new build 1075 w/29 smoothbores - idling questions

Finally got the old girl(73 Z1) running after 2 years of rebuilding. Have a MTC 1075cc kit, andrews 3x cams and 29 smoothbores. The bike fired right up and settles into a high rpm @ 2000 and will then fall and die. It has a Dyna S timing on it when I move the F marker to the timing mark it dies immediately. Carb wise I have 120 Mains, 0.9 air jet, o_6 needle jet, 20 pilot and the clip is at the center position. Air screw is 1 1/2 turns out. Where would you guys start to get the idle set. I know there are a million variations and many senario's, but I could use some help getting started. Thanks in advance.
Jim

Do you know what slide cutaway you have on your slides? 1,5mm or 2.0mm cutaway?
If you don't know, pull the carb top off - and using a flashlight see if 1.5 or 2.0 is stamped on the top of the slide. It makes a big difference to the pilot circuit tuning.

Typically the 2.0mm cutaway was sold for Suzuki GS models - but with parts changing hands over the years you can't rely on what you are told.

Also, have you checked/set the fuel height? 23mm is the dry setting (+/1 1mm) - measured with the carb upside down from the gasket surface (with the gasket removed) to the top of the brass float.

What petcock are you running? It's worth checking you are flowing enough fuel. Take the hose off the carbs and run into a can - when you turn on the petcock you should have a steady stream - if it starts out fast and slows - check the gas cap vent (on the underside of the gas cap and/or the petcock filter.

Jeff.Saunders wrote:

Do you know what slide cutaway you have on your slides? 1,5mm or 2.0mm cutaway?
If you don't know, pull the carb top off - and using a flashlight see if 1.5 or 2.0 is stamped on the top of the slide. It makes a big difference to the pilot circuit tuning.

Typically the 2.0mm cutaway was sold for Suzuki GS models - but with parts changing hands over the years you can't rely on what you are told.

Also, have you checked/set the fuel height? 23mm is the dry setting (+/1 1mm) - measured with the carb upside down from the gasket surface (with the gasket removed) to the top of the brass float.

What petcock are you running? It's worth checking you are flowing enough fuel. Take the hose off the carbs and run into a can - when you turn on the petcock you should have a steady stream - if it starts out fast and slows - check the gas cap vent (on the underside of the gas cap and/or the petcock filter.

what jeff said......also make sure your cam timing is dead nuts on.....i chased down what i thought was carb problem for a long time(3 sets of carbs of diff sizes)only to discover i was a tard on the cam timing.....thing would idle at 1500 and any attempt to lower it resulted in silence.....your carb settings dont seem that far off that you cant adjust out the problem......let us know how you make out......29's with 20/120 should have you in the ball-park......

Jeff, I am using a new pingle high flow with one of your inline filters. I also have your 29mm float tool so I will check the fuel float height as well.
Thanks jim

Jeff is the 1.5 or 2.0 stamped on the inside or outside of the slide cutaway?
Jim

Thanks Keith1,
The cam timing is spot on. I had it done by a great mechanic that works exclusively on these bikes and he sold me the andrews 3x cams. He is a great source. I could probably drop the whole bike off to him, but I love working on this thing. I will keep fiddling with your suggestions,
thanks jim

lewisj wrote:

Jeff is the 1.5 or 2.0 stamped on the inside or outside of the slide cutaway?
Jim

It's stamped on the top of the slide next to where the linkage bracket attaches.

Just for giggles, try your air screws at 1/4 turn out. Some of the 29's like this setting instead of the 1 1/2 turns out. I don't know if it's the differences in the slides or something else.

Gman wrote:

Just for giggles, try your air screws at 1/4 turn out. Some of the 29's like this setting instead of the 1 1/2 turns out. I don't know if it's the differences in the slides or something else.

Bingo!

Jeff,
I checked last night and the slide cutaway is 1.5. haven't had a chance to measure float height yet.
jim

Gman and Larry,
I figured I would have to mess with those a little. I will give it a try tonight.
Thanks Jim

lewisj wrote:

Gman and Larry,
I figured I would have to mess with those a little. I will give it a try tonight.
Thanks Jim

Close them all up, then back them out 1/4 turn. I've never seen a rack of 29's that didn't work with 1/4 - 3/4 as the final setting. Idle circuits on those carburetors are not very refined. Air screws can sometimes be all over the place. Don't think for one second they all have to be the same setting because often, they're not.


3x cams have a lot of overlap lift. That in itself leads to a weak signal at the carburetor at low RPM. Also they would on occasion spit shims. I wouldn't run them with S.O.T. buckets myself but there are those who would argue that...