Carb Issue

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Hello all,
I got my bike completed now, carbs cleaned, brakes rebuilt, rotors ground, fork seals, tires, etc.
This weekend took it for a ride and it ran great, no missing, wobbling or anything weird at least for first half of the ride.
What i started having are the symptoms of running out of gas. Ran great on the highway, no issues but once i'm on the street riding, when taking off from red light and twisting the throttle through the gears to a bit higher RPM's, only for about a block, after stopping at the next light and attempt to take off, bike would behave as if its running out of gas. Moving the petcock to reserve has no effect. I tried blowing into the auto valve vent hose that i left extra long and the bike started.
This happened second time, same scenario, after revving it higher for a bit and then stop at the light and when taking off, same symptoms. I had gas in it and right after it happened second time i put more gas in it.
It happened again for third time, this time i gave it a choke and bike started and idled at about 2k which is a bit strange as i don't have any fast idle on cold starts( this is something i did not adjust before installing the carbs)
Other then that, bike runs great, i think is still needs fuel mixture adjusted and carbs synched but pretty good so far.
Does anyone have any suggestions as to what could be happening? Perhaps auto fuel valve? This only happens after fast acceleration and, not when riding it normally.
Also any suggestions on fast idle adjustment? Manual states to adjust by opening and closing fork end of fast adjusting arm. Do i need to open or close it to gain some fast idle?

[NobleHops]

Did you get into the autovalve itself to see if it's intact?

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I did when I took the carbs apart and also tested it with vacuum pump.
Everything was good.
But this only happens if I ride it hard from light to light but on the hwy I had it up to 80 for about 20 minutes and did not have this issue.
I have to take it apart and see what's going on.
Thanks Nils

[daves79x]

If fuel delivery is not an issue from tank (make sure it's venting), then you either set the float level way too low or your bowls aren't venting. You did replace the vent 'T's or just left them out between 2-3 and 4-5 carbs? If you by chance put solid rubber tubes there - that's your problem. I've worked on carbs that had solid rubber tubes connecting all bowl vents. The system has to vent somewhere.

Dave

[Goss]

Connect a fuel pipe to the vacuum outlet pipe and switch on fuel with the vacuum valve open, I am guessing the fuel will flow initially faster or just trickle constantly.

Sounds like you have fuel flow but it is restricted. Vent hole in tank cap clear? Filter in tank clear? Tank clean? I assume the small filters in the needle valve have all been cleaned.

I had the same problem and the fault was fuel tap congested with muck in the tank, the fuel tap itself had a nasty build up of what looked like limescale?

Regards

Goss

[Larry Zimmer]

A quick-check on the autovalve would be to run a by-pass from the petcock to the carbs. If it still does it, go to Dave's thoughts. (Either the tank isn't venting or the carbs are not venting.)

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I did not replace the T's, but i did notice that they were cracked though.
Float levels, i changed that only on one carb, others were good, at least i would like to think so.
Tank has been cleaned, petcock filter cleaned, needle valve filters also cleaned.What bugs me is that this does not happen on hwy cruising at 75/80, only on sudden acceleration.
One other thing that i can remember adjusting is the accelerator valve. NIxons book stated that the lever should be just barely touching the accelerator valve shaft and mine was actually pushing it a bit so i adjusted it.
Carbs do have stock jets and i did not shim the needles as suggested by you Dave, i still need to order them but i don't think this has anything to do with it.
Perhaps i should recheck float levels, maybe they are too low and i should also adjust fuel mixture too as i think its running a bit rich but then again, there still should not be any fuel starvation.

What about the fast idle adjustment, any tips on adjusting it? I don't have any fast idle when choke is on.

Thanks guys

[spencer]

What about the fast idle adjustment, any tips on adjusting it? I don't have any fast idle when choke is on.

I think that to increase fast idle, you should close the fork you referred to. Maybe you should wait for some confirmation from Dave or Mike Nixon, or one of our other carb experts, but that is what I think you should do.

[cross]

I'll give it a try,
Thanks

[Goss]

Is the fast idle another issue or do you think that the fast idle will cure the fuel starvation? When the bike is on choke you would expect the fast idle to keep the revs at around 2,500 rpm. This is the only time that the fast idle will operate. If the bike accelerates hard through the gears then the accelerator valve is doing its job, I assume that you tested the acc valve and saw all of the jets working? The fuel starvation you are experiencing seems to be after high demand for fuel so makes me think that your fuel levels in the float bowls are still filling up after hard acceleration.

