Bike stalls after starting up and flat spot off idle

[Donkey Hotey]

Can you try opening the throttle all the way and cranking it? If the plugs are wet at least a corresponding amount of air might start it.

That could suggest a failing throttle position sensor (dumping fuel as if the throttle is opened more than it is).

I hate to send you on a wild goose chase but one of my bikes did have a dead crank angle sensor. I don’t know if one can gradually start dropping its connection and sending bad pulses to the ecu.

I had a road speed sensor that did that: intermittent low readings, then off altogether. They operate on the same principle and it wouldn’t run with that kind of signal.

[Donkey Hotey]

One other thought for the night: do you have a standard OBD2 reader for a car? I just tried mine and I was able to read all the sensor values the ECU thinks it’s getting, including throttle position and rpm from the crank sensor (even during cranking).

[mendonjo]

Hi Greg,

My buddy has the fancy code reader and I will get that today.  We can compare values to see if something stands out.

Joe

[Donkey Hotey]

The thing the OBD2 reader will tell you is if the throttle position sensor is responding smoothly and the values somewhat match where the grip actually is, does the air intake temp look like a real temperature, ditto  for the “coolant temp” (cylinder head temp sensor) etc.

While all of us have our opinions from past experiences, just one of those things being terribly off could cause problems for the bike.

Also: nothing “fancy” about having an OBD2 reader these days. You can buy a WiFi OBD2 plug on eBay for about $20. Download any of a number of apps to your phone and you can read all of that stuff, reset codes, etc. 

[wytfut]

And it's all very handy..!!

[mendonjo]

Hi Gang,

I do have a code reader but its just a simple one - it only reads codes but doesn't give any input values.  I agree they are a must-have.  Anyway I borrowed my buddy's that does display all kinds of info and hooked it up.  It will not display anything while the engine is cranking in fact it turns off when cranking.  However, even at rest it does display some data.
ECT 9 degrees Celsius
SHRTFT1 0%
Spark Advance 0%
IAT 10 degrees Celsius
Throttle position 11.4% at rest and 65.1% at full throttle position

well, that's all I get from the data.  This morning it did fire for half second and then die. 

The positive battery terminal was not tight, I have taken the ground bolt/nut off and everything looks clean.  One of the loop terminals on the back of the battery box had a crack in the loop so I should replace that and I will stop by NAPA today to see bout a ground strap.

Joe

[Donkey Hotey]

It’s times like this when I have to remind myself what an engine needs to run:

• Fuel
  
• Oxygen
  
• Spark at the right time
  

The one thing that old rule doesn’t state but I guess is included under oxygen is, compression.

You say you have good compression. Without a gauge we’ll have to take that on faith. While I agree with your thumb test, I’ve had some lawn equipment recently that would not run but felt like it had compression. Varnish on the valve stem made closing very gummy. It was holding the valve slightly open. Drove me nuts until I found it only had about 40 psi of compression.

I hate to start recommending more expensive parts but I’d be taking a hard look at the crank sensor at this point. Your can pretty much eliminate the fuel system by:

• Spraying a few shots of starting fluid in the throttle body (known fuel)
  
• Wide open throttle (plenty of oxygen)
  
• And cranking it.
  

If it doesn’t start, the only electrical things remaining are damaged wiring, damaged ECU (not likely) or the crank angle sensor is bad and giving false information to the ecu.

I’ve had one bad crank angle sensor (when I bought the bike) and one intermittently bad road speed sensor which is similar. Hmm—now that I think about it, they were both on the same bike. Anecdotally that tells me they can be suspect. Unless you have access to an oscilloscope, I can’t think of a good way to test it without replacement.

[mendonjo]

Yes I have convinced myself that the fuel supply is fine so it boils down to the ECU or the injectors themselves.  I have to assume the ECU is OK (or ship it out to be tested) or look at the injectors.

