87 vfr700 - two wet plugs.... Please help

Dear VFR know-it-alls, I have a 1987 VFR700F2 with 22K miles on it. Today I took it out on a 55 degree day, which is very warm for Syracuse, for only 20 minutes before i noticed lag in power and a different sound coming from the motor. I could smell gas but there was none on the ground. It lacked power and would have stalled if i didn't keep the RPM's up. I got it home and discussed the problem with my father as I started taking the bike apart... The front two plugs under the radiator were covered in gas and the back two were dry. I was hoping that only one plug was bad so it would be a plug or the coil that goes with it... with both plugs wet i am guessing it's some kind of ECU module or something that controls the firing of these two plugs. Anybody had this problem before where two cylinders side by side are not firing? Anybody know how to fix it? ON A SEPERATE NOTE, anybody know what kind of oil I should run in this bike and what spark plugs it takes? Thank you in advance for your responces... -Patrick- Syracuse, NY

 

Pick up a Honda service manual for the bike. All the lovely specs like oil and sparkplugs are in it (and many others).

There are a few places I'd look at first:

1) airbox

Make sure no enterprising rodents have moved in and blocked the air to the front cylinders. No joke, I've found mice nests in crazy places (including the blower moter for the heating/ac in my 350Z).

2) Ignition

The ignition on these is separate for each cylinder, and while both fronts are acting the same, I'd go over the wiring carefully, and make sure that you're getting spark to each cylinder (clean the plugs up first).

3) Carbs

The front carbs might be leaking, but again, they're separate for each cylinder, and the front left is the one with the throttle linkage, and so everything else comes off of it. The floats or float valves in both front carbs would need to be stuck to do something like this.

 

it sounds like stuck floats.... you can check the plugs for spark by pulling one out and turning the bike over and seeing if it arcs...

 

#2&4 pulse generator, cdi box or cam pulse generator. Not a fuel problem.

Or connector/wiring for any one of those. Got a wiring diagram? Helps if you want to ohm out the wires.

 

Dropping of two cylinders front or rear is classic ignition system failure for gen 1 and 2.

 

ok... 1st, what are floats? where are they? How do I unstick them? Can I just have one person press the start switch and i can visually watch the tips of the plugs for spark?

 

now we're talking... is the "pulse generator" the module that is attached to the spark plug via the wire?

The CDI box... is that the thing that looks like a computer chip with heat fins on it under the seat?

The cam pulse gererator.... if that went bad it would stop both the cylinders on that side from running? where is it and is it an easy fix?

 

This sounds like a confident answer.... When you say gen 1 and gen 2 are you saying cam pulse generator 1 and cam pulse generator 2?



I want to thank everyone for your responses... You guys rock...

 

By gen 1 and gen 2 he means generation 1 (1983 to 1985) and the second generation is 1986 to 1989 (only sold in the US in 86 and 87).

I'll also rely more on Toe's ideas more than mine (he's seen a lot of these bikes).

The heatsink under the seat is the rectifier/regulator, part of the charging system. The CDI unit is way up in the back of the tail, per the service manual (have you ordered one yet? )

Toe, since the cam pulse generator is present to determine which cam phase the bike is on (vs. the crank position), wouldn't that be an all-or-nothing sort of issue?

Given that the 2&4 pulse generator is the only thing that I see in common with just the #2 and #4 cylinders (everything else is one-per-cylinder or shared across them all), I think GreyVFR and Toe have it better than my thoughts on the floats in the carbs.

btw, this is all in chapter 18 of the FSM.. Complete with diagrams on the wiring and where all the sensors and pieces of hardware are.

 

No offense but it sounds like you haven't done much troubleshooting with bike electronics. You need to have a Factory Service Manual and a wiring diagram would really help. I think you can find a FSM on line. You'll just have to search or may be someone here knows of one.

You need a VOM to run tests on circuits/sensors etc. Can you troubleshoot electronics? If not you need to find someone who can properly. The thing at the end of the plug wire is the coil. For some reason I was thinking your coils were good. It could be the coil or the wires going to it. Odds are (IMO) connectors/wiring, CDI box, pulse generators then coils.

I don't know about the cam pulse generator. I'd have to read up on it and see exactly how it works. I don't have one on my antique.

 

87's did not have the cam pulse generator and had the digital ignition system. It was a much more reliable CDI than the previous but still ran the cylinders in pairs. This is a much easier system to trouble shoot and that two cylinders are firing eliminates power issues at the CDI. You need to check the resistance of the pulse generator at the CDI connector,spec is 450-550ohms. The connector is four pin at the CDI and are in colored pairs, yellow and white yellow are for coil 1 and blue and white blue are for coil 2. If you get a bad reading a the CDI connector check it at the coil itself to be sure it not just a damaged wire.

 

Pretty sure I have spares of both parts in question, if you figure oot what the issue is I will start the hunt through the piles of parts.

 

ok... now we're cooking with gas... yes grey, I have no experience with trouble shooting motorcycle electrical problems but I am about to get a lesson on it. I guess I need a VOM.... does that stand for VOLT OHM METER? I think I can grab one at work. yellow thing with two probes yes?

Ok, Sir Toe. i have to find the pulse generator at the CDI connection and probe away... maybe i should get that field service manual.... thank you guys, I'm going to have to find this Pulse Gen, etc etc... i knew it wasn't a spark plug or a coil. i really doubt they would crap out in pairs.

 

you have floats in your carbs. they determine when to stop the fuel flow into the bowls.... but forget that it sounds like the "professionals" have your problem almost licked.....

 

It's highly unlikely that two floats from two different carbs will stick at the exact same time on a set of cylinders that are fired by one set of electronics. But hey weird things happen. If the floats are sticking then you should see fuel spillage out of the carb overflow vents at idle/low rpms. Is that happening?

If not. Then the logical thing to look at would be the electronics for those cylinders.

 

Any progress on this?

 

ok... sorry for the delay. I replaced the plugs and per the suggestion of my local shop owner, i started it up. I took right off and after 20 minutes almost all of the gas in the exhaust was gone. it had an idle that wasnt stable but after it warmed up it did settle down.

THEN I noticed the top of the engine was wet. between the heads was covered in gas so i shut her down and looked around. I started it back up and noticed (the bike was running just fine at this point) that the area under the right rear carb was leaking gas out of it. Could this be the issue that caused those two plugs to foul? Is the really a float/carb problem and not an electrical issue after all?

At this time the bike will run but it's leaking gas from the right rear carb near where it goes into the head. Where do we go from here?

 

oh wow... i think this is it... how do I "unstick" floats?

 

Float needles that are leaking are more often caused by debris or defects lodged on the rubber tip of the needle than any "sticking," and most commonly, the debris is from rust in the fuel tank. Another cause can be oxide deposits building up on the sides of the needle, restricting its movement.

Despite any opinion otherwise, based upon my limited experience of 40 years carb fettling, i do not believe in "stuck floats," but rather bad needles. Only twice did i see floats that were filffy enuff not to pivot easily, a '73 CB750 that hadn't run for about 20 years and an older 250 2-stroke dirtbike that had been resting on its side for awhile.

 

my local mechanic says sometimes he uses a wooden dowl and taps the carb and whatever is on the needle can come loose and fix it. Does this sound like the right way to go or what?