OT motorcycle won't work in rain, any pilots out there?

It certainly would if I only had one carburetor. With this MC my usual SOP is to turn off the fuel a mile from my house using the petcock on the tank the bike will continue to run on gas in the float bowls for that long.

The engine leans out a lot and may not idle without stalling, but will run at partial throttle and wide open - different symptoms than the wet condition - won't go a mile when wet, won't run wide open, partial, or idle. Problem first kicks in during partial throttle between 20 and 70 MPH - haven't really tried running 15 mph in the rain so can't say if it will maintain that speed without quitting. I don't drive over 60 in rain as a general thing.

When the float bowls are running out of fuel the level drops, but there's still fuel. It may run rough but continues to run. Opening the throttle tends to suck more fuel even with a low float bowl levels.

Hold your sprayer nozzle at the ground and spray upwards.

Good Luck! Rich

If you can get the air cleaner off fast enough, and if you can see in the carburetor throats, stop and take a look when it dies -- sometimes you can see the frost melting away (or not, if it's cold enough). This makes a nice definitive check to your frosting problem. If your intakes are fairly well protected from direct road grime, it may even be worth while to do a couple of runs without the air cleaners on their at all, if it means being able to see your venturis quickly.

A friend of mine was recently telling me about a hot rod motorcycle he built when he was a kid -- he'd shimmed the cylinder on the case to change the port timing, with corresponding shaving done to the head, he'd put on bigger carbs, and to top it off he was running methanol/nitro (on the street, no less).

He said that after a half hour of running fast the carburetors were sitting in big balls of ice. Now _that's_ obvious carburetor icing!

I used to own a '69 Toyota Corolla. It was obviously a California car originally (it had the air pump), and it had _no_ carburetor heat. It would regularly ice up going over the coast range in the winter in northern Oregon.

While the Toyota engineers had not provided the car with carburetor heat, they were thoughtful enough to make the ignition key just a hair smaller than the venturi opening. I could go 20 miles, stop, remove the air cleaner, poke the key in the venturi to knock off the ice, put the air cleaner back on, drive 20 miles...

Fortunately I usually only had to do that a couple of times each trip. I think I ended up jury rigging carburetor heat on the thing.

Years ago I coasted down that long hill down the west side from Jerome (AZ)... in a 1964 Dodge Dart.

At the bottom I applied throttle... nothing. Pulled air cleaner... it was completely full of snow-like ice crystals ;-)

...Jim Thompson

Have you checked your alternator output. I've owned two 1981 CB750F models and both had alternator problems. One I bought new and the one I still have I bought in 1999. Both had under 6000 miles on them when one had a short in the rotor and the one I have has a short in the stator. I can't buy a new stator, discontinued. But I am thinking of having a place that rewinds small motors and all sorts of things give it a try. One thing is the 750 motor needs 13.8 volts or it will sputter and spit. However it wouldn't cause it to die unless the battery was down and I don't think this is your case. But check the output voltage none the less.

News==----

Its definitely a fuel problem as pulling on the choke fixes it. Sounds like shit in the carb or fuel system somewhere.

Well I can try unplugging the alternator and running it in rain the next time it rains. It will start and run without an alternator. I could see how noise on the battery could cause the trigger point of the transistor switch to shift and cause a misfire.

This one did have a shorted rotor. I took it out and rewound it and added an expanded scale voltmeter to watch it. No amount of water in the alternator housing will cause the problem when it is stationary, but it is easy enough to unplug so the next time it rains I'll try that.

Actually you can buy rotors both rewound with a core charge, and brand new for about the same cost ~$70 last time I checked. Place over in England is manufacturing them and with shipping the cost was comparable to buying one rewound in the US. I had a quote of $300+ from the Honda shop so spent $50 on a 6# spool of 22 AWG magnet wire before I discovered I could get a new one. My rewind works well. There's a little bit of run-out because the slip rings are a little crooked but it has been running fine that way. There's still enough left over magnet wire to wind several more (takes about 12 ounces of wire for a rotor)

I also found a source for a new stator for it for a few hundred dollars. I don't need a stator though - and it looks easier to rewind than the rotor I already did.

That rewinding stuff isn't that tricky. Stators are wound on formers external to the poles then put in place and epoxied in. Rotors are more hassle - take apart the pole halves with a large gear puller, and scrape out or unwind the wire.

I have used two techniques for the coils - a bobbin made of very thin PCB material and soldered together then just insulate it and fill it with wire brushing on epoxy as you go (the bobbin could be almost anything including cardboard or tin can material - just has to be strong enough to hang together long enough to mount and epoxy it in, and thin and insulated.

