Super Jet Dual 38 fuel delivery problem?

[amitchell]

So I have stuck the front piston on my 62T/61x motor several times now. Yesterday being the latest, going about 7/8 throttle for 20 seconds and its started to fade. I let it cool for a minute or so and rode back to the ramp. I got home and checked compression and it was an even 180, but I know I stuck it so I tore the head off.

I have put about 10 hrs on it since it was bored.

Front piston transfered Aluminum to the bore on one side of the exhaust port and 180 degrees from that on the intake side. Nothing that catches a fingernail but just blotches of smooth aluminum. I haven't pulled the jug to look at the piston. I don't think the rings are clogged as the compression did not drop.

I feel like it could be an issue with the slave(front) carb, possibly not metering fuel like the rear. Or not getting enough fuel after the rear carb uses its share. Any thoughts on this? I have gone through the carbs several times and everything looks new. All filters are clear from tank to carbs.

My setup is as follows.

Passed 10psi leak down 20 minutes 0 drop.

94 Octane 32:1 Amsoil HP Marine.

62t/61x at 82.5mm(sudco pistons 0.0045 clearance)with the freestyle sport port. 0.055in squish and ADA head 180psi

Dual 38's 1.5NS, 95gr spring, 42psi pop off, 75 pilot, 140 main, 1 turn low, 1.25 front high and 1 rear high

MSD enhancer with 0 deg static timing advance

B-pipe (47mm) top screw 3/4 bottom screw 1/8 1.75mm stinger restrictor and networks valve

Dual cooling both to manifold. front of head to pisser no restrictor, rear of head to bottom of pipe. top of pipe tee'd to stinger and pisser no restrictor.

Solas 144 with 9/15 hooker.

Help appreciated.

 

[amitchell]

I should add that I was just starting to get some piston wash and have about 1/2in of clear piston around the perimeter.

 

[NVJAY775]

Just went through a buddies carb on his b piped 61x which was freshly gone through and the diaphragm had a small tear in it, along with a sticky needle n seat. On a long WO pass it shut down on him. Other than that, the only thing I can think of would be an air leak in a fuel line, intake etc... Sorry bro, it's all I have. Hopefully others with more experience will chime in. Bump!

 

[amitchell]

It passed another leak down before I pulled the head.

 

[amitchell]

Bore looks like it just needs a hone, I took care of the smear with some muriatic acid.

 

[amitchell]

Black mark on first pic is sharpie.

 

[kevbo]

You got the combustion temps a little hot, I have done the same thing many times since 1993. First make sure your fuel line will hold vacuum from the tank pickup all the way to the carb. Once everything is back together open the top screws 2 turns, see how it runs and start leaning if power is lost. You want to be a few RPM rich of peak power at full throttle. Avoid holding 80% throttle area, it is always a lean spot. If you are going to cruise on the pipe go ahead and pin the throttle. Avoid doing this if your tank is less than half full. I use a separate pump and a header tank to remove air bubbles in the fuel lines so I can run the tank dry without hurting a piston.

 

[Harbor]

Bloody piston!..... I like what Kevbo has to say about it. hope you get this sorted, btw I do have an extra high volume external fuel pump I'll let you have if you feel it would help, just pm me your address and I'll ship it to you to help out

 

[amitchell]

I think I will go up a half jet on the main to 142.5 and open the high speed screws to 2.5 front and 2 rear.

I gave the front bore a good hone last night hopefully I opened it up a hair.

This piston seized in the exact same spot as the previous piston did, I really don't know why the heck the front is that much hotter.

Oh well, gaskets and another piston and ring set is ordered.

 

[amitchell]

Back together, passed 10psi leakdown 10mins no drop.

 

[amitchell]

Did not feel like taking flywheel cover off this time. new ars crank seals 10 hrs ago should be good.

 

[Crab]

Just for kicks inspect the restrictor in the slave carb to make sure it wasn't drilled out. If so you will need to run a jet in the line.

 

[amitchell]

Just for kicks inspect the restrictor in the slave carb to make sure it wasn't drilled out. If so you will need to run a jet in the line.

Great idea!

 

[amitchell]

Just for kicks inspect the restrictor in the slave carb to make sure it wasn't drilled out. If so you will need to run a jet in the line.

Restrictor was in place looked like it was about .75mm in diameter. Return line flowed fuel well.

