GT750 not flowing fuel

[adigati]

Background, Bike had bad crank seals so crank was removed and sent to be rebuilt.
Reassembeled bike and everything was perfect, ran great, revved nice, smooth, all was good.
Rode it about 15 miles and it just died, seemed like it ran out of fuel and never ran again.
After days of checking pretty much everything, we re-check the crank seals and it was leaking again
Remove the crank and send it back to be redone (lovely)
Reassemble bike again, recheck crank seals (holding well)
Bike will not run, only tries to run.
Plugs are dry
float bowls are full
remove carbs and plugs place hand over intake and yes they suck although I would have expected more
ignition all spot on
carbs were not messed in between running and not running, nothing was changed except remove and replace
I'm at a complete and total loss of even where to check anymore, any help ideas would be appreciated!
Thanks in advance
Tony

[teazer]

If the float bowls are full but the plugs are dry, suggests that jets have blocked from sitting around while the crank was out for a rebuild or two.

You could try to spray engine starter fluid in the carbs and see if it fires up, but that will only prove that it runs and won't tell you much about what is wrong.

Pull the carbs and clean them out and check flow through every orifice by spraying WD40 through one passageway and then repeat on the other two carbs for comparison of flow. Then move on to the the next circuit. Rinse and repeat.

Don't forget to include the starter jet because they are clog prone and hard to clean. http://pinkpossum.com/GT750/carb/BS40carbs.htm for more details.

BTW, it helps if you provide an introduction that tells us where you are located and how much experience you have working on bikes. That makes it easier to provide answers that make sense.

[adigati]

I apologize for that, been working on bikes 30+ years, but mostly 4 strokes in the last 10 and I'm in California, it's a early J model with VM carbs.
It will not run on starter fluid only pops.
Since last post, yes all the jets and orfices are clean and seem to be flowing properly.
I have cleaned out the enrichener circuit, both the air in and fuel out and yes they appear to be clean as well, however I'm not familar with the starter jet. Is that in the little inlet holes on the intake side (nothing in mine) or unique to the BS carbs? Never saw that before in a VM type carb.
Thanks for your help, yes, I'm quite perplexed.
Tony

[teazer]

Ah Cali. That explains everything probably the weed or moving techtonic plates mate.

Interestingly enough most if not all Mikuni carbs of that era had a starter jet in the float bowl, just like the BS40 link I posted earlier. It's a PIA to clean out because it's only 0.6mm diameter (#60 in Mikuni speak). Remove the float bowls and one at a time, try to blow through that with WD40 (less obnoxious) or carb cleaner down that "tunnel" and see if it squirts out of the hole into the bowl.

Did you also check that the idle bypass holes were clear? Those are the tiny holes point up at an angle in the floor of the carb just ahead of the slide and connect to the pilot jet. You can use the straw on your carb cleaner can to spray in from the engine side and see if it comes out at the idle (pilot) jet.

It's odd that it won't start with a blast of starting fluid though. Usually that's enough to get any motor going as long as it gets into the cylinders. Are you 110% sure that the starter clutch key didn't drop out when you put it all back together? A quick easy check is to see if the points open at 3 - 3.5mm before TDC on either outer cylinders and that the marks on the timing disk (propeller) more or less line up.

[adigati]

Yes I thought that was odd as well, usually a blast of ether will get it to at least spin up.

You've given me a few things to check and I'm on it. Starter clutch key......hmmm. I will assume that locates the whole mess on the left side, point drive included. I have not checked that but would explain a lot. I have nice fat blue sparks, but at the wrong time is useless, lol.

Thank you, I'm on it and will report back!

Tony

[adigati]

Boy I thought for sure it would have something to do with that keyway. Removed down to the crank seal, key was there. Reassembeld all and check piston is at 3.5mm BTDC (left), agrees with the pointer. Set points and timing, checked wires go to correct coil. One thing I did not like is when the cover goes back on and then the point plate, the shaft that holds the point cam has a slight bit of play (up down and side to side) not a lot. It does turn smoothly and bearing feels OK, but I did see a variance in the point gaps as I was turning it over to adjust the points, again not a lot but doesn't seem right to me.

Nice blue spark but that play is weird.

The starter jets are clear (yes they are there) accupunture needles are your friend for this job.

The straight up hole out of the pilot jet are clear as well as the angled holes

Now when you try to start it, it is better.... kinda of an occassional rolling popping, but stll no joy. Plugs still appear dry.

Starting fluid again, nothing. Few drops of gas in the spark plug holes, then try it, same occasional rollong popping but no start

Hand over one of the carb bells while cranking and you can feel suction (such as it is) and your hand gets a little wet with gas.

Weird things happen to me.....welcome to my world

Any suggestions would be appreciated.

Tony

[willowden]

Have tried a compression test ?
I had a similar problem sometime ago , it turned out to be the head gasket. It was blowing across two cylinders.

[adigati]

First thing I did, yes compression is good and lower seals passed presure test!
Thank you,
Tony

[teazer]

Did you check the timing on all 3 cylinders and are all 3 pots giving big fat sparks? Have you checked battery voltage and voltage at the coils? A weak battery or corrosion at connectors can cause those issues.

Try a more generous spray of starter fluid and see if that changes anything. Starter fluid is very easy to ignite, so test outside with a fire extinguisher just to be safe. It should fir up with a wet starter fluid soaking and if not, it suggests the problem may be in the ignition side of things.