jKsled

ok that sounds good. the drill bit thing is a good idea, i might use that from now on. it does seem like you can get them very close using feel, but obviously it would be better to use something that actually measures it. thanks for the idea

Polaris87

Ive never heard of the drill bit idea. May be worth a shot. I was going to buy the edelbrock sync for 70 bucks but never did get around to it. The old fella had one where I used to live and he always synced my carbs for me. On a triple I think you absolutely need one. If you dont, like you say, your engine doesn't perform like it should because every cylinder isn't running like 3 separte engines....I posted this the other night before I read this thread and now I'm not sure if I said it correctly. I'm just going by what the old fella did. I'm sure he synced the carbs at idle, then reved it up and put the sync tool on each carb to see where the ball was. If it was lower on one carb he adjusted accordingly. Is this correct? I might get the sync tool and would like to know how to use it properly...lol.

This is what I posted on another thread and am not sure if what I posted was correct....

When dealing with tripples, everything has to be in sync. Each carb has to run each cylinder the same as the next one. It is almost impossible to set the idle on all 3 carbs the same. This is where the carb sync tool comes in. Edelbrock makes one for $70 Can. I need one but just havn't got around to buying one yet. You set the idle on each carb according to where the ball is on the tool. The ball moves up and down to how much air the cylinder is sucking. Eventually you get the motor idling around 1800 and the ball is in the same spot on the tool on each clyinder. Now...all cylinders are sucking the same amount of air with the carb plunger all the way closed. By you trying to idle the motor down a bunch it's probably messed up pretty bad.

Now, you need to make sure when you pull the throttle all 3 plungers are moving at the same time. This is done at the top of the carbs. Theres adjustments on the cables. You adjust the cables so you still have a little play at the thumb lever, but tight enough that the bottom of the slides go past the throat of the carb at wide open throttle. If the cables are too loose, the thumb lever may be wide open but the plungers are only 3/4 up. Also if the cables are too tight, the plungers wont close and adjusting your idle screw out wont lower your RPM's. The way I test this is I put my finger in the throat up push the plunger up and let it snap back down again. You should hear it hit the idle screw....

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1995 Polaris 600 XLT Touring
1995 Polaris Indy 500

Smackhq

Wow brothers, thanks for all the help. I didnt expect this much response as some forums are pretty quiet so thank you for all the help. It is refreshing to see. I'm learning a lot through this process but the snow is starting to fall in the nw cascades so I hope to have this beast repaired so I can get out there.

Here is the page from my manual on syncing the carbs using a drill bit. (hope this ok to post)
Picasa Web Albums - Rob - skidoo repair...

Cheers

mrholmquist

Here is a homemade tool you can make yourself. I have not tried it but I see no reason for it not to work. Cheap to make and easy to use. The fourth hose would not be used and would have to be capped off. You would obviously have to cap off two hoses if using it on a twin. I think it would be worth a try to build for the minimal investment it would take.

Homemade Manometer - VFR Discussion

I think if i was building it I would use two stroke oil , the blue color would be easy to see and if I messed up and sucked some into the engine it should not hurt anything.

Smackhq

I made something like that a long long time ago but it had a funnel on one end that we used to pour beer in... ;-)

Dbl R

This one is far less complicated and probably way cheaper to build


Round Slide Carburetor Synchronization How To:- Build And Use Your Own Sync Tool! - - Snowmobile at Off-Road.com

mrholmquist

Great link ...great idea and as you say cheap and easy. Still on a three cylinder not as handy as the first tool though. The addition of one tee at the bottom and a third line would be handier.

sbeck

Hello,
Hope someone might have any ideas. Picked it up used couple weeks back and it started great. Towed it home, started great again and drove it to the back yard. Sat for 1 week. Cannot start now. I have done the following:
'Thumb' compression check seems OK, verified getting spark, cleaned the carbs today, put new plugs in. Also has 3/4 tank of year old gas with some stabil.
Fuel on/off is definately ON. Plugs are wet.

Any suggestions?

Thanks,
Sean

TwinsofMLB

Flooded. When you brought it home the gas in the carbs went to the engine and it hasn't worked itself out yet. Let it set for a while.

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kevin2502000

Turning IN the a/f screw leans the mixture, turning OUT richens it. Everything else I completely agree with. When using mercury synch, it's best to set the idle temporarily higher around 2k to get more of an accurate reading. Don't rev too high or you could suck that nasty silver stuff into the engine. For those that have twins and don't have a synch or want to make one, an old hillbilly method sometimes works. Warm up the engine to normal temp, pull one wire off a cylinder and restart. Set that idle to half the reccomended idle, ie; 1200, you would set it at 600. Repeat the procedure for the otherside. Not perfect but better than nothing at all. Can't do this on triples.

mrholmquist

Sorry Kevin but you are dead wrong .....turning the screw in causes the mixture to be richer. Turning the screw out causes the mixture to be leaner. Unlike other carburetors this screw controls the flow of air to the idle circuit not the flow of fuel.

