High idle on my commando first start from basket case build

Hi,
I just finished building a 74 commando from a total basket case. I fired it up for the first time today. Everything seems good except it idles too high. It is idles around 2000rpm. I have the idle adjust screws all the way out. I took the air filter off and compared the slide positions to a spar carb i have with no idle screw in it. The slides are all the way down. (so the throttle cable is not holding them up).
Can worn carbs cause this high of an idle? or would that just make for an erratic idle? How about ignition timing? I put a Pazon ignition on it. One sticky point is, i don't have a timing mark on my primary cover. What is left of the rivets is ground off flush what the aluminum cover. I could not get the rivets out to replace the timing mark. With the primary cover off i used a degree wheel on the crank to set the static timing in conjunction with a dial indicator in the spark plug hole. Any clever solutions for a new timing mark? or how to get the rivets out short off an EDM machine?
Thanks for the help -Dale

Re: High idle on my commando first start from basket case bu

I would back the timing off a bit.
(and check for intake manifold leaks).

Re: High idle on my commando first start from basket case bu

high idle with the slides checked as you did indicates too lean

how are your air screws set, at the stock 1 and one quarter turn out from fully seated?

total rebuild, if the air screws are spot on and still idling high I would drop the carb bowls and take a little screw drive to the pilot or idle jets to verify what number it says on them, maybe they are to damn lean

and as Mark mentioned verify you have no possible air leaks between the carb to manifold and there to the head


as far as timing without benefit of primary mark to strobe, I would advance it to the point of obvious kick back at starting and then retard until it goes away, you will then be very close, in fact good enough

Re: High idle on my commando first start from basket case bu

Will the slides bottom out if the stops are backed all the way out? It not, check your cable adjusters. This is the first part of the first steps in pre-startup and carb sync-ing.

Re: High idle on my commando first start from basket case bu

I set the air screws to 1 1/4 turns out (they were about one turn out), started it, didn't seem to make any difference. I advanced the timing ~4deg, it kicked back hard and started up revving to about 2000 rpm. I set the timing back to where i had it. I check the bolts on the carb + intake. They are all tight. New gaskets all around. I'll pull the bowls later and see what is in there for jets.
Thx-Dale

Re: High idle on my commando first start from basket case bu

If you haven't set up the carbs by the JBA method you need to.

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

That's a good place to start. Sounds like you idle circuit is not working yet, and it won't until the idle is down. Check the float height too.

Dave
69S

Re: High idle on my commando first start from basket case bu

beanprofit said:

I set the air screws to 1 1/4 turns out (they were about one turn out), started it, didn't seem to make any difference. I advanced the timing ~4deg, it kicked back hard and started up revving to about 2000 rpm. I set the timing back to where i had it. I check the bolts on the carb + intake. They are all tight. New gaskets all around. I'll pull the bowls later and see what is in there for jets.
Thx-Dale

Click to expand...

And what about the throttle stop screws?

Re: High idle on my commando first start from basket case bu

just to test to make sure the cables are not hanging up

back off both slide adjusters all the way out so the slides drop down with a clang on the carb body

then start it, it should not idle at all

I think Peter is right, the slides are hung up

Re: High idle on my commando first start from basket case bu

1up3down said:

just to test to make sure the cables are not hanging up

back off both slide adjusters all the way out so the slides drop down with a clang on the carb body

then start it, it should not idle at all

I think Peter is right, the slides are hung up

Click to expand...

I do not know if I am right, but I do think these preliminary basic details need to be confirmed. Once the simple, and sometimes easily missed, aspects are validated, then the troubleshooting progression can continue in an orderly manner.
First things first, keep it simple and never assume.

Re: High idle on my commando first start from basket case bu

Then Again , it could be the Throttle Cables . particularly the silly Junction Box . Plastic :evil: THING .

