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xvz1200 carbs


graeme morris
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hi guys . ive recently aquired a 1200 venture royale 1985 imported from the US{im in the UK] i have a problem with one cylinder not firing  , but it fires on the choke then imeadiatly drops the cylinder as if running out of fuel on the idle side of the carb  , could it be the float level. the carbs have been off and ultrasonically cleaned  cheers Mog

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Unscrew the spark plug caps and look for green stuff on the spark plug wires.  The connections are not moisture proof and the copper core wires corrode.  Usually you can cut off a half inch or so of the wire to get rid of the green corrosion and screw the caps back on.  While you are at it, check the cap resistance.  The stock caps are about 9k ohms and the aftermarket NGK caps are 5k ohms.  

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Since you say clean the carbs, I am hoping you set the idle screws and also balanced the carbs after the cleaning. If not I would do that also.  Yes it could be a float level off but if that was the case I wouldnt  think the cylinder would fire with the enrichment activated as I believe it gets the fuel from the float bowl. When you rev up the engine, does it seem to be firing then on all 4 cylinders? You could also pull off the air cleaner lid and observe the 4 plungers and see if they are all moving at idle or at a slight rev up. The bike wont run proper above 3K rpm with the lid off so it wont work to leave it off to ride it.

Good luck and lets us know how it goes.. 

Rick F.

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1 hour ago, graeme morris said:

CIMMER. done what you suggested and observing the piston and needle it appears to be spitting back thru the front right carb so im gonna take them back off and inspect again . any suggestions before hand ?. cheers Rick

Yep, do a compression or leak-down test and set the valves to proper specs.

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15 hours ago, graeme morris said:

CIMMER. done what you suggested and observing the piston and needle it appears to be spitting back thru the front right carb so im gonna take them back off and inspect again . any suggestions before hand ?. cheers Rick

have you adjusted the idle mixture screws yet on the carbs? best practice is to lightly screw them in counting the revolutions as you do this. Use a light touch as it is easy to distort the end of the mixture screw if you tighten them too hard. Back them out to the number of turns that you counted and see if that helps. Do one at a time and you should be able to hear a change in how the engine sounds when they are closed off. I would start with #2 since you saw issues with that one. It is possible you have a clogged idle circuit and it might be why you see gas in that carb.  If you need some pictures and reference, the service manual is available to be download from  here. https://www.venturerider.org/manuals/1983-1985 Yamaha Venture Service Manual.pdf

Also if you havent already, you might want to browse thru this forum looking for information also..   https://www.venturerider.org/forum/forum/10-venture-and-venture-royale-tech-talk-83-93/

Let us know how it goes and if you have questions.

Rick F.

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16 hours ago, graeme morris said:

CIMMER. done what you suggested and observing the piston and needle it appears to be spitting back thru the front right carb so im gonna take them back off and inspect again . any suggestions before hand ?. cheers Rick

I would go along with what @Marcarl since carbs do not cause spitting back. Before pulling the carbs out. If its spitting back up the carb this suggests that the cylinder is drawing fuel in but during compression the intake valve is not sealing allowing the fuel to spit back out through carb. This can be caused by a sticking valve. Sticky valves can be caused by a bent stem or extremely dirty valve. Often this can be determined by noticing the valve clearance being exceptionally high. Valve clearances that are too tight can keep valves from fully seating. A broken or cracked valve or seat. Much of this can be determined by a compression but better yet pin pointed more accurately performing a leak down test. .

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