Almost out of desperation I sprayed starting fluid around the outside of the injectors.  It ran and kept running until the starting fluid vapor was consumed.  Okay that's a big deal, so it must be sucking in air around the injectors.  I will take them off next and see what the O rings look like.

I suppose it could be the intake manifold though..

Joe

[mendonjo]

It was easy enough to take the intake and injectors out.  None of the O rings look horribly bad but I will order a set from Atlantic and see how it goes.

Joe

[Donkey Hotey]

Joe,

If you sprayed starting fluid around the outside of the injectors and the bike started, you must have a terrible vacuum leak there somewhere.

The o rings are a good start. I've never needed to have any of my injectors cleaned but, that might also not be a bad idea. Do you know the history of the bike before you got it? How long it was sitting, etc? I don't remember but if your factory filter had died, it's possible something got picked up and shoved downstream into the injectors. That would either plug them or keep them from closing. I guess if they weren't closing, you could end up with the fuel dripping from the manifolds as you described earlier.

There are conflicting symptoms here that suggest there may be more than one problem going on. Rest assured that correcting these things isn't a waste of time. Most of this stuff would have eventually happened simply due to the age of the bikes.

Greg

[mendonjo]

I totally agree Greg.  Lots of mixed symptoms.  Possibly the intake leak was causing the injectors to overcompensate for a lean condition which lead to flooding (?).  I'm not sure I really believe that but it does seem that something was leaking.

The intake seals look OK to me but not perfect - heck they might have shrunk some with age or temperature (the last ride was on the cool side).  The front injector was really hard to pull out of the manifold like the O-ring was fused to the manifold but it did come out intact.

I cleaned the injectors with carb cleaner (pressurized) and put some power to them.  I was about 3 feet away from a piece of big blotter paper and I circled the spray patterns.  Both injectors performed the same so I think I'm good there.

I think now I just have to wait for the seals to arrive.  I will take the opportunity to have the muffler hanger welded up as it has a crack in it.  It's rainy-cold here so it's a good time to wrench 

joe

[Donkey Hotey]

I haven’t worked on nearly as many of these as some in this community but I’d also recommend buttering up the manifold seals with a light grease or even silicone grease if you have any. It helps them to find their happy spot during installation and clamp-up. If they’re free to squish around during the heat cycling of the engine, just that much better.

On the muffler hanger: broke out around the mounting tabs?

[wytfut]

The injector holes are very porous.... I've fought a few trying to get them out. It appears the "0"ring seats into the pores...

These cast parts make for some tougher situations at times of removal.

The exhaust bracket.....   I can't prove it, but to me it happens when any one of the exhaust components didn't get proper tightening.... Just loose enough to bear extra weight thru wobble onto that weak webbing of the bracket. Because of it I double check my exhaust bolts/clamps on the exhaust ...

[Donkey Hotey]

Bruce,

Yes, there is truth in what you said. Generally speaking: when designing holes like that, the rule of thumb is something around 2D edge distance (or greater).

That means if the screws are 5/16 (0.312) then the minimum distance from center to the outside of the material should be twice that--5/8 (0.625). At least that's what gets used on aircraft. Let that be a lesson to anybody designing a beefier plate to weld onto their bracket.

If you check most of the busted-out ears on the few things that fail like that on our bikes, they aren't that generous (throttle body bracket, shifter bracket, muffler bracket). You can get away with less edge distance on thicker parts but, those were neither thick, nor wide. There was simply not enough meat for the job. Like you said: if they come loose, things start hammering around and it's just a matter of time before they give up.

[mendonjo]

Actually my crack was not bad, probably in the early stages.  Its the rear mounting bolt sleeve - its about 1/3 cracked away from the surrounding plate.  Nothing is loose or wobbly, I just noticed it when I got down on the ground to check things out.

I got the seals ordered from Atlantic today.  They don't have the one that goes between the intake and the butterfly piece.  I think mine is ok but Marty said they don't have anymore.  I will definitely butter  up the O rings prior to installation and I'm guessing I make the final tightening of the intake clamps after everything is aligned.

Joe