717 NO fuel from PTO carb and other issue...

[Waterluvr]

Ok, here is some new info. When starting, the mag carb shoots out fuel from the carb meaning back out of the carb like pressure is forcing it outside the carb while the pto carb dosent deliver fuel. Could this be a timing problem? Could it be the rotary valve needs adjustment?

Sounds like the metering arm on the mag carb is wide open and the primary circuit is dumping all that fuel, you'd never see that much from the regulated circuit with the throttle plates closed.

When you rebuilt the top end you now have manifold pressure's back in spec and there's plenty of pull making it past the closed throttle plate ends and hitting the stainless air restrictor, that's working your high side and allowing the fuel pump to give up most of the volume it can push through to the mag carb high circuit.

Once you pull the stainless air restrictor out to have a look you're really stepping up air velocity and increasing the draw on the high side, even a timing issue wouldn't spit that much fuel back at you.

Look on the bright side, sounds like your fuel pump is working fine go find out why your needle is wide open.

 

[Sportster-2001-951C-Stock]

How did you determine which cylinder is not firing, did you shoot pre-mix into the dry carb and it began firing?

Put your hand over the PTO carb while engine is running, it should wet your hand with fuel and will pull fuel through all orifices if there's any fuel to be had. This is like maximum choke for the carb.

 

[powerslave]

I have my flame arrestor off while I am firing it up. Here is a video to show if this helps. My PTO carb sends no fuel to the cylinder while the MAG carb is spitting fuel all over the place, lol.

[video=youtube_share;DuXj4L9oVLw]http://youtu.be/DuXj4L9oVLw[/video]

 

[Waterluvr]

That's the high circuit causing that your needle is wide open and it's not closing. Something has your control level hung up with that much fuel in the chamber the diaphragm should be totally compressed against the atmosphere cover plate and completely out of the loop at that point.

 

[powerslave]

So no way it could be a timing problem? I was going to dig into my rotary valve and see if timing is off. I would think that is the only way it would literally spray fuel outside the carb like that.

 

[powerslave]

So i think im confussing myself. Is the problem my mag or pto carb?

 

[Waterluvr]

So i think im confussing myself. Is the problem my mag or pto carb?

When you remove the carbs, take a minute and look at the inside of the throttle plate near the mounting flange as it sits closed, see the primary exit point in the low side regulated circuit? If you open the throttle plate just a little bit you'll see the three small points of exit in the same circuit, those all flow fuel from the low jet and that entire range of operation is controlled completely by regulated pop off of the needle and seat.

Now, flip it over and have a look just past the choke plate see that round air venturi horn? That's where the high circuit delivers all the fuel, your problem is the needle and seat is wide open and not closing and the fuel chamber in the carb is being kept clear full from air velocity flowing past that high circuit.

Your fuel pump is pushing everything it can straight through the point of least resistance, that's why you're seeing all that fuel on the top side of the closed throttle plate.

 

[powerslave]

I did pop off test and poped at 40. Does that tell me anything? Also, thank you for taking your time to help diagnose my problem.

When you remove the carbs, take a minute and look at the inside of the throttle plate near the mounting flange as it sits closed, see the primary exit point in the low side regulated circuit? If you open the throttle plate just a little bit you'll see the three small points of exit in the same circuit, those all flow fuel from the low jet and that entire range of operation is controlled completely by regulated pop off of the needle and seat.

Now, flip it over and have a look just past the choke plate see that round air venturi horn? That's where the high circuit delivers all the fuel, your problem is the needle and seat is wide open and not closing and the fuel chamber in the carb is being kept clear full from air velocity flowing past that high circuit.

Your fuel pump is pushing everything it can straight through the point of least resistance, that's why you're seeing all that fuel on the top side of the closed throttle plate.

 

[Waterluvr]

I did pop off test and poped at 40. Does that tell me anything?

Frankly unless you somehow managed to locate one of the original Mikuni test fittings for the fuel filter inlet (those haven't been available since 1990 something) and tested from the filter inlet who knows, I guarantee you if we sit down together and I test them from the filter inlet and you test from the fuel fitting with all the other outlets plugged the results are going to be nothing alike, as many of the guys here in the forum know first hand I have a pretty open door policy for those who want to learn or just see it done, pull up a chair I don't mind.