A good inspection , see if the single cable end stops the silly slide from bottoming - if the cable end protrudes from the centre silly plastic thing .
So try with NO cente Cable ( set up Twin to Carb & check movement , then see if top single cable stuffs it up )



Discerning Types use a Twin Cable Twist Grip , so when you crash into a hedge the Twin Ferrules can challenge your determination to recover ( them )



perhaps a drop of silastic there mightnt be a bad idea . The LOADING is HALF on twin cables , so the resistance is less & sticking less problematic .
unless your fancy new cables are WELL LUBED and checked for fredom of travle before fitting , binding can be a issue . Which is why dedicated perfectionists
:x run OPEN curves / bends on the cable runs. Any TIGHT bends are liable to Jam Things Up . And ONE always checks the condition through the full movement of the handlebars . If you dont like someone you can set it up so the throttle increases while theyre doing tight U turns . :shock: This IS why . :roll: :wink:

Re: High idle on my commando first start from basket case bu

Quality Ferrous Junction Box for Ye Olde Salts .



Pisspotical el Cheapo plastic coppy .

Re: High idle on my commando first start from basket case bu

I found out cable routing is also important. I had mine coming around the right hand side of the head steady and the angle was too sharp on the left hand carb causing it to bind. I ended up routing them through the head steady with junction box in front of it. I also had binding trying to run the cable through the fork. Now it just comes out the front of the tank and over to the twist grip.
With that said, I still am chasing a steady idle after four months of effort. This is after a complete rebuild about 600 miles ago. I put on a new set of Premiere carbs and flattened the mating surfaces on the manifold. I've used the Bushman's method to synch slide height and lift. I'm positive the slides are dropping all the way. I set the fuel height using a tube next to the float bowl.
When I start the bike, the idle is low but quickly climbs to about 2000 rpm. After riding about 5 minutes it will idle at about 1500 rpm. If I ride for about 20 minutes it will drop into a nice idle at about 1000 rpm although occasionally it will jump up to 1500. It has done this consistently every time I have rode it on the old carbs and the new ones with a variety of carb settings. I'm starting to think it is an ignition advance phenomena and not carb related. It has the basic Pazon ignition. It is very sensitive to small changes in the idle screws, a 1/16 of a turn on both sides can make a 500 rpm change. I have quit trying to adjust it. Basically it is set now to idle correctly when completely warmed up. If I try to lower the idle after first starting it, it will die when completely warmed up.
Has anyone else with a Pazon seen something similar?

Re: High idle on my commando first start from basket case bu

Did you replace the needles in your carbies, I got caught out once when I got new needles, put them in the carbies and when I started it my idle went high as well , did all the usual stuff then I put the new needles beside my old ones and found they were shorter, the bike shop gave me the wrong needles, didn't think to check them before I put them in, I think they were for a Triumph???

Ashley

Re: High idle on my commando first start from basket case bu

By advancing the timing you made it worse, retarding the timing will lower the idle speed.

Re: High idle on my commando first start from basket case bu

I just got back to this project. You guys were correct, the slides were held up just a bit in both carbs from the cable being too tight. I had to remove the locking nut on the cable adjuster on top of both carbs. I then screwed the adjuster all the way into the top of the carb. This allowed just enough room for the slide to fully close. I have new Barnett cables on it (with the metal 2 into one thing). I checked the cable assembly and it seems to be correct. Maybe they made this one 1/8" too short? The single cable going to the grip is loose. Now it won't idle at all (as expected) with the idle screws all the way out. I just need to go through the carb tuning routine now an should be off and running!

Thanks for the help. -Dale

Re: High idle on my commando first start from basket case bu

so it was as we all suspected a binding cable issue!

glad you confirmed that and now to just set the idle screws and then take up any slack in the upper cable, all set!

Re: High idle on my commando first start from basket case bu

We had this problem with MarshalNorton's bike. Have found some of these "improved" metal 2 into 1 cable junction boxes will cause this. The holes for the cable outer sheaths are not deep enough. Also aftermarket cables can do the same.