PLEASE HELP

550surf

550surf

Hi,

I just finished for the first time a carby rebuild, bn 38/44 round body/pump style DUAL set up.
The ski has a westcoast pipe, probablly bored too, was a race ski.

One thing i noticed is that there is 2 jets only not 3. the other hole has no thread but looks like either a 3rd jet could be installed or is for air.


Im asking for a step by step guide on how i tune this ski, ive never done it before so i need a good explanation, ive searched and read a lot but still got problems.

tunning my 550 dual round body bn carbs for race setup
from the start of screwing in the jets all the way to the base and how many turns back?


( before rebuild, the ski didnt have the idle set up, just low and high )
so please, run me through what to do since we have dual, round body, performance engine.

thanks alot from downunder



550surfff
 
550surf

550surf

thanks for this information.
ill look into it, i tried tuning at the river today but ended up getting to lost and then couldn't get back to my desired default setting. maybe you could give me a number of turns from the base. Its a 550 ( maybe bored- has wisco pistions ) with a westcoast pipe and DUAL 38s both round body pumps. It has a lightened fly wheel, total loss ignition and ocean pro high compression head. I despressly need for both left and right carbs a number of "turns" from the base as a base/default setting for now and future. somthing like 2 or 2.5 i tried for low and 1.8 for high. its not what i want.
also, my understanding of what a "turn" is a 360 degree reveloution. not just a turn of the wrist. is this correct? about the "turn" is a full 360 rev.


also if u feel like taking a stab at this question go for it.
so after alot of wasted ignition on trying to find the idle point and even just start i think the engine may have been quite hot at some times. like u dont wana hold ur finger there really hot. so i pull plugs out and go to turn it over ( plugs out) i notice by covering the holes that the front cylinder is barely pushing my finger off while the rear is pumping even harder then normal, i have now, super low compression in the front cyclinder.

why is this?
how did this happen?
what is possilbly the problem? reed valves? pistion rings?


most importantly tho, i need a default carb setting for my race set up 550 ( was actually ex racers ski ).
it only has 2 screws. LS and HS. id like to be able to idle, never had that.

thanks so much guys,
day 64 of working on this ski and finally got it up on the plane! 90s stylin on you brah! :)


cheers

550surf
 
kswiatk

kswiatk

Location
Minnesota
Well first off.. test your compression with a reliable gauge, the thumb method isn't anyway to test it. Since you are probably running advacne with total loss, you may need high octane gas, or your engine may detonate at high revs.. You should make a post of pwctoday.com, the website tends to be more focused on the vintage ski and there are some very knowledgeable people on there. Make a complete list of all engine modifications on the site, other people are bound to have your setup and give you a base line. i've rarely worked with round bodys let alone dual ones.
 
Last edited:
550surf

550surf

kswiatk said:
Well first off.. test your compression with a reliable gauge, the thumb method isn't anyway to test it. Since you are probably running advacne with total loss, you may need high octane gas, or your engine may detonate at high revs.. You should make a post of pwctoday.com, the website tends to be more focused on the vintage ski and there are some very knowledgeable people on there. Make a complete list of all engine modifications on the site, other people are bound to have your setup and give you a base line. i've rarely worked with round bodys let alone dual ones.
Click to expand...



thanks man,

i just stripped it today, entire ski pretty much.
will clean and rebuild it. 140psi in rear and 15 in the front cylinder......
was only a 15% diference an hour earlier,

how could this happen?
 
kswiatk

kswiatk

Location
Minnesota
Since you were tuning you were probably lean- either from your settings or an air leak. Post some pictures once you get the head and cylinders off to inspect the damage.
 
naticen

naticen

Site Supporter
Location
wilmington, nc
A turn is one revolution of the tuning screw. Also, don't bottom them out hard at all to find the bottom. Just barely touch it and count back from there. Clockwise leans it out and Counter Clockwise richens it up. And the vintage section of PWCToday.com will definitely have more people that are up to date on their 550 knowledge.

Also to clarify, you have jets, just not replaceable jets. They can be drilled out bigger, but there is no going back. I didn't last long with Round Body Mikunis before I went to the SBN. I've never seen a Round Body with two screws but that means nothing about if they exist, just means that I have no idea how to tune them.
 
550surf

550surf

cheers man
i have low compression 10 psi in one cylider and 140 in the other. could still start and flush.
but ive stripped it and will restore, i will try and sell the dual carbs and run a single sbn.
 
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