Strange 86 v max block jet assembly question

volsung · Jul 19, 2009

Hey,

New here and I joined because I just purchased and 86 vmax.:eusa_dance: But I have a very odd carb question. The bike ran great but after a while, it started to backfire when I let off of the throtle so I figured it was ready for a rebuild on the carb since I was not sure of what the previous owner had done or how offten it had been ran. I began romoving the carbs and opened up the first one. In the bottom of the carb there is a Bock Jet assembly with two jets. Each jet had a rubber cap. Now here is the question. The holes in the rubber caps were plugged with short pieces of cut up finishing nails. :ummm

oes anyone know why this would be done? The bike ran great and idled fine. The only reason I tore the carbs apart was because it started backfiring wich it didn't do when I bought it. Is there a reason for blocking fuel to these two jets. When I found this, I stopped so I don't know if any of the other carbs are plugged off. I don't want to put this thing back together without plugging the jets off if there is a good reason and I'm not going to put them back in if there is no reason for them to be there. I hope someone can shed some light on this soon so I can get it back together.

maleko89 · Jul 20, 2009

My originals had those small tubes too. The replacements do not and I'm not sure why the are there. The purpose of those plugs is to allow access of the pilot fuel jet (left) and the main bleed pipe (middle). The fuel to both is supplied via the main jet which is the brass jet on top of the jet block. If you look closely you can see a crossover passage that connects the middle chamber with the left chamber. The right chamber is for the choke circuit.

The reason for the backfire could be an air leak caused by loose or bad rubber boots, bad/dirty coasting enricheners, or lean pilot circuit. Could also be from leaky exhaust or leaky exhaust pipe connection to the heads.

volsung · Jul 20, 2009

So in a nut shell, Plugged or unplugged either way it doesn't matter.

I bought all new rubber caps and all of them have holes.

volsung · Jul 20, 2009

I'm leaning towards coasting enricheners for the backfiring but when I first test rode the bike it wouldn't get out of its own way. The dealer changed the plugs and drained the floatbowls and the tank put fresh gas in. It made a world of difference and I rode for about a month. I'm going to make sure it's all clean before I put it back together.

naughtyG · Jul 20, 2009

Check out by carbs rebuild posts, but I'm pretty sure that my rubber plugs were solid - no holes in them at all. So yours being plugged kinda makes sense.

volsung · Jul 21, 2009

maleko89 said:
My originals had those small tubes too. The replacements do not and I'm not sure why the are there. The purpose of those plugs is to allow access of the pilot fuel jet (left) and the main bleed pipe (middle). The fuel to both is supplied via the main jet which is the brass jet on top of the jet block. If you look closely you can see a crossover passage that connects the middle chamber with the left chamber. The right chamber is for the choke circuit.

The reason for the backfire could be an air leak caused by loose or bad rubber boots, bad/dirty coasting enricheners, or lean pilot circuit. Could also be from leaky exhaust or leaky exhaust pipe connection to the heads.

I wonder if the holes are year specific. You mentioned that your originals had holes but the replacement ones were solid. I just ordered new ones from Yamaha for an '86 and all of them had the holes.

Any one have an idea?