In your case it's not just a pop off issue though, rather I would say either your control arm is in a bind from the pin being installed wrong or possibly a piece of something made it's way on top of the diaphragm between it and the cover plate as it's not closing at all.

 

[powerslave]

I've taken them apart 3 times now. Check out what my knowledge will allow. I did not change the pin or spring but changed everything else. My knowledge of these and lack of trouble shooting skills are what is taking so long to diagnose. I'm almost tempted to have someone rebuild them correctly.

Frankly unless you somehow managed to locate one of the original Mikuni test fittings for the fuel filter inlet (those haven't been available since 1990 something) and tested from the filter inlet who knows, I guarantee you if we sit down together and I test them from the filter inlet and you test from the fuel fitting with all the other outlets plugged the results are going to be nothing alike, as many of the guys here in the forum know first hand I have a pretty open door policy for those who want to learn or just see it done, pull up a chair I don't mind.

In your case it's not just a pop off issue though, rather I would say either your control arm is in a bind from the pin being installed wrong or possibly a piece of something made it's way on top of the diaphragm between it and the cover plate as it's not closing at all.

 

[Waterluvr]

I've taken them apart 3 times now. Check out what my knowledge will allow. I did not change the pin or spring but changed everything else. My knowledge of these and lack of trouble shooting skills are what is taking so long to diagnose. I'm almost tempted to have someone rebuild them correctly.

Find a local service provider that can help you, I final tune and water test as many of the carbs I build as possible it's the only way to know the job is finished properly. I'm your #1 fan for turning your own wrench and saving $$$ but sometimes it's worth it to pay someone for things like this.

The two biggest problems with most PWC carbs are the last guy that worked on them, and the guy before that. If you don't have anyone local shoot me a PM and I'll be glad to get on the phone with you and see if maybe something simple got missed while you have them on the bench next time around.

On Edit:
As they are right now, you should be able to pressure test from the mag fuel pump inlet with everything else capped off and I wouldn't expect to see the carb holding any pressure at all everything should be going right by the open needle.

 

[powerslave]

I will do the pressure test as you suggested. One other note, a friend seems to think it may be the RV timing. He says a possibility is, it is out of timing, blowing back fuel outside the choke side of the mag carb. And, since if I pour a little premix in the pto carb and the pto side does not fire (there is spark), says it is a good possibility its the RV out of timing...In any event. I think I will check to RV and if that is good and I am still having a problem, I might just locate someone here who can rebuild these for me. I want to learn and have learned alot here but time is not on my side as well. Thanks for you help, I did learn from this exchange.

 

[powerslave]

Thanks. The reason for the rebuild was a hole dead center in the pto piston, small oil line broke off.

Well, you only did a top end correct, so as long as you didn't pull the rotary valve cover your "should" be good, if it was a running ski before. Is it possible the RV was obstructed at any point during your rebuild and you turned over the engine? That could have possibly jammed the RV and stripped the gear, long shot I guess. Only thing you can do is either pull the carbs again and look at the RV or look thru the carb to see if it's moving. That still doesn't confirm it's in the correct position. The only time you would set that timing is when you physically remove the rotary valve, other than that it doesn't get adjusted.

 

[Waterluvr]

Thanks. The reason for the rebuild was a hole dead center in the pto piston, small oil line broke off.

Get a 1/2" brass hose splice to put everything back together, pinch the main oil supply line to the rotary valve in two places about 4" apart. Install a single pincher on the return/vent line back to the tank and cut the main supply line between the hose pinchers.

Use your hand pump and the necessary fitting to connect to the supply line going to the rotary valve, remove the pincher and see if the inner crank seals will hold 4-5 psi for any length of time. A hole in the middle of the piston is not a usual suspect of an oil problem, you were running on a very lean cylinder.

Every year I get old Rotax engines with broken injector lines through here that we haven't worked on before, every one of them that still blow decent compression and run pretty well fail the inner crank seal leak test it's the only thing keeping them alive at that point with oil.

Your PTO carb killed that piston or you have an outer crank seal leak.

 

[Waterluvr]

Here's one of the better piston failure charts I've come across that fit on one page. Compare the lean seizure photo to the failure you experienced, see any similarities?

