CB750 Dohc Misfire

[pateli]

 I am still having problems with my 1982 CB. I have cleaned the Carbs,Jetted 68/102, pilot 1.5 turns out.New Air filter (standard)Re set valve timing it was 2 teeth out.Valve clearances ok.Ign timing ok,New Plugs D8EA and new ign leads.Coils Swapped Earlier.It starts ok but will not idle and there is spitting from L/h Ex with odd back fire.Which I Traced to No 1 cyl ,I removed No2 Lead and still spitting replaced it and removed No1 lead spitting stopped. Comp No1 cyl 130 psi any ideas where i go from here,am I chaseing Fuel or Ign.

[Re-run]

Well if it is electrical and i not affecting #4, then it would be wire, plug cap, and plug. So start with the easiest. Swap the #1 plug with the #2 plug. If the spitting stops and moves to #2, then bad plug. I would also test the plug cap. I am assuming the dohc uses resistor caps like the sohc does. If you set you multimeter to ohms and put a probe in each end, you should get about 5K. If you get nothing or it is 10K or higher, new plug cap. When you have the cap off the wire, clip 1/4 inch off the wire and screw the cap back on. See if this helps. If not, then it is most likely fuel related but visually inspect the rest of the wire for cracks.

Issues like this when they are fuel related end up being plugged idle jets. In the write up section is a small entry about cleaning the dohc carbs, you should check it out.

[pateli]

Thanks for taking the time I have tried 2 different sets of leads and replaced plugs still the same I screwed the Pilot in 1/2 turn and spitting is less But I have Lumpy running and idle wont go below 3000rpm any lower and it cuts out
 

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Date: Fri, 4 Jun 2010 06:04:31 -0700
From: [hidden email]
To: [hidden email]
Subject: Re: CB750 Dohc Misfire

Well if it is electrical and i not affecting #4, then it would be wire, plug cap, and plug. So start with the easiest. Swap the #1 plug with the #2 plug. If the spitting stops and moves to #2, then bad plug. I would also test the plug cap. I am assuming the dohc uses resistor caps like the sohc does. If you set you multimeter to ohms and put a probe in each end, you should get about 5K. If you get nothing or it is 10K or higher, new plug cap. When you have the cap off the wire, clip 1/4 inch off the wire and screw the cap back on. See if this helps. If not, then it is most likely fuel related but visually inspect the rest of the wire for cracks.

Issues like this when they are fuel related end up being plugged idle jets. In the write up section is a small entry about cleaning the dohc carbs, you should check it out.

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