Not reallly sure what you are getting at as far as raising the idle to sync. When you sync the carbs at idle speed you have to finish by adjusting the throttle cable clearance. Elevated idle speeds would just complicate that process . You would have to re adjust the idle rpm then the cable clearance and recheck the sync anyway. Of coarse after that was done you still have to sync the cables too. (part throttle operation)

kevin2502000

Interesting now you have given me some study material. Yes other Mikuni carbs is what I am basing this on, turning the a/f srew in regulates the FUEL not the airflow so if it does inded work the opposite on this carb then you are correct. As far as raising the idle, it takes the a/f screw out of the circuit. SO, if by some chance you have a dirty idle circuit then it won't affect your synch since your running off the main jet. Here is a page from Factory Pro which is tuning a CV (constant Velocity) carb, yes they are different but didn't think the a/f worked the complete opposite. Please correct me if I am wrong, not trying to give out misinformation. I'm trying to remember my 2-stroke dirtbike days, I do kinda remember opening the screw made it run more lean.....dammitt now I have to research that for my own satisfaction.

kevin2502000

I just did some research and indeed you are correct sir. The flat slide and round slides do work the opposite of the CV's that I'm used to. I have copied some info........This is what we call "idle drop" setting the a/f screws. This info is from one of the Mikuni tuning sites, not BS, it's genuine.

The idle circuit is from an air hole in the mouth of the carb, past a screw that sticks into the air passage, to adjust the amount of airflow, past a special jet that draws fuel from the float bowl, and then through the discharge hole - or holes - in the main bore of the carb.

The screw that sticks into the idle air passage is called the pilot air screw, or the idle air screw. The jet that limits fuel flow into the idle circuit is usually called the pilot jet or idle jet. Sometimes the air screw and associated jet are called slow-running screw and jet.

The idle mixture is controlled by three adjustments:

A throttle stop screw which goes into the side of the carb right beside the throttle slide. It limits how much the slide can close. The slide is never fully closed, so some air ducks under it and flows into the engine when you think the throttle is closed.

You adjust the throttle stop screw for the idle speed you want and the idle air screw for mixture strength at that idle speed. These two controls interact and a good adjustment procedure is as follows:


When the slide is raised, fuel flow from the idle circuit decreases.

Turn the idle speed up a little higher than you want it to be, using the throttle stop screw. Now turn the idle air or pilot air screw inwards until the engine runs poorly.

Usually turning this screw inwards makes the idle mixture richer, and when the engine begins to stumble it's because of a too-rich mixture. Stop turning the screw inward when the engine acts like it is about to quit running. Start backing it out and count half-turns of the screw as you do it.

The engine should speed up as you back the idle air screw out and then start slowing down as you continue backing it out. When it runs poorly, stop backing it out. Count the number of half-turns you made while backing the screw out from run-poorly to run-poorly. Set the idle air screw halfway between these extremes, or at a nearby setting where the engine runs fastest.

Back out the throttle stop screw to reduce the idle speed to what you want. Then re-check the idle air screw adjustment and reset to the place where the engine idles fastest or smoothest.


Here are some great reference pics for those new to carbs................I'm still sticking to my guns about raising the idle to get a more accurate synch. These are representative of the round slide, the xlt should be the flat slide but SHOULD be the same principle. I cannot stress how critical float height is too proper carb tuning!

mrholmquist

I am not here to argue with you , in fact if you can teach me something I don't know by all means please do, no one is above learning something new.

As for the adjustment procedure you suggest using the pilot air screw I think you will find it does not work. Because the pilot air screw controls an air bleed passage which leads to the pilot air jet it never will stop the flow of fuel through the pilot fuel system regardless of position. It will not react in the same way an idle mixture screw will on other carbs. In the case of a carburetor equipped with an idle mixture screw screw there is no pilot jet.The idle circuit fuel flow is controlled and can be directly adjusted or even stopped by turning the mixture screw. You will not get near as drastic results turning the pilot air screw on a mikuni carb. It will not cause the engine to in your words " act like it is about to quit running" even if screwed in all the way and bottomed. Remember the fuel flow is controlled here by the pilot fuel jet not the pilot air screw. The procedure you describe would be fine if you were adjusting a carburetor which used an idle mixture screw which controlled fuel flow.
Adjustments made to the pilot air screw on a two stroke snowmobile engine are much more subtle and sometimes hard to even detect. the more cylinders you have the more subtle the results are apt to be.

