Have an 87 VFR700 w/35,500 miles. Only rode it twice last year as I have two other bikes. Went to jump start it and stupidly reversed the jumper cables and blew main fuse. I replaced fuse
and then had no power. Went thru and tested all elec. per shop manual and the only thing I believe was out of spec was the pulse generator.
Fast foward to today. Put a new battery in and it fires and idles but severly stumbles on throttle and breaks up. It would stumble past idle and run rough at higher RPM's.
Pulled the carbs which were pretty clean. Pulled each jet and blew them out with compressed air. Didn't pull the float seat valve and clean filter (forgot). Reinstalled and bike does same thing. Idles fine w/full choke and won't accept more throttle.
My first thought is could the pulse generator cause an issue like this? I think I got 230ohms instead of the 450-550 per manual.
What about a dirty float valve and filter?( not enough fuel into bowls?)
I'm also going to check the fuel pump tomorrow. If it's not up to snuff, maybe I'm only gravity feeding the carbs and not getting enough fuel.
make sure your lines are not kinked for the grav feed ..
if the main fuse popped and thats all.. everything else should be fine..
how long was it sitting?
do your self a favor.. pull the wires off the starterrelay.. and trace them back to the harness.. make sure they are not melted together..
find your main green wire in the harness.. add eyelets and ground it to the FRAME .. front middle and back of bike.. CLEAN all your contact areas on the connector blocks.
also.. if this was my bike.. the green wires from the R/R.. ground them straight to the frame.
and use silver heat transfer compound from the computer store.. put a BIG glob on the back off the R/R
.. add a computer fan while your at it..only cost 10 bucks. :fing02:
oh.. unlock your gas cap..
jack the back of your tank up.. to see the fuel line curve.. start your bike.. if it runs fine then you know either the gasline was kinked or the tank got vapor lock.
Tested the fuel pump and it checks out. Bike idles fine w/choke. With no choke, it breaks up btwn 2000-4000rpm. Not sure why its breaking up
or runs better w/choke on because I checked all jets and they were clear. Tomorrow I'll pull the diaphram needles and blow out the orifice.
remove the top of your airbox.. remove the filter..
test the slides with your finger..they should slide back down kinda quickly..and all about the same.. if one is stuck.. things can go wacky..
look inside as the bike runs..
twist the throttle,.. if the slides move up.. evenly..
then they are not the problem..
are you getting a spark on all 4 cylinders?
if the bike is still wierd..
remove all the jets AND the air/fuel mix screws..blow out all tubes and passageways in all the carbs.. forward and backwards with an air compressor..
if it looks like a hole.. blow it out!!.
triple check the jets.. blow them all out with the compressor..
oh,, the "needle jets/" emution tubes.. what ever you want to all them..
the are the long ones that the MAIN jet threads into..
they have holes on the sides..
the front 2 should have the holes like this>>>>> ****
the back should shave this>>> *** *
look in the book for the stock main jet sizes.. sometimes if they are too BIG the bike will not make the transfer from the low to main jet..
hope you get it going smooth. :fing02:
Yea, were are thinking the same here.
I tried the slides and none were sticking and I watched them as I blipped the throttle. All jets were blown with compressed air.
I'm thinking its the needle/slide issue because the problem seems to be the transition from the idle jets to the main jets.
I'm going to pull the needles and clean that out. BTW, I'm running 128 mains with a K&N fitler, no snorkel.
was going to pull the rear plugs but couldn't find the right socket. Is it an 18mm?
if I remember correctly the fronts are a pain to get to.
[image: View Post]megavites, on 05 August 2010 - 11:02 AM, said:
Yea, were are thinking the same here.
I tried the slides and none were sticking and I watched them as I blipped the throttle. All jets were blown with compressed air.
I'm thinking its the needle/slide issue because the problem seems to be the transition from the idle jets to the main jets.
I'm going to pull the needles and clean that out. BTW, I'm running 128 mains with a K&N fitler, no snorkel.
was going to pull the rear plugs but couldn't find the right socket. Is it an 18mm?
if I remember correctly the fronts are a pain to get to.
check the spark pllugs!!! I've had the same problem last winter...you will find gas on some of them, also on the threads...this v4s love to burn spark plugs expecially if they are left for long periods off :fing02:
pulled and changed all 4 plug and pulled (2) rear cylinder diaphragm needles and blew out orifice.
No change in running. Bike will start and idle w/choke on but doesn�t climb in rev�s if left in that state like during normal startup procedure.
Upon throttle operation bike stumbles slightly thru low throttle operation w/choke on. If I keep high revs and operate with no choke,
bike stumbles thru 2500-4000 rpm range. Engine dies without choke on.
It�s almost like it loads up at that rev range and stumbles. I see a little whisp of smoke from right front cylinder exhaust where it attaches to slip on exhaust.(unburned fuel?)
Engine sounds like its firing on all cylinders. I guess I could pull that plug and check for spark.
The only thing I have left in the carb to clean is the float valves. I�ll pull them and blow out everything again.
pulled the carbs again and blew everything out. Had to adjust idle speed and throttle cables but seems to be
running alright now. Still a small hesitation on initial throttle but I think with a little more adjustment on the cables
might do the trick.
[image: View Post]gll429, on 12 August 2010 - 11:17 AM, said:
try running the bike with no cables... and turn the throttle by hand..
Went to take the bike out and its back to not running w/o choke. I can keep it running with no choke and take it on the hiway if I keep the revs up and it runs fine on the main jets but when it idles down w/o choke it dies ( ie, below 2500 rpm approx). I've pulled and cleaned the carbs twice now. Used compressed air and carb cleaner.
It has to be a fuel problem. I'm going to drain the 1yr old fuel and try fresh, but I would think it would stumble all over if it was fuel.
[image: View Post]megavites, on 06 September 2010 - 07:53 PM, said:
Went to take the bike out and its back to not running w/o choke. I can keep it running with no choke and take it on the hiway if I keep the revs up and it runs fine on the main jets but when it idles down w/o choke it dies ( ie, below 2500 rpm approx). I've pulled and cleaned the carbs twice now. Used compressed air and carb cleaner.
It has to be a fuel problem. I'm going to drain the 1yr old fuel and try fresh, but I would think it would stumble all over if it was fuel.
More thoughts??
From the "maintenance questions" comments, i think you could mark this problem thread as "Solved"-- Clogged Slow Jets (Keihin also calls them pilot jets)...
Ethanol fuel turns to varnishy goo if left in a tank after only several months. i consider Ethanol fuel as only 90 % gasoline and 10% water since alkyhol can absorb moisture from the atmosphere...and they sure aren't using 200 proof when adding it to the gas. It's kinda like some of them sissy party liquors that city folks drank...
End of thread · 13 posts recoveredWayback Machine snapshot 4 Jun 2011