Fuel Delivery issue (I’ve tried just about everything)

[Nicotheskiguy]

Man it’s one thing after another with this ski I feel like…
I have a fresh engine build with 0 hours on it and I can’t get it started for the life of me.. Yamaha based setup with dual 46mm carbs.
84mm pistons
R&D cylinder
62t case +8mm crank


I took the diaphragms off sprayed out all the jets they’re clean and flowing good. Put the carbs back on and still nothing. (I did not take off the pulse plates)
H 110. 3/4 turn out
L 125. 1 1/2 turns out
Pop off unsure don’t have a tester

Fuel is flowing through the return line so gas is running through the carbs just not getting to the plugs for some reason. I can get it to fire by priming it, spark is good so that shouldn’t be the issue either.
The plugs do not smell like gas/aren’t too wet.
Here’s a pic of how the lines are plumbed in and of the ski that I have yet to ride this year!

Can pop off stop an engine from starting if it’s too high?
Anything else I’m missing here? I appreciate the help, if anymore information is needed let me know!

 

[kevbo]

Remove the flame arrestors and choke it by hand.

 

[Nicotheskiguy]

Remove the flame arrestors and choke it by hand.

I tried, it looked like it pulled some fuel in but still wouldn’t start.

 

[fx1mark]

Have you checked the filters on the fuel pump side of the carbs?

 

[Nicotheskiguy]

Have you checked the filters on the fuel pump side of the carbs?

I will give this a look just found a parts diagram for them.

 

[fx1mark]

I will give this a look just found a parts diagram for them.

they like to clog up and will starve your motor for fuel.

 

[OtherDonnieGuy]

Agreed check your carb filters.

if that doesn't fix your issue... it will run on a prime until that fuel burns off correct? Do you have a return line restrictor installed?

never seen a ski not run because of too high of pop off myself, but I have seen needles that would stick, usually had some varnish on them. Hard to imagine both of yours are stuck, but never know!

 

[Nicotheskiguy]

Agreed check your carb filters.

if that doesn't fix your issue... it will run on a prime until that fuel burns off correct? Do you have a return line restrictor installed?

never seen a ski not run because of too high of pop off myself, but I have seen needles that would stick, usually had some varnish on them. Hard to imagine both of yours are stuck, but never know!

I checked one of the filters so far and it’s spotless, gas did come out of the pulse side so fuel is on that side of the carb. Yes I can get it to fire and run for a second while priming it. No return line restrictor. Both mains were stuck when I first popped them open, freed them up and they were moving nicely now.

Ultimately what is happening is the diaphragm’s aren’t getting/filling up with fuel. Maybe completely taking them apart and spraying them down real good will do I just couldn’t imagine the mains get that plugged even with gas sitting in them for 6 months. I don’t use the cheap stuff either.

 

[OtherDonnieGuy]

I checked one of the filters so far and it’s spotless, gas did come out of the pulse side so fuel is on that side of the carb. Yes I can get it to fire and run for a second while priming it. No return line restrictor. Both mains were stuck when I first popped them open, freed them up and they were moving nicely now.

Ultimately what is happening is the diaphragm’s aren’t getting/filling up with fuel. Maybe completely taking them apart and spraying them down real good will do I just couldn’t imagine the mains get that plugged even with gas sitting in them for 6 months. I don’t use the cheap stuff either.

Check your carbs over, but your likely gonna need an external return

I checked one of the filters so far and it’s spotless, gas did come out of the pulse side so fuel is on that side of the carb. Yes I can get it to fire and run for a second while priming it. No return line restrictor. Both mains were stuck when I first popped them open, freed them up and they were moving nicely now.

Ultimately what is happening is the diaphragm’s aren’t getting/filling up with fuel. Maybe completely taking them apart and spraying them down real good will do I just couldn’t imagine the mains get that plugged even with gas sitting in them for 6 months. I don’t use the cheap stuff either.

Check your carbs and see if they have internal restrictors, if it does not you will need to add one regardless. No restrictor means low fuel pressure, may be part of your issue.

 

[Nicotheskiguy]

Check your carbs over, but your likely gonna need an external return


Check your carbs and see if they have internal restrictors, if it does not you will need to add one regardless. No restrictor means low fuel pressure, may be part of your issue.

