Topic: difficult cold starts/ fine tuning the 718

[paulages]

Interesting that you're tuning for proper a/f ratio at idle. I've understood that the non-pumper carbs like to idle quite rich so they don't stumble so much on throttle.

i'm not- i've tuned for best off-idle response, which is a hair richer than the best idle position.

[paulages]

TT- this is the closest picture i could find with the carbs installed:



my idea for the airbox is basically to build an aluminum box to surround velocity stacks, much like the cb750 airbox, but with an air chamber/filter in the rear triangle like the 550 to allow maximum air flow. that area is wide open, so i can make it as large as i want to allow lots of stable air. constructing it so that i can get the carbs on and off with ease seems the real challenge...

[TwoTired]

Hard to picture where the legs are when riding.  Those are going to effect air flow, too, of course.
Not too hard to see where the inner carb inlets might get higher pressure than the outers, though.
Given any thought to adapting the stock air plenum? (I know, heresy...)

I suppose none of this has any relevance to start up issues, really.  If your choke plates don't give enough enrichment, there's really no point in making the idle circuits richer just for cold start.

Start procedure suggestion:
With the choke plates closed give'r wide open throttle for a kick or two after you know the carb bowls are filled.  This should draw extra fuel from the mains needle jet to flood the cylinders.  Then kick with about 1/8 or less throttle.
You could also do a shop test with the coils turned off.  Close choke, kick four or five times with WOT and then pull plugs to see effect.  They should be wet with gas.   If not, you have to find out why the choke is ineffective.

[paulages]

Hard to picture where the legs are when riding.  Those are going to effect air flow, too, of course.
Not too hard to see where the inner carb inlets might get higher pressure than the outers, though.
Given any thought to adapting the stock air plenum? (I know, heresy...)

I suppose none of this has any relevance to start up issues, really.  If your choke plates don't give enough enrichment, there's really no point in making the idle circuits richer just for cold start.

Start procedure suggestion:
With the choke plates closed give'r wide open throttle for a kick or two after you know the carb bowls are filled.  This should draw extra fuel from the mains needle jet to flood the cylinders.  Then kick with about 1/8 or less throttle.
You could also do a shop test with the coils turned off.  Close choke, kick four or five times with WOT and then pull plugs to see effect.  They should be wet with gas.   If not, you have to find out why the choke is ineffective.

my knees are about two inches behind the tails of the fairing when riding. i don't believe the stock plenum will work with the 750 carbs, but maybe i could open the holes up to accept the 750 rubbers... that might work. i could then build a larger airbox to allow high flow. hmm... not a bad idea, lloyd.

my usual startup procedure us actually similar to what you describe. i learned it from having a triumph with no choke... on the honda i use full choke, kick the engine through a few times with WOT, and then reduce choke and kick with ignition on.

i'll do more tests as soon as i can get some clean D7EAs.

[paulages]

dragging out an old thread here...

finally got time to to some diagnostic on the bike. using a large battery (BMW i think) to ensure adequate voltage, i tested for spark again, only to find strange erratic spark. i decided to recheck the timing on the dyna 2000 pickup, only to find that one of the pickups had lost a screw and was hanging by the other, out of position. the pickup was close enough to allow occasional firing, but it was obvious this was my main problem. so much for "set and forget" with electronic ignition... 

re-timed that side and it fired up fairly easily on the 1.5 AH battery i run in my points-ignition BSA. on to fine tuning...

[turboguzzi]

now go stand in the corner!

[paulages]

now go stand in the corner!

seriously.. but wasn't that stupidity punishment enough?