Engine starts but won't idle

Me again! (This bike will drain the life out of me)

1. Took the bike in for a general inspection + valve adjustment (that I did wrong - too loose. Whops).
2. Started right up at the shop, drove home.
- I did notice the bike was idling at 2k when I am stopped at stop lights, higher than what it used to be, at ~1.5k
3. Two days later (now cold), bike started, but won't idle (even with full choke).

Called the mechanic and he said to turn the throttle stop screw clockwise (well, he said the screw on the bottom of the carb, left side of the bike). Turned it clockwise all the way down till I cannot turn anymore (at 1.75 turns), bike stayed running for longer (like 10-15 seconds), but still stalls.

Note to self: throttle stop screw turned 1.5 turns clockwise right now.

Question #1: Is this where I need to do a carburetor synchronization?
Question #2: The throttle stop screw simply increases the overall idle speed by opening the throttle slightly, hence increasing the fuel mixture?

Bike: 1986 VFR700f

Thanks!

 

Does it stay running if you manually add some throttle ? If yes then the bikes fuelling & ignition would seem to be OK. Thus I'd look at the last thing done to it before this behaviour started !

Interesting that you set valve clearance too loose & bike was OK at idle, but now with tighter settings bike won't idle. I'd be inclined to return it to the mechanic & !

 

You need to keep the bile idling by holding the throttle while adjusting the screw so that it holds the idle, not the throttle. Turning screw clockwise (viewed from bottom !) increases idle speed.

Check the battery voltage and charging system output.

 

Opening the throttle (at neutral) stalls the engine instantly.

I'm guessing the mechanic actually took things off/apart, since it was a general inspection, as well a valve adjustment. He did mention he couldn't remember if they took just the clutch cover off or took it apart, as well as drained the liquids from the bike at point point (which points to they took a bunch of things apart).

The shop owner also mentioned something about "they probably adjusted the idle when it was hot, so now that the bike is cold, it is different".

squirrelman - what might the charging system/battery have to do with the bike idling? AFAIK the electrical system is only used to turn the motor at start?

 

After reading that, I wouldn't take it back to those "so called" mechanics. Thery fault you describe sounds like fuel starvation. Did they take the carbs e off ? They had to take the tank off to do the valves, so check your fuel line from tank to carbs that they fitted the vacuum tap hose they could be pinched, cracked due to age or hjave come off !

 

Yo, Mohawk, no vaccum line to petcock on that bike.

Low battery voltage and weak charging system won't fire plugs around idle speed.

 

After charging the battery (now reading 12.85v), the engine is idling, with full choke, at about 900 rpm, for roughly a minute before stalling. This is not great, but a big difference compared to the 10 second idles before, so that is good. squirrelman might be right, point this to an electrical problem. (opening the throttle will still stall the engine right away)

According to the manual, I should check for power leakage:
- Disconnect the battery's negative terminal
- Measure negative and the ground cable
- This should read 0v on the voltmeter

Mine came up as -12.85 - does that point to a leak? (it has been a long time since I studied physics).

 

fuel: clogged carburetor, pilot and choke circuits, not getting any fuel.

electrical: measure battery voltage while idling and at 3 to 5 krpm if possible. Also If you are measuring any voltage from the naked battery negative terminal to the bike chassis, then you have a fault in the wiring somewhere.

 

Electrickal checks out OK, so problem must be in carbs or pump or fuel tank crap, maybe plugged fuel filter or tank vent.

 

I didn't check the pump's rate of output, but it seems to be functional (drained the [see-through] in-line fuel filter, started the bike, and fuel was flowing).

There is fuel in the carb's float bowls... I hadn't tried draining them and running the bike - but for the amount I've kept it at idle, I think fuel is getting there.

Opening the throttle any amount stalls the engine right away. Also, the mechanic did mention over the phone that they probably just set the idle speed too low. When riding the bike back, I did notice the bike idling higher than before (at around 2000-2300 rpm, as opposed to around 1000-1500rpm).

All these points to the fact that my air/fuel mixture is set too lean, hence, now opening the throttle gave me an even leaner mixture, hence stalling. I've tried setting the throttle stop screw, but that gave little to no effect. Was I supposed to tune the pilot screws on the carburetor instead? If so, is the screw in my image the correct screw?

