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Author Topic: sohc 750  (Read 1621 times)

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Offline neil10

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sohc 750
« on: January 15, 2008, 06:39:23 PM »
Hi,   got spark ,  got fuel in bowl, have set points and timing. the other threee exhausts blow out hot gases but no1 just cool gas.
help
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Offline 750goes

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Re: sohc 750
« Reply #1 on: January 15, 2008, 06:58:32 PM »
check your spark on #1.

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Offline flipprboi

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Re: sohc 750
« Reply #2 on: January 15, 2008, 07:02:05 PM »
how's the spark plug? Could be fould from carb mixture or weak spark.
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Offline neil10

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Re: sohc 750
« Reply #3 on: January 15, 2008, 07:08:52 PM »
new plugs good spark
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Offline flipprboi

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Re: sohc 750
« Reply #4 on: January 15, 2008, 07:15:06 PM »
Hows the carbs? Are they clean and in sync ?
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Offline Sam Green Racing

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Re: sohc 750
« Reply #5 on: January 15, 2008, 07:19:22 PM »
You have fuel in bowl but, is it going into the combustion chamber.
If the number one plug is not getting wet, check your main jet in the coresponding carb.

Sam. ;)
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Offline neil10

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Re: sohc 750
« Reply #6 on: January 15, 2008, 07:42:22 PM »
spark plug is clean i'm suspecting no fuel in chamber. Bike was sitting fo 3 months without use
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Offline Patrick

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Re: sohc 750
« Reply #7 on: January 15, 2008, 08:15:18 PM »
Pull the drain plug on carb no. 1 and see if gas is getting into the bowl. If not, then check your float and your valve needle for movement.
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1979 Yamaha XS11
1969 Yamaha DT1B
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Offline mattcb350f

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Re: sohc 750
« Reply #8 on: January 15, 2008, 08:21:36 PM »
I don't trust new plugs much. swap the plug out of the "bad" cylinder with one that runs and try again. (After making sure it's getting fuel)  ;)

This is the quick way to isolate a dud plug.
 Matt.
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Offline 754

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Re: sohc 750
« Reply #9 on: January 15, 2008, 08:33:58 PM »
Do you have seperate air filters.. if so pour a teaspoon of gas on the air cleaner for that cyl.. if it flashes right up,  its carb.. process of elimination..
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Offline neil10

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Re: sohc 750
« Reply #10 on: January 15, 2008, 08:45:34 PM »
I have the one air cleaner for all carbs, so what I did is undo vaccum  screw and squirt wd 40 in there which activated that cylinder so I guess it's carb problem. I bought the kit wander if I need complete rebuild or just clean
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Offline cafe750

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Re: sohc 750
« Reply #11 on: January 15, 2008, 08:56:49 PM »
Assuming the bike ran well before this, your carbs probably just need a good clean...I once had #3 drop out on my '73 750, and it was just a little piece of crud that wedged itself into the mainjet. If you have the type of carbs with the "bail" that holds the float bowl on, you wont even have to pull the carbs to clean it.... :)
« Last Edit: January 15, 2008, 09:00:21 PM by cafe750 »
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Offline City Boy

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Re: sohc 750
« Reply #12 on: January 15, 2008, 09:13:40 PM »
I'm catchin on to this late,but have you checked compression?
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Offline neil10

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Re: sohc 750
« Reply #13 on: January 15, 2008, 09:31:40 PM »
thanks everyone  it's nice to have  different ideas  I do have rebuild kits maybe I will go hold hog and do the rebuild
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Offline Patrick

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Re: sohc 750
« Reply #14 on: January 15, 2008, 09:39:37 PM »
One last thought - unless your rebuild kits include needle jets, you may want to forgo putting in the new jet needles (I'm not referring to the fuel valve needles). The needles included with many aftermarket kits don't match up well with the stock needle jets (that's the jet in the middle of the carb that the needle slides through). You can have real problems adjusting the carbs if the needle and the jet don't mate well. If your original needles look ok, leave them alone.

Patrick
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1970 CB750 K0
1982 VF750S Sabre
1987 VT1100 Shadow
1979 Yamaha XS11
1969 Yamaha DT1B
etc.

Offline neil10

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Re: sohc 750
« Reply #15 on: January 15, 2008, 09:46:37 PM »
this is the bike I had as a 17 year old  now 51 so I put this one, must be to live old memories. thks all
ps there was ni internet back then.
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