05-14-2015, 02:04 PM #1
a mystery hopefully someone can explain
I bought two gti's from a elderly couple. 720 engines haven't been run in 2-3 yrs so I drained fuel and started rebuilding the carbs. The carbs came stock with 2.0 needle and seat. Pop-off should be 36-38psi. I replaced the needle and seat with a 2.0, black spring. Now pop off is 22psi. thats what was in it when I took it apart.
Here's my question. If the manual calls for 36-38 pop off, how did this ski even run with a 2.0 and black spring. Pop off with black spring is 22psi. By the way, it wouldn't run when I tried to start it with this combo. I'm going to have to down to a 1.5 to get the pop off anywhere near 36-38. How did seadoo ever get 36-38 psi with this combo? You can't get a stiffer spring than black. Am I missing something?
05-14-2015, 10:27 PM #2
You need to run the 115 gram spring (platinum or gold in color) in conjunction with the 2.0 needle and seat, about the best you'll see with that combination is low 30's for pop off. The black spring you're currently using is the 80 gram spring.
It's no mystery, that combination was in response to the increasingly restrictive CARB emission standards at the time.
05-15-2015, 08:48 AM #3
05-15-2015, 11:10 AM #4
I have no trouble getting the 115 gram spring and 2.0 N/S to yield low to mid 30's on pop off, here's a recent example of a carb that was a DIY project the owner threw in the towel on and dropped off to have me finish when they couldn't get the correct range of pop off using the right combination.
See any issues here?
05-15-2015, 05:29 PM #5
That's not mid thirties. Thats maybe 28psi. Just a few lbs more than what I'm getting. How can you get it to 36-38 without changing the N&S?! This isn't the first carb I've rebuilt. I'm familiar with down sizing the N/S to achieve a higher pop-off. I just don't understand why if I put the 2.0 as seadoo recommends and the strongest spring I can use (gold) why it doesn't pop at the range it should. I'm going to order another spring and try that.
05-15-2015, 05:43 PM #6
I found another gold spring in my arsenal. I'm getting the same as you. 27lbs. I wonder which is better, pop off at 36-38 range with a 1.5 or staying at 2.0 N&S and having a 27lbs pop off.
05-15-2015, 08:27 PM #7
That's a measuring caliper, specifically the depth measuring blade of the instrument clearly showing the control arm being set .027" too low which has a drastic effect on pop off pressure and the ability of the diaphragm to utilize manifold pressure and air velocity to run the pilot and main circuits of the carb.
Last edited by K447; 05-15-2015 at 09:45 PM. Reason: too low
05-15-2015, 09:42 PM #8
Waterluvr that's great you have no problem getting 36-38 pop-off on your carb. I have 4 skiis I had no problem getting the proper pop off for too. If you're not going to give some insight on what I'm trying to figure out then please move on. Otherwise I'm all ears and willing to learn something. I have my needle lever level with the shelf on the carb too. Set it with a straight edge. Something is causing the pop off to be low. I'll figure it out. Not getting anything on here.
05-15-2015, 10:20 PM #9
Well aren't you the bitter little ingrate? This is what you get sometimes trying to help people that can't help themselves.
There's two more issues aside from high or low control arm adjustments that will cause the problem OP is having with pop off pressure, but since he's so disrespectful of my time I won't waste any more of it trying to help him.
Last edited by Waterluvr; 05-15-2015 at 11:55 PM.
05-15-2015, 10:46 PM #10
Bitter little ingrate? Wow! First of all you weren't helping at all on the problem. Just boasting that you had no problem getting mid thirties pop off on a carb you worked on. How is that helping me?! These are the people you'd love to see on the street. I hope you get well!
Last edited by actis; 05-16-2015 at 02:41 PM.
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