twin pipe timing ?

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Old700

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Nov 27, 2007

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Rimbey

• Nov 29, 2007

• #1

I have a 99 SKS that I put PSI twin center bleed pipes on last year, my problem is that they tend to make the sled run lean on WOT pulls regardless of jetting. I also have 40mm Mikuni Flatslide carbs off of an 01 700. I took 1 degree of timing out but am wondering if there needs to be more taken out to make these things run better. Majority or riding is in Revy/Golden areas with 19/40 gearing,151 track,ATTAC system,RCS titanium primary spring, 10-58 weights and a R12 helix with stock secondary spring, head shaved 5 thou. Motor is fresh with no leaks and good compression, any advise would be great.

 

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allblowdup

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Nov 26, 2007

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• Nov 29, 2007

• #2

How do you know that it is lean? Plugs,pyro?

 

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Old700

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Nov 27, 2007

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Rimbey

• Nov 29, 2007

• #3

plugs, wash and pyro. The longer I hold WOT the hotter it gets until it squeaks pistons. I took it to the limit last year to find out how hot too hot is with my probe placement etc. Jetting never seems to cure it, thats why I am thinking there is too much advance in the ignition. Trying to get some info before I change the timing again. PSI said dont worry about it, but its kinda hard to pull long hills when you melt down every time.

 

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allblowdup

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Nov 26, 2007

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• Nov 29, 2007

• #4

The center dump pipes are kinda known for that at low elevations but you are riding higher up. Is your compression stock? I have seen pyros keep climbing even with rich jetting if the pipes are to tight.

 

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Backcountry

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Nov 26, 2007

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• Nov 29, 2007

• #5

What is the coolant temp when you squeak? Ive ran into an instance or two where no matter what jetting go thrown at it- the cooling system couldnt keep up on long pulls and she got hot and squeaked...

 

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Old700

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Nov 27, 2007

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Rimbey

• Nov 29, 2007

• #6

Yes compression is stock, the head shave was just to square things up, the 5 thou didnt change the compression. As for cooling, I dont have a guage but I have added a rear exchanger out of a Cat 580 in the back of my tunnel extension in series with all the other coolers. The temp light would come on all too frequently after I put the 151 on it but last year it never came on once, and yes it does still work. What do you mean if the pipes are too tight? Thanks for all the suggestions, and please keep em coming. Been sledding for a while but haven't ran twins before. They really wake that 700 up but this one has me stumped. Thanks

 

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allblowdup

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Nov 26, 2007

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• Nov 30, 2007

• #7

The pipes being to tight means that they do not flow enough to let out the exhaust gas properly. On the dyno these type of pipes usually show great instant numbers but will loose power as they heat up or the pyro temps will just keep going up no matter what you do. If you have never run twins before then you should know that running twins on that engine will create a inherint lean spot at around 3/4 throttle that you can't get rid of. It is kind of the nature of the beast.

 

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Old700

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Nov 27, 2007

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Rimbey

• Nov 30, 2007

• #8

Thanks Allblowdup for that info, Is it mainly just the center dump design that does this or the non ves 700 with all styles of twins. It does seem like the pipes run very strong for the first bit, but as they get hotter, my power definantly falls off with EGT's still climbing. I took the ATTAC off last trip out last year in Radium and at times was at 8-9000 ft, went up to I think a 520N 540N main and it still would want to burn down, let alone being pig rich and hardly driveable. Maybe I just have to give up on those twins?

 

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allblowdup

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Nov 26, 2007

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• Nov 30, 2007

• #9

Well the center dumps seem to be known for it even if they flow enough on the bench but end dumps can do it also but they are much easier to check. All twin pipes have the 3/4 throttle lean spot on these engines,VES engines are a little better but still do it some. On long pulls does it start to missfire a little also?

 

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Old700

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Nov 27, 2007

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Rimbey

• Nov 30, 2007

• #10

No misfire, but gets hotter and hotter till I have to let off amd turn out of the hill on a big climb. Blipping the throttle helps a little but not enough. Makes it tough to longcock my buddies when the thing acts like this. Short pulls I can take most 800's of that vintage of sleds, till I cant push EGT temps any higher. Thats why I thought maybe take a couple more degrees timing out to see if that helps. Timing on my nitroused 383 chevy is key, same principals apply to a sled too I'm thinking.

 

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allblowdup

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Nov 26, 2007

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• Nov 30, 2007

• #11

Yes, but it can lie to you also. Your egt's will be lower if you are detonating slightly and will rise when you back off timing. How far out from the flange are your pyro's and how hot of temps are you seeing?

 

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Old700

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Nov 27, 2007

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Rimbey

• Nov 30, 2007

• #12

6" from piston skirt and plugs/wash looks really good at 1250 - 1275. Any higher and plugs start looking more and more white. It will melt down around 1350 from the 2 pistons on the shelf at home.

 

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allblowdup

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Nov 26, 2007

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• Nov 30, 2007

• #13

Looks good, are the pistons holed or are the edges melted and if so what side is the worst.

 

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Old700

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Nov 27, 2007

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Rimbey

• Dec 1, 2007

• #14

The damage is always around the edges of the pistons. Threw pistons away a few months ago so cant remember what side.

 

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XC700116

ACCOUNT CLOSED

Oct 2, 2007

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Milliken, CO

• Dec 1, 2007

• #15

What about fuel? what kind and what octane rating? may want to mix a little race gas just to slow the burn a touch.

 

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700millwright

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Dec 6, 2007

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• Dec 6, 2007

• #16

Man am I glad I found this thread as I just completed rebuilding my 98 700. Same type of pipes(psi-centre dumps), v-force 3s, factory carbs(not sure what to jet yet), pod filters. Sure would be nice to see if you solved the problem.

 

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Old700

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Nov 27, 2007

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Rimbey

• Dec 6, 2007

• #17

Probably wont know for a while, shoulder surgery wont let me ride till maybe late spring. However when I was running the Kehein carbs at 3000ft I found that 200/205 were fairly close. Just watch plugs at 3/4 to WOT because if your setup is like mine, you will stop in a hurry without warning! I think the key to making these things run better is to pull the timing back a few degrees and probably throw in a bit of race gas in every tank. Good luck and let me know if you find a good setup.

 

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440truc

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Feb 27, 2010

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Vancouver Island, BC

• Mar 23, 2010

• #18

Just found this thread! I have the same problem with mine, but rear bleed jaws pipes. 98 700, cheater head, reeds, cone filters, porting, 40mm flat slides from 02 800, spi pistons, wondering if you ever figured it out, also wondering about running 800 pipes if that would fix it, they would flow better but thinking you might loose bottom end?? mine also seems very very lean on mid range, cant hold half throttle at all, pyro's go up real quick!!