Choke causes backfire, but my bike is addicted at start..

[Anonymous]

Whenever I start my bike from cold I need to engage my choke to about 1/2-3/4 to keep the bike running... after a short while she warms up, or seems to, and I'm able to start dropping it. I usually get it down to about 1/4 (idling around 1k-1.5k) and it starts acting as though the timing is off, backfiring, stalling (if I drop the choke too far, or I don't raise it now and again). At this point it could idle all day... like $hit... but I couldn't possibly ride it as it boggs to a stall with any throttle. I can give it juice when the choke is further up (back to about 1/2+), and sometimes quickly pound the choke off and let the idle fall to normally when I release the throttle and the problems are gone... else after I'm sure the bike is fully warm I drop the choke, the bike dies, and I restart it w/o choke and it runs great..

I have checked the timing and point gaps, they were off, but better now.. the plugs *last time I checked before the timing change* were a bit sooty.. but that's almost useless info without proper timing..

Short recap (because I'm nearly unintelligible):
1. Start with choke at 3/4
2. Bike warms and RPMs naturally rise well above normal idle
3. Drop choke to 1/4-1/3 - RPMs now around 1.5k
4. Bike is now backfiring, not too loudly, like mad... sounds like timing, I cannot give the bike any throttle w/o increasing choke first..
5. I'm stuck, I cannot run w/o choke unless I kill the bike and restart... hoping it is now warm enough to run w/o choke

The bike runs well aside from this... though I think the exahaust may smell a tad off... no smoke though.

[earlfor]

I've recently been experimenting with my points ign 79 750E due to some of the same characteristics, though not as severe as yours seem to be.
Best results have been with the points gaps set to 12 thou. I found that as little as 1/2 degree difference in timing synchronization between the 1,4 points and the 2,3 points made an obvious difference in how the engine idled and started. If you havent already, I would check input voltage to the coils also. One coil getting more volts than the other will play havoc with startup and idle. I have my fuel pilot screw set to 1 1/4 out and the airscrew at 1 3/4 out. Stock intake and exhaust.

Earl

[Anonymous]

I have a simular problem with mine when I start from cold. I can start mine with full choke, but it runs very ruff, as I lower the choke the rpms start to die and continues to run ruff and stalls out, if I try to give it throttle it boggs and dies out. However, once its warmed up it runs and idles perfectly.
Here's the work-around I do now:
Start with full choke, let it run for 30 secs or so, give it just a smidgen of throttle so the RPMS rise to about 2500 -3000 rpms, hold it steady at this and start to slowly lower the choke to the off position, at the same time keeping the RPMS around 2500 - 3000. Once the choke is fully off, I can let off on the throttle and it idles normaly around 1100 - 1200 RPMs and I can rev it normaly without it bogging out.
I have a feeling its somthing to do with the idle mixture screw adjusment on the carbs when its cold. When I put it at that 2500 - 3000 RPMs it isnt using the idle mixture jet. When its warmed up then then everything is in "tune" to use the idle mixture properly. This is just my guess though...

P.S. mine also runs sooty when the choke is on, but that stops when its warmed up and choke is off.

[earlfor]

1979 and earlier models have VM mechaincal slide carbs. VM carbs do not have mixture screws. Only the CV carbs have them. VM's have a fuel pilot screw and an air screw. The two adjusted in conjunction regulate mixture.

Earl

[quote="gammer"]
I have a feeling its somthing to do with the idle mixture screw adjusment on the carbs when its cold.

[Anonymous]

I'll try to check my timing tonight after work, see if maybe it's slipped out of alignment... certainly not impossible, especially if I forgot to tighten the screws or something...

[Anonymous]

<1979 and earlier models have VM mechaincal slide carbs. VM carbs do not have mixture screws. Only the CV carbs have them. VM's have a fuel pilot screw and an air screw. The two adjusted in conjunction regulate mixture.

Earl>


Sorry, I must mean air screw? When sitting on the bike, its the screw on the left side on carb 1 and 2 and the screw on the right side on carb 3 and 4.

[earlfor]

When setting the static timing of the points with a continuity light, I strive to be as anal retentive as possible. :-) :-) Getting it as close to perfect as you can will pay off in the running.

Earl

I'll try to check my timing tonight after work, see if maybe it's slipped out of alignment... certainly not impossible, especially if I forgot to tighten the screws or something...

[earlfor]

You're right. Thats the air screw. The fuel pilot screw is the one that is vertical and sticking down and underneath the front of the float bowl.

Earl

Sorry, I must mean air screw? When sitting on the bike, its the screw on the left side on carb 1 and 2 and the screw on the right side on carb 3 and 4.

[SqDancerLynn1]

I use a timing light on mine NO guessing!!

[earlfor]

But but Lynn, I'm not guessing when using a continuity light. I am certain when I'm wrong. LOL

Earl

I use a timing light on mine NO guessing!!

[Anonymous]

Didn't get to it today... little stressed because I think, after this 3 week work related injury (that I am now back working after), I am soon to be jobless. Yay for loving corperations who look to make an example of any "problems"..

I'm afraid I will be soon to use this line as my friendly employer has a habit of conducting illeagle "interviews":

"I refuse to submit to this interrogation because I fear that I will suffer severe discipline or termination of my employment and I demand my right to have union representation present on my behalf before this proceeding continues and if my demand is not acknowledged, then I refuse to participate in this process."

My union has distributed countless copies of a card with that printed on it to counter this new Kroger tactic.. YAY!