Cylinders 1 and 4 not running

If it's broken or just needs tweaked

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Rileykehler
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Joined: Wed Sep 20, 2017 11:54 am

Cylinders 1 and 4 not running

Postby Rileykehler » Thu Sep 21, 2017 10:26 am

Hey guys, I have a 80' Cb650C. Alittle bit of backstory is I bought it, got it running good, saftied it, then stripped it down to restore it. Rebuilt the top end, replaced spark plugs, coils, wires, and boots, rebuild the carbs, and cleaned up everything else. Starts up great and can drive it. but its only running on the inner two. I reverted back to all the origonal electronics i had the bike running with, double and triple checked engine timing, and sprayed fuel into the engine without carbs (to eliminate it being a fuel issue. I get strong spark on all 4 plugs, but the outer two still looks brand new even though the bike has ran plenty. when i spray fuel into the engine directily i can get it to fire up for a moment on the inner two but nothing on the outer two. my Compression on all 4 is 130, so that shouldnt be an issue. So to recap ive replaced and checked any fuel, electrical, timing, or compression issue i can think of and i still get nothing. Anybody have any other ideas of stuff i could try?

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GeorgeSweety
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Re: Cylinders 1 and 4 not running

Postby GeorgeSweety » Thu Sep 21, 2017 10:33 am

Hi Riley, after you have started the bike then switched off have you pulled plugs 1 and 4 to check if they are wet with fuel? any signs that fuel is getting into the cylinder? What type of carbs are on your bike, slide or CV's. When you cleaned them did you remove the idle jets to get them properly clean? Please don't think I'm doubting your abilities, I just have to ask.

Rileykehler
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Re: Cylinders 1 and 4 not running

Postby Rileykehler » Thu Sep 21, 2017 2:36 pm

Hey George, I have the slide carbs, and yes, i have checked the pilot and main jets, and im alttle unsure about fuel. I'm not super convinced they are getting fuel by the feel of them. but they do smell like fuel and ive sprayed fuel directly into the engine. So i cant see any reason they wouldnt be getting fuel.

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GeorgeSweety
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Re: Cylinders 1 and 4 not running

Postby GeorgeSweety » Fri Sep 22, 2017 1:21 am

Hi Riley, for a cylinder to fire you need spark, fuel and compression. If you have a good spark on all plugs, compression of 130 on all cylinders and it still won't run on all four, leads me to suspect that the fuel isn't getting through.
You said that you, "sprayed fuel into the engine without carbs (to eliminate it being a fuel issue." . I'm not really understanding how you think that spraying fuel into the engine without the carbs can eliminate a fuel issue. If fuel isn't getting through your carbs then it won't get into your engine, by leaving the carbs out of your test isn't actually testing the carbs.
On all of the PD 50 slide carbs that I have worked on the idle jet (slow jet, whatever you call it) is the pressed in type. Have you physically pulled these jets out of the float bowl body with a pair of pliers to clean them ? Trust me, you will not have gotten them clean unless you have removed them to clean them. Before I knew about how crucial these idle jets are to smooth running, I stripped a bank of these carbs, ultrasonic cleaned them, rebuilt them, stripped them, cleaned them etc....etc. you get the idea? Only when I pulled the idle jets did I see how blocked with crud they still were, ultrasonic cleaning will not shift the crud from these jets if you leave them in the carb body.

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Folsoml
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Re: Cylinders 1 and 4 not running

Postby Folsoml » Fri Sep 22, 2017 4:53 am

Sometimes I have to clean carbs two or three times to get them REALLY clean--and I completely disassemble them.
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Rileykehler
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Re: Cylinders 1 and 4 not running

Postby Rileykehler » Fri Sep 22, 2017 8:07 pm

The reason I tried spraying fuel is to ensure the engine was getting fuel. So by spring it it guaranteed it was. So when it still didn't work I figured fuel wasn't the issue, because the engine can't get fuel any better that me spraying it straight in. I did the same thing on the inner two and unlikely the outer two the inner two started.

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GeorgeSweety
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Re: Cylinders 1 and 4 not running

Postby GeorgeSweety » Sat Sep 23, 2017 12:24 am

Hi Riley, this is what you need to remove and clean if you haven't already done so.
https://s20.postimg.org/m2yynqisd/sdc12800.jpg

Rileykehler
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Re: Cylinders 1 and 4 not running

Postby Rileykehler » Sat Sep 23, 2017 4:26 pm

My pilots are brand new and I've inspected them. But thanks for trying! All the suggestions are logical causes. I've just tried everything most people would think of

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GeorgeSweety
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Re: Cylinders 1 and 4 not running

Postby GeorgeSweety » Sun Sep 24, 2017 1:52 am

Hi Riley, it is just a process of elimination, we will get there. Ok, so you have new pilot jets, how did you clean the carbs? Did you replace all of the o-rings, gaskets, air cut off valves and accelerator diaphragm? I'm not saying that you should have, unless of course they needed replacing, I'm trying to build a picture in my head of what has been done so that we can eliminate each problem.
Here are a couple of things for you to think about, one time when I rebuilt my carbs and installed them on the bike I couldn't get number 1 cylinder to fire. After much head scratching I removed the air cut off valve cover on the side of carb number 1 and found that the small o-ring was missing inside, I'm still not sure whether I plain forgot to put it in when I rebuilt the carb or if it just fell out when I was holding the cover down against the spring, easy to check on number 1 carb but not on 4 unless you part the rack. Replacing that o-ring made the bike run perfectly on all four.
I read somewhere (not sure if it was on here) about a guy with a very similar problem, he'd checked everything and it was all looking good but his number 4 cylinder just would not fire. It turned out that when he had installed his outer valve cover he had forgotten to put the cup shaped washer under the rear bolt, causing the bolt to sit lower than it should, interfering with the inlet valve under the cover. Of course every time he removed his valve cover to re-check his valve, he had removed the bolt that was causing his problem, each time he refit the valve cover he was re-installing the problem.

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Folsoml
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Re: Cylinders 1 and 4 not running

Postby Folsoml » Sun Sep 24, 2017 7:20 am

He has the 1980 Custom model. That has the PD51A carb bank on it. It has no air cutoffs or accelerator pump.

I'm now curious about your carbs--they have air cutoffs? If so, is that stock for the 650 Nighthawk in the UK? The US versions use a VB44C carb bank that does not have them.
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GeorgeSweety
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Re: Cylinders 1 and 4 not running

Postby GeorgeSweety » Sun Sep 24, 2017 8:00 am

Hi Folsoml, the carbs I'm referring to are on my US import 1980 CB650C Custom which had PD50B carbs from stock but I changed them for a set of PD50A's from a UK bike as one of the PD50B's had a broken casting and getting spares in the UK is very hard. Both PD50A's and B's have got the air cut off's and accelerator pumps.
My US import 1982 650 SOHC Nighthawk has VB44C carbs without air cut off's but does have the accelerator pump. Sorry for any confusion :oops:

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GeorgeSweety
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Location: UK.

Re: Cylinders 1 and 4 not running

Postby GeorgeSweety » Mon Sep 25, 2017 2:03 am

Hi Riley, please can you confirm which type of carbs you have? You said they were slide carbs but can you tell us the number stamped on the side just above the float bowls. This is why as much info as possible is good for trying to eliminate problems when we can't actually see the bike :D If you don't have air cut off's on your carbs then it is one less thing to cause problems.


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