High rev, no idle

[LoHo]

A friend was foolish enough to ask my help with his bike.

I figured out the no-spark part and felt like a NASA scientist. However, my powers failed when it came to the carbs. We set everything spec as per the manual, but all we get is a high-rev start for a couple of seconds, then nothing. I know it has to be carb settings, but I don't know whether to drop the floats for richer mix, or play with the air screws, or what. Any help out there?

The jets wouldn't really figure in until she runs a bit. I helped clean the carbs and blew out the passages. It looked pretty good...the air blew out the cleaner and then passed freely.

The bike has been mostly sitting for the last decade. It has not run properly while he's owned it. The PO bump-started it and rode it to his house, keeping it running by keeping the revs about 3000. The #3 cylinder had an oversized plug JB welded in place as the hole was stripped out. Matt cleaned it all up and helicoiled #3. We didn't check compression, as Matt didn't have the equipment and I didn't plan to be that involved.

[D0wn5h1ft]

A friend was foolish enough to ask my help with his bike.

I figured out the no-spark part and felt like a NASA scientist. However, my powers failed when it came to the carbs. We set everything spec as per the manual, but all we get is a high-rev start for a couple of seconds, then nothing. I know it has to be carb settings, but I don't know whether to drop the floats for richer mix, or play with the air screws, or what. Any help out there?

The jets wouldn't really figure in until she runs a bit. I helped clean the carbs and blew out the passages. It looked pretty good...the air blew out the cleaner and then passed freely.

The bike has been mostly sitting for the last decade. It has not run properly while he's owned it. The PO bump-started it and rode it to his house, keeping it running by keeping the revs about 3000. The #3 cylinder had an oversized plug JB welded in place as the hole was stripped out. Matt cleaned it all up and helicoiled #3. We didn't check compression, as Matt didn't have the equipment and I didn't plan to be that involved.

Yikes. Do the floats move freely and is the petcock actually flowing fuel? Sounds like the floats are filling and then quickly running out with no replenishment. Somebody is definitely going to say it's a dirty carb problem so I won't even go there. What about your idle mixture screws? Did you set them to the appropriate number of turns out? Clogged fuel line [my best guess]?

If this was sitting for a decade and all the carbs got was a quick blow out of the passages, they're probably just clogged with varnish still. I just finished a carb rebuild that had sat for 10 years and it took me a week after dipping, chasing threads, etc.

[LoHo]

It was a pretty thorough cleaning, but I know it has to be carbs. I didn't check his float setting, but he said he set them a bit rich.

[D0wn5h1ft]

It was a pretty thorough cleaning, but I know it has to be carbs. I didn't check his float setting, but he said he set them a bit rich.

A float setting by itself wouldn't prevent it from running unless he set the float super low (high if you're doing the upside down measure test). I would also check to see if his floats are even moving in the first place.

[motoman]

.......may have missed somethin' here, but what is the bike?

[LoHo]

It's an 84 Kawi ZX750 with Mikuni BS34 carbs, but don't tell anyone, 'cuz if I get exiled to the Other Bikes Forum, I'll never solve this.

[DGXSER]

So, just to be sure we look at all possibilities, a bench synch been done?

[LoHo]

Yep, I did all of the stuff an XSer would do. I heard that there is a gas puddle on the floor, so I think we're going into the carbs again. It was from a remote tank that is either on or off. When on, gas overflowed a couple carbs. We need to see about those floats and needles.

[DGXSER]

Try tapping the bowls as they fill. I have developed a practice of turning on one petcock, tap bowls for both carbs fed from that side, after about 60 seconds I assume the bowls are filled. The turn that side off and repeat on other side. Then try to start it.

[LoHo]

Hmmm...his manual calls for a float height of 18.6mm, which he did, but that meant that he had to bend the tangs out, not in. I have never seen a bike that called for tangs flexed away from the needle. I think we'll start by putting all of the tangs flat, then adjusting them to all the same height.

No flooded floats, by the way. At 18.6mm, the floats barely move until they hit the bottom of the carb body (meaning "up" in real life). Perhaps they are not able to fully compress the needles. And perhaps he has the wrong needles. Who knows....

[LoHo]

Yeah, my first thought was a bound needle sticking somehow, but now I'm thinking the lack of wiggle room for the floats might be the problem.

[DGXSER]

Based it being in this forum, I will assume it is an XS11. In that case the floats should be 23mm or 25.7.

[LoHo]

Not exactly, DG. A '84 ZX750, but the Other Bikes Forum is a hopeless exile. And Carbs is Carbs, right?

Matt rebuilt the carbs with fresh kits a while back and inserted plugs that came with the kit into the pilot jet opening in the carb body. They were not there originally, and he thought he'd discovered something. If these are later model BS34, they shouldn't have plugs....

[DGXSER]

The plot thickens. Do they have the crossover from pilot to main jet? If bo passage, then no plug.

[LoHo]

Yeah, those plugs need to come out...no crossover. We'll set all of the floats the same and then see what happens.