A few months back I was fueling my 85 vf500f a mile from my home. Inspecting the motor, I touched the vacuum hose that ran from the fuel petcock to the back cylinder and it crumbled (obvious from age). On my way home the bike was acting like it was starving for fuel to the point where it died. I pushed it home. Later I replaced the vac hose and the bike has never run the same since. Symptoms of no idle and a starving non-smooth acceleration. The bike has never had it's carbs cleaned so I took them out and cleaned them. They looked not as bad as I expected, every so slight varnish. I checked all jets and bowls for varnish, blew them out with compressed air, I used carb cleaner and sea foam. Checked all cylinders for spark - check.
As a pro-active measure, I have been reading about how to remove the fuel pumps from the 85's and switch to gravity feed. So i did this as well thinking it could be a vac/fuel pump issue. I started the bike up and it runs almost the same. It has to be choked to idle and it has a slow hesitation in acceleration and slow return in rpms down to an idle (with the choke on). Does this sound like a vac leak or maybe they're really out of synch? Any help/advise is appreciated.
Definitely sounds like it's a fuel delivery problem. First thing I would check is for good fuel flow from the petcock. Remove the fuel line from the carb inlet, place it in a container and see if fuel flows freely from the tank, let it flow for at least 30 seconds to make sure that flow is steady. Keep us posted on your progress.
[image: View Post]anvil, on 12 November 2010 - 12:50 AM, said:
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Symptoms of no idle and a starving non-smooth acceleration. The bike has never had it's carbs cleaned so I took them out and cleaned them. They looked not as bad as I expected, every so slight varnish. I checked all jets and bowls for varnish, blew them out with compressed air, I used carb cleaner and sea foam. Checked all cylinders for spark - check.
I started the bike up and it runs almost the same. It has to be choked to idle and it has a slow hesitation in acceleration and slow return in rpms down to an idle (with the choke on). Does this sound like a vac leak or maybe they're really out of synch? Any help/advise is appreciated.
This sounds like a classic case of clogged circuits, pilot that is. Or a cracked or misplaced rubber boot causing a vacuum leak.
Assuming you used the correct size vacuum hose such that it is not leaking vacuum, and that the rubber petcock diaphragm is not cracked and leaking, then fuel should flow when vacuum is applied to the pcock. If fuel will flow then, if the carbs are clean, the bike should run great.
But when you pulled the carbs did you just blow out the brass jets with snake foam and sea oil, or did you unscrew them and push a metal wire thru them and hold them up to the light, or use a magnifying glass to inspect that all the varnish was gone? Maybe the varnish was loosened up by the chemicals and then pushed into the tiny orifices that are the pilot jets (only 0.014" diameter), and now they are clogged.
The other factor could be the reassembly didn't seat the big rubber carb boots completely and there is a big air leak downstream of the carburetors. That is why it only runs on the enrichment, which dumps lots of fuel and lets the motor run even with the air leak. This would have similar symptoms to clogged pilot jets. Start it up then spray carb cleaner or wd40 at the base of the rubber boots and below the carbs to see if the rpm changes--would indicate the air leak. Look at the gaps around the boots and make sure the carbs are pressed down into the boots and the boots pressed down onto the manifold. i use a little grease on everything to help ease it back together--a dry boot is tough to put back on. The boots might be dry and cracked from age too. Good luck and endeavor to persevere...
First off, thank you guys for your help, I really appreciate it!
The behavior of the motor is exactly the same as it was before I removed the carbs and eliminated the fuel pump, so I don't believe it's was from taking them apart. I didn't use a wire to clean the jets, only compressed air, soaked them in carb cleaner and sea foam. They were perfectly clear. The fuel is flowing especially fast now that it's converted to gravity feed which eliminates the vac line to the petcock. The boots are well seated and i did use WD-40 and boiled them to make them pliable. I will try the WD test on the boots later today to see if that effects the rpms.
Can you buy the boots new?
Also I found another forum that someone had mentioned this:
"Just an update. I didn't do any work on the carbs, but I replaced the two boxes (one of which controls the spark plugs/tach), which actually solved my problems for the most part. The bike idle's perfectly, starts up just fine, and has no problems. I guess the box was just fried. "
Link to thread
I think what has happened here is that a piece of the crumbled rubber got stuck in the vacuum port that is supposed to provide the vacuum to open the petcock. I'd check that first. If you use a pipe cleaner or something through the nipple on the motor it should clear it out. If the motor sucks up a piece of rubber it won't hurt anything. Just don't rev the bike up high when you first start it.
Thanks Hawkrider but the fuel is flowing quite fast so I believe the vac issue has been ruled out.
I did get the bike to idle but at about 1500-1800 rps and then I did the wd-40 test, which seemed to have no effect on the rps. Now that it's idling, if i blip the throttle it jumps way up in rps and slowly comes back down... super touchy. It's not a smooth acceleration, almost boggy. If I hold the throttle to one single position, it isn't smooth. It will slowly rise and fall. The motor's behavior is almost the same as before I cleaned the carbs.
At this point I'm kinda out of options unless it's what kennybobby suggested that the pilot jets are still clogged. But they were clean upon disassembly. Any other suggestions? Because at this point I may have to take it to a shop.
Thanks
[image: View Post]anvil, on 17 November 2010 - 01:12 PM, said:
Thanks Hawkrider but the fuel is flowing quite fast so I believe the vac issue has been ruled out.
