Topic: The only thing SCREAMING now is the bike on the highway!

[medic09]

When I bought my '78 750K last August it ran erratically.  It would start out okay, and at highway speeds just die.  On the slightest incline, it would lose power and speed.  Sometimes it did that on the flats for no apparent reason.  Gas mileage was in the high 20s to mid 30s.

After changing plugs, air filter, points, timing, and running Sea Foam through the tank a few times, it ran well enough that I could use it on my daily commute (~ 130 miles round trip, mostly on the interstate).  The bike would happily do 80 or more, with power to spare.  Gas mileage was still poor.  I figured over the winter I'd pull the carbs, and that would straighten it out.

Over the winter I straightened out electrical problems, and cleaned and rebuilt the carbs. Remounted and synched. Last night I went for a test ride.  A few miles in town, and few miles on the interstate.  Bike ran well at all speeds, but still don't have the idle quite right.

This morning it was very hard to start.  In town it was fine.  Accelerated well.  Once on the highway, it lost all guts.  At about 60 mph the bike just loses all gumption.  Downshifting doesn't help.  The same strips of road where I'd do 85+ with power to pass, I could barely do 65.  At one point, while just starting up the entrance ramp, I thought it would stall till I downshifted and goosed the throttle.

What's going on?  What do I do?  I COULD SCREAM!  (thanks, I feel better now...)

 

[eldar]

Does it stink when you first start it up? If so, then it is probably rich. The whole plug chop thing can be done at various rpm. Not just wot. That only tests that range. You can do it at idle too. Have you checked to make sure your accel pump is shooting gas into the carbs? Have you played with your choke while driving to see if closing it changes anything? Are you sure it is opening all the way?
What did you set your idle mix screws too? Starting point is 1.5 turns. One thing to remember is that these are fuel screws NOT air screws. Out makes the mix richer, in is leaner. When you cleaned your carbs, did you pull the slow jets out and clean them so you could see light thru ALL the holes?

[toycollector10]

If you have done your points and timing I think you should start thinking about the supply of fuel to the engine.

Start at your petcock and follow the supply line....cheers

[bill440cars]

             Are you getting your gas from the same place all the time? Have you got a good fuel filter. Maybe your gas is contaminated. Is it possible that you're picking up trash in your gas? After you make your ignition settings (points, plugs, timing) are they staying the same? I do better if I'm dealing with it myself. I'm just trying to through some stuff out there to see if it might be in that general area. LOL

                                                     Later on, Bill

[scondon]

   Also, you might not be getting spark to one or more of your plugs(bad plug, bad plug cap, plug wire needs clipping, condensor, etc..). This type of thing usually shows up after the bike is fully warmed up and operating at higher rpm(peak alternator output).

    Or, the mechanical advance could be sticking.

Just a couple thoughts.

[medic09]

Okay, let's see what you all are saying:

The bike always ran a little rich in the past.  I thought that might be part of living at 7000 feet with stock jets. 

I'll go clean the plugs and try a chop.

I measure the floats settings before closing up the carbs.  They seemed correct.  I have put in an inline fuel filter.  How would I check for air leaks at the boots?

I didn't think the accel pump would be the problem, since I took off and worked up through the gears just fine at first.  I did thoroughly clean it (it was full of tan colored crud) when I rebuilt the carbs.  It moved freely, and I don't hesitate coming off a stop except for that one strange hiccup going up the entrance ramp.  Choke seemed to be working when I remounted the carb rack.  It seems to work when starting the bike.  I haven't played with it while riding.  Idle mix screws are presently at the 1.5 turn starting point.  That's where I set them when I rebuilt the carbs.  I haven't played with them yet, since remounting the carbs.  Slow jets were thoroughly cleaned and checked.  Since my problem seems to appear at speed, I wouldn't have thought the idle mix or slow jets would be the issue. 

I think I'll recheck the timing, though I don't know why that would have screwed up.  I haven't checked individual spark.

May I SCREAM now?

[mrbreeze]

Lots of good troubleshooting tips in this post.Even with freshly cleaned /rebuilt carbs.....what does the inside of the tank look like? How about carb synch? You will usually have some issues after taking down carbs and getting everything good again. Float heights...... I measured mine at overhaul but still had low fuel level in #3. I pulled the floatbowl and tweeked the adjustment until the fuel level matched the other 3 carbs. Made everything sunny again. You will get it right my friend......just do all the detective work and go away from the bike for awhile when you scream!!!!!

[mrbreeze]

Just reread your post.....check for airleaks by spraying carb cleaner around the boots with engine running.Any change in RPM.....there is an air leak.

[TwoTired]

Is your air filter and exhaust stock?
How does it run when you temporarily operate without the air filter element?
Is the air filter new?
Are your spark plugs fouling?  What number is marked on them?
Do your spark plug wires have any cracks in them?  Particularly near or at the coil body?

[medic09]

Needle height is fixed on the '78 carbs.  Those main jets were spotless when I finished cleaning.  Actually, the carbs were altogether pretty clean even before I rebuilt them.

Plugs were replaced a few months back with stock spec plugs.  Bike ran well enough at the time, till I put it up for winter.  Wires were okay, but I can recheck that.  Plugs were a little black sooty, but I knew I was running a little rich.  I haven't looked this time, yet.  Air filter is an oil type that I've been using with no problems since Fall.  It's fairly clean.  Exhaust isn't stock, but it's the same as I've been running all along.