Technique two is to just wind a "self supporting coil." Build/make a two part wood mandrel of about the right size, then cover the wood with Teflon plumbers tape (for a mold release agent). For the sides I use a pair of polyethylene can covers like one sees on Planter's Peanuts, cut an undersize hole and slip it on the mandrel. Brush it with a light coating of machine oil (mold release again), then just paint the core with epoxy and wind adding epoxy after each layer or two (the epoxy creeps out between the lower windings so it isn't necessary to do after each layer). Let set then pry it off the mandrel. I add a layer of cloth soaked in epoxy to the pole pieces to keep it in place and protect the sides. Only caveat is to carefully route the wires to the slip ring connections along the pole so they aren't allowed to move and epoxy in place.

My alternator output is more like 14.4 volts, but it always has been.

There's no good way to get a look inside the carburetors. Too much junk to remove to get at them. The slides come down when the engine is off so I'd also have to move them out of the way. Might be worth running without a filter (not like there's a ton of airborne dust in the rain) and mounting a mirror in there. I probably only have a few seconds to stop and look at it because it restarts after a brief pause most times.

Obvious would be nice - I've been screwing with it for over six months now - mostly with the ignition components.

Probably not in all four carburetors - this thing runs rough for a second or two then dies completely, then will generally restart in about 30 seconds.

So I'm thinking ice now.

I think only one carb is choked if I recall. Been awhile.

You are probably thinking of the accelerator pump diaphragm. That is on only one carburetor. Choke is a single cable that links to choke plates on all carbs.

Those bikes have a accelerator injector in each carb - the pump is located on one of the middle two carbs. Cracking the throttle several times quickly should give it a couple of good shots of gas - if it responds well to that (and doesn't run really bad from the terribly rich mixture), then it is very likely a fuel starvation problem. Another thing to check is cracked rubber boots between the head and the carburetors.

News==----

Newsgroups

=----

My accelerator pump is on the #2 carburetor. I'll try pumping it in the rain.

There's an air cutoff diaphragm on the #1 carburetor

The carb to head rubber hoses appear to be intact. Pulling them is a royal pain so I'm not anxious to do that except when absolutely necessary. I did inspect them visually and did spray water at the junctures and all around the carbs from a stream to a mist.

I did discover something that I haven't been maintaining properly. Apparently my bike has an exhaust gas re circulator system, comprised of a lot of tubing and a reservoir. It feeds into the air box after the filter. Says to check it every 4K and I have never checked it. There's a drain for the reservoir. also says to drain it more frequently when riding hard or in the rain . . .

That could be a factor or even the cause. My money is on contamination in the gas tank that is moisture sensitive somehow. My recommendation: drain and flush the gas tank and hoses clear to to the carburetor connection, drain the carbs as well, replace the fuel filter, and put it all back together and refuel with fresh, known clean, gasoline. Do not reuse the fuel removed from the tank, just dispose of it. When i was much younger i saw a similar problem with a lawn mower, a little different though it would just stop at about half a tank of gas. Took me months to find the problem. With the drained fuel was placed in a glass container you could see the contaminated layer in it though.

The reservoir looks like it holds about 6 ounces maybe more with the tubing and I drained what appeared to be about 2 ounces of clear water out with only a faint hint of oil (light sheen) on it.

I've dealt with a few recalcitrant outboards that got a contaminated load of fuel - haven't had one die like this though. Outboards use multiple carbs.

I've been draining fuel looking for contamination. Each carb has a drain at the very bottom of the float bowls - I drain it into a glass jar and see nothing but gas - even after being in the rain. Not a speck of rust or water - and even if there were, the fuel supplied to the cylinder is from the top of the float bowl, so if there were enough contamination there I should see it, or if the level was so low as to cause it to stop I should see that too by draining the bowls.

Four carburetors dying all at the same time quickly? Then restarting again after a 30 second pause? only to die again? When I deliberately cut the fuel off and drive, it takes close to a mile for the bike to stop - then it usually works fine except may die when idling. Even when it seems totally out of fuel it will still fire intermittently - this problem is rough running for a second or two and total death on all four cylinders immediately after. Adding choke may make it run for awhile longer.

Those symptoms would seem to rule out interrupted fuel supply - the onset of death is too quick.

I can pull in the clutch and coast for the 30 seconds it takes to restart which leads me to believe it isn't water being thrown up into some sensitive part from the road surface like someone suggested.

Plan A is to go back to the ignition system - I think I've ruled out water in most of the system. Right now I plan to add some LEDs to the ignition coil primaries. Looking for ways to steal a little energy to light a led only when the coil is firing and do it without an active circuit, and monitor the failure should one occur - does the primary stay high, or low, is the primary power there or not- Five LEDs should do it.