ET 967 Tuning Thread

[Jcary85]

Tuning questions: (current jetting calibration below)
ET967, runs great and is crisp BUT.... carbs dribble out of the booster venturi at idle. I can see this looking down the carb bores at idle. This gives us an off idle hesitation after say 20-30 secs of idle (that is certainly rich and not the lean bog), and fuel consumption is pretty high. And as I'm the sort that is a perfectionist, this drives me nuts. Our engine shakes/vibrates considerably at idle, and I suspect it's this vibration that's opening the needle valve.

Our pop-off is 22-24 psi (verified with a pop off tester) we're at 2.3 w shiny silver spring. Needle and seat were new last season, if I replace the shiny silver spring with new, the dribble stops for a little while, but returns after a few tanks of fuel. If I raise pop-off pressure to the next spring step (2.0 w black ), I get the beginnings of the lean bog, especially if you stab the throttle repeatedly under load (in the water).

So here's my question, if I changed my needle valve size, can I still get to the 22-24psi range but have a better resistance to dribble? Like if I went to a 2.5 with a gold spring. Haven't tried this yet but my thinking is the stronger spring would have a better chance of keeping the valve closed. Or would a smaller needle valve have a better chance of staying closed because of less surface area exposed to the fuel pressure vs. the spring trying to keep it closed?

Is this the reason folks drill out the return restrictor and put a jet the the return line after the "t"? I'm sort of leaning away from this and quite frankly haven't done this because it's irreversible. (I guess I could always replace the fuel pump cover)

We do not have a carb brace, would that sort of thing reduce the vibration the carb "sees" at idle?

Any help would be appreciated.

Video of ski running with engine audio:

ET967
Stock SBN 46s
High Speed Jet 110
Low Speed Jet 125
Pop off 22-24psi wet 2.3 w black spring
LSS 1.75 turns out
HSS 1 turn out
PFP pipe and water box
Zeel 62T

Most people double or triple layer the check valve on the kidney block to lessen the dribble.

Edit: sorry didn’t see your follow up post that you did this

 

[fastgtfairlane]

Y

I pulled the carbs tonight and doubled up the clear plastic check valve on the kidney shaped valve body. I got everything all back together and ready to test. I made no other changes.

Verified pop-off and I should note I've got the shiny silver spring (the slightly shorter one with less coils) and a 2.3 needle valve giving me 22-24psi pop off. Black spring gives me 26-29psi pop off.

I should get a chance to run it after work tomorrow.

You could bypass all the extra nonsense of adding another valve or replacing the kidney blocks by simply adjusting your fuel pressure with a gauge. I have a/m sbn44s on my ported 735 which is considerably smaller displacement than the et967 and proper fuel pressure adjustment made my engine soo much easier to tune and idle like stock. You can do all of the valve and kidney block mods and you'll still dribble fuel because your fuel pressure is too high. I ended up with a 80 main jet in my return and it made a huuuuge difference in performance as well as better fuel economy. You're chasing your tail trying to tune the engine if you don't drill out your returns and properly adjust the fuel pressure.

 

[DylanS]

^ FYI this guy has a life time ban from the annual freakfest so keep that in mind….

 

[Big Chris]

Ran the ski tonight. It is significantly better, but it still dribbles. It does it when the throttle is closed and the engine is losing rpm., decelerating from a throttle "blip". I imagine that this is because signal to the pump is high and fuel demand low, so fuel pressure is probably highest here.

I'm going to follow all your advice and drill out the carb restrictor and add a main jet to the "T" of the return line. So I have a low pressure fuel pressure gauge on the way.

Several people have offered up 1.5 psi as the target at idle. What is the generally agreed upon number here? Any thoughts on how I measure fuel pressure before I drill so I know what I started with?

 

[fastgtfairlane]

1.5-2.0psi. In that range will be fine at idle. 4-5psi at wot. I did this on a trailer backed into the water. Novi recommends to ride the ski and check the fuel pressure but I wasn't able to run a fuel line up the pole so the hood could be closed so i ran it on the trailer. With a 70 jet I was at almost 3psi at idle. 80 jet was right at 2 psi. I haven't tried a 85 yet, it might be better but it ran much better with the 80 so I left it. I'm running a 735, not a et 967, but the procedure will be the same. Someone posted a link t9 a thread all about fuel pressure a few pages back. Definitely check it out, I think it will help your situation tremendously.

 

[hornedogg79]

.035" mig tip is .889mm and what I used to stop the dribble. Had a #60 jet before that. Not a 967 but close. 900ss, pfp, fs46's, external fuel pump.

 

[kevbo]

Does the dribble happen while the engine is decelerating or while it’s idling? Can you make the idle lean enough by closing the lower screw?

 

[hornedogg79]

It was when decelerating for me. Quick full throttle then letting off like you would do with aerial tricks. First flip it would be crisp, then 2nd it would hesitate a bit. Pull the hood and would have blowback residue on hood liner above carbs. Ran it on the hose and tried to mimic riding style. Dribbled after full throttle as soon as I let off.

 

[kevbo]

The joys of tuning oversized carbs. How much spring tension can you apply to the needle before its too lean at 1/2 throttle? Finding that point may help prevent dribbling.

 

[bsipp215]

Check fuel pressure... The larger engines seem to have more vacuum, i even up with i think a 90 main jet in my return line, you will need to drill out the restrictor in your oem 46s if it's not already done, want i think 1.5 psi, smaller jet higher psi, larger jet lower psi

How big of a bit do you recommend when drilling out the restrictor?

 

[fastgtfairlane]

You just drill to the ID of the channel the restriction is in. I believe it's 1/8 inch.

 

[nick matthews13]

Bringing this back from the dead.. so what was the consensus with novi 48s ? I’m at sea level and 180 compression

Was the best starting point this ?

135l
125m
2.3
17psi pop off
60 in the return line

 

[Miggy]

I'd say you got a good starting point.
I had 48 Novis on my 967 and I was running
125M
130 P
21-22 psi pop off (raised from 17 by stretching springs since I didn't have 2.3 N/A)
Doubled up the check valves

Ran really good, I'm about 800 feet above sea level...

For the return, I'm pretty sure I had a 60... To get that right, I set up a pressure gauge between the returns and the restrictor.

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[Miggy]

I was running race gas done (240 psi) with C12

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