Carb/airbox Vent Tubes

I have an 85 vf500f. I removed the carbs for cleaning but when I completed reassembly i noticed I had one left over vent tube that is 1 of 2 that runs from the airbox area and runs down the right side as a blow off. The one connection attaches to the back carbs. Does the other one attach to the front carbs? I don't recall a front carb connection? Thanks in advance.

There are two vent tubes, one between carbs 1 & 3 and one between carbs 2 & 4. If you don't reinstall it, you will most likely see some occasional fuel drippage from the vent holes. Also, there is the possibility of dirt & crud getting into the carbs.I just got done with a complete carb assembly teardown on my VF500F for cleaning and seals replacement, what a PITA. It was worth it though, engine now runs like it should.

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Thanks creaky - thanks for the diagram. I thought so, and frankly i had the fear of having to remove the carbs again, because we all know how fun removing those buggers are. I see you have an '85. Did you ever have fuel pump/vacuum issues? I see lots of post eliminating the fuel pump and going gravity feed with out a hitch?

[image: View Post]anvil, on 09 November 2010 - 11:56 AM, said:

Thanks creaky - thanks for the diagram. I thought so, and frankly i had the fear of having to remove the carbs again, because we all know how fun removing those buggers are. I see you have an '85. Did you ever have fuel pump/vacuum issues? I see lots of post eliminating the fuel pump and going gravity feed with out a hitch?


I've only had my VF for 3 weeks. I have been busy adjusting the valves, rebuilding the carbs, rebuilding the clutch slave, have not ridden it yet. The headliamp will not light up, I am currently tracking down the problem, think it is the dimmer switch screwing up. I got the engine running yesterday after reinstalling the carb assembly, sounds great. I don't have any experience with the fuel pump situation, mine is working OK, I plan to leave it as is unless a problem crops up.

In contrast I've had mine since 1990! It did a lot of sitting and thus the carb cleaning.

I had a similar issue with the headlamp cutting out and i narrowed it down to the throttle side switch, which i believe is the engine kill switch. I would tap it with a screwdriver and it would turn on. I cleaned the contact points with contact cleaner and it seemed to fix the problem. My tail light goes on and off on occasion as well, haven't fixed that one yet.

FYI: I am removing my fuel pump and switching to gravity feed. If you read the following forum it explains that the '86 eliminated the pump and went to gravity feed. Honda didn't implement a fuel pump in the vfr until the newer fuel injection models. My bike has been starving for fuel because of a vacuum issue directly related to the fuel pump. I'll let you know how it pans out.

Fuel pump forum

Yeah, I read a couple of threads on another forum about changing from the pump to gravity, might need to do that at some point. I fixed the no headlamp problem, it was the start switch. It seems that the headlamp circuit runs through the start switch so that when you hit the start button, the headlamp turns off until the engine starts. My wonderful Clymer manual did not show that. I sprayed some contact cleaner and dielectric grease/antioxidant in the switch, works fine now. I took the first ride today, put about 40 miles on it, runs like a dream. This is going to be a fun bike. :beer:

A couple of thoughts.....I have an 86 VF500F but the carbs are from an 85. I have two sets of carbs. On one set the 2 vent tubes just vent to outside air. On the other set of carbs the vent tubes go into holes in the plenum (with rubber gaskets around it.) This routes the vent into the airbox, and it seems to be the more correct way. I've used both sets of carbs. On the set where its vented to outside air I have to use larger jets in the carbs. I'm guessing that it sucks some air into the carbs and makes it run too lean. I also notice more of a gas-smell in the garage with the set of carbs thats vented outside.

Mine is also gravity fed. My tank/petcock is from an 86, which has a different size outlet than on the 85's. So in my case the outlet from the fuel petcock is a different size than the inlet for the carbs. If you have the same situation you can't just run a hose directly. Mine runs fine with no fuel pump, never had a problem.

I've also recently had the problem mentioned here with the headlight, thanks for letting me know where to look!