First break down!

So I rode to work this morning and didn't quite make it. I only had to push it 500 feet to one of the parking lots at work. Didn't get a chance to look at it yet, as I would have been late for work (heaven forbid), but I get an hour lunch, so I'll have a look then.

It started, idled and ran perfectly. I rode the highway at 65 mph all the way, smooth as usual , got off the exit and let off the throttle and I could feel it trying to die. I clutched and got down to second gear and it stalled. I was still going about 30 mph I would say, so I tried bump starting a couple times. It started every time but when I let the clutch back out to continue on, it would die. Finally coasted to the side and tried kicking it over in neutral and it wanted to start but wouldn't run. I put the choke on and it started right up, ran at high rpms and I "think" it was only running on one cylinder. As soon as I took the choke off it died. Trying to rev it to keep it running would kill it faster.

Am I correct in thinking ignition? It's a '74 850 with single mikuni and boyer. I'll check the connections at the coils and at the points cover. What else should I be looking for?

Thanks!
Ben

It sounds like a fuel shortage to me Ben. A blocked tap, filter, or possibly needle seat in the float bowl.
The fact that it started and revved with the choke on seems to say there is a leaness.
If you find that it starts and runs OK for a short time after sitting for a while, but then returns to not wanting
to rev, then it is probably a blockage. That just means, that it is not filling the float bowl quickly enough
to keep up with demand.
Do you have a dirty tank, Fibreglass ?
At least with the Mikuni you only need a phillips head screw driver to remove the carby and to then remove the float bowl.
IF YOU DO THIS, BE VERY CAREFULL NOT TO LOOSE THE PIN THAT HOLDS THE FLOATS IN PLACE.
Hope this helps.AC.
Of course it could be... coils getting hot, brocken wire in boyer, spark plug dying................

Might be fuel flow. You can either unscrew the plug on the bottom of the carb or undue the line at the petcock and check flow there too.

Check the battery and stator output.

I had excatly the same thing happen, same symptoms. There was gas in the tank but, not enough to go out the primary petcock!!! It has a two inch tube and will not let gas through to the carbs once you get less than two inches of gas in the tank! DOH! I turned on the reserve tap and continued to the gas station to refill.

Thanks guys, I'll check out the fuel flow issue.

Aussie - It's a steel tank, that should be clean (I did not confirm). It was lined and I can see that the liner is starting to come off around the filler, so I imagine it's coming off everywhere else inside the tank. New petcocks, new inline filter and new fuel line. Fuel line is clear so I can see whats going on.

pvisseriii - I'll see if one of the guys in the shop has a meter that I can check the battery with. The stator was working awesome when I checked a few weeks ago, and it hasn't given me any problems starting (boyer) so I have my doubts, but worth checking anyway.

king - def have enough gas, but this helps confirm a starvation issue.

Thanks,
Ben

Brly said:

Thanks guys, I'll check out the fuel flow issue.

Aussie - It's a steel tank, that should be clean (I did not confirm). It was lined and I can see that the liner is starting to come off around the filler, so I imagine it's coming off everywhere else inside the tank. New petcocks, new inline filter and new fuel line. Fuel line is clear so I can see whats going on.

pvisseriii - I'll see if one of the guys in the shop has a meter that I can check the battery with. The stator was working awesome when I checked a few weeks ago, and it hasn't given me any problems starting (boyer) so I have my doubts, but worth checking anyway.

king - def have enough gas, but this helps confirm a starvation issue.

Thanks,
Ben

Click to expand...

Liner could have easily came off and clogged the petcock. Try opening both.

Had a look at lunch time. Both petcocks flow very well and I get steady flow through the inline filter.

I did not take the carb bowl drain out to check for flow through the carb. I have heard of cases where the rubber tip on the needle vavle will swell and stick in its bore.
If I drain the bowl with the taps off, then turn the taps on with the drain still out and don't get any fuel, then I know that rubber needle tip is stuck, correct?

I didn't get a chance to check the battery or the wire connections at the points cover, but they're on the list.

Any other suggestions?

Thanks,
Ben

When you pull the float bowls, see if both needles are still held up by (and) move up & down with the throttle cable.

Dollars-to-donuts a retaining circlip let go and dropped one of the needles down into the jet, effectively blocking it off.

Can't add much but back up mentioned, with choke on might be sucking loose carbs tighter for less air leak but I'd check electrical first.

Gents,

I haven't had much time to work on the poor girl, but heres what I've eliminated so far.

Fuel flow is fine. Flows very well through both petcocks and filter.
Had the carb off. I couldn't find any problems but I blew everything out with carb cleaner anyway. All passages were clear.
I checked my wiring connections at the points cover (boyer ign) and coils, no problems. I have good spark at both brand new plugs.
Checked valve clearances. The right intake valve was a bit open so I adjusted accordingly (I probabaly did a poor job settting it when I checked them a while ago). All other valve clearances were in order. I could not see anything out of the ordinary through the valve covers. Everything moved like it should have when I turned the engine over.

I will check to see if the timing rotor has slipped next.
I will also check the plugs after kicking over to see if they are wet, should help eliminate the carb.
I haven't officially checked for compression with my tester, but I did the thumb over the hole thing and it has compression. I will check with the gauge though.
*EDIT* - checked battery, still at 12.4 volts.

It just seems to be different when kicking it over. Doesn't really feel different, but sounds different. Seems like air is being pushed out somewhere. There is no oil anywhere (like a head gasket blew or something) so I don't understand. I'm still thinking it might be some crazy fluke in the carb, or more accurately the carb boot or manifold (single mikuni), as the air sound seems to be coming from that area.

It doesn't even come close to starting with my normal starting routine.

Ideas are welcome and appreciated.

Thanks,
Ben

Well, I figured it out. There are four allen head bolts that hold the MAP manifold to the head. Two are inside the mainfold (cant be seen with carb and carb boot on) and two are outside. One of the two inside bolts backed its way out and was letting air in (they're not blind holes like I thought). The bolt was just laying in there on top of the intake valve, so I fished it out and put it back in, this time with loctite. The other inner bolt was a little loose as well, so I put the loctite to that too. I never re-tightened those two bolts when I first got it running, obviously because they are a pain to get to. Lesson learned. Put it all back together and it fired right up like normal. Went for a 30 mile ride in heaven!

I had cleaned the clutch and installed dynodave's clutch rod seal while she was down. Wowie did that make a difference in how it shifted. Wayyyyy easier with a clean clutch. Really was a nice night for a ride.

Glad shes makin' noise again.

Thanks again,
Ben

I had the same problem. I caught it before it stopped the bike.

On the road is good. Bend over and kiss that the screws did not totally go through the motor,clanging about for a while eating up the combustion chamber , O.M.G. $$$, ride on.