Throttle sync problems. Extremely frustrated.

[BeerIsSoAwesome]

So I built the aquarium-tube sync tool (with the valve sensitivity adjustment) and had a crack at syncing the carbs on my project bike today after work. The bike seemed to be running alright but needed a sync.

When I started it up, I was having *serious* pull toward the better cylinder. When I tried to adjust it, the engine started revving VERY high. I tried to compensate by spinning down the idle control, and in the process totally lost track of my baseline settings. The bike is definitely running far worse than it was, but I ran out of daylight.

Do I need to pull the carbs and do a bench sync of the butterfly valves to get back to "zero" again?

[Snake2715]

I had that same issue and built this one. cost the same and was a million times easier to use.

http://faq.ninja250.org/wiki/How_do_I_synchronize_the_carburetors%3F#The_two-bottle_method


Would you have to pull the carbs? Maybe just the air box so you can get a look at the butterflies..?

Not sure hopefully someone has that answer as far as bench synching.

[BeerIsSoAwesome]

I had that same issue and built this one. cost the same and was a million times easier to use.

http://faq.ninja250.org/wiki/How_do_I_synchronize_the_carburetors%3F#The_two-bottle_method


Would you have to pull the carbs? Maybe just the air box so you can get a look at the butterflies..?

Not sure hopefully someone has that answer as far as bench synching.

You're thinking like me. I actually BUILT one of those 2-bottle tools, and I really like the way it works, but I left it at my buddy's workshop over an hour away. I tried to build one today (even bought two Nantucket Nectars lemonades for lunch today) but it turns out that the Home Depot I pass on the way home is a *freak* store that doesn't carry rubber stoppers. All of the ones outside of my city carry rubber stoppers, but the one I pass on my 5-mile bicycle commute home from work doesn't stock ANY stoppers or corks or anything. Jerks.

Allegedly, the other HD at the other end of the city has 2 of them in stock (want to place bets on the likelihood that this inventory is accurate?) and there's a Lowe's nearby, so maybe I'll get lucky there...

Anway, I tried to sync the tools by sight after work today by pulling the airbox and lifting the slides to see the butterfly valves on the front end. I thought it looked *alright* but I think the idle was set too high. When I put the bike together and started it to take a run around the block, it was idling on one cylinder but the other was kicking in at around 2,500rpm.

Thanks for the tip on the bottle tool; you've confirmed that I just need to build another one of these so I can avoid the mess with the oil getting sucked through the vinyl tubing. It's really a better design, and I can actually modify the one I built yesterday to incorporate bottles and keep the air bypass valve for fine-tuning.

[Snake2715]

I had water in mine with purple food coloring. Turned on the bike and bam left side sucked it all in. I was honking the horn trying to cut the engine.. didnt prep right and new to the bike..


it took me a while as I am a freak about stuff being right. I let it idle in the 1500 range if I recall correctly and once the bottles got level I left it for over 1 min and it barely moved. I figured that was dialed in... getting there was a bit rougher as the closer you get the more patience you have to have.. it will be a very fine adjustment and then wait for the bottles to level.. if they go the opposite way re adjust..

I know you know this but it took me a good 30-45 to get mine dialed in. I will recheck it in a couple hundred miles cause my float height was off when i did it so now I am curious.

Plus I have now ridden the bike I adjusted mine before taking it out after buying it and going through it to get it street ready.

[weedahoe]

See, I went out and bought two vac guages from Harbor Freight and used a 20% coupon for each and connected one to each carb and synched them that way. Much easier IMO

[Snake2715]

See, I went out and bought two vac guages from Harbor Freight and used a 20% coupon for each and connected one to each carb and synched them that way. Much easier IMO

Yeah I have a harbor freight close.. that may be what I do for the second time around at least as a double check.

[adidasguy]

Anything with liquid, in fact, ANY vacuum gauge needs a restrictor close to the carb.

A restrictor is a piece of tube with a very tiny opening. What it does is cause the remaining foot of hose to act like a smoothed out buffer. On the carb side, the vacuum fluctuates wildly. Due to the restriction, the remaining hose has a very smooth vacuum. For liquids, it prevents the liquid from being sucked into the carbs. For gauge types, it stabilizes the gauges so they don't fluctuate wildly.

Note the clear restrictor close to the carb end. It is a tine piece of tube with a pin hole size passage through it.
Also, the restrictor keeps the vacuum at the carbs where it should be. Without it, the carbs see a 3' hose and that really messes up the vacuum (and sucks everything into the carbs).


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[rowbvp]

I had the same problem. I fixed by checking the mid and main jets. The mid look about the same as main, after cleaning them the right side carb was pulling way to much gas.I had swich jets on right side carb. 60 main and 130 mid. some times the jet numbers get hard to see,after a few screw driver scratches.check your jets, Bench sync ,set idle mix to 2-3 out and go form there, also check your petcock turn to PRI they try idle mix screws.

[ohgood]

why not just use wire ? if anything is bumped out of wack, a piece of wire can be used anywhere, anytime, side of the road.


are folks remembering to adjust valves before doing this ?

[Snake2715]

Yeah make sure valves are adjusted.

I would also say check float height and adjust as well.

[BeerIsSoAwesome]

Valves are adjusted, float heights are correct.

After seemingly endless problems, I narrowed it down to a lean right cylinder at idle. Seemed to be a vacuum leak at or near the right-cyl intake tube. Replaced the factory stock clamp with a stainless hose clamp from Lowe's. Best damn dollar I've ever spent. Bike runs beatifully, immediately drops back to idle after an hour running at Turnpike speeds. No more popping or backfiring at idle. I couldn't be happier!

Thanks everyone, for all of your help.

[ohgood]

Valves are adjusted, float heights are correct.

After seemingly endless problems, I narrowed it down to a lean right cylinder at idle. Seemed to be a vacuum leak at or near the right-cyl intake tube. Replaced the factory stock clamp with a stainless hose clamp from Lowe's. Best damn dollar I've ever spent. Bike runs beatifully, immediately drops back to idle after an hour running at Turnpike speeds. No more popping or backfiring at idle. I couldn't be happier!

Thanks everyone, for all of your help.

Replace both the intake boots then, the clamp may be covering a hole, for now.

Congratulations