Carburetor pop-off pressure????

[avi8or3117]

1st question
Can someone please briefly explain to me what pop-off pressure is?


2nd question
SeaDoo manual says my pop off pressure should be between 30-40 PSI. I tested 4 times and came up with an average pressure of 45psi. I am attempting a carburetor rebuild and this was the before pressure with all the existing hardware still in place. Being a higher pressure, is that ok? Should I keep it at 45 or should I lower it by cutting my new spring?

I have a 98' SPX.

Thanks in advance guys!!

 

[Dr Honda]

1) Pop-off pressure is the pressure that takes to force open the needle, to allow fuel to flow into the carb. The pressure is equivalent to the float bowl hight in a conventional carb. It is mostly a tuning tool for low, to low/mid fuel flow... but if the pressure is too high, it can cause other problems, and you can melt your engine because it could cause a lean run.

2) NO... do not run the carb with higher than needed pop-off pressure, and DO NOT CUT YOUR SPRING. You need to replace it with a spring with the proper tension. (or put the old ones back in)

The problem is, if you cut them... yes, you will drop the pop-off pressure... but the spring is still too stiff, so the needle will open, but under a high demand... it won't allow the arm to pivot enough, and could cause a lean run up top.

SO... when you cut it... you get the number needed for "The Test"... but the operational function is still wrong.

 

[avi8or3117]

ok heres the thing. just bought the seedoo and I dont know the history. So the old pop values in each of the carbs is about 45-46PSI (SeaDoo says between 30-40 PSI). So I think who ever had the machine last built the carbs worng? Is that a correct assumption?

Secondly, The rebuild kit I just bought came with two springs. This kit fits 3 or four different carbs. (34mm/38mm/44mm/46mm) So I dont know which spring to use. I tried both of them and one pops off at 48-50psi and the other pops off at 28-30PSI. Which spring should I use? You stated earlier that having too high of a pop off might hurt the engine, what about too low? Any recommendations? To be on the safe side I will probably install the spring with the less tension. Would I hurt the engine that way, lose performance, cause engine to bog down, etc?

Thanks

 

[Dr Honda]

1) Yes... people do it all the time. They don't know about properly setting the carbs... and they just throw in any spring they have.

2) If you have a spring that is getting you to 28-30... then you are close. I would use that, and bend the arm down slightly. That will get you to the 30/32 range, and then you will be in spec. (do not bend the arm down more than 1mm past level with the carb body)

If you run the pop-off pressure low... you may cause the bottom end to be a little rich... but that can normally be corrected by turning in the low needle a little. If the pop-off pressure is excessively low, you could get a hard starting problem. (it will act a little flooded) also, you could get a mid transition that is a little rich. BUT... at 30 PSI, it shouldn't have a problem.

As always with a 2-stroke... you want to error on the rich side to be safe.

 

[avi8or3117]

Dr. Honda, your great. Thanks for always responding to my posts!!!

I have another question. As stated earlier, I dont know the history of these machines and I think the carb was built wrong, especially since the wrong springs were installed for the pop off pressure. This question is directed towards the pulse pump body and cover.

The Mag cover(that covers the top of the pulse pump body) When I removed the cover, attached to the under side of it, there was a hard clear plastic sheet covering the whole under side. So it covers the large circle opening and its not a diaphragm or gasket. I dont think this is right and it looks like it prevents fuel from flowing it to or out of the pulse body. Should fuel be flowing? How does fuel enter the carburetor anyway? Next, on the pulse body, I see the check values and them see to be installed properly. Once the body is removed from the mag carb, should I see a gasket and then the fuel diaphragm(maylar material) or just the diaphragm?

Thanks again for putting up with my questions. This is my first attempt to rebuild the card and aside from a few set backs and your advice, its going ok.

 

[hotrod6927]

Hey I was reading your thread and I too am rebuilding my carbs. I found a link here that has a really good write up on how to rebuild the carb here is the link hope it helps. You may already be don with the rebuild but it is still a good source.



http://www.seadooforum.com/showthread.php?t=5563&highlight=fuel+delivery+system