74 Running Super Rich

[hippiedreads]

As the title says, my 74 is running super rich. If you don't know the background it's been sitting for years and I just recently got it running again so there's probably a build up of crap and will run better after she sees some miles.

Now on to the problem, stock 74 carbs running a 127.5 main and a 45 pilot with the needle set to the lowest position, number one clip position if going from top to tip. I've got the mikesxs air filter on it (I know they suck but I just want to get the bike running well before winter so I can tear it all back down for paint). Floats are 25mm from gasket and finally the mix screw I've played with from everywhere between 3/4 out to 3 turns out with little difference. I'm kind of stumped as to why I'd be so rich, I'd think with the more open air filters it would be running lean.

I guess I'm looking for advice from those who have played this game before. Should I bumped down the main jet another size or step up my pilet jet another size. Maybe even both? Any suggestions would be appreciated.

 

[Gcraay]

If it ran fine before with these jets and such in them that can't be the issue. I suspect garbage and buildup in the float bowl. I had the same thing happen with my generator. The float stuck and it flooded the bowl, causing an overflow and leak. I just popped off the bowl, wiggled the float, added some Seafoam, and it was fine.

 

[5twins]

Have you checked the needle number? Some aftermarket rebuild kits come with a generic Y-22 needle and it's way too short, like by 5 or 6mm. Even set at the leanest position like you have it, it would still be too rich.

 

[TwoManyXS1Bs]

Also check your choke system and plunger...

 

[peanut]

if its running rich on idle as it sounds like I would check and resolve the idle mixture first before touching the main jet and jet needles . They have nothing to do with idle mixture.

You almost certainly need to strip, clean and resync the carbs . The likelihood is that the idle mixture air jets at the venturi mouth are blocked and possibly the choke valves are sticking open and not fully returning but the main culpret is likely to be the float settings .
Make sure that your idle speed isn't set too high and the throttle disks are in sync and returning fully .

I would disconnect the throttle cable completely and just set up the idle with the throttle adjust screw and the idle mixture screw. Check that the butterfly disks are not binding due to residue on the venturi walls . A good way to bench sync the carbs is to blow into each carb from the butterfly side in turn and adjust the sync screw until the pressure is equal. its surprisingly accurate.

use finger pressure on the choke valves and the throttles whilst idling to make sure they are fully returning and add a external spring to assist the throttle shaft springs if necessary.

You might find something helpful in this video

 

[hippiedreads]

GCrray, I thought it might be floats too and I actually have watched this video a couple times now, peanut. 5twins, as for the needle it's a 4N8. All parts appear to be original throughout the whole bike except for all the rust and decay. I have stipped the carbs fully once and done 3-4 quick strip down some and clean with a very fine wire and carb cleaner. As the bike sits nothing but wiring is hooked up to get the motor running so I'm basically bench synching the carbs. Question on the method you gave though, the old carbs connect the the choke with a hose. Should I leave the two carbs connected and do procedure as described or do the carbs one at a time and cover at brass barb with a finger whilst blowing through the butterfly side?

I'm going to spend the day tearing them down completely again and seeing if I missed some of the things listed. And keep you guys posted. I appreciate all the responses.

 

[5twins]

If you're still using the original jets, it's possible they're worn or eaten away by gas residue and are now larger than they're supposed to be. This applies to the needle jet in particular. Unfortunately, you can't get replacement needle jets any more. MikesXS does sell a Z-6 needle jet but it's the long style for the '73 and older carbs. It won't work in your carbs.

Float settings should be measured from the gasket surface, not the gasket. Your spec is 24mm not 25. Measure both sides of the float. Often they're twisted or bent so one side sits higher or lower than the other.

 

[peanut]

Should I leave the two carbs connected and do procedure as described or do the carbs one at a time and cover at brass barb with a finger whilst blowing through the butterfly side?
.

yes sorry I forgot the early models had a vacuum take off on the inlet rubbers.
Just pull them off and put your finger over the barb .

You are trying to compare the amount of effort to blow into each inlet in turn and adjust the sync screw so they match. It will get you as close as you need to be to get it running well . Later you can use a carb balancer or vacuum guages to get it spot on if you have them.