Excuse my ignorance but how would I know/ where should I look for internal restrictors? I did forget to mention that these carbs were on the ski last year and the ski ran rather good for needing a engine rebuild.

 

[Quinc]

did you buy the carbs used? Have they ever worked? You might need to rebuild them or make sure the gaskets are installed correctly.

 

[fastgtfairlane]

If your carbs still have the internal restrictor it will look like this. The little dot is the restrictor. One in each carb if they're drilled out, you'll need to get a main jet for the the restrictor. You'll need a fuel pressure gauge determine what jet you need

 

[Jcary85]

pop off ridiculously high could cause this. are the arms bent at all going to the needles? they should be basically straight but if they are very bent it could prevent the needle from ever opening. dumb question, but are you sure you have the feeds hooked to the correct spots on the tank? two spots have pickup tubes and two spots do not.

beyond this, i'd suspect the fuel pump side of the carbs is assembled wrong.

removing flame arrestors, choking with hand, and looking for fuel is a good test as mentioned earlier.

 

[Nicotheskiguy]

What you called " Both mains were stuck when I first popped them open, freed them up and they were moving nicely now", are probably the Needle Valves. If they were stuck, it could be that the Needles are worn and are no longer traveling plumb thru the Valve Body and binding when "cocked".

Are the Needle Valve Springs properly positioned? The Spring Top has to be Centered under the Lever Arm Button.

How old are those Needle Valves? A Pop-Off Test is a smart thing to do. It's easy to build one. For $25 each, you can have New Needle Valves installed.

Were the Regulator Diaphragms wrinkled or did they have stretch marks? If so, they are worn out.

Do the Regulator Diaphragms have Red Anodized Center Buttons? If not, those Diaphragms are NOT Genuine Mikuni.

Golden Rule is to always do a Complete Carb Rebuild (with Genuine Mikuni Kits) on a New Rebuilt Engine. Don't blow your Expensive Rebuild to save a little Money on Carb Kits...Unless the Carbs were rebuilt properly within the last few months, cleaned and tested before installing them with New Engine.

Just in case, the Fuel Supply Lines connect to the Carb LOWER Nipples and the Return Lines connect to the HIGHER Carb Nipples.

Also, make sure the Throttle Plates are opened slightly to allow the Engine to Idle.

Took a few picture here’s the 2 diaphragms, I may or may not have found the problem and I will let y’all know in an hour or so when I can get them back on. Pulled both sides of the carbs apart and I was kind of surprised what I found. The passage way was almost completed clogged between the needle valve/seat and the inner filter. If this doesn’t correct it I will be getting a genuine rebuild kit from Chris at JetManiac. I appreciate all the great info!

 

[keith t]

check you havnt swapped the return and feed lines ?

 

[fastgtfairlane]

the clogged passage could definitely cause your problem your describing. was there plenty of fuel behind the diaphram when you removed it? if not then that is most likely your issue.

 

[Nicotheskiguy]

check you havnt swapped the return and feed lines ?

Bottom feeds that are in the tank are hooked up to the bottom inlets on carbs, return is on the top nipple so they’re on correctly. I just got them back on the ski and still I do not see any gas coming out of the high/low pin holes in the carb body when turning over. I tried manually choking it and will still fire over when primed. The diaphragms don’t look terrible in the pics above but maybe they’re no good anymore?

 

[Nicotheskiguy]

the clogged passage could definitely cause your problem your describing. was there plenty of fuel behind the diaphram when you removed it? if not then that is most likely your issue.

There was in one diaphragm when I had them taken apart the other was still dry.

 

[smoofers]

Do you have one or two pulse lines on your crankcase? Does each carb have a fuel pump?

 

[fastgtfairlane]

There was in one diaphragm when I had them taken apart the other was still dry.

If the one that was dry was the one with the clogged seat that's most likely your issue. The 46s have a weaker signal than 44s so you have to run a lower popoff and that usually means larger n/s. Especially with the open filters. I think you got it figured out. I'd put it back together and see how it runs. I can see a big difference between the seats in your pics