Topic: IT RUNS! (awful)

[e_b_c]

Thanks everyone for the starter help a few weeks ago. I'm back to killing the battery only when i want to.

But, on to the current issues with my 72 CB350F.

Air intake: All the original equipment is missing, and it seems to be that it will be less difficult to put on some pods and re-jet than to find the original parts. That is until i tried to find out what size jets i will need, and where to get them. Does anyone have any experience/advice on making this conversion on this particular bike? I know the previous owner and he seems to think that the jets are stock. I read somewhere that in general the jets need to be 25% larger to compensate for the pods. Is this fairly accurate?

(In the mean time i crammed the velocity stacks that were on the bike with air filter foam, just to get the bike to start consistantly, and it idles much better now.)

Plugs: 1 and 4 look dreamy! 2 and 3 look to be VERY carbon fouled. Is there a reason that this would happen? Could it be that I have put too much filter foam in the inside stacks? or are there other issues that i should be checking out?

[dusterdude]

could be an ignition issue since 2 and 3 run off the same coil

[dusterdude]

at least on the 750 it is

[Lumbee]

..sounds like not enough spark on 2/3...maybe swap 2/3 plug wires with 1/4 and see how it runs...

[e_b_c]

if i swap the plug wired and it is lack of spark, then i should expect that 1 and 4 will be fouled?

Sorry, i'm REALLY new at this. Thanks for the advice guys.

evan

[Caferacernoc]

If the ignition system turns out to be fine, then yes, maybe you have too much foam in the stacks that are fouling the plugs. Getting the jetting just right will be tricky. They don't make different sized jets for your bike. You will need to find tiny metric drill bits so you can drill out your main jet. Do it in increments until you find the right size.

[TwoTired]

Just thinking out loud here...

Let's see, you have 4, 90cc motors linked to a common crank. The carbs likely have pretty small carb venturis and jets where small changes in barometric pressure in and around the carbs have a large effect on jet flow.
The velocity stacks on the machine face rearward in the partial vacuum/ turbulent flow of air around motor and human legs.  Whereas, the stock airfilter draws air from a single intake under the seat to feed all carbs evenly.  And, now, we've stuffed an unknown, random, quantity and density of foam into 4 different carb stacks.  (I wonder if there is any screening to keep bits of foam from entering the cylinders?)

Yep, must be an ignition problem.  My this armchair is comfy...
 

Just curious...
Do we know when the bike had it's last thorough and complete tune-up?  You know, the timing, point gap, and tappets, etc.
Any compression test numbers?
What about carb balance?
Probably not important, though.

Cheers,

[e_b_c]

If the ignition system turns out to be fine, then yes, maybe you have too much foam in the stacks that are fouling the plugs. Getting the jetting just right will be tricky. They don't make different sized jets for your bike. You will need to find tiny metric drill bits so you can drill out your main jet. Do it in increments until you find the right size.

Arg! That is information that i'm glad i have, but not glad to hear. As the stacks filled with foam (and yes, a screen at either end) were only meant to be a stop-gap measure while i figure out the filter situation. It sounds like i will have to be looking for tiny metric drill bits regardless of the pods i end up with.

I'll consult good ole Clymer's about the ignition system and get back to you!

thanks for the information!
Evan

[e_b_c]

Just thinking out loud here...

Just curious...
Do we know when the bike had it's last thorough and complete tune-up?  You know, the timing, point gap, and tappets, etc.
Any compression test numbers?
What about carb balance?
Probably not important, though.

Cheers,

I'd venture to say that the last COMPLETE tune-up by a person who is able to look at a motorcycle and see how it all fits together was many moons ago.

I have however, set the point gap, timing, and a buddy of mine brought over his mercury-thingy (not thermometer) and balanced the carbs after they were rebuilt. ...the tappets haven't been touched in at least the 4 months that i've had the thing.

Your armchair may be comfy, but my dunce cap is starting to chafe. 

[Caferacernoc]

If you end up having to drill out the jets to get this bike to run, buy a wire guage drill bit set numbers 60 - 80. To run right with stacks, I would then drill out the pilot/idle jet one size bigger than stock. Then, moving to the main jet, go one size bigger at a time until it runs, fully warmed up with the choke off, without hesitation. You can find the drill bits online for about $20. And don't fret, without an airbox hooked up it's easy to remove the carbs to get at the jets. Just make sure you put them back on tight when testing because an air leak will throw off the whole thing.

[TwoTired]

The tappet adjustment can effect the valve timing, and therefore the breathing characteristics of the motor.  Carbs are the LAST thing to adjust on the engine.
For example, let's say that, hypothetically, the valves on cyls 2&3 didn't open as far as those on 1&4.  They wouldn't pull as much vacuum on the manometers while doing the carb sync.  But, you could adjust the carb slides to achieve equal vacuum across the 4 cylinders.  The carbs are sync'd to the cylinders, but the throttle positions aren't equal across all cylinders, and some of the cylinders are loafing and wasting fuel.  Then the next time you adust the valves, wham, your carbs are out of sync again.
This is why you do the carbs last.

When you get to the point where all your plugs indicate equal combustion conditions, you may well find the need to alter; idle air jet screw settings, pilot jets, needle clip position/taper, or main jet.

If you can't find a source of sized jets, changing what you have may be your only alternative.
Ordinary drill bits can leave a jagged, irregular hole where turbulence can effect the flow rate at different speeds.  It is better, in this case, to use jet reamers and carefully measure your changes with jet guages.

This link offers both:
http://www.cbperformance.com/catalog.asp?ProductID=525

Lastly, I wouldn't start making jetting changes, 'til I was absolutely, 100% certain that every single jet orifice (both air and fuel), and passageway in each of the carbs was spotlessly clean.