 

[hippiedreads]

If you're still using the original jets, it's possible they're worn or eaten away by gas residue and are now larger than they're supposed to be. This applies to the needle jet in particular. Unfortunately, you can't get replacement needle jets any more. MikesXS does sell a Z-6 needle jet but it's the long style for the '73 and older carbs. It won't work in your carbs.

Float settings should be measured from the gasket surface, not the gasket. Your spec is 24mm not 25. Measure both sides of the float. Often they're twisted or bent so one side sits higher or lower than the other.

Yes sorry, measuring from gasket surface. My generic service manual (I think it's Haynes) says 25mm plus or minus 2mm. What's the tolerance for the 24mm you give because if it's plus or minus 2mm I'll rock on with it because everything else is perfectly aligned in the floats. Edit: partzilla has a the original blueprint which states 24mm plus or minus 1mm.

When you say needle jet are you talking the 4N8 or are you talking the pilot screw? After pulling everything back apart and this time inspecting everything through a magnifying glass I see that one of my pilot needles is not quite perfectly strait while the other one is. The sad part about it is that the couple sites I've checked are coming back with part obsolete. I'd prefer not to purchase a whole rebuild kit for the one part that if seems I need.

Being that only one is bent though and both plugs are fouling is it really gonna come down to being the floats to get them to the 24mm specs?

 

[5twins]

I'm not sure what you mean by "pilot needle". There's no such animal. The needle jet is that brass tube that the 4N8 needle fits into and works through. The hole in it is sized like any other jet but it's quite a bit bigger of course. It is a slight press fit into the bottom of the carb body and has an o-ring around it to seal it in the body hole. If that o-ring is shot, you can suck fuel up past the outside of the jet. Place your finger over the top of the jet (tube) and see if it will wiggle in the carb body. It shouldn't. Here's a pic. The needle jet is that big brass tube between the 2 air feeds .....

Here's what they look like removed. The shorter, fatter part with the o-ring around it is what sticks up into the carb body .....

 

[hippiedreads]

I'm not sure what you mean by "pilot needle". There's no such animal. The needle jet is that brass tube that the 4N8 needle fits into and works through. The hole in it is sized like any other jet but it's quite a bit bigger of course. It is a slight press fit into the bottom of the carb body and has an o-ring around it to seal it in the body hole. If that o-ring is shot, you can suck fuel up past the outside of the jet. Place your finger over the top of the jet (tube) and see if it will wiggle in the carb body. It shouldn't. Here's a pic. The needle jet is that big brass tube between the 2 air feeds .....

Sorry working and typing at the same time I meant needle jet and not pilot needle. Just combining two different things to make one lol. There is no free play in either of the left or the right carbs. Is there reason to pull and check the condition of the o-ring if there is no wiggle? And you stated earlier that the Z6 won't work for my year of bike. Based on that what would be an alternative route? Buy a whole rebuild kit and just use the parts that I need?

 

[5twins]

Grasp the needle jets and see if they easily pull out. If they're stuck in there good, they're probably still sealed up OK. There really is no good alternative for a replacement needle jet for the '74-'75 carb set. It's the one set out of all the 650 carbs sets that you can't get that part for. If you did find a rebuild kit that contained replacements, they would be those generic ones and there's no telling if they would be sized right.

You're blaming your carbs but you could have a weak ignition problem. Are you getting a good, strong blue spark on the plugs?

 

[hippiedreads]

I'm running a pamco and sparks good when the plugs arent fouled. Checked both needle jets and they are snug. Think I'll buy a new air/fuel mix screw and see if thats the fix.

 

[peanut]

does it need choke to start from cold ?
If so..... when it starts ....does it struggle to idle immediately ?
What is the idle RPM ? Are you sure that the idle adjust screw is set low enough ?

I would stongly suggest that you get the engine starting and idling first before you start tackling jet needles and diaphrams and Main jets etc

It sounds to me like you are trying to tackle too many throttle settings at the same time. If you cannot get the engine to start and idle successfully you are wasting your time trying to tune your other throttle settings and throttle pick up etc. Every throttle setting up to WOT still utilizes the fuel air mix from the idle circuit so in my opinion it should be the first carb setting to get right.

