701 dual 38s tuning issue?

Mechzxeng

Mechzxeng

Location
Winnipeg canada
I’m stumped!
New build fresh bore 701 with dual 38s, ported cyl, msd enhancer, triton head (should provide 165ish psi), b pipe, solas impeller all in an fx1.

Assembled with the following jetting:
70/130 jets, 1.5 n/S, 95gr spring, high idle screw 2 turn, low 1.5
Low to mid was ok, no top end tho 4500rpm max. Toyed with the high idle found it started to run better if i leaned up the high idle. If you punched it ski would crisply run to 5000rpm then lose some power when holding wot and settle at a gurgling 4500. (All testing done on trailer in water)

Took the carbs off my round nose and threw them on. The fx1 ran way better. So I copied the settings and jets moved to
75/137.5 1.5ns 95 for high idle screw starting point was 1.5 low was 1. After tweaking best setting was low 1.25 and high .25!!! And the performance was barely better then the first set of jets. Still a gurgling 4500.

Am I missing something? I’m questioning if my spring setting is way off? Maybe I have another hidden issue somewhere..
The carbs are clean and crisp with fresh rebuilds.

Thoughts?
 
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Pro-pulsion

Pro-pulsion

Location
Ontario, Canada
First things first, don't go by the spring according to its color and the chart. These springs are rarely exact. I have several that are different colors with the same pop off pressures. You need to check the springs according to the pop off pressures using a pop off gauge. Are you running the stock airbox? If so then you should go back to the original 115 gram springs at about 50 psi pop off. The most common jetting you will find for the OEM 38's with a B-Pipe will be 75 low, 135 high, 95 gram (42 - 46 psi) springs if aftermarket flame arrestors are being used, low speed screws set out to 1 1/4, high speed screws around 1-1/2 to 1-5/8 out. These seem to be the most common starting point settings. Also make sure your carb kits and reeds are in good shape. If after everything checks out and you are still having issues, try swapping out the coil with a known good one. Sometimes when the 701 coils get old they get too weak to put enough spark out making it run like a Lawnboy with water in the fuel :)
 
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Pro-pulsion

Pro-pulsion

Location
Ontario, Canada
I kinda figured that but ya never know lol

Hey I just noticed you're in Winterpeg! I would go for a visit to help you out with that but 20+ hours of drive time kinda killed the idea :p
 
Pro-pulsion

Pro-pulsion

Location
Ontario, Canada
I did just miss something too...it didn't dawn on me until now. You have an MSD enhancer, I have had them where the pot switch takes a dive and won't let the ski rev up past half throttle or so. Your MSD could be the problem too, they have a little history of doing that. Keep a good stock CDI on hand.
 
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