It's worth your time to pull that engine and get it on the bench for a pressure test if you haven't already done so, a crank seal leak pulling air will turn your new top end into an expensive paper weight post haste no matter how well the carbs are dialed in.

 

[powerslave]

So the RV wont get out of time without an obstruction? A seized piston would do it?

Well, you only did a top end correct, so as long as you didn't pull the rotary valve cover your "should" be good, if it was a running ski before. Is it possible the RV was obstructed at any point during your rebuild and you turned over the engine? That could have possibly jammed the RV and stripped the gear, long shot I guess. Only thing you can do is either pull the carbs again and look at the RV or look thru the carb to see if it's moving. That still doesn't confirm it's in the correct position. The only time you would set that timing is when you physically remove the rotary valve, other than that it doesn't get adjusted.

 

[racerxxx]

Nope, the pistons were stopping(seizing) gradually. If a screw drops and stops the rv, the pistons are still firing and will overcome the brass gear on the rv.

Sent from my SGH-T889 using Tapatalk

 

[powerslave]

Well i noticed the RV is spinning, so I am taking my carbs to a local pwc mechanic that is familiar with these. Thanks for all the help. I'll post if this solved my problem.

 

[Sportster-2001-951C-Stock]

So the PTO cylinder isn't firing b/c the carb isn't spitting fuel all over the bilge like the Niagra river.... Hopefully that's not the only criteria used to reach this conclusion.

Why not disassemble and inspect the rubber tips of the metering needles for wear and tear while the carbs are off, no better way to know for sure there's not something wrong, could be some junk caught in there. I had a carb with a piece of grain stuck in the float valve the other day. I'd never seen a seed stuck in a float valve before, usually chunks of rubber or rust.... or a piece of teflon tape some bozo used on the fuel fittings.

 

[powerslave]

Basically, I've exhausted myself on this one. I don't have the time, I just lost the transmission in my work truck over the weekend and have that to deal with now too. I give up, lol.

Many thanks for all the help, I've learned allot more about these carbs in the last few days. Wish I could spend more time on it. But I'd rather pay $100 get them done.

So the PTO cylinder isn't firing b/c the carb isn't spitting fuel all over the bilge like the Niagra river.... Hopefully that's not the only criteria used to reach this conclusion.

Why not disassemble and inspect the rubber tips of the metering needles for wear and tear while the carbs are off, no better way to know for sure there's not something wrong, could be some junk caught in there. I had a carb with a piece of grain stuck in the float valve the other day. I'd never seen a seed stuck in a float valve before, usually chunks of rubber or rust.... or a piece of teflon tape some bozo used on the fuel fittings.

 

[powerslave]

Had my carbs rebuilt by knowledgeable mechanic. put them back on (carbs only), hooked up lines and same thing. It will fire but only on mag cylinder. If I put my hand over the mag carb I can feel the suction and I of course get fuel all over my hand. I feel no suction and no fuel on my hand over the pto carb. Bottom end leak?

 

[Sportster-2001-951C-Stock]

Agree, if you're completely covering the carb inlet with your hand, your hand should be very wet with fuel due to the vacuum pulling fuel from the carburetor. If there's no vacuum, the carburetor won't provide fuel.

Normally, the crankcase should have a positive pressure build as the piston moves down the cylinder bore, this pressure abruptly forces the fuel/air mixture waiting in the crankcase up into the cylinder once the intake port is uncovered. The RV is essentially a one way valve that closes while the piston is moving downward. Then, a negative pressure builds drawing air/fuel through the open RV and the carburetor as the piston moves upward in the bore.

 

[powerslave]

Thank you for your attention. Think I'm narrowing it down.

Agree, if you're completely covering the carb inlet with your hand, your hand should be very wet with fuel due to the vacuum pulling fuel from the carburetor. If there's no vacuum, the carburetor won't provide fuel.

Normally, the crankcase should have a positive pressure build as the piston moves down the cylinder bore, this pressure abruptly forces the fuel/air mixture waiting in the crankcase up into the cylinder once the intake port is uncovered. The RV is essentially a one way valve that closes while the piston is moving downward. Then, a negative pressure builds drawing air/fuel through the open RV and the carburetor as the piston moves upward in the bore.