Regards

Goss

[cross]

Yes, i made sure all acc. jets are working before i mounted carbs and bike did run very well. It just started having these symptoms this weekend. Yesterday i took the bike for a ride around my neighborhood to see if it will have the same problem and it did only this time i think its happening even when not accelerating hard. Mostly it seems after stopping and then taking off.
I'm still suspecting that it is the auto valve and i'll be taking it apart tomorrow to remove the diaphragms and see if things will change otherwise, i'll have to remove these carbs again.
I also took my gas cap off to make sure that the tank is venting and there was no change.
When you said that after hard acceleration, fuel bowls are still filling up, did you meant "not" filling up?
Fast Idle is separate issue. After installing carbc post cleaning and started the bike, it ran a bit higher then 2000 rpm and once i closed the choke, it was still running that high so i turned down the idle tumb screw and it idled nicely at around 900 but, next time on cold start, i did not have fast idle at all.
So, in the manual it shows where to adjust it but i was just wondering if i have to spread or collapse forks to adjust it.
I'll be doing that tomorrow as well.

Thanks

[Goss]

Yes, I meant that in your case they are not filling up fast enough due to possible fuel starvation.

You say stopping and pulling away is the where the problem is? Are the manifold rubbers in good condition as well as the clamps? How many turns out have you on the idle jets, 2.5? Sounds more like air leak on the intake which if it is will show up more when the engine is cold, once hot the idle revs will fluctuate.

I would bypass the the valve for a quick test ride first, they can be a pain in the arse.

For the fast idle with the carbs removed operate the choke and watch the fast idle cam and fork, gently bend the fork closer to the cam, it all makes sense once you understand how it all works. Once adjusted on operation of the choke you will see the throttle butterflies open up very slightly, don't go too mad with the adjustment or your fast idle will be too fast!

Good luck and let us know how you get on.

Regards

Goss

[daves79x]

Goss' advice on the fast idle is correct, but you can't properly do it or check it with the carbs in place - they need to come off. The fast idle linkage is quite complex and the 2 parts on the fast idle spindle tend to stick together and don't work properly in any case. Everything needs freed up and adjusted, as Goss points out, so that the butterflies open slightly when the choke is fully engaged. The manual gives a spec for this, but I sort of go by sight. I never get too hung up on the fast idle anyway - it's just a sure way to blue your pipes if you let the bike sit on fast idle.

Dave

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The air box boots did have few holes in them which I patched using the inner tube repair. Today I checked for leaks with carb spray and there are no leaks.
Fuel mixture screws were left at 1 1/4 turns out by the manual and bike ran really smooth when I first started it after cleaning. I also did not shim the needles as I did not find to buy thin ones but this morning I read one of Dave's posts that tiny washers from pilot screws are good to use and luckily I saved old ones so I'll be installing them when I tilt the engine for valve adjustment. I do have a flat spot I think between 3/4 and 6k RPMs.
I hope that shimming the needles and syncing resolves some of that.
So yesterday I took bike again around the block and still experiences fuel starvation.
I took the tank off and removed the auto valve and tested it and it seemed fine.
I took it apart and inspected diaphragm and it looked good.
I assembled it back and tested agin with vacuum applied and it works just fine.
So I installed it and attached aux. fuel tank with some fuel in it, started the bike and it ran fine.
I let it warm up a bit and it still Revs nicely.
I installed the tank and took it on 5 mile ride and no problems at all.
I will go today for longer ride to see if anything changes.
I also removed the petcock and filter is clean and so is the inline filter that I have.
It's possible that it was the auto valve after all.
I did started hearing chirp from the alternator after revving it higher.
I'm headed out for a ride, I'll report later
Thanks guys!

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I just got back from a ride and bike ran nicely, fuel starvation problem is now gone.
I did however notice that my bike now if revved a bit off idle, stays around 2k RPMs for few seconds before drops to 1000 and I can't get it to idle below 1000.
All this once warmed up.
Other then all this, bike runs great!
All I did today was try to adjust the choke cable at the carb which didn't make any difference and adjusted idle from 800 to 1000.
What are the chances that carbs somehow got dirty again?
Or perhaps they just need syncing and fuel mixture adjusting?
Should I do the valve adjustment first and then adjust the carbs?
Thanks once again guys