My '84 700F crapping out ...

Hi,

Last week I rode my 700F to/from work a couple of days & everything was fine. Sat. I pulled her out to run around town & she would hardly go around the block. Got her home & used the truck instead. Once done, I put the battery on charge, didn't appear to need it, but it's always been a good 1st step :^).

I tried starting her up again. With choke & at idle she appeared to be ok, off choke or off idle she seems to run on 2 cyls. Slapped an Ind. timing light on each SP wire in turn, the rear cyls. looked good, the front appeared erratic. Removed the clutch cover & checked pulse gen. resistance & air gap, both seem to be ok.

Checked the resistance of each SP wire, all are reasonably close to each other. Same for coil resistance values, both the good side & the 'bad' side are similar to each other.

So, I think I'm down to the timing generators (please God no), or fuel delivery. Does anyone out here have other ideas, or see something I missed? Any/all help appreciated, I want my 'mistress' back on the road ;^).

TIA,
Anders

 

Ok, additional info from todays look. Fresh start this AM, timing lite now indicates only the left rear (viewed from seated) spark nice/steady. Removed plugs, found 3 non-resistor & one resistor type installed (huh, whoops), must of happened when I replaced coils/wires (Dyna) a couple of years ago. Installed all matching plugs, same results. Swapped coils side - side, strong spark remains on lt. rear, swapped timing generators under seat, strong spark remains on lt. rear. At the moment, I'm stumped.

 

I am also having the same issue with my 1985 VF750F. Strong spark on the rear cylinder bank (1&3). Weak faint blue spark on front bank (2&4). The bike will run but only on the rear cylinders, barely. I have changed plug wires, coils, and CDI boxes with NOS (parts from eBay). I have also tried swapping these parts between banks with no luck. The only other part I haven't checked is the pulse generators. The compression is good on all cylinders, so I'm thinking it's not mechanical. Have you had any luck solving your problem? Because it sounds similar to mine. Thanks.:sad:

 

No, no luck yet. Discovered timing light appears to be flaky, so must start t-shooting over again. Have spent some time with this to date, very frustrating.

Bought a new '07 VFR yesterday, so my t-shooting will be at a leisurely pace now :^).

 

The front two carbs are downdraft. Under rare circumstances, excess fuel can varnish on the slides, causing them to stick. Once the throttle is opened... instant lean burn.

1st gen bikes are plagued with heat-related carb problems. Next time you have the carbs off, put a heat shield in there.

 

Checked the fuel delivery today. Removed airbox & checked slide movement, which felt good across all 4 carbs. However, I decided to open the drain on carbs 1 & 4 (easy to reach). Carb 1 drained fuel as expected, not so carb 4. I got some kind of dark blop, and then a hesitant trickle from 4. Carbs coming off this week for a look-see :^).

 

Yeah, I think you are getting closer to the source. Chances are there is a lot of varnish buildup in the carbs. It's not a bad idea to check the condition of the slide diaphragms too, a small crack in one of those would cause a lean condition as well.

Keep us up to date on your progress.

 

Well, pulled carbs tonight. Looks like they need a going over. There are some black wet fuel? rings near the butterfly valves. Fuel is also bubbling around one of the small choke/fuel enrich rod gaskets (if that's what they're called).

 

That's not good! There is only supposed to be air behind that dust seal. The plunger is not sealed so if fuel is up there you certainly have something going on. Carb rebuild here you come!

 

Began the rebuild process by opening carb #4. There is varnish & a bit of gunk in the bottom of the float bowl, but the jets, inlet needle, needle seat/strainer, are all fairly clean. However, the slide diaphragm is torn, about 3/8 inch. Fortunately, some time ago I bought an entire set of carbs off Ebay for about $100. The slide/diaphragm in carb #4 from this set is in good shape :^).

 

I don't know why that would make it quit running on the highway, but nonetheless it sure sounds like something that is contributing to the problem. Those diaphragms are not cheap so it's good news that you have some spares.

 

Spares are good :^), but I'm not going any farther until I have a set of rebuild kits ... still looking for these.

BTW, I never got out of the neighborhood after the first sign of trouble, much less to the highway, so highway running was never attempted.

Thx,
Anders

 

Got around to yankin the carbs yesterday. They were fairly clean except for the three stuck float needles and the two torn diaphrams. There's the problem. I was lucky I have a spare set of carbs to rob parts off of. Also, all four floats needed adjusting. Specs state 7mm and they were all around 10mm. I haven't put them back on yet, but I'm hoping this solves the problem. I'm dreading putting 'em back on; that parts a bitch.

 

Are you using the same process that I show on my site? If you do it that way it's pretty much a cake walk. Ok maybe not that easy, but it's pretty easy. I don't dread removing or installing carbs, it's the rebuilding (all those linkage pieces!) that gets me.

 

It rides again! I used a rachet tie down strap to get them back on. I got it off of a link on the website "the V-4 files". Instead of an hour, it takes about 15-20 minutes. But its still a pain. Bike runs great now. :thumbsup:

 

The tie strap method is pretty overkill I think. In fact, I think you could easily damage the carbs that way. Using the method I show on my site you can install them by hand in about 2-3 minutes. You should try giving it a shot next time, assuming there will be a next time!

 

I've used the tie down strap twice now and I do take great care (going very slowly) not to damage anything. Next time I will try your method. By the way cool website. Your VF1000F looks awesome. :biggrin:

 

There is always a next time...:drum:

 

My rebuild kits have arrived so I'll be working on my carbs over the long weekend. When it comes time to re-install, I'll have a look at Jamie's site for the install tips :^). I've always done this by hand in the past, so any tips to make it easier will be welcome. I'm too much of a clutz to attempt using tie-downs ;^).

Anders

 

The manual says to loosen all four boots, then partially install the rear carbs, etc... the manual also says the engine must be removed to replace the countershaft seal. Don't listen to the manual.

-Keep all the carb boots tight.
-Install the front carbs, and seat them. Don't tighten the clamps on the front yet.
-Use two of the largest flat-head screwdrivers you have, and pry the rear carbs into the boots. I use the giant Snap-On flat head screwdrivers, they have about a 3/8" blade and are about 16" long. Long tire irons should work too. There is a raised part on the top of the carburetor body, right behind where the boot clamps to the bore... this makes a good leverage point. Use the top rail of the frame as the fulcrum, you will be passing the screwdriver under the top rail, resting the blade on the carb body, and pulling up on the handle to force them into place.
-Be careful of the clutch line on the left side.
-If you park the bike in the sun while you're messing with the carbs, the heat will make the boots easier to work with.
-you may need a couple smaller screwdrivers to "shoehorn" the carbs into the boots. This can be done one at a time.

I've done this the hard way, and it takes nearly an hour of hissing and spitting to get it done. this easy way gets it done in two minutes, leaving 58 minutes to think about how stupid Clymer manuals are.