Is this arm too high?

[x2ryder]

Not the greatest picture but is this n/s arm set too high?

 

[#ZERO]

Looks about right but you should check the pop off pressure just to be safe.

 

[SUPERTUNE]

Yes, I think it's too high...(Very fuzzy pic)
Use a flat edged razor blade across the carb body and should be level with it

Come on #0...
Are you running your carbs like that? :shocked1:

 

[x2ryder]

I will check with a razor blade. But pop off with a 2.0 n/s and 95 gram spring is dead on 25psi.

 

[smoofers]

I will check with a razor blade. But pop off with a 2.0 n/s and 95 gram spring is dead on 25psi.

Fill the cavity w/wd40, put the diaphragm on, and screw the cover back down....

Does it still pop at 25 PSI? or does it not pop at all?

If it doesn't pop the arm is too high and the needle is being held open.

 

[#ZERO]

Come on #0...
Are you running your carbs like that? :shocked1:

Yes

If the arm is close to being flush with the top of the valve body it's good.

Those arms aren't completely straight and they all have a slight bend upwards which is normal.

 

[x2ryder]

Ok I bent the arm a bit laid a razor blade over the carb body and it's flush now. It isn't opening the at all just sitting there. But now my pop off is more like 30psi.

 

[Speedfreak]

The height of the arm really has nothing to do with your pop off when testing it because the diaphragm isn't on the carb. BUT it will have everything with how the motor runs. It is a must to make sure they are flat with the carb body. I just ran into this on a jetboat with 2 new motors. Neither motor would start cold but I was in a hurry and used new arms and didn't check their heigth.

 

[x2ryder]

See that was my problem. The damn thing does not want to start!!!

 

[SUPERTUNE]

Try a 80 gram spring and see what your pop-off is then...Lower pop-off is better for starting cold engines.

 

[Polish jet pilot]

Sorry to ask a stupid question (but after reading mikuni carb tuning manual and some other information I am still disoriented). Pop off is a term used for pressure needed to "pop up" the needle (which has a specific weight in grams??) from the needle seat by means of diagpram and spring. YES?

Ok, assuming I am right in the above statement: taking all of the above into consideration, how would I know whether my pop off is ok (except gauge test - maybe there are symptoms)? Are freestyle carbs set up differently than e.g racing skis? If so, why?

Thank you for helping out!

Andrew

 

[WaveDemon]

Sorry to ask a stupid question (but after reading mikuni carb tuning manual and some other information I am still disoriented). Pop off is a term used for pressure needed to "pop up" the needle (which has a specific weight in grams??) from the needle seat by means of diagpram and spring. YES?

Ok, assuming I am right in the above statement: taking all of the above into consideration, how would I know whether my pop off is ok (except gauge test - maybe there are symptoms)? Are freestyle carbs set up differently than e.g racing skis? If so, why?

Thank you for helping out!

Andrew

you need a guage. you can make one for less than the makuni one costs and it will work better too. get a hand pump, a tee and a guage.

My problem with tuning by feel is that when you need to change springs. sometimes springs don't do what there color indicates (or have some amount of veriation). to get dual carbs to read the same pop off with the same color springs takes bending of the arm or multiple spring changes to get it right.

 

[Polish jet pilot]

Ok, gauge I will make then, no problem. What about setting the pop off for freestyle (if I used this wrongly, please excuse me)? How a freestyle carb should work?

 

[SUPERTUNE]

What about setting the pop off for freestyle

All depends on the engine builder and carb builder.
Just look at it this way...the pop-off is your fuel pressure regulator, if you lower pop-off with a bigger needle valve size and a lower gram spring you increase the fuel pressure to the jets, hence the richer the carb will meter fuel, the same the other way, raising the pop-off lowers the fuel pressure to the jets will lean out the fuel metering.

High pop off usually means you'll run bigger jets and low pop-off usually means you'll run smaller jets.

Does that make sense to you?

 

[Polish jet pilot]

Finally somebody said it in ENGLISH!

Supertune - thank you a lot! (as always)

Andrew

 

[x2ryder]

Ok went to the 80 gram spring like chuck said to do. Got pop off down to 25psi. So with what I had I went to a 2.5 n/s and a 115 gram spring getting it down to 20psi. Tank is on reserve I would say about 4 inchs from the bottom. I still cannot get it to start and the primer only works now and then? I have the primer hooked into the reserve line. Is it possible these carbs could have something wrong with them from Riva? I have had Novi's, and Blackjacks and never had a starting problem before.

 

[#ZERO]

What carbs are they; 48mm Riva powerbombs?

Did you check and see if the return fuel restrictor is still in the carb body???

 

[x2ryder]

I am running a restrictor in the return line right before the tank. It has a 100 main jet in it. I was gonna switch to a 60 like all my Novi's always had.

 

[#ZERO]

Defiantly lower it between a .60 or .70 main jet to increase your fuel pressure.

Those carbs like lower pop off pressures so use a 2.3 or 2.5 needle & seat with a 80 gram spring.

 

[x2ryder]

I have a 60 on the way. Do you think this could be my problem?