Honda-SOHC
SOHC.co.uk Forums => CB750 => Topic started by: jerbear48 on January 08, 2013, 08:44:05 AM
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Hi All
As mentioned in previous posts I am restoring my CB750ss, well its all back together and looks really nice but and its a big BUT, it will not start. The engine was stripped during restoration and has been rebuilt , timing was checked and double checked before I put it back in the frame, points have been set correctly new plugs,plenty of spark and fuel.Yesterday I was tinkering with and when I checked the plugs they were as dry as a bone. Any ideas please cos it's doing my head in... >:( :'(
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Squirt some easy start into the air filter box, it should fire up, if it fires up but does'nt run on then you know it is fuel problem, then you will have to see why, start by check ing fuel tap and lines, then undoing the drain screws at bottom of carbs to see if fuel is in float chamber
Pete
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Agree with Pete. Dry plugs imply a fuel problem. If it coughs on one or two cylinders most likely to be a problem around the carbs, if its totally dead then has to be something that affects fuel to all cylinders so likely to be blocked line or fuel tap problem. Check as Pete says
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Pretty much as above if your cranking it and its not firing and the plugs are not wet then there's no fuel, if check all the plugs to make sure it's the same for every one then is work back from there, check the float bowl by opening the big brass screw, if there's no fuel in there then it's either a fuel line, fuel tap, or an empty tank ;)
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Or the old blocked vent on the tank stopping the flow of fuel, for all the plugs to be dry it has to be on the common line, tank, tap, fuel pipes.
Cheers
Den
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Thanks for the info guys. Does the air box need to be fitted or will it run without it
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No it should start without the airbox
Pete
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Hi All
Tried to start it by spraying easy start into the carbs and notice that the vapour was not being sucked in as expected but being force out so I am thinking the valve timing could be out by 180 degree's. Any suggestions would be very much appreciated
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I'm not sure that could be the case without there being serious consequences of pistons meeting valves but you can check by taking the tappet covers off and looking at the ignition timing marks under the points cover.
When 1/4 are at TDC then 1 will have both valves closed and 4 is on the exhaust stroke and its exhaust valve is (I guess) all but closed.
Ok I'm assuming its all similar to the 400f and by 1/4 Honda mean 1 is firing (it could be 4)
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If the inlet valves are not seating on compression stroke then it will blow out the carb like you describe, check the tappet gaps, as well as the valve timing
Pete
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That 180deg and blowing back out the carbs sounds worrying if true.
I'd try to be certain of the cam position/timing as a priority......bent valve are a possibilty if wrong.
Did you put the cam in? and how was it timed if you did? i.e. what position was the crank and the marks on the end of the cam.