[kevin1971]

Trying to tune in a carb on my sons ds x 90. I have purchase a exhaust, cdi box, 20 mm carb, and clutch kit. Does any body have any tips on what size of jets should be in the carb, right now I have 58 slow pilot and 85 main jet. The quad has very little response off the line and sounds like it what's to back fire when a full throttle under a load. I have tryed moving the clip up and down on the needle, also tryed a few different main jets 80, 85 plus different slow jets 38, 40 and a 58.

Thanks
Kevin

[Go Hard]

kevin1971, on 23 July 2010 - 07:52 AM, said:

Trying to tune in a carb on my sons ds x 90. I have purchase a exhaust, cdi box, 20 mm carb, and clutch kit. Does any body have any tips on what size of jets should be in the carb, right now I have 58 slow pilot and 85 main jet. The quad has very little response off the line and sounds like it what's to back fire when a full throttle under a load. I have tryed moving the clip up and down on the needle, also tryed a few different main jets 80, 85 plus different slow jets 38, 40 and a 58.

Thanks
Kevin

We would require elevation, temperature, to help you man!

Your location would be required, fuel differs mucho!

[cobe]

Make sure your carby hasn't got any air leaks around the seals, manafold side and on the head, then start from standard jetting again usually theres enough scope with raising and lowering the needle to get it right depending on your elevation. Then jump or lower jet size

[Go Hard]

Cobe is right!

I just tried to tune your exact set-up but did not have the correct jetting. When Downhere returns from holiday's he should be able to shed some light on it. I'm thinking that the 38 pilot and 80 MJ will be the best bet but without knowing elevation, who know's. Rule of thumb for the needle is that one clip position equates to 1/2 MJ size.

DH found some smaller jets but I don't remember where they ended up and we are at 2300' elevation.

[drtracer27]

I have been working on tuning the same setup on a DS70. I have pretty much the same problems as you right now, the quad wont take off. Once you get the RPM's up it is good. I think I have a 44 Pilot and 84 MJ. I had a 40 Pilot jet in it but it wouldn't idle and changing the fuel screw and even the idle screw wouldn't do a thing. I went back up to the 44 and everything smooths out and the idle screw and fuel screw work as they should but it stumbles badly till you get the RPM's up and carbons the plug badly. Somebody said to check the float so I will do that when I get back from vacation. Hetrick suggested a 58 Pilot and a 90 MJ but that was terrible. I know the black plugs should mean it is too rich but I hate to lean it out too much until I have checked everything else.

[kevin1971]

Go Hard, on 23 July 2010 - 08:13 AM, said:

We would require elevation, temperature, to help you man!

Your location would be required, fuel differs mucho!

The elevation is 3500 feet above sea level and temp is about 20 C or 70 f

[kevin1971]

Go Hard, on 23 July 2010 - 08:13 AM, said:

We would require elevation, temperature, to help you man!

Your location would be required, fuel differs mucho!

Calgary alberta the elevation 3500 feet and temp of 20 c or 70 f

[kevin1971]

elevation 3500 feet and temp 20 c or 70 f

[mbarryracing]

Might be the profile of the needle or the slide cutaway that is contributing to that throttle response issue.
You didn't mention what brand carb that was, they all tune differently.

[cobe]

Sometimes bigger isn't necessary better smaller carb higher the air speed, better fuel air atomizing. Ive seen some quads fly with the small crby

[mbarryracing]

cobe, on 23 July 2010 - 04:09 PM, said:

Sometimes bigger isn't necessary better smaller carb higher the air speed, better fuel air atomizing. Ive seen some quads fly with the small crby

X2
But 20mm isn't that drastically bigger then the stock 16mm. With the right pipe even a 28mm can run very very good.