Author Topic: Weber + ARD Mag setup no start issue  (Read 5050 times)

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Offline valt

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Re: Weber + ARD Mag setup no start issue
« Reply #25 on: June 25, 2020, 07:01:36 am »
Just throwing this in the mix, as I experienced it in my race engine: have you checked that the valves didn't hit the piston and then bend a little when you were using cycle-x camshaft? Probably not since you have checked compression...

I remember my engine was behaving exactly like yours when this happened to me, although I bent a couple of valves after missing a gear and consequently the engine revved past the red line.

If I were in you I would probably double-check cam timing anyway...

Hmmmm I hadn't considered this. As far as the cam timing I have had the cam in and out a half dozen times so far. Plus I had several other people that are familiar with 750s confirm my cam timing. I'm going to pull the head this week and make sure the valves aren't bent in some way.

At least I have several other good heads with valves so I can always swap valves in if that ends up being the case.
« Last Edit: June 25, 2020, 07:13:18 am by valt »

Offline scottly

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Re: Weber + ARD Mag setup no start issue
« Reply #26 on: June 25, 2020, 08:52:27 am »
Just do another compression test; if valves are bent the test will show it.
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Offline valt

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Re: Weber + ARD Mag setup no start issue
« Reply #27 on: June 25, 2020, 08:54:59 am »
I have done multiple compression tests after installing the cyclex cam and they all showed good compression. All cylinders are at least 170psi.

Offline scottly

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Re: Weber + ARD Mag setup no start issue
« Reply #28 on: June 25, 2020, 08:59:30 am »
Then valves aren't bent...
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Offline 754

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Re: Weber + ARD Mag setup no start issue
« Reply #29 on: June 25, 2020, 09:34:05 am »
Well something has slipped, changed, broke or moved, just have to find what.  Or something between the 2 motors is missing ?
 When you said you had checked the accelerator pumps , you did this how ? On mine , it will shoot a stream of gas about 5 feet or more out of the manifold, mine may be rich.
 Mag can be checked for spark with grounded plug, correct?
 Like I said, when my Webers were on several motors  (no magneto)   turn my throttle 1/2 turn , it will  light and run a few seconds every time I kick it.
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Offline scottly

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Re: Weber + ARD Mag setup no start issue
« Reply #30 on: June 25, 2020, 10:41:58 pm »
The way I verify timing is there is a mark on the mag body and a mark on the wheel that drives the mag. That mark indicates when the mag fires #1, so I pull the mag and put on a stock advance mechanism and move the motor to where cylinder #1 is firing at full advance. Then make sure when I put the mag on the two marks line up.

You need to verify that when the two marks line up is when the points open, using the method I mentioned with the ohm meter.
As far as the carbs, if I were to pump the throttles as much as you do in the videos, it would flood the bike; one or two twists is usually enough fuel for a cold start.
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Offline scottly

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Re: Weber + ARD Mag setup no start issue
« Reply #31 on: June 25, 2020, 11:05:14 pm »
I completely rebuilt those carburetors and I am using jetting that was recommended by Kiyo.
What jetting was recommended by Kiyo? Main jets, pilot jets, choke size, aux choke emulsion tubes, air jets, etc.
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Offline valt

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Re: Weber + ARD Mag setup no start issue
« Reply #32 on: June 26, 2020, 12:07:18 pm »
The way I verify timing is there is a mark on the mag body and a mark on the wheel that drives the mag. That mark indicates when the mag fires #1, so I pull the mag and put on a stock advance mechanism and move the motor to where cylinder #1 is firing at full advance. Then make sure when I put the mag on the two marks line up.

You need to verify that when the two marks line up is when the points open, using the method I mentioned with the ohm meter.
As far as the carbs, if I were to pump the throttles as much as you do in the videos, it would flood the bike; one or two twists is usually enough fuel for a cold start.

I should note that is how the marks on the mag were made. So the two marks indicate when cylinder #1 is firing on the mag.

In an answer to your other question this is per Kiyo:

"here is set-up for dual weber cb750.

wiseco 836cc 10.25:1
stock camshaft
ARD magneto fixed advance

weber DCOE40 dual
idle jet  45F9
main jet #130
emulsion tube F16

lowerend is always little rich but ok to ride,
mid range to topend is awesome,

good luck!!

Kiyo"

Which seemed to be in line what I saw other people mentioning they were running.

Offline Tintop

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Re: Weber + ARD Mag setup no start issue
« Reply #33 on: June 26, 2020, 05:19:04 pm »
I'm with 754 on this, something isn't 'in spec' inside that motor (given you can move the ignition & carburation over to another & they work).
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Offline 754

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Re: Weber + ARD Mag setup no start issue
« Reply #34 on: June 26, 2020, 05:24:18 pm »
Not sure where the change is but something is not the same.. obvious , but can't tell what .
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline BPellerine

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Re: Weber + ARD Mag setup no start issue
« Reply #35 on: June 26, 2020, 06:39:13 pm »
I run webers and an ard mag,I too used an old auto advance unit to bring the piston to full advance,then made sure the rotor was pointing at no 1,then with the marks lined up put both pulleys at the same time,started up after 4 or 5 kicks,my cap has no 1 marked on it so no guess work,seeing how you get a diff response when you change the wires around,I would guess something is not timed right,although you say it has been checked many times,bill
1978 CB 750K ard and webers
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Offline scottly

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Re: Weber + ARD Mag setup no start issue
« Reply #36 on: June 26, 2020, 06:44:52 pm »
What do the spark plugs look like?
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Offline valt

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Re: Weber + ARD Mag setup no start issue
« Reply #37 on: June 26, 2020, 06:51:58 pm »
What do the spark plugs look like?

