Help please... '00 M750 fuel issues

[UK_DoubleDuke]

I had my 900 ss coughing when opened up past 6000 rpm.
It was the fuel filter, on my model inside the tank.
I replaced it and cured all the problems.

Previously on a 1969 ford escort, a minor amount of silt build up in the float bowls had the car lose power and stop. Then restart with full power straight away, to start drawing in the silt again.

Hope to help.

[Raziel]

Really appreciate all the helpful posts.

Borrowed an auxiliary tank from a buddy at work and got it running beautifully with a line straight to the carbs, so at least I know it's not the floats. Also noted in the meantime that fuel was flowing from the pump, strangely enough.

Then returned it to its standard routing and it died. No fuel from the pump at this point! So I bypassed just the petcock and went through the pump with the auxiliary tank again and it ran like a champ. I lowered the tank to the ground and ran it for a long while to see if the pump could handle it without a gravity assist. No problems.

So... either the petcock is hosed, the fuel filter is clogged (forgot about it until just now) or the pump is only working intermittently. Guess I'll put in an inline shutoff valve and 86 the vacuum petcock. This is the one everybody recommends below, and I don't see anything I can readily mount without a plate or something. Seems like it might be difficult to access it, I guess it only needs to be shut off if I'm transporting the bike?

What have others done to mount one of these???



Also found this item but again mounting is an issue:

[ducpainter]

A member on TOB mounted the right angle unit in his airbox with the lever on the outside.

Very clean and easy to access.

[citizin]

Ok - so now you've ruled out the carbs....that's real good.

You'll want to check that petcock and pump now...

[MongoReturns]

Looking at the schematics (extremely helpful over the years) it looks like the petcock is operated by the fuel pump.  So, if the pump is buggered the petcock won't work, no?  And gas will still dribble out of the pump if it's not working - gravity & all.

You people have me paranoid about that stupid petcock now!  So, for the manual one, I guess you have to turn it on before you ride?  And off when you don't.  I don't want to do that.

[ducpainter]

The petcock is operated by vacuum as is the pump, but they work independently.

[Howie]

My manual petcock is just sitting in the hose running by the airbox and doing fine.

[Raziel]

From what I can tell, the only likely problem with not turning off a manual shutoff seems to be during transport where a fuel pump and float failure can lead to a cylinder full of gas, but this seems highly unlikely so I'll guess that most who've installed one don't turn it on and off for every ride.

Howie do you have it inline between the tank and fuel pump? Or is it between the fuel pump and carbs? Running it near the airbox seems like a lot of extra line if it runs tank > shutoff > fuel pump... not that big a deal I guess. I just don't have any grasp of how critical it is to turn on/off before/after each ride. make the beast with two backs it. Tomorrow I'm bypassing it altogether so I can ride the bike for a while and will install a shutoff when I get one next week. Hope I don't burn in hell (or in the seat). If the fuel pump is hosed I'll find out the hard way and get some exercise. 

[citizin]

If he's got up by the airbox, it probably runs tank > pump > cutoff > carbs.

[Raziel]

That makes sense citizin. Seems like the best way to do it based on what little I know.

Mongo, here's a schematic. The red line is the vacuum to the petcock from an outlet on the horizontal cylinder manifold. The blue line is the vacuum to the fuel pump from the vertical cylinder manifold. They are entirely independent. This is a '00 M750, YMMV:

[Howie]

From what I can tell, the only likely problem with not turning off a manual shutoff seems to be during transport where a fuel pump and float failure can lead to a cylinder full of gas, but this seems highly unlikely so I'll guess that most who've installed one don't turn it on and off for every ride.

Howie do you have it inline between the tank and fuel pump? Or is it between the fuel pump and carbs? Running it near the airbox seems like a lot of extra line if it runs tank > shutoff > fuel pump... not that big a deal I guess. I just don't have any grasp of how critical it is to turn on/off before/after each ride. make the beast with two backs it. Tomorrow I'm bypassing it altogether so I can ride the bike for a while and will install a shutoff when I get one next week. Hope I don't burn in hell (or in the seat). If the fuel pump is hosed I'll find out the hard way and get some exercise. 

Between the pump and the carbs.  I guess the answer to how critical is very critical after your crankcase is filled with gas.  Do I turn mine off all the time?  No.  Should I?  Yes

[MongoReturns]

That makes sense citizin. Seems like the best way to do it based on what little I know.

Mongo, here's a schematic. The red line is the vacuum to the petcock from an outlet on the horizontal cylinder manifold. The blue line is the vacuum to the fuel pump from the vertical cylinder manifold. They are entirely independent. This is a '00 M750, YMMV:

Ah I see!  I was confusing the lines up.  I like wine   

[Raziel]

Success! It was indeed the vacuum petcock.
I ran a new line direct to the fuel pump and then took her out for a LONG OVERDUE ride tonight. Thanks all for the troubleshooting help and suggestions. 

I do still need to put in a manual shutoff. I was thinking about installing a face mount version on the triangular rear side cover but am not convinced it's solid enough with all the flex from the lightweight plastic and only two mounting points. Otherwise I will probably just put it inline somewhere below the airbox. The "in airbox" solution is great too, but I hope to put pods on this Winter, masochist that I am. Will post up a thread whatever I do as there seems to be a dearth of info/photos for this common issue.

In the meantime, I'll be giving her the 'ol Italian tuneup before she goes to bed for Winter!   

[MongoReturns]

Good news.  I need to figure out where that thing is in case I need to do a roadside "repair."  She's been doing some st-st-stuttering lately.