I did get the bike to idle but at about 1500-1800 rps and then I did the wd-40 test, which seemed to have no effect on the rps. Now that it's idling, if i blip the throttle it jumps way up in rps and slowly comes back down... super touchy. It's not a smooth acceleration, almost boggy. If I hold the throttle to one single position, it isn't smooth. It will slowly rise and fall. The motor's behavior is almost the same as before I cleaned the carbs.
At this point I'm kinda out of options unless it's what kennybobby suggested that the pilot jets are still clogged. But they were clean upon disassembly. Any other suggestions? Because at this point I may have to take it to a shop.
Thanks
To get the bike to idle at 1500-1800, i'm gonna guess that you had to turn the idle adjust screw in quite a bit to keep it running --what that does is open the butterfly valve in the venturi, and so the bike is now "idling" on the main jet and not the pilot circuit. When the revs are up and you let off the throttle, it doesn't really close the butterfly now and the revs stay high. All symptoms point to classic case of clogged pilots, unless you are using the choke lever pulled back to keep it running, but in that case you still have clogged pilots.
Unless you unscrewed them and looked thru and saw a 0.014" hole to daylight, then they are likely clogged. If you saw daylight but it was only 0.008", then it still won't run--you need the full orifice diameter to be open...
What is the status of the pilot screws? have the covers been removed, how many turns out from the bottom are they, did they get cleaned and reassembled correctly...
Thanks!
Yes, I had to turn the idle screw way up and the choke was completely off.
I did see daylight thru the jets. Not sure of what the exact diameter but they looked clean, I did soaked them in carb cleaner, sea foam and blew them out with compressed air. Now, the pilot screws on the other hand still have the factory covers on them and haven't been removed (I didn't want to mess with the settings). So they remain untouched. I do have a clymer manual that explains how to do this. Once I remove and clean them, how many turns our from the bottom should they be set at?
All this reminds me of the fun I had with my old VT250. The damn thing would starve for fuel all the time and it bugged the crap out of me.
The solution was to buy a set of carbs from the wreckers and learn how to completely tear the whole thing down, clean it all within a whisker of its life and then reassemble. After I did that the bike ran great!
You asked about buying carb boots. Yes, you can buy them. I picked up some at Classic Cycle Depot (
http://classiccycled...p?productID=124). About $55 for the set of 4.
You also asked about how the screws need to be set. The factory specs are in your Clymer manual. If you're using the OEM jets then you should start with the screws 2 turns out from seated.
I had the same problem on my 86 VF500, and it did turn out to be that the idle jets weren't clean enough (I thought they were clean the first time). I soaked them in carb cleaner, ran a wire through them, then blew them out with air. I also replaced the carb boots (you have to be careful that the carbs seat into the boots properly, if they don't then its easy to get an vacuum leak that will cause problems, ask me how I know.)
You may also want to make sure that your throttle cable is adjusted correctly and that its lubricated and not hanging up.
Carb boots..........When I pulled the carb assembly from my recently purchased '85 VF500F, the boots were so hard and inflexible, I figured that new ones were in order. I had read that soaking neoprene in auto transmission stop leak or silicone solution would soften things up. Since I had a gallon of silicone solution of the type that is used to waterproof tents and awnings, I decided to try it. I placed the boots in a large ziplock bag, filled it with the solution and let the boots soak for 3 days. Amazingly, the boots are now quite soft and pliable, not as good as new probably, but plenty soft enough to use. When I installed the carb assembly, I applied a film of silicone grease to the carb horns and cylinder head tubes, tilted the boots slightly on the heads, the carb assembly popped right into the boots with little force.
[image: View Post]anvil, on 17 November 2010 - 03:18 PM, said:
Thanks!
...
Yes, I had to turn the idle screw way up and the choke was completely off.
... Now, the pilot screws on the other hand still have the factory covers on them and haven't been removed (I didn't want to mess with the settings). So they remain untouched.
if the pilots jets were clean, then the obstruction is likely at the end of the pilot screws between the pilot jets and the venturi ports --and since the covers are intact... the pilot needle screws never got cleaned.
You would do better to remove the carbs for this and clean everything, but you could try doing it on the bike, but if it doesn't get thoroughly clean it might run anyway although poorly. And then you will have to pull the carbs to clean them anyway...
But you could carefully drill a small hole in the covers and pop them out of the way, then unscrew the pilot screws with spring, washer and oring, clean everything and try to blow the crud thru the pilot circuit--but the openings into the venturi are tiny and easily clogged by varnish,etc. and crud is hard to dissolve if there is no flow of solvent to attack it...but it might work. If it were me i would just pull the carbs and be done with it.
There are also brass air jets that feed the pilot circuit and main, etc. located in the air horn upstream of the venturi--be sure to spray carb cleaner thru those and that they are open, no dirt dobbers, etc. You are almost there to having it run and scream...
Great info from everyone. Looks like the carbs are coming off again and I'll be giving them a real good second shagging + pilot jet cleaning/removal. I had to adjust the valves anyway so carb removal was enviable. Thanks for the carb seal link flwoolybugger. Anyone know of a resource to get a rebuild kit for the carbs or valve cover gaskets?
Found a resource for replacement parts.
http://www.oldbikeba...0-F-Interceptor