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Discussion Starter · #1 ·
My Shadow(has 18k miles) was running fine when I bought it last fall but maybe +- 500 miles after it started to show some hesitation when accelerating about 1/4 throttle or more and backfiring as well. So I gave it a rest as it was starting to get cold here in Mass anyway.
A couple of weeks ago I took the carb off, cleaned, and used most parts from the rebuild kit. Got a new set of plugs (RA6HC) as well, double-checked the gaps and they are fine.
I can get the carbs to sync, but it keeps popping at idle and I feel that the rear exhaust sounds strange and there is not much pressure like the exhaust from the front cylinder. Also the front exhaust gets hotter than the back one, however, it does not sound like I have a gasket/flange leak there. Btw exhaust is not stock but it does have baffles in case anyone asks.
I have the air/fuel mix about 2 1/2 turns, sprayed some starting fluid around the boots and I didn't notice any changes, so I don't think I have any leaks there.
I don't have any problems starting the bike, a little bit of choke starts right up when cold, or no choke is needed when warm.
Got the carb out twice already and everything seems fine, float level seats at 8mm. Got the spark plugs boots out, cut 1/4 in of the wires off and twisted the boots back on, and checked ok for sparks.
So my next step would be valve adjustment, but I would like some opinions before getting into that if possible.
There's one thing I'm not sure about when syncing the carbs, when I rev it up, the levels go off, but it's fine when at idle. That should not happen, right?
 

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'83 VT750C
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I‘m not one to talk, because I tore my front cylinder apart to address a similar issue. Much older bike, though. In this case, hearing the hoofbeats, I would think horses, not zebras. Even after going through the carbs, they could still be the culprit. But try checking your fuel hoses and filter. You may also want to invest in a compression tester with the fitting to fit your spark plug hole. Never hurts to know, and that’ll immediately show up any ring or valve issues.
 

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Discussion Starter · #3 ·
I just realized that it's sucking air from the rear exhaust which might be valve issues. Unfortunately my compression test won't fit, looks like I will buy another kit.
Fuel lines are fine and I forgot to mention that I put a new fuel filter
 

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1999 Shadow 750 ACE VT750CD3 Modified
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It sounds like you have found the problem and that goes along with the poor carb balance off idle.
It will be a little lean with the floats at 8mm, spec is 7mm, but I don't think that is the root of the problem.
 

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Discussion Starter · #7 · (Edited)
Automotive tire Wood Motor vehicle Gas Rim

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Update: adjust all the valves, did compression test on both cylinders open throttle and results are: front has 200psi, back has 210psi. Carburetor removed again, float level between 7-8mm both sides. Table sync adjustment near perfect IMO, as you can see the pictures, following instructions in the forum, each side the hole show just a little bit, just about the same on both sides.
Put carburetor back, starts easily and just not even 1/4 turn and sync was perfect.
Unfortunately something still wrong on the back cylinder and bugging down and popping giving some throttle.
One thing worth to mention, I can close the air fuel mixture for the rear cylinder and the bike still running. BTW boots for the intake are very ti, I doubt that is leaking there, however I don't have more starting fluid to check spraying there a little bit. Might go out to buy one tonight
One of the images is a little bit blur, but the holes are just about the same
 

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1983 Honda vt750 Shadow
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Carb cleaner spray also works well for vac leak checks.
Maybe a jet is clogged, esp the pilot jets.

But usually when you can screw the mixture screw in all the way, it is running richer than normal on the idle circuit.
There are small brass air bleeds jets in the bottom of the slide chamber housing that feed the low speed circuit. The large opening in the carb throat lets air into that chamber.
If you have a pod air filter that closes that off, it can restrict the amount of air flow in there.
Do the plugs on that bad cylinder look darker?
 

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Discussion Starter · #9 ·
Carb cleaner spray also works well for vac leak checks.
Maybe a jet is clogged, esp the pilot jets.

But usually when you can screw the mixture screw in all the way, it is running richer than normal on the idle circuit.
There are small brass air bleeds jets in the bottom of the slide chamber housing that feed the low speed circuit. The large opening in the carb throat lets air into that chamber.
If you have a pod air filter that closes that off, it can restrict the amount of air flow in there.
Do the plugs on that bad cylinder look darker?
Spark plugs are brand new, so can't tell the difference between front and back cylinders. Jets are new

I know for sure it's something with the carburetor now, yesterday night I took it apart again and switch sides, bowls, jets, sliders, everything and now the problem is with the front cylinder.
Just not sure what it is yet.
 
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