The pilot air screw adjustment and the size of the pilot fuel jet are specified by the manufacturer based on the engine the carb is installed on. If you will refer to the hood sticker or the shop manual you will find a pilot air screw adjustment specified for whatever sled you are working on. Remember these carbs are used on many different engines and the combination of the size of the jet and the amount of bypass air is specific to the application. In the case of the 1996 XLT that is the topic of this thread Polaris recomends the pilot air screw be adjusted to one full turn back from lightly bottomed and a #35 pilot fuel jet to control the idle fuel mixture. They recommend no other adjustments be performed to the pilot air screw after that setting is acheived.
Of course the screw and jet may need to be changed from the factory recommended settings if the sled were to be used at higher altitudes and or for the use of oxygenated fuels. In that case the main jet size as well as other changes should be made also.





I also don't understand what you are acomplishing by raising the idle speed to syncronize
the carbs?

As I stated earlier the syncronizing procedure is done so the slides are all at the same height. This is a two part operation.

In the first step the slides are adjusted so the slides are exactly the same when the throttle is released and the cables are slack the slide height is now being controlled by the slides bottoming against idle stop screws. The adjustment is performed by turning the idle stop screws. The idle speed is adjusted at this time and you ensure the slides are at exactly the same height. The fluid in the mercury sticks will all be level when it is right.
If you elevate the idle before doing this then you would have to reset the idle to specified rpm and resync the slides a second time . To me this is just adding a step to the process.

The second step is to ensure the slides are at the same height and syncronized when the throttle is applied and the cables are now controlling the height of the slides. I like to block the throttle partially open at the thumb lever with a match book or something of similar thickness so it does not move while I am making my adjustments. You then adjust the slides they are the same height and tthe carbs are open exactly the same. The adjustment is performed by turning the cable barrels at the top of the carbs which will shorten or lengthen the throttle cable in question. Once again you ensure the fluid in the mercury sticks are all the same level.

After the cables are adjusted to the exact same length the throttle is released and the Cable slack is adjusted to specification (0.10" to 0.30" )
by turning all the barrels exactly the same amount of turns and locking them in place. The throttle is then applied again and you ensure that the fluids in the tool are still level and you have not put the carbs out of sync by adjusting the cable slack. In this way you have ensured the idle speed is correct and all the carbs are syncronized and flowing the same at idle as well as at speed.



I re read your previous post and now I think I understand where you are coming from re the syncronization and idle rpm. It would seem you are basing this on procedures used for multi cylinder carbs which would be installed on street bikes. Unless I am incorrect most street bikes use a single throttle cable and a solid linkage across all the carbs. So the syncronization procedure is different because all the carbs are linked it is only necessary to sync them together and not individually. So you can sync them at idle speed or if you prefer at elevated idle speeds for more accuracy. There is no need to syncronize each individual carb at idle speed and also off idle as is the case for a snowmobile as there is usually only one idle stop screw on the linkage. As you re adjust that one idle screw back to base idle you will have not altered the syncronization and it would not have to be rechecked. You must consider that bikes and sled are somewhat different and require different procedures to acheive the same goal.

kevin2502000

Yes that is correct, basing that synch off a common (1) idle screw instead of the 3 individual on each carb. I haven't quite made the transition this season from motorcyce to snowmobile yet, another week I may. As for the procedure that was highlighted in red, that was copy and pasted from a tuning site, not my own words. I think we are in agreement for the most part, just a few differences on technique is all. Synching sleds is FAR easier than 4 cylinder bikes, there you have to synch, 1 to 2, then 3 to 4, then the 2 sets together. I also agree you only need to set the a/f screw to the factory specs unless you have added a jet kit and even then it is usually specified.

RJ Gleason

The difference between rack carbs and individual cable pulled carbs was your issue.

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mrholmquist

I knew it would all make sense if we thought about it enough. My experience working on motorcycles is quite limited, especially late model motorcycles. Now I know someone I can ask if I need help on one.

Smackhq

Hey Brothers,

Get ready..noob question here. I have cleaned the carbs out and they were pretty dirty but nothing too back. I didn't see any blockage but I soaked them in cleaner overnight and sprayed out some I'm hoping they are ok. I did see that the main jet needle position was in wrong slot from stock. According to what I found it should be in position 3 but it was in #2. I moved it to stock for now. Main and Pilot jets are stock. Anyways onto my main question.
The unit has the ACCS system but the carb has a air screw (as you guys talked about above) but there is no setting for that in manual, it just says "ACCS" instead of how many turns out it should be. I checked it and it seems that they are all set at 1 turn out. Is that correct?

Thanks.

mrholmquist

If you are still talking about the 96 XLT I already posted above the factory recommended setting for the pilot air screw was 1.0 turn out from lightly seated. This information is from the Polaris shop manual.

Smackhq

thx, and that's the same with the ACCS system. Like I stated, the manual lists all the turns out for every model but not on my engine with the ACCS system, like it doesn't have one. Thus my confusion.