If the idle mixture is running excessively rich it should be a very simple matter to track down where the extra fuel is coming from. The cold start and idle system are simple circuits

 

[hippiedreads]

Yes, this is totally a idle issue which I'm really learning a lot about carbs. I've read the carb guide through twice now and some parts way more than twice.

The first couple initial start of the day needs the choke but everything after that the choke just fouls the plugs. The choke plunger looks find the connecting tube is clean and clear and seems to operate as intended. The mix screws are what I'm thinking the issue is. One of the two has a slight bend at the very tip of the head (pointed end). Now it's hardly noticeable unless under a magnifying glass but it's the only thing I can find.

With that being said I've got the one carb seeming to run relatively well with the adjustment at the 3/4 turns out. Let me run this past you guys quickly because I have a little confusion on the terminology each person uses for the mix. People on the forums I've seen say it's the air mix screw and some say it's the fuel mix screw. Being that the screw is on the engine side of the carbs that would indicate that it's mixing fuel correct? So when I screw in I'm leaning the mix and when I unscrew I'm richening the mix? Guess it's not really a question but more of reassurance.

 

[robinc]

So when I screw in I'm leaning the mix and when I unscrew I'm richening the mix? Guess it's not really a question but more of reassurance.

That is correct.

 

[5twins]

Yes, that's correct. On the 650 CV carbs, this is a true mixture screw not an air screw. It regulates fuel flow from the idle circuit, or more correctly, some of the fuel/air mix flow from the pilot jet. The fuel/air mix is made at the pilot jet and that is what flows to the mix screw. Notice I said the screw gets "some" of the mix. There are 3 more "bypass" holes that get the rest. You can't adjust their flow.

 

[hippiedreads]

Yes, that's correct. On the 650 CV carbs, this is a true mixture screw not an air screw. It regulates fuel flow from the idle circuit, or more correctly, some of the fuel/air mix flow from the pilot jet. The fuel/air mix is made at the pilot jet and that is what flows to the mix screw. Notice I said the screw gets "some" of the mix. There are 3 more "bypass" holes that get the rest. You can't adjust their flow.

Just regurgitating information, the mix screw is used to set the idle speed and the main jet and pilot jet determine the mixture at riding speeds (3000rpms). Hence why messing with my jets is silly because my issue is at idle and not while running. Make sure my mix screw area is clean of debris (checked now like a dozen times) and go from there. So things I shouldn't worry about until I figure out the idle problem are jets and needle.

Now this is just a thought. Since the one mix screw is buggered up a tiny bit, would it be beneficial to temporarly place an o-ring in the mix screw hole and see if that gives me a better searing so less fuel flows through? I would think that it would be okay and allow me to determine whether the light damage to the screw is the cause of the issue. Or would doing this cause a bigger headache than it will yield being useful?

 

[hippiedreads]

And just a side note, I really appreciate you guys taking the time to help me through some of my questions pertaining to getting this XS back from the grave.

 

[XSLeo]

The mix screw does not set idle speed, the idle speed screw does that. The idle mix screw adjusts the mix at idle speeds.
Main jet controls wide open throttle mix.
Pilot jet controls the flow of fuel to the three small holes shown in 5twins pic post #17 and the flow of fuel to the idle mix screw. At idle the engine gets fuel from the pilot jets through the three holes. The idle mix screw fine tunes the mix.
Running at speeds a bit above idle to about 3/4 open is controlled by the needle and needle jet. Fuel flows up from the main jet through the needle jet. The hole through the needle jet is partially plugged by the needle. When at idle the large part of the needle blocks most of the fuel flow. As the engine speed increases the slide lifts the needle up out of the needle jet. The needle being tapered allows the fuel flow to increase.
At wide open throttle the slide has lifted the needle almost out of the needle jet and the tip being very small hardly impedes fuel flow.
Being as how your too rich at idle and the mix screw is not changing things I might try a smaller pilot jet. This will cut back on the volume of fuel flowing through the three small holes and the mix screw will have more effect.
Leo