Wet with fuel on all 4.

Offline scottly

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Re: Weber + ARD Mag setup no start issue
« Reply #38 on: June 26, 2020, 07:59:04 pm »
Now we are getting somewhere. Wet and black, or wet and white on the porcelain?
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Offline valt

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Re: Weber + ARD Mag setup no start issue
« Reply #39 on: June 26, 2020, 08:25:13 pm »
Now we are getting somewhere. Wet and black, or wet and white on the porcelain?

Definitely wet and white since it barely fires. Though I have verified spark on every cylinder.

Offline scottly

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Re: Weber + ARD Mag setup no start issue
« Reply #40 on: June 26, 2020, 08:36:45 pm »
It's probably flooded from too much accelerator pump use? Get the cylinders dried out by cranking the motor with the plugs out. What is the plug gap? I seem to recall mags that used a smaller than stock gap, because at low speeds like when kick starting the mags don't make as much spark.
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Offline valt

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Re: Weber + ARD Mag setup no start issue
« Reply #41 on: June 26, 2020, 09:13:55 pm »
It's probably flooded from too much accelerator pump use? Get the cylinders dried out by cranking the motor with the plugs out. What is the plug gap? I seem to recall mags that used a smaller than stock gap, because at low speeds like when kick starting the mags don't make as much spark.

I have done this multiple times and replaced the plugs. I can ask manley but the spark should jump a quarter of inch as that is what their bench test is.

Offline scottly

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Re: Weber + ARD Mag setup no start issue
« Reply #42 on: June 26, 2020, 09:19:08 pm »
At what RPM?
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Offline valt

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Re: Weber + ARD Mag setup no start issue
« Reply #43 on: June 26, 2020, 10:00:20 pm »
At what RPM?

I was told by manley that if you turn the mag over it should produce a spark that can jump a quarter inch. The big bore motor certainly has more compression the the stock motor. But both motors produce a good blue spark and even cranking speeds.

Offline scottly

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Re: Weber + ARD Mag setup no start issue
« Reply #44 on: June 26, 2020, 10:17:43 pm »

 not knowing how the motor wants to start.
Too much use of the accelerator pumps, flooding the engine...
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Offline BPellerine

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Re: Weber + ARD Mag setup no start issue
« Reply #45 on: June 27, 2020, 04:58:59 am »
just a thought,how is your lash set on the cam,could they be too tight?the mags do give a healthy spark,I too found out you can flood them easily
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Offline turboguzzi

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Re: Weber + ARD Mag setup no start issue
« Reply #46 on: June 27, 2020, 05:16:34 am »
admittedly i have experience only with lucas magnetos on british bikes, so cant say anything on an ARD other that they also spark when flicking the rotor with your hand

but one suggestion: sometimes you need to rule out sources to find a fault. would it be too humbling to mount back the points and coils, feed them with 12V and see if bike starts well?

will give you a much better idea where the problem might be.

my 2 cents

Offline valt

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Re: Weber + ARD Mag setup no start issue
« Reply #47 on: June 27, 2020, 06:40:38 pm »
just a thought,how is your lash set on the cam,could they be too tight?the mags do give a healthy spark,I too found out you can flood them easily

It has a stock cam with new valve springs, the lash is set to stock settings so .002" intake and .003" exhaust. Its entirely possible that I am flooding it, but I have tried starting it without any throttle at all and I get nothing. The only time I get anything is when I pump the throttle like you see in the video.

In response to Turboguzzi:

I don't have easy access to a full points setup with coils and stock plug boots. I have verified spark on both the big bore motor and other motors I have put the mag on. So I am confident spark is not the problem, that being said you certainly have a point. It could still be a timing issue, which a stock points setup would eliminate since I would be able to set it without full advance and be confident in my timing settings.

I really appreciate everyones input here, I am very confused as I have checked and double checked everything I can think of.

Offline scottly

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Re: Weber + ARD Mag setup no start issue
« Reply #48 on: June 27, 2020, 06:53:05 pm »
How is the pulley attached to the crankshaft? That was the issue Jim F fought with, IIRC.
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Offline valt

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Re: Weber + ARD Mag setup no start issue
« Reply #49 on: June 27, 2020, 07:01:38 pm »
How is the pulley attached to the crankshaft? That was the issue Jim F fought with, IIRC.

It interfaces with the crankshaft the same way the stock advance mechanism does. The pull is held onto the lower shaft with two set screws.