VF500F idle doubles after an hour

Too far away for me to help.

 

Well, emotional support is very welcome.

I'll be honest and say that I picked up this bike within the last year. I really don't know what one of these is supposed to sound like at idle. It's always had idle issues. First, it just wouldn't idle at all without the choke on. So I pulled the carbs and cleaned the slow jets. Put it back together and then it would idle without choke, but it has never been particularly smooth. I figured that was a carb sync thing, and I had the sync on the to-do list for a while. That did improve the smoothness of the idle, but it is not even by any stretch, and it has to be driven three or four miles before it will think about idling completely without choke (but then it is fine, except for the racing that come after getting driven at speed for 10 miles or so.

I had been ignoring the fuel mixture setting, as my manual said that they are "factory set". But this weekend I noticed that the plugs were gone, so someone has been screwing around with them. And it was clear from the settings that whoever did it last didn't know what they were doing. I suppose there is some chance that the stuck mixture screw is stuck all the way in.

But I don't think so. There is at least some chance that it is stuck at the factory setting. I just don't know. I'm not sure that I am able to just leave it as it is, but I don't want to go overboard either. It's a good question as to whether the cylinder is firing at idle. Guess I should be able to disconnect the spark plug and find out. (Although I haven't changed the plugs and so I have no visual memory as to where they are, sitting here.)

I feel like I ought to be able to use a left-handed drill bit to extract the screw, and then cut a new slot in it. But there are several way s that might go wrong. There are carb bodies on ebay currently, so that is a potential fall-back.

 

Finally check the header temp. The right front header (the one with the stuck mixture screw) is running about 10% hotter than the left front header. A bit over 430 F compared to a bit under 400, at idle. I guess I'm thinking it could be worse.

 

I pulled the carbs to address the stuck mixture screw. One of the boots is cracked, so I guess I won't be putting it back together prior to procuring a set of boots. Can anyone suggest a vendor that can get the boots shipped quickly?

 

Try Bike Bandit.com .... they are like 10 bucks.

 

I'm having the same issue with an 86 VFR700. Rebuilt the carbs (twice), and have the same stuck screw. I tried and easy-out and broke off the top of the screw, so it is staying where it is. Bought new boots and air filter, but haven't tried to sync them. Ran pretty well for about 15 minutes until the idle thing happened. (Currently only the left two cylinders are firing, but that's another post...)

 

Mine was doing the same thing. While it was hot I adjusted the idle down to normal.
Whenever I start it now, warming it up on full choke is absolutely necessary and takes about 15 minutes, but it stays at 1,500 rpm throughout any ride.

 

Using the choke for more than about a minute is a very bad practice as it carbons-up the plugs & valves, wears out the cylinder bores and piston rings.

Instead, to get a higher idle during warm up, use the adjustment screw, not the choke !!

 

Hi. I thought I would report back and let everyone know where things stand.

I pulled the carbs and gave everything (well, the jets) a good soak. I replaced the boots. I tried like the devil to solve the case of the stuck idle mixture screw, but to no avail. I couldn't get anything to bite, including a screw extractor. It's just going to be that way until I replace the carb (should I decide to do that). The bike runs just like it did, which is pretty good. The racing idle has not reappeared. That could be because I replaced the boots, but it could also be because the temperature had fallen by 20 degrees and the engine just isn't getting as hot. I don't know for sure. Won't know until Spring, probably.

I would share a story of the joy of working on a 27 year old bike. I got the carbs back into place, and the bike would *not* start. Sigh. What was interesting was that it was obvious to me that the fuel pump was not pumping. I jumpered it and it pumped, so that left the ignition. I spent several hours trouble-shooting the ignition system with a multimeter until I discovered a pair of wires had been spliced into the wiring harness, apparently to install a now-removed security system. I guess I banged it around too much wrestling the carbs into place, because it was shorted. I removed the wires and soldered the splice back together and the bike lit right up. Cost me a weekend.

 

Yes, but a satasfying weekend of tweakin on your girl and finding hidden problems in the garage instead of on the road. Much easier to repair things in the garage with a beer than on the side of the road with traffic flying by, full gear baking you in the sun, and little to no tools to do the repair correctly, which just leads to a shortened ride and doing the job over again properly once back in the garage.

Hopefully you sorted out the funny idle issue now that you've got some new better sealing boots on her and the problem does not reappear.

 

I'm a little late in replying; but I had a hell of a time sorting out this issue on a rebuild I did some time ago. When Spring hits and the temperature rises, your issue will be back again. Just like mine did. I had ruled out a vacuum leak or carburetor issues, and narrowed it down to the valve adjustment being off in one cylinder. The temperature of the header pipe on that cylinder was also noticeably higher than that of the other three which I believe is a symptom you're experiencing. These valves are trickier to adjust than one might think - I don't want to relive that nightmare.

I suggest you take it to a reputable shop willing and capable of adjusting these valves properly, which is an impossible task in itself, or you try to adjust them on your own. If you do it yourself I highly suggest using a special tool: http://vfrworld.com/forums/1st-2nd-generation-1983-1989/34491-vf500f-valve-lash-adjustment-oem-tools.html I didn't, and I almost gave up a few times because of it.

Good luck and enjoy your 500 - It's a wonderful bike!

 

New to the Hondas, but not bikes to be sure, not aware when Honda went CDI ignition, seems like to me if it is a "points" (wtf is that ??) bike, the advance springs need replacing and lubed just a bit. :mechanic:
I don't think carb mixture changes with heat much, but what Durk suggested is a good point, the rubber intake boots will change with heat and cracks will open causing lean mix and high idle. IMHO

 

remove carb, get a drill bit teh size of the screw ON THE INSIDE OF THE THREADS. make a perfectly centerd hole in the screw leaving the threatds still in the carb. use a tap to push out the threads.

 

I'm not sure when Honda started using CDI modules, but the VF500 does use them.

 

easy to suggest, very hard to do.

 

true. woudl be hard to do. woudl save a few bucks. so it woudl depend on if saving a few bucks is worth all the extra work. i know a guy that had to do this to alot of block bolts on an old vintage vehicle. was the only option. was darn expensive too.