Intermittent starting issues

My bike has been having issues starting since about half a month ago now. It will sometimes not start no matter how much I crank it or manipulate the choke/throttle (when cold), but I find I'll leave, come back like an hour later and it'll start first crank. The bike has been running a bit rich since I bought it, so I figure maybe it's just too rich with the warmer temps in the air? I haven't pulled the carbs off yet, wanted to get some insight from anyone else who may have had this problem before.

Bike is a 92 750. Plugs were recently replaced and it does have an aftermarket muffler.

 

Too many possibilities to say with any certainty, but...

If you've never done it, or have knowledge of it being done properly in the last decade or so, it's time to go thru the carbs. Eliminate them as a culprit and gain some piece of mind. The rest of the systems on those VFRs are pretty damn resilient. And if it wants to start after sitting some, it's what I'd do if I have already installed new plugs and know the condition of the air filter. But it's also something I always do after purchasing a used VFR anyway.

Pulse generators usually fail after getting hot, not when sitting cold and then get better an hour later. And coils don't get better going from cold to an hour later either.

 

Got most of the carb off only to be stopped at the throttle cable. Both of the screws are pretty damn stuck and stripped out to hell and back. I've heard of people JB-welding a cheap screwdriver to screwed screws like this, but saying as you seem to have some experience do you have any recommendations? Can't fit a dremel in there to saw a slot for a flathead.

 

just loosen the nuts and pull the cables off the holder, the only way i do it because too many of those screws are buggered up by inept hacks lacking JIS.

 

After you remove the cables from the carbs, remove the handlebar with the switch and cables. Then you can flip it upside down on the bench and start soaking it. You will also have the best access to the screws to apply proper pressure when attempting to loosen ( with a fresh JIS screwdriver).

 

Lol no kidding. I didn't have any wrenches that fit the nuts though, but I managed to work the dremel in by pulling out the ignition coil(?) on that side and got a nice hold for the flathead.

As for the actual problem: The slow jet was all gummed up and the pilots were backed out for a smog bike when mine has been (mostly) desmogged, so two birds with one stone there.

 

OOhhhhh... the cable holder on the carbs?! I get it now.

Glad you're starting to get it sorted.

What size pilot jets are in it?

 

I neglected to check. I'm gonna rejet it soon anyways, maybe even a whole new carb so I can completely wipe out the smog junk. Just need it on the road as it is right now for transport purposes.

I've got it all put together and backed out the screws twice as per (mostly) the manual's direction and there's no more smoke coming out the exhaust pre-warmup so I'm guessing I got rid of the rich problem, but now I feel like I'm hearing a slight knock as it's running. You can't make it out that great but I recorded a video:

I've got 91 Canadian pump gas in it so I feel like it'd be strange for it to be knocking after just being put back to the correct tuning.

 

2 things:

A: You don't need new carbs. Everything is easily defeated. I just did it to my 92 (plus about 6 other VFRs, mine and friends)

II: Pull in the clutch while it's idling in neutral and see if the "knock" goes away. If not, it's WAY more likely your carbs need to be synched. You can do a bench synch when you have them out next.

 

Knock did infact go away when I pulled the clutch in. Also noted that the knock wasn't as constant as it was when I first started it up. Does this mean my clutch is buggered? Gears? I have been having a bit of trouble finding neutral sometimes.

Is there a guide for a full desmog? Cause it looks like a few lines have been capped off on mine but the canister is still there aswell as some additional vacuum lines. I'm planning on running through this bike completely in a few months (have Uni to attend in the meantime) so I figure I could do it properly next time I get in there.

Thanks for all the help so far.

 

Clutch rumble / knocking is normal (99.9% of the time). I'd be more concerned if it didn't have it. There's a lot of gears and parts in there that have to have some clearance. They will all make noise until some load is put on them. You should hear some of the CBRs. Ever hear a Ducati at a stop light? Our clutches have thick aluminum covers and are bathed in oil, that's why they are more quiet. This comes up every now and then and everybody thinks it's the end of the world. Google "motorcycle clutch knock" sometime and look at all of the makes and models with people inquiring.

I summed up de-smog pretty decently here recently:

https://vfrworld.com/threads/86-vfr750-evap-system.60809/#post-640468

That was on an 86, but it's pretty much the same except you have hard lines going to your rear head too.

Some more on the subject here:

https://vfrworld.com/threads/1992-vfr750f-ended-up-on-my-trailer.60160/




Regarding finding neutral, when was the last time you bled your clutch system or checked the condition of the brass bushing in your clutch lever?

 

Haven't done clutch.. anything as of yet. I'll make sure to add an inspection to the list once I get the time, though may do a bleed earlier than that.

Thanks for the desmog guides btw.