You got the combustion temps a little hot, I have done the same thing many times since 1993. First make sure your fuel line will hold vacuum from the tank pickup all the way to the carb. Once everything is back together open the top screws 2 turns, see how it runs and start leaning if power is lost. You want to be a few RPM rich of peak power at full throttle. Avoid holding 80% throttle area, it is always a lean spot. If you are going to cruise on the pipe go ahead and pin the throttle. Avoid doing this if your tank is less than half full. I use a separate pump and a header tank to remove air bubbles in the fuel lines so I can run the tank dry without hurting a piston.

Pressure tested the lines and tank at 2psi and it held for 10mins solid. Copper coated the carb base gasket just to be safe. Fuel lines are free from bubbles, I am running a JSS fuel clunk setup and it seams to do its job. I rarely run less than a half tank, I check level regularly.

I was out yesterday for a few hours and things were good. The 142.5 mains and 2 and 2.5 turns out on the highs cleaned the wash off and it ran pretty good. I am sure I can come in at least a half turn on the highs, but i was just free styling not tuning yesterday.

I do notice that the Amsoil HP leaves a red/orange tinge on things. It makes plug reading a bit tougher. I think I am going to switch to quicksilver after I am done with this case of oil.

I am sure now my Mag cylinder just runs leaner for whatever reason.

 

[Crab]

.75 MM sounds big, check with kevbo on proper size, or try #60 jet in return line perhaps

 

[amitchell]

.75 MM sounds big, check with kevbo on proper size, or try #60 jet in return line perhaps

Hmm is a #60 jet not 0.60mm diameter? I was just estimating size not measuring "d'oh", so I think it probably is stock. I have a number drill index I could poke in there and try to get a real measurement. That will give me something to do during nap time.

Maybe @kevbo can chime in.

 

[JetManiac]

Stock restrictor is fine dont touch it.

 

[Crab]

Stock restrictor is fine dont touch it.

what he said, I only posted this as I have had to drill out 2 in the last year from ethanol/water issues. They can corrode closed and be doomed.

 

[schicks]

i have had the same issues with mine for years, even with my old 701 motor which ran great for years and is still going. I am on to a BB now, but seems the front cylinder always wants to run lean still. I have not figured out how to correct it, does not hesitate (lean bog) at all and seems to be tuned right even though the front plug is a bit white. I wonder if its just due to the 38 front carb is a slave carb; not really sure. Motor is tight, carbs are mint, jetting is good. Some items that I 'thought' could have been causing my issues are: leak at the extra pulse line cap, crack in fuel line, plug gaps, pop=off pressures off. Any other advice on the topic is still helpful. I thought about putting a resistrictor in the return line to try to back flow more gas to the front carb, but have not done so b/c i thought that would change my carb pressures and through my pop-off off. I am about 3/4 of turn out more on the low speed front carb than the back as well, which helps. The front plug does have color to it, but it is now where near the same as the rear cylinder

 

[amitchell]

i have had the same issues with mine for years, even with my old 701 motor which ran great for years and is still going. I am on to a BB now, but seems the front cylinder always wants to run lean still. I have not figured out how to correct it, does not hesitate (lean bog) at all and seems to be tuned right even though the front plug is a bit white. I wonder if its just due to the 38 front carb is a slave carb; not really sure. Motor is tight, carbs are mint, jetting is good. Some items that I 'thought' could have been causing my issues are: leak at the extra pulse line cap, crack in fuel line, plug gaps, pop=off pressures off. Any other advice on the topic is still helpful. I thought about putting a resistrictor in the return line to try to back flow more gas to the front carb, but have not done so b/c i thought that would change my carb pressures and through my pop-off off. I am about 3/4 of turn out more on the low speed front carb than the back as well, which helps. The front plug does have color to it, but it is now where near the same as the rear cylinder

I am now a half turn rich on the front high screw.

I added a 4mm restrictor to my stinger pisser, the stinger itself is restricted to 1.75mm. This helped to even out my cylinder temps(more water through front) and pressurized the pipe chamber a bit more. My plugs now look closer in terms of colouring.

My piston wash is crap though, I can't tell what the heck its doing. This Amsoil HP Marine is just leaving a slight orange stain on the piston. I think I am going to switch to a semi-synthetic blend to get some real wash showing up.