EDIT: I forgot to mention the only way I am able to keep the bike idling all this time is to keep my hand pushed down on the choke lever, to keep it definitely closed, otherwise, it stalls as well.

More thoughts?
Thanks!

 

Idle mix screws set to about 2 1/2 ??

 

I haven't played with the screw indicated in my attached image yet... I want to make sure that that is in fact the idle mix/pilot screw(s) before I do so. The PDF manual I have is too pixellated to read clearly.

 

Yes that is the #3 pilot screw you circled and yes you need to adjust them to get the proper mixture at idle and the idle speed. Were these carbs ever removed and cleaned? If so the pilot screws should have been removed and cleaned also.

But it appears to still have the limiter cap installed? which doesn't make sense unless it was not cleaned properly--you have to break the caps to get the screws out...

 

Hmm.. I guess i will have to ask the mechanic if they did that... Chances are, that they did not remove/clean it.

I'm assuming this is the screw I keep hearing about having to "drill out"?

Is there another place I that I can set the idle mixture? From the behavior I've described, does it sound like an idle mixture setting problem?

 

No that is the only way to adjust idle mixture. Can you keep it running by using the choke? The choke lever opens up a circuit to pull fuel into the intake that by-passes the butterfly valve. If you can then that is another indication that the mixture ports are clogged.

Other generations had the caps that needed to be drilled out, lucky you got the ones that don't. i can't tell for sure from the photo if the limiters are present, but you could always back the screws out and clean them, spray carb cleaner and compressed air into the opening to blow it out. Then put them back in lightly seated against the bottom and back them out according to squirrel's post.

There is a tiny spring, flat washer and oring with each pilot screw that you don't want to lose--use a toothpick, paper clip or small metal wire to fish them out before cleaning and air blasting...

Of course it could be that the pilot jets are clogged--who cleaned the carbs and how did they verify all the jets and ports were open?

http://vfrworld.com/forums/mechanics-garage/22449-cleaning-carbs.html

 

I don't recommend ever removing the tab cap on the screw. Instead, once the carbs are off, switching the float bowls around eliminates the stopper against the screw cap tab for easy adjustment. Without the cap it's difficult to turn the screw and the brass head is fragile, strips out easily.

 

Update on pilot screws!

#1 - No cap, but the brass head looks good... I'm going to see if there is a good way to get to it/I can somehow find a cap online so I can do this the easier way... See #2...
#2 - Looks like someone's been here. No cap, AND the brass head has half of it chipped off... So I am stuck not really knowing what alternatives there are to getting to it (other than taking the carb off, which I am avoiding.
#3 - All the way in. Maybe just a quarter turn out... I am guessing this one is because the mechanic told me I have low compression (75lbs) in cylinder #3... They are perhaps forcing more power out of that one by giving a super rich mix? Perhaps this one is the one I should just keep at at least 1.5 turns out?? Will that help?
#4 - Already at 2.5 turns out... yay!

Thoughts on my #2? tricks to get to it while carb still on the bike?

#1 is a tricky spot... Anyone know where I can find just caps? Or is a long, fine tipped flathead screwdriver my best bet?

 

Update:

Finally got all those pilots at 2.5 turns out... still no change - the bike does not stay idling if the throttle is opened, or if the choke isn't hung onto with my hand on it.

Any other things?

 

Dija recently remove the vaccum diaphrams for inspection and cleaning ??

Very often jets can look clean but are not fully cleaned until a thin steel wire about .010-.012" is able to slide through.

 

Weehee! Bit the bullet and pulled the carbs off for cleaning... Following Toe Cutter's tutorial (here) and cleaned all the jets. (This was surprisingly easy... installation back onto the bike might be challenging though)

An assortment of main and pilot jets were dirty (cannot see through). Blew through them and the carbs are reassembled. My guesses are that either I have rust in my fuel tank, or that my fuel filter is not doing its job. Dirty jets seems like a logical sign that I was getting a lean fuel/air mix.

If it is my fuel tank, what do you guys think of the vinegar approach outlined here? If it is my fuel filter, which the shop decided to swap my original to this odd clear thing, what are some good ones you guys recommend for this bike?

Also, might there be anything else that would cause dirty jets?