Trouble Firing Up

[Guest Thainglo]

Some improvements made in the long saga of getting a stripped 83 back on the road. With a new TCI, I've got good spark on all four cylinders. Bike will fire up when I shoot carb cleaner into the throats, but dies shortly afterwards. Like it isn't getting any fuel at all. I start it with the choke half-way, throttle slighly cracked open.

 

I've pulled the carbs, took apart, cleaned, and put back together. Using a gravity fed tank to get gas to the carbs.

 

Wondering a couple of things:

1) Carbs are certainly out of sync as I stripped them all the way down. Could being out of time that far prevent it from idling, even roughly? The sliders all move in and out smoothly when the engine idles briefly with the carb cleaner.

2) Do I need to be using the fuel pump to provide a pressurized shot of fuel into the float bowls? This question hit me yesterday, always assumed the gravity tank would work fine, but you know what they say about "assumption."

[Yammer Dan]

Mine acted like that and it was fuel pump. Wouldn't keep carbs full I guess? Maybe takes a little pressure to push it thru needle valves? Still haven't finished that one. It was one that had sat for a while. I think you are on the right track. I would try hooking up fuel pump to see. You are right carbs have to be out. You could look into throats as you worked throttle and try to get them close. All sync does is make sure they are opening togather. Look in there and make sure they are closing and then adjust then til they look like they are opening togather. But I'm betting on fuel pump.

[Gearhead]

Gravity feed should work fine. Raise the supply can higher to increase pressure a bit.

 

When you cleaned the carbs, did you pay extra-special attention to the pilot circuits? Pull the pilot screws, clean out in there. Make sure carb cleaner can travel from the pilot jet in the bowl area to the screw area and thru to the outlet holes in the barrel.

 

Jeremy

[Squeeze]

Probably you just need to mount the Airbox and it will fire up and idle as fine as the unsynchronized Carbs allow. Gravity feeding the Fuel should be fine up until 2500 RpM.

[Neil86]

Another issue with 83-85 Ventures are leaks on the YICS chambers causing vacuum leaks and leaning out fuel mixture to cylinders. Some have just abandoned the YICS in place and capped the intake runner ports. You could try this and then later vacuum test YICS chambers to pinpoint leaks. They tend to leak on the seams of the plastic chambers.

[mbrood]

Neil,

 

If a guy PROVED that his YICS chamber was properly sealed and the hoses were good... do you see any reason (let's say a guy happens to be in there at the time) not to still just rip it out and cap the plugs? First doing away with the future leak problem and also just getting it out of the way... I've read LOTS of theory of the YICS purpose but never read that there's any "real" change in tossing it.

[Neil86]

Mike as you know, Yamaha dropped YICS on the 86 1300 redesign. From what I recall the idea is the chamber "fills" when the intake valve closes, and "empties" when it reopens to create a swirl on the intake charge. I guess the only fair comparison would be a known good YICS hooked up and unhooked on the same bike.

Even getting a good leak test requires duplicating running conditions.........engine heat and vibration while testing the vacuum in case theres a split that opens as the chamber flexs.

[GeorgeS]

Do you hear the fuel pump clicking for about 5 to 10 seconds each time you turn the Key to the ON position ??

 

If you don't hear it, its not working.

[Venturous Randy]

Mike as you know, Yamaha dropped YICS on the 86 1300 redesign. From what I recall the idea is the chamber "fills" when the intake valve closes, and "empties" when it reopens to create a swirl on the intake charge. I guess the only fair comparison would be a known good YICS hooked up and unhooked on the same bike.

Even getting a good leak test requires duplicating running conditions.........engine heat and vibration while testing the vacuum in case theres a split that opens as the chamber flexs.

 

I pulled and plugged the YICS on my 83 due to some rotten hoses. The bike ran so much better than it was running that I am glad I did it.

RandyA

[Guest Thainglo]

I did the YICS mod posted somewhere on here to route the lines back and forth, since I already had everything torn apart. Thanks for the tips on how to get the carbs synched close enough to get it running. Once I can get it to idle, can hook up a manometer I've got from another project.

 

Hadn't thought about trying with the airbox back on. Perhaps that pressure drop will help pull fuel into the throats?

[mbrood]

Actually, I think the constant velocity carbs NEED a restriction to the airflow to create more vacuum to make them work properly, so with no airbox (and restriction) they bog down to a very lean condition. The airbox inlet was carefully designed.

[Gearhead]

Well, not all CV carbs need this as this is the first bike I've had that's so sensitive to the airbox. I think it has to do with the jetting, relative to both restriction and resonant effects in the airbox. It is true, though, what you say about the Venture's airbox.

 

Jeremy