Restrictor

[fyrfytr33]

I am working on a 1997 GTX. Idles fine @1200, high speed runs great, instant throttle response over 4000 rpm, but... low speed to 3/8 throttle it bogs and sputters. Plugs look normal gray/brown and dry. Turned the low speed out to 1 1/2 turns and it helped some but didn't fix it. They were at 1 1/4 turns so I don't know what changed. I feel like I'm masking some other problem. I have to admit I mixed up the new springs with the old when doing the carbs but pop off was 38 before and after rebuild. I think I got them right.
Still had original fuel lines. I have replaced the fuel lines and tossed them before I knew about the restrictors. I have new restrictors but am not totally sure where they go. Thinking one goes in each return line but is this correct? At first I read don't worry about them, then I read the Mikuni manual stating they act as fuel pressure regulators. I say "they" as I thought I read there were two restrictors. Now I'm not sure where to put it/them. Any advice?

1997 GTX 787
New fuel lines
New fuel selector
Cleaned fuel pick up fixed fuel level indicator
Fuel filter cleaned
Rebuilt Carburetors, Mikuni kits. Followed rebuild thread
Pop off 38 both carbs
New 1.5 Needles and seats
Check valves working
New rectifier
Compression - 155 mag, 157 pto
New plugs, gapped to .024
Plug wires clipped

 

[mikidymac]

Your 1997 GTX does not use fuel line restrictors.
You need to make 100% sure you are using the correct 80 gram springs.
Make sure the fuel strainer isn't sucking air.

 

[fyrfytr33]

All good advice. Will check things out.

Thank you.

 

[etemplet]

That's your transition range. I'd have a look at the 4 port nozzles in the carb throat. Test them and make sure they are flowing well. You'll have to look in the carb thread to see how to check them. Basically pull the low speed jet, leave the low speed adjuster in place and use electra-kleen with the red nozzle and shoot down the jet hole. Cover the large port in the carb throat with your thumb and see what kinda of patter you get from the 3 small nozzle ports. That's a rough description. LOL You might have a rave issue but that RPM is a little early UNLESS the thread pulled out of the rave piston. Good Luck !!

 

[fyrfytr33]

So, jets are clean, look just like the example in the rebuild thread. Replaced the plug wires with a kit from OSD. Replaced the RAVE valves, bellows and gaskets. Water valve repaired and appeared to be working.

Pop off is 32psi, low speed adjuster is 1 1/4, high speed adjuster is 0, idle is 1300 in the water.

Idle is smooth at 1300, high speed is instant from 4500 up to 7000 rpm. Sputtering from 3500 - 4500 and a little when releasing throttle.

Could a coil misfire only at a certain RPM range?

I haven't replaced the fuel filter gasket, could that cause this?

 

[etemplet]

Raise the pop-off to 36-38 psi that might solve your problem. I have extensive testing on a 1996 and 1997 GTX. My wife's 1997 wouldn't get over the 37mph hump unless the impeller unloaded.

There is a technical service bulletin on upgrades to the rave housings and rave blades themselves (slotted). See ATTACHMENT
If you install the standard 80 gram (black) springs in the carbs the pop-off pressure will be 36-38psi The ski runs MUCH better with the higher pop-off pressure. Good luck !

 

[fyrfytr33]

I am in no way disagreeing with anyone, but trying to better understand how these circuits work together.

Pop off was at 38. I tried lowering it to 32 to help with a lag in acceleration in the mid RPM range. I'm thinking lower pop off lets the needle open earlier to smooth the transition from the low-speed circuit to mid-range circuit. Seems better to avoid running lean. I did achieve better response in the mid-range, idle is smooth at 1300, above 4500 rpm it runs as it should, snappy up to about 7000 rpm. But....

I still have a slight mid-range lag, a little hard start and an annoying sputter in the 2500 to 4500 range.

I did replace the spark plug wires and replaced the RAVE valves with upgraded/slotted ones.

Let me know if you think I should re-think this. If I change back to 38, anyone have any more ideas on how to solve mid-range lag and stuttering?

 

[Grim]

I got roughly the same issue with my 98 GTXL (951), its annoying to me but the ski still runs ok in the water. Let me know if you figure this out and if I do, Ill do the same.

 

[etemplet]

I'll describe this again in a bit more detail because this is very very important.

There are 3 very small ports in the barrel of the carbs. If they are not flowing properly the carb will have trouble transitioning in the range you mention. I bought an ultrasonic cleaner to help with those kinds of issues. Problem is you can go poking around on those ports. They are very small and need to be the size they are. It is a bit difficult to explain how to test them but it's easy enough. They should flow nice strong streams during the test.

First pull the diaphragm so you can get at the carb jets. Remove the low speed jet. The low speed adjuster must be in place. I use lectra-kleen for the test and put on the red tube so you can stick the tube down into the hole where the low speed jet was. Put on some goggles and keep your mouth closed. There are 4 ports in the barrel; the 3 small in line ones I mentioned and the 4th is on the left side and is much larger. Put your thumb over that hole to force the spray into the 3 ports alone. I hold the carb up to the light so I can see down the barrel and verify good flows from each port. If they a dribbling or one is not flowing you have to try to clear them. If these are not flowing properly you'll have trouble with the transition.

Below 36-38psi the carb still works but its a bit rich and rich affects everything, even high speed. I wouldn't even put my skis on the water with less than 36psi pop off but I know my skis. I fought that crap too many times.

How are you lowering the pop-off? I don't bend that metal piece like they recommend... NO WAY. I make sure it stays even with the carb housing. If you have the correct spring and a good needle and seat the pop-off should be spot on. Good Luck !

 

[POPPS]

The mikuni manual states that you want the highest pop-off possible,,,get the necessary mikuni parts to spec,,,springs,,,needle and seat,,,pilots,,,and make sure the restrictor orifices are clean,,,they are very small