Poted 701 vs stock pipe and jetting...

[jetx]

Did a search and couldn't find what I was looking for...

I am running a 701 61X RIVA ported cylinder on 62t cases, dual 38 mik, and stock pipe...the previous owner had been running this setup with stock jetting and by the sound of it it ran fine...I have not personally ran this motor yet so I can't confirm...but i ws wondering if a rejet is needed becuase of the cylinder porting. ANyone have any experience with this???

Jetting that was in it...
130 main
70 pilot
Not sure on spring

Also if adding Flame arrestors and removing choke plates I am thinking if the stock jetting is right I should go up on the pilot to a 75 and was thinking going with a 95 gram spring. Does this sound right or should I stick with a 115 gram spring to start?

ANy help would be great. Thanks!

 

[Mark44]

Yes you should always check the jetting with a tach, there is a differance in ported and not ported motors and jetting.

Mark44

 

[jetx]

thats what I was thinking but when I cracked it open it had stock jetting and its been run for a couple seasons...I know that doesn't mean it is right so I wanna make sure everything is just right since I have it all ripped apart.

I know when adding a ported cylinder and pipe you need to rejet becuase you increase air flow...what I have been wondering is if you port a cylinder but restrict it with the stock pipe do you still have increased airflow and need to rejet??

Still looking for some more input on this...

 

[Mouthfulloflake]

from what I have read, and been told, its not a big change if any, considering the same carb/ and pipe are used.

 

[Mark44]

thats what I was thinking but when I cracked it open it had stock jetting and its been run for a couple seasons...I know that doesn't mean it is right so I wanna make sure everything is just right since I have it all ripped apart.

I know when adding a ported cylinder and pipe you need to rejet becuase you increase air flow...what I have been wondering is if you port a cylinder but restrict it with the stock pipe do you still have increased airflow and need to rejet??

Still looking for some more input on this...

I don't know if a stock pipe has ever been put on a ported motor but I would have to say yes jetting would be different. I have both types of motors ported and non ported with a B pipe same case and cylinders and both require different jetting.

Mark44

 

[jetx]

Yeah I know...not normal to run ported cylinders with a stock pipe...but that is what I have for now. So far I think I am going to run the stock jetting and see how it goes unless anyone else has any input...

 

[SharkB8]

My uneducated opinion: I would buy a tach and methodically go through the high speed screw settings, if only for the experience of doing it.

Someone correct me if I'm wrong, but if results improve all the way up to the point where the high speed screw is turned all the way out, then it would be time to start replacing jets.

I have my Group K motor here, and when I start it for the first time this spring, I will be starting with their jetting, which they guarantee to work, but I'm going to go through the whole process with the low and high speed screws anyway.