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Carbs and Fuel System
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post #1 of 15 (permalink) Old 09-17-2010, 06:20 PM Thread Starter
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Need help please

Well, I'm not entirely sure this falls within the carbs and fuel system area, but I'm guessing here.

I got my bike to start, however I'm getting some backfires from it and it also seems like it's only running on the rear cylinder. I came to this conclusion because if I remove one or both plug wires from the front cylinder there is no change in how the bike is running... if I remove a single spark plug wire from the rear, the bike stalls... I didn't remove a second one, it'll probably die if I do.

What I did to the bike recently was to plug the reed valve hoses and I also took out and cleaned the carbs. I removed all the hoses that connected to the reed valve hoses, including that thing that is at the middle, where the vacuum hose from a carb plugs into and another hose goes into the airbox and the other hoses go to the reed valves (don't know the name of that thing in the middle, so this is my description, hope you understand it). I didn't think this stuff was necessary for the bike to run, since I'm plugging the reed valves anyway it didn't seem like there's any use for them.

I also adjusted the mixture screws 2.5 turns out.

Here's something else I noticed. I have 2 inline fuel filters, one on each fuel line. The filter that goes to the carb that IS working is never full, you can see fuel in it but never full. The filter that is in line with the cylinder that is NOT working is always full of gas.

As I type this, I'm thinking the first thing that would come to mind is a clogged filter... I'll go try it without the filter just to rule it out. I'll report in a bit... meanwhile, what else could it be?
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post #2 of 15 (permalink) Old 09-17-2010, 06:43 PM Thread Starter
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nope, it's not the fuel filter... removed it completely, same thing happens.
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post #3 of 15 (permalink) Old 09-17-2010, 09:56 PM
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Pull the line from the filter to the carb and make sure it isn't clogged. Neither one of the filters should ever be full in my experience. Have you checked for spark on the front cylinder?

I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!
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post #4 of 15 (permalink) Old 09-17-2010, 11:01 PM Thread Starter
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Yes, there's spark. My hand got jolted pretty good when taking off the wires lol. I doubt the lines are clogged, I just replaced them with new hoses. It does seem odd that one filter was full of gas, and it was the one for the cylinder that isn't working, so that's a definite giveaway that there's something wrong there. I just have no idea what it is.

I am dreading having to take out the carbs again, it's such a hassle!! but the way I'm seeing things, I think that's the only way to go :-/

I also noticed a sound kinda like a vacuum leak, but I really can't tell where it's coming from, so again, taking out the carbs seems like the only way to really get in there and check.

Any way that vacuum leak sound may cause it to run on one cylinder? Not sure if it can be related.
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post #5 of 15 (permalink) Old 09-18-2010, 12:21 AM
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Try using 1 or 2 feet of garden hose, or the like, as a stethescope around the carb boots etc. to your ear, to isolate where the vacuum sound is coming from.

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post #6 of 15 (permalink) Old 09-18-2010, 02:12 AM Thread Starter
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Good one Hoss!! I always forget the "stethoscope" technique lol. I'll give it a try, probably tomorrow... I'm kinda getting sick of working on this thing and not seeing any breakthroughs, but that's the way it goes with all vehicles sometimes.
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post #7 of 15 (permalink) Old 09-18-2010, 11:41 AM
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Have you tried seeing if you can blow through the fuel filter that stays full? It may not be passing enough fuel to the cylinder. Would also explain why it stays full.

I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!
_____________________________________________
"Black Beauty"
1989 VN750 acquired December, 2008, 6,711 miles
Currently 23,298 miles

Old Blue
2001 Honda CMX250 Rebel acquired July, 2008

1987 VN750 project bike, acquired August, 2009, 33,000 miles and balancer sticking out of the case, currently awaiting attention and parts
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post #8 of 15 (permalink) Old 09-18-2010, 02:04 PM Thread Starter
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Yea, I can blow through both filters just fine... I also removed the filters and started it up again and same thing happens.
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post #9 of 15 (permalink) Old 10-02-2010, 01:43 PM Thread Starter
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Hi guys. I pulled out the carbs and found where the vacuum noise was coming from. One of the carb's diaphragms didn't seat well at one point and that left an opening. In any case, I don't have that problem anymore.

I still get backfires though, I adjust the mixture screws 2.5 turns out, I'm thinking I may have to set them differently. I was wondering something though, when I turn the screws counter-clockwise, am I going for a leaner or richer mixture?

I also put in Iridium plugs and the master cylinder is back on, I just haven't added the fluid and purged the brakes.

I'll also check the reed valves... I think there was no gasket there. If there isn't, I'll use a bit of silicone and see if the backfires stop.
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post #10 of 15 (permalink) Old 10-02-2010, 01:51 PM
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If your reeds are still in place and you have not marbled, I don't think that you can get rid of the back fire. The raw air is coming in through the reed valves and burning off the unburned gases in the exhaust and causing the back fires.

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