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Discussion Starter · #1 ·
Ive read the main sticky on rebuilding rejetting for pods, 125 and 90s.... and followed it to the T; less the 127.5 jet for straight pipes.
I jetted with 90s and 125s and running pods off the back of carbs, no stacks, and headers only. So I really didn't follow the main sticky to the T.
I get one carb and cylinder hitting in perfect time at idle but the left cylinder, if sitting on bike, gives a pop and occasional backfire and exhaust from it not as strong.

In talking to a friend knowledgeable on scooters he told me this. Put carbs on turn each pilot screw to specs or two turns, crank....
Set idle at 1200 rpms with black idle s rew and adjust one pilot screw till it idles in idle mode itself, smoothly, but not in run mode. Then match the other carb with it till they idle low and smooth - the carbs themselves - virtually without the idle screw.... make sence?

This is what I tried and failed at... I remember doing this with my dirt bikes back in the day so I understood him.

However, it didn't pan out today. I have an idea it could be valve gap, carb mistake, or any number of things but feel it could be something else I'm missing....

Any suggestions are appreciated.
 

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Discussion Starter · #3 ·
Thanks lDR, that's how my buddy said sync them... adjust one pilot screw till running smooth then the other till they nearly match.... Then back off the idle screw and let the carbs idle on their own; hence correct air/ fuel mixture. If that makes sense? I noticed no cracks but didn't change the washers in insullators... Sitting on the scooter the right side sounds great, left side, however, pops and spits at idle and at speed. But, when engaged in 1st gear with clutch held both cylinders almost sound good. Idlevcan be eratic as well.... sometimes sounding good and other times i get the pops and spits. Cold it's bad, warm can sound good, hot bad...
 

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That would work if the idle on these carbs wasn't dependent on butterflies, that sounds like it would work perfectly for slide carbs. These carbs have a screw+locknut between them that replaces the function of the idle screws on slide carbs, you can find the pictures in the rebuilding VB carbs sticky. Basically if it's really far off it's like one has the throttle opened and the other is closed.

Do you have the factory service manual?

Also here's a video on the general idea:

 

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Close, but: set idle at 1200, adjust one mixture screw to achieve highest rpm. Re-set idle at 1200, adjust opposite mixture screw to achieve highest rpm. Re-set idle at 1200. This assumes properly sync'd carbs. Bench sync might get you close but dynamic sync is better.
 

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Discussion Starter · #6 ·
Didn't get to finish but was roughly the same as the other blade.
 

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Discussion Starter · #8 ·
Understand the concept of synching, in the video though, his bike looked factory and my bike is no just headers, pods, no filter box, no muffler ballist or baffle. It's been re-jetted. An engine is still an engine
 

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Just sync as they do in the video then adjust the mixture screws. I bought pressure nipples M5 to connect the hoses to the syncronization ports.
GF-2010-003_0.jpg
 

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Discussion Starter · #10 ·
That would work if the idle on these carbs wasn't dependent on butterflies, that sounds like it would work perfectly for slide carbs. These carbs have a screw+locknut between them that replaces the function of the idle screws on slide carbs, you can find the pictures in the rebuilding VB carbs sticky. Basically if it's really far off it's like one has the throttle opened and the other is closed.

Do you have the factory service manual?

Also here's a video on the general idea:

If my cylinders only sounded as good as his. His could have nearly be dine by ear less the bottles. I have one that does sound good and the other that randomly pops and backfires; especially when trying to adjust or sync by idle screw and mixture method. I have a short video where you can hear the pops. I shall attempt to post it if possible.
 

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I assume he bench synced his carbs so they were close then did the final tune. Yours might be way off and you can probably play around with the screw to see if that's the case. If it isn't that, one cylinder being much different means there is probably something going on with one of them (adjustment can make a bad cylinder appear good). Maybe a vacuum leak, maybe the jets were reversed (it does happen), maybe the choke spring isn't attached properly and one flap is down. Hard to say, I haven't tried pods either so maybe something weird is going on with them
 

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The carbs on these models can only be sync'd using some form of vacuum gauge, manometer or air metering device. You can get close doing the wire method while the carbs are off the bike but close doesn't count.
First step is to get them sync'd properly. Then set the mixtures properly. If there's still a lean popping from the left side carb that means there's a vacuum leak or there's a plugged jet/passage.
 
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