Fuel, Spark and Compression - But No Start!

[ericheath]

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Just clarifying: one coil fires cylinders 1 and 2: the other coil fires 3 and 4. Both 1 and 2 fire simultaneously. One cylinder “fires” because it’s on the compression stroke, the other doesn’t because it’s on the exhaust. The next time the valves are opposite so the other cylinder fires.

Having spark is a good thing, but it has to be at the right time. I’m wondering if your timing could be off.

[Dr. Frankenstein]

Actually, I was able to change over to the new 5-ohm coils and the stock air filter housing went in just fine! And the bike runs hot on all four cylinders now, and sounds terrific, BUT...! (There's always a 'But' in there somewhere, isn't there...) it starts right up and idles at 1,000 but sounds 'clunky', like the tranny is thrashing....I have yet to put the timing wheel on it, but could that be it, the timing?

[ericheath]

Carbs out of sync cause the timing chain to rattle. A sync usually does it.

[gltriker]

and Increase the hot engine idle speed to 1100-ish rpm when the synch is finished.

[redglbx]

As Eric said, carb sync OR ignition timing between the cylinder pairs will cause the primary chain to rattle or clunk so check both. Also as Cliff mentioned set your idle to around 1100rpm as things will just be happier. But,,, (there it is again) on my 76 once I got everything right, carbs setup right with a good sync and I did a careful dynamic timing setup my bike would easily idle down to 400rpm cleanly and quietly BUT I also run it at 1100rpm because it keeps better oil pump flow along with other things, it’s just better.

[Dr. Frankenstein]

Okay, so I went out today and tried to synch the carbs; I got them all to within 5 Hg on my Carbtune II, set the idle at 1100 and it sounded and responded great! She was running fine on the table for, like, half an hour while I dialed the carbs in. Okay, Cool - so I decide to take her out for a test run, back her out of the garage, hit the starter and CrankCrankCrankCrank - nothing.

CrankCrankCrankCrank...she starts up; I put her in gear, roll on the throttle and she dies, immediately

CrankCrankCrankCrank - BOOM! - a backfire out the back end. Now it doesn't look as though she's getting gas...WTF??

I take it back into the garage, put her up on the centerstand - and she fires up! Revs great! I back her back out to the garage apron, and she has about a gallon and a half of gas in her at this point, so I add a bit more. Positive fuel flow to and from the pump...she fires up, I put some throttle to her and she dies. WTF??

CrankCrankCrankCrank...Nothing. I roll her back into the garage, and contemplate rolling her back out and using what little gasoline I have left to burn her down to the axles. But I thought I would ask this Esteemed Forum as to what it could be first.

I'm thinkin' floats, maybe - or needle jet? Or did I screw up the sync? No idea...

[ericheath]

It is very easy to forget to tighten the clamps on the rubber manifolds. I’m about 50-50 on remembering them. If loose, they will cause hit and miss performance. There’s your first check.

Tighten them again when fully warmed up.

[gltriker]

It is very easy to forget to tighten the clamps on the rubber manifolds. I’m about 50-50 on remembering them. If loose, they will cause hit and miss performance. There’s your first check.

Tighten them again when fully warmed up.

I Heartily agree with Eric's recommendation to , when hot, re-tighten the intake manifolds' clamps.

You may find it makes a very surprising change in the engine's behavior.
A repeat idle speed synchronization session may be prudent too if the clamps weren't tight.

[ericheath]

Plus one on the re-synch.