsnetwork.com/fiche/images/Honda/1986/Motorcycles/2962_CARBURETOR%20(COMPONENTS).gif

Edit: talked to the local shop, looks to actually be box 4. Ordered it through them; will update here when they're in... thanks for the help, all!