I sprayed carb cleaner on the boots while the bike idled just now.  RPMs went up.  Air leak, eh?  Okay, now to pull the tank, loosen everything, and see about reseating?  I hope that does it.  I dread pully these off and putting them on again.

[Geeto67]

last time I had something like that happen it was on a DOHC and the spark controller had just gone bad. I had it pinned WFO jut to maintain 65mph. You said you straightened out some electrical problems, might any of these involve the points or timing in some way? If so I would check your points with a dwell meter and check the timing.

[andy750]

I had something similar on an F2 and it turned out to be a bad condenser - very cheap to change. Check all your connections as well just to make sure.

Good luck,
Andy

[medic09]

The electrical problems were bad splices (what was the PO thinking?), fried wires, etc.  Never had a problem in the area of the timing plate.  I'll recheck the timing anyway; can't hurt.

While redoing the clamps on the manifold boots just now (or the 'insulators' as Honda calls them) I also found that the little 'foil' cap on the side of #1 carb where the fuel tubes run in a line between the carbs was missing.  Took one off another old carb and tamped it into place.  Maybe that effected things, too?

[eldar]

I must say that it is almost impossible to run rich with these carbs. You are at high altitude but even so, the mains are hard to run that rich. HOWEVER, I had a huge rich problem that turned out to be dirty slows. They affect things more than you think even more so once you add in the accel pump. You may also want to turn in your fuel screws a quarter turn.

[medic09]

I must say that it is almost impossible to run rich with these carbs. You are at high altitude but even so, the mains are hard to run that rich. HOWEVER, I had a huge rich problem that turned out to be dirty slows. They affect things more than you think even more so once you add in the accel pump. You may also want to turn in your fuel screws a quarter turn.

Well, I'll bet all the jets are squeaky clean.  I could try turning in the fuel screws a tad.  Can always reverse it if I don't like the effect.

[Jerry Rxman Griffin aka MuthaF'er]

Your other post says it's not charging. If it's not charging and your battery is cooked where is the electrical current to come from to fire the plugs?    No/low juice = weak /no fire = unburnt gas = rich = #$%*ty mileage = eventually walking home so don't go too far.

I say to work out your electrical problems first. One thing at a time.

[medic09]

Your other post says it's not charging. If it's not charging and your battery is cooked where is the electrical current to come from to fire the plugs?    No/low juice = weak /no fire = unburnt gas = rich = #$%*ty mileage = eventually walking home so don't go too far.

I say to work out your electrical problems first. One thing at a time.

Good point.  Taking into account Lloyd's observation in my other post, I may have overestimated the problem.  In the meantime, I switched out the new voltage regulator.  That's where the problem might have been.  I've thoroughly been through the rest of the electrics stem to stern.  They work better than when I bought the bike.

Timing was still close to dead on, so that's not it.

I tried to address the air leak problem, so we'll go for a little ride an exit or two up the interstate and see what develops.  I hope not to be walking home!

[TwoTired]

Timing was still close to dead on, so that's not it.

Timing isn't the end all.  Did you check dwell or point gap?  This can effect the charging of the coils, the duration of the spark, and be RPM related.

Cheers,

[medic09]

Well, after my little ride I can say my bike runs like a piece of excrement.   

1.  Can't get a good, stable idle.  Doesn't want to idle less than 12-1300 on the tach.
2.  Top speed on the highway was a whopping 60 mph.  Got up to 70 by downshifting.   
3.  Again had one of those hiccup moments applying throttle at low speed in 2nd gear.  But all other times it moves off of a stop and through the gears without a prob.
4.  Very hard to start when cold.  Worse than before.

I checked for air leaks around the boots again.  Didn't see anything this time.  Timing was okay when I rechecked it.

Take the carbs back off?  Assure nothing's stuck, bent, etc.?  Could I have messed up when I put the new cables on?  Where'd the guts go?

 

[medic09]

Timing was still close to dead on, so that's not it.

Timing isn't the end all.  Did you check dwell or point gap?  This can effect the charging of the coils, the duration of the spark, and be RPM related.

Cheers,

TT, I don't have a dwell meter.  I did check the gaps carefully when I did the timing a while back.  Since the timing looks pretty good, I figured the gaps are probably still okay.  ?

[KB02]

I'd say check the fule filter again, too (or just reoplace it with new). There might be a blockage in there.

Did you pull the air filter on your test ride?

[medic09]

I'd say check the fule filter again, too (or just reoplace it with new). There might be a blockage in there.

Did you pull the air filter on your test ride?

Simple enough.

I didn't pull the air filter.  I'll try that later or tomorrow.  I'm blowing-off a pile of school work that's due, so I'll have to leave this till tomorrow.  I'll pull the fuel filter, though.  That's quick enough.

[medic09]

Okay, I removed the fuel filter.  On the highway topped out at 80-85.  Just wouldn't keep accelerating, like it had a governor.

Also, there's definately a hiccup when trying to throttle open in 2nd.  I crank the throttle, and the bike just stalls a moment before resuming to run.

 

[techy5025]

Any chance you could borrow and try a different set of coils? I would second the
suggestion to check the dwell, too. That becomes more important at higher rpms.

Jim

[heffay]

i had a similar running issue on the gf's ex500... her petcock was inadequate 
we got her a new one and the bike runs fine.
her petcock is now quite adequate.