Engine tuning

[Smith]

Reaching out for some tips on tuning my rebuilt engine.

I have a DASA 950 that was modified with a 4mm stroke , running black jack 44s with a zeeltronic(wax curve) b-pipe, pump gas, vforce 3 reeds.

Engine has been reassembled and is operating. I ran 10 gallons of 25:1 mixed gas for break in and then took it back to 50:1. I have ran about a 7 gallons of the 50:1

First time breaking a engine in, not sure how quickly the cylinders should seat up but compression is 160psi on front cylinder and 150psi on the rear (my gauge is quite old so not sure if the readings are accurate but used them for comparison)

I'm running Blackjack 44s with 125 jet on high and I believe a 30 on low, but it is hard to read the print

The ski will idle ok buts seems a little rough in my opinion. Playing around and trying some things I found that when I lean out the low jets the idle roughness reduces but seems to exaggerate the roughness when transitioning to the high end

Performance improved when I leaned out the high jets as well, but still having some low to mid range roughness

Currently have my highs at 3/4 turn and my lows at 7/8 turn

Anyone else experience similar issues? Is this common with the bigger piston engines? Any other 950s with similar set ups? Any suggestions for carburetor settings?

I also see the white oil/water stuff on the intake to the carburetors, this was present before the engine was rebuilt but I'm not experienced enough to know if this is typical - thought it was an indicator for reeds not sealing up, but current setup has brand new reeds?

Thanks in advance

 

[kevbo]

Two stroke engines have the ability to run very rich, its actually necessary for best throttle response. Jetskis will often need to be four-cycling from just above idle until the pipe hits. I know this is annoying for long slow rides. You can install smaller pilot jets and lean the idle mixture screw to clean up low throttle operation. The only down side is throttle response will go away. Tune for best response, it will be chugging when you are going slow.

 

[Pro-pulsion]

And from lots and lots of experience here, I strongly recommend you get one of these flow meters because you can't synchronize carbs by just matching hardware settings. They must be set up according to how they flow air equally or else you will have one carb pulling more air than the other. It will basically be like having two totally different single cylinder engines when one wants to flow this much and the other only wants to flow this much. I have corrected so many setups that ran like absolute out of balance washing machines, it really surprised me to see how lazy a lot of people are. It's so easy to do, so critical to having a really well tuned setup and yet so many just assume the hardware is identical therefore the flow rates are too. If one set of reeds is a little more flexible than the ones on the other cylinder, you have a reduced air flow, that carb needs to be opened up ever so slightly to balance that. A slightly tighter fitting throttle valve, reduced air flow...so many variables but all so easily corrected with a decent meter. I use this one below. Stuff it in the carb throat with the throttle cable, read the flow, adjust the other one to match it. Best addition to carb setup next to the popoff gauge.

Snail Type Syncrometer Carb Sync Tool, GERMAN, SK Model - Aircooled.Net VW Parts

The best carburetor syncronizing tool made for us to syncronize dual carburetors. Rather than measuring manifold vacuum via a restriction, it sensitively and accurately measures airflow WITHOUT RESTRICTION. This is the top quality GERMAN SK Gauge.

vwparts.aircooled.net

 

[Pro-pulsion]

Throttle valves, they are the only thing that control air flow through the carb. The screws control fuel flow for fine tuning. Just do a basic setup, get your idle set close to where you like it, check the air flow, if the carb without the throttle cable is reading differently then you need to adjust the throttle valve only at that time.

 

[Smith]

Thank you for the responses

Kevbo, what do you mean by 4 cycling? Is the roughness or vibration common? Is it more common with upgraded engines? I don't remember my stock engine doing it much but it does seems to be more of a trend with my more upgraded engines, this engine seems to be the worst for it and it is my largest engine

Also the oily water at the top of the carbs, is this normal?

Thanks Pro-pulsion for the advice and link, to clarify the tooling suggested is used to set the throttle plate positions.? How is the linkage adjusted for this between the two carbs? with the syncrometer, do I use it at idle,full, in between? Thanks

 

[Pro-pulsion]

Idle only, the airflow volume will be balanced all through the full range after syncing. On aftermarket carbs it's a little more difficult because you have to backoff the little set screw on the throttle shaft and make minimal adjustments. The best method I do for those is find out first which direction you need to go, if carb 2 (the one without the throttle cable) is pulling more airflow your throttle valve is too open, take a 0.002" shim gauge put it into carb 1 (with the throttle cable), back the idle set screw out counting how many turns out until the idle screw is not holding the throttle open but the valve is resting on the shim guage. Tighten the set screws on the throttle shaft coupler and check the airflow again. If the flow is less, you put the shim gauge behind the throttle valve on carb 2 only and let the butterfly properly close on carb one, tighten your set screws and test. You only adjust one carb to match the other. On OEM carbs you only need to adjust the second carb to match by the screw pointing up toward the air box. I'll try to get a pic of each. It's really not hard to do, the little set screws on the aftermarket shaft couplers I do admit are a bit more of a challenge and unfortunately sometimes the #1 carb is the one needing adjustment, but it's pretty rare and the end results are very much so worth it.

 

[Pro-pulsion]

Wow, the word filters on here are getting a little ridiculous lol...I tried 2 different methods of spelling out the name of that cluster of flat shim gauges, you know, the ones that touch in between 4-stroke valves and tell you the clearance...they have a touchy feely name to them, and that was censored?? lol

 

[Smith]

awesome thanks for the info

 

[Pro-pulsion]

I'll put together a little tech how to of how I do it, everyone will have their own methods but this can at least be one option for at least one person if not a few. I'll link it here for you when I get it done.

 

[Pro-pulsion]

I just posted how I sync carb air flow in my build thread. It's not a standard in how it should be done, it's just a detailed breakdown of how I do it and it has worked pretty good so far. Hope this helps.

Super Jet - 1996 Round Nose SuperJet Project

I'm resurrecting my old thread. I can't believe I have had this ski for 8 years now :oops: But, I am back into the tray hauling it all apart again. My reason is that the bottom deck of my tray section has broken open leaving a rather substantial breach on both sides. My thoughts are this...

www.x-h2o.com

 

[Smith]

awesome thanks for the tip, I will give it a try see how it goes, thanks again