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Author Topic: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.  (Read 823 times)

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Offline Hayley

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Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« on: May 19, 2019, 04:09:55 PM »
Going through the starting of my build. Lots of spark with gas even being dumped into carb 2 and 3 but the 2 and 3 plug are dry with no smell of fuel on the plug. Cylinders 1 and 4 are firing. Timing is set properly as are the valves. No electric start connected so kick only. Engine is rebuilt with great compression. Carbs are rebuilt completely and ultra sonic cleaned. Does anyone have any suggestions as to why I'm these issues having issues?
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Online calj737

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Re: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« Reply #1 on: May 19, 2019, 06:01:21 PM »
Condensers are shot
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Offline Airborne 82nd

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Re: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« Reply #2 on: May 19, 2019, 08:13:52 PM »
Quote from: calj737 on May 19, 2019, 06:01:21 PM
Condensers are shot

To find out if this is it try swapping condensers to see if the problem moves to 1-3 before buying parts. I think that is the way they are paired but I could be wrong.
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Online calj737

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Re: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« Reply #3 on: May 19, 2019, 08:34:48 PM »
Quote from: Airborne 82nd on May 19, 2019, 08:13:52 PM
Quote from: calj737 on May 19, 2019, 06:01:21 PM
Condensers are shot

To find out if this is it try swapping condensers to see if the problem moves to 1-3 before buying parts. I think that is the way they are paired but I could be wrong.
You are incorrect. They are paired 1/4 & 2/3.
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"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline Hayley

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Re: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« Reply #4 on: May 20, 2019, 06:06:52 AM »
Hey thanks guy!
Brand new condensors in the unit.
All four plugs have spark.
Compression is tip top.
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Offline BenelliSEI

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Re: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« Reply #5 on: May 20, 2019, 07:00:06 AM »
Hayley...... have you tried opening the float bowl drain screws on #2/#3 carbs. Is there actually fuel there?
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Offline rotortiller

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Re: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« Reply #6 on: May 20, 2019, 09:00:14 AM »
Quote
Lots of spark with gas even being dumped into carb 2 and 3 but the 2 and 3 plug are dry



That would suggest to me those two cylinders have no vacuum to pull the mixture in. Bent valves, burnt valves, holed pistons come to mind. I would do a compression test.
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Online calj737

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Re: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« Reply #7 on: May 20, 2019, 12:00:31 PM »
More likely that the valves are incorrectly adjusted. Probably the 2/3 were adjusted on the compression stroke, not the vacuum stroke.
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"Of all tyrannies, a tyranny sincerely exercised for the good of it's victim may be the most oppressive. It may be better to live under robber barons than under omnipotent moral busybodies. The robber baron's cruelty may sometimes sleep, his cupidity may at some point be satiated, but those who torment us for our own good will torment us without end for they do so with the approval of their own conscience." - C.S. Lewis

Offline BenelliSEI

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Re: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« Reply #8 on: May 20, 2019, 03:10:13 PM »
+1 on checking valve clearances (assuming the carbs have fuel in them).
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Offline Dolomite

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Re: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« Reply #9 on: May 21, 2019, 10:10:31 AM »
I'm curious why so many people jumped to ignition issues when she stated it had spark, compression but no fuel. As others said with the bowl drain, I would start at the carbs and work forward.
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Offline Tracksnblades1

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Re: Halppp! 1978.cb750K Plug 2 and 3 dry. No start.
« Reply #10 on: May 21, 2019, 02:56:12 PM »
Quote from: Hayley on May 20, 2019, 06:06:52 AM
Hey thanks guy!
Brand new condensors in the unit.
All four plugs have spark.
Compression is tip top.

Can we read your post as a success.👀
Are you running on all 4,  too...?
👍

« Last Edit: May 21, 2019, 03:00:33 PM by Tracksnblades1 »
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