Enrichment problem! (Choke = runs on one)

[Tombo]

If you monitor the pipes IMMediately upon starting the bike, they won't be too hot to touvpch for probably 20 seconds. When I first noticed the running on one, I would routinely hold both headers full handful just to make sure they both got warm. If you use this technique, you'll be fine.

If it has been several minutes or more, I won't touch. The headers, but instead, I will hold my hand about a half inch from the header tofeel the heat coming on off. If you're careful, you won't get burned.

 

[16VGTIDave]

I've used a spray bottle with water in it to test for temperature differences. Set the sprayer for a stream and squirt the pipes. The hotter the pipe, the more the water will dance when boiling off. Can't get burned that way!

Dave

 

[DriverSideImpact1008]

Is there any update or solution to this probelm??

I am having the same issue. When the choke is on Full or Half my bike only runs on the left cylinder (I can touch the right header after it's been running for a while). When I turn the choke off, it will start to run on both cylinders sometimes...if not... I'll give it a little throttle, let off and then it will run fine on both cyl.

Last summer I had the carbs cleaned, synced, floats replaced, and up-jetted for straight pipes.

 

[XSLeo]

If your bike runs on just one cylinder without the enrichener at idle but kicks in when throttle is applied is most often the idle circuits in the carb on that side or partially or completely plugged.
When cleaning the carbs you need to be sure the passage from the float bowl to the pilot jet and from there to where the fuel is sent in the air stream is clear. Often it stays plugged between the mix screw and the holes by the throttle plate.
With the mix screw out, use the tube on the spraycarb cleaner, put it in the mix screw hole. Now look into the carbs by the throttle plate. At the top of the venturi you will see some tiny holes. Spray the carb cleaner, does it come out all those tiny holes, If not your plugged.
Clean them better.
With these passages plugged the air fuel mix from the pilot jet can't get to the engine. No fuel = no run.
Leo

 

[Tombo]

DSI1008 -

Ultimately, I had many more problems than just the enrichment circuit, but the enrichment issue did get me to search them all out and find solutions to them. I invite someone else to jump in and give their story - but as far as I can tell, these bikes just have a quirky enrichment circuit. Every other motorcycle I've worked on, owned, etc. cause the rpm's to run high (2-3k), either immediately, or after the bike has warmed. One of my yamaha air cooled 4 bangers will only start on full choke, and will run a REALLY low idle at first, and work it's way up to 3k by the time it's warm, and then when I switch the choke off, it has normal idle, runs awesome, etc.) BOTH of my 400's start more easily, and will warm up more successfully in half choke - but the rpm's never shoot up.

In the long run - even with my bike running pretty much awesome now, it still won't fire both cylinders when the enrichment plunger is pulled out to the second notch (even to the point that if I have had the bike warmed up or running for hours, I pull the plunger to full choke, one cylinder stops firing and the bike dies if I don't nurse the throttle. Not that I EVER suggest doing that, but just a point that even all said and done, the full enrichment doesn't seem to work for me.)

Even with the bike not running on full choke un-nursed - I still use the setting on particularly cold mornings, or times when Im having trouble starting the bike. I will pull the plunger to full choke, give it a kick and give it some throttle, it will start up and race to 2k rpm or so, then I will move the choke position to half choke, and hear the other cylinder kick immediately. Then I can let off the throttle, walk away and let it warm up. I always warm up for at least 2-3 minutes if I have the time (I used to smoke a cigarette to time the warm up, but now I just go inside and get all my gear on, maybe take a leak).

As for half choke - that works just fine for me - and in fact, it's how I start and warm my bike up, because it will idle without being nursed compared to starting it cold with no choke (unless, as stated above, i'm having a tough time starting, or it's cold outside).

My bike has been running this way for the passt 2000 - 2500 miles or so, hasn't changed in any significant way - and like I said, I'd say it runs awesome. I have two of these bikes now, and the other one (not the subject of this topic originally) has the exact same issue (but now, after my tuning and rubber parts replacement, runs AWESOME). I am not sure if this is a coincidence, or if I'm good at cleaning and tuning everything but enrichment circuits.... (to that I'm not so sure of, since I have several other motorcycles I've revived whose enrichment or choke circuits work great).

So my question for you - how does the bike run otherwise? How is idle? Is it easy to start? hard to start?

 

[Tombo]

xsleo is describing something different than what I experienced - and actually, most people will read the topic of this thread wrong.

My issue was NOT that it wouldn't idle without choke. NOT!!!!

Even when not tuned up, it would idle - albeit, a little rough till I cleaned everything, replaced exhaust gaskets, float bowl gaskets, raised floats, cleaned idle circuit (as xsleo is described), etc.)

My issue (and the issue BOTH my bikes have, and that DSI1008 seems to be exibiting) is that if you try to run the bike on full choke, only one cylinder fires.

I am not saying that DSI1008 doesn't need to pull the idle circuit and run a wire-guage cleaning tip through each of the (12? 16?) tiny holes - but just that people seem to have a hard time reading this subject without making other assumptions.

 

[DriverSideImpact1008]

xsleo is describing something different than what I experienced - and actually, most people will read the topic of this thread wrong.

My issue was NOT that it wouldn't idle without choke. NOT!!!!

My issue (and the issue BOTH my bikes have, and that DSI1008 seems to be exibiting) is that if you try to run the bike on full choke, only one cylinder fires.

In the long run - even with my bike running pretty much awesome now, it still won't fire both cylinders when the enrichment plunger is pulled out to the second notch

Thats exactly what mine is doing. It idles fine w/o choke (rpm could maybe be a little higher), and performs well throughout the RPM range. Just not when the choke is on.

It doesn't seem to affect the starting. I started it last week when it was 17degrees out, and it started well for a small CC, carbed engine. Only kicked it a few times, and it only died when I took it off choke too soon.
The only thing I'm worried about is if it will do any harm in the long-run, running on just the one cyl on startup.

 

[16VGTIDave]

Sounds to me like the start circuit in one carb is not delivering fuel. Remove the float bowl and make sure that the opening in the float bowl that the brass tube goes into is clear. It has a small orifice at the bottom. Also check the brass tube. It has a small hole on the side of it, close to the float bowl mounting surface.

 

[DriverSideImpact1008]

Is the start circuit the same thing as the enrichment circuit that was being talked about?

My bike starts fine when its cold and the choke is on. It just runs on one cylinder. But if it's warm I can start it without the choke and it will start and run normally, on both cylinders.

 

[16VGTIDave]

Is the start circuit the same thing as the enrichment circuit that was being talked about?

My bike starts fine when its cold and the choke is on. It just runs on one cylinder. But if it's warm I can start it without the choke and it will start and run normally, on both cylinders.

Yes, Yamaha calls it the start circuit. As in "for cold start". They labeled it a choke to avoid confusing the masses. But it is not a choke in any way, except in it's intended use. It does more than just mixture enrichment, it also adds more air to increase the engine RPM. If the fuel delivery is blocked in one of the carbs, it will cause a very lean mixture, which won't ignite in a cold engine. This could explain your bike only running on one cylinder with the "choke" on.

I hope this isn't too confusing...

 

[DriverSideImpact1008]

Nope I follow. Just making sure the semantics were the same. Maybe I will need to tinker a little. It's nothing that has really bothered me...because it doesn't really affect the performance or starting much. But back to my main concern...will it cause any harm if I don't get it worked out?

 

[16VGTIDave]

I don't think it will cause any short term harm. I do wonder how the engine will tolerate one cylinder warming up while the other doesn't. Head gasket failure? Warped cylinder head? Nothing? I don't know...