Xs 750 won’t start after exhaust and intake modifications

[750triples]

View attachment 250578

 

[jpdevol]

View attachment 250587

In the abscence of specs to the contrary, I'd raise that up a bit and try it

 

[Jan_P]

In the abscence of specs to the contrary, I'd raise that up a bit and try it

Nothing wrong servicing ..but again why on 3 carbs all off a sudden ..causing no start.
The aircraft's have several motors so if one fails ---or two even one can still fly .

I have been wrong before but I cannot se it here .just now. Feels like barking up the wrong tree
But servicing it to specs is good.

 

[jpdevol]

Nothing wrong servicing ..but again why on 3 carbs all off a sudden ..causing no start.
The aircraft's have several motors so if one fails ---or two even one can still fly .

I have been wrong before but I cannot se it here .just now. Feels like barking up the wrong tree
But servicing it to specs is good.

I agree that it's a bit curious, that it kinda sputtered, kinda ran before and now no-start: the only thing we know-of that was changed was carb jets. It would be more curious to be ignition - on a fixed-timing electronic system - with spark reported present & good

Fuel level might make sense at this point

 

[Bruno_c]

How did it run before modification?

 

[750triples]

How did it run before modification?

Ran fine, a little bit of bogging I think because the previous owner hollowed out the stock exhaust.

I agree that it's a bit curious, that it kinda sputtered, kinda ran before and now no-start: the only thing we know-of that was changed was carb jets. It would be more curious to be ignition - on a fixed-timing electronic system - with spark reported present & good

Fuel level might make sense at this point

I’ll definitely adjust with the floats tomorrow, I’ve had enough of messing with these carbs for today. I don’t really think it has anything to do with spark either, but if the float adjustment doesn’t work I’ll look into it.

 

[jpdevol]

Ya got brass floats or plastic?

 

[750triples]

Ya got brass floats or plastic?

Brass

 

[Signal]

From XS 750 E supplementary manual :
XS750-2D , XS750E Specification should be changed Float height 25.7 plus or minus 2.5mm.
No mention of where measurement taken from.

 

[Jim]

No mention of where measurement taken from.

'bout all Mikuni's I've worked on use the base of the float chamber... the face where the gasket sits. Don't recall any of 'em being different. I'd guess those are the same.

 

[750triples]

I agree that it's a bit curious, that it kinda sputtered, kinda ran before and now no-start: the only thing we know-of that was changed was carb jets. It would be more curious to be ignition - on a fixed-timing electronic system - with spark reported present & good

Fuel level might make sense at this point

I’ve adjusted the floats, still nothing. This is making absolutely no sense to me.

 

[Jan_P]

I’ve adjusted the floats, still nothing. This is making absolutely no sense to me.

Please give info about what ignition is installed is it points ore electronic
if electronic is it a waste spark ( unlikely ) system firing all plugs at the same time

Assuming you have spark that is good the question remains is it delivered to the correct cylinder at the correct time
Ignition Timing ??
Spark plug caps with wires flipped ?

 

[750triples]

Please give info about what ignition is installed is it points ore electronic
if electronic is it a waste spark ( unlikely ) system firing all plugs at the same time

Assuming you have spark that is good the question remains is it delivered to the correct cylinder at the correct time
Ignition Timing ??
Spark plug caps with wires flipped ?

I don’t know if the 79 model is a waste spark style, but I know it’s electronic. The plug wires aren’t flipped, they’re in the same position as when it ran normally

 

[jpdevol]

Just for giggles......

 

[Jan_P]

How old is the battery ?
If you have a Voltmeter
Please measure Voltage across battery ignition Off
Then measure ignition On
Are you trying to e start if so if possible measure Voltage across while attempting to start
Does the headlight turned on look bright

 

[750triples]

Hi all, a small update:

SHES RUNNING!

Against my better judgement, I decided to hit the intakes with some starting fluid, and she cranked right up. I have no clue why it wouldn’t start on its own, maybe one of you know.

She’s now running like a hot pile of crap (better than not running at all), any throttle off idle just results in it bogging out to a stall. but I’m guessing that’s because I put the pilot and main jets essentially back to stock when it needs much bigger sizes.

Thanks a lot to all of y’all for helping me out.

 

[jpdevol]

I have no clue why it wouldn’t start on its own, maybe one of you know.

I'd guess the choke circuits are clogged-up

 

[750triples]

I'd guess the choke circuits are clogged-upView attachment 250664

Checked the holes, and went 2 sizes up on pilot, 3 up on main jets. It didn’t need starting fluid after the first crank yesterday when it was 1 up on pilot and stock on main.

Now it needs starting fluid every time I start it, but it makes it all the way through the rev range. Do I need to richen the mixture to help it start up without starting fluid?