Just recently after adjusting my cables for full-turns left and right, I had to also adjust the carb again for idle and such.

The bike starts just fine with just a second or two of hitting the switch, *but*, when the bike is warm and I park it and come back and start it, if the engine is still even a little warm, I don't give any throttle and hit the start button and it always gives a loud (real loud) backfire-like sound from my pipes.

Is this a sign it's too lean or too rich? The idle is at 1000, and I've set the air ratio screw out 2 and 3/4 turns. I use the enrichener only with cold starts, and for only a short time in the summer months as necessary.

The bike seems to run just fine and at 70+ mph I'm getting 40 mpg and at 65 and slower I get 45 mpg. It's just the warm starts and seems to do it pretty much every time I start it if it's still even a little warm.

Any ideas what this might be?

 

Need more info. What carb and motor and any mods ????

A cold start can always handle more fuel, A Hot soak cannot.. Most likely a little rich...

 

Stock carb and motor, no mods at all. I'll turn the air mixture screw out a little more to lean it some more and see how that goes.

 

Out is richer on the mixture screw,
check for exhaust leaks, get a few feet of small hose, hold one end to your ear, pass the other end around the flange gaskets and muffler joints.

 

 

Oh, turning the screw out (from seated) is richer? Figures I'd screw that up, heh. Luckily two and a half turns out from seated is *supposed* to be a good place to start.

Anyway, I took the float bowl off the bottom of the carb to look at the jets on it and found that I had a 185 main jet in and a 45 idle/slow jet in. My book says stock is 170/42. I put a 175 in and ordering a 42.

Changing the jet helped, but I guess I made it too rich with the air mixture screw because it starts slow now, a real slow idle even if warm. I'll fiddle some more with idle speed and rich/lean and let everyone know what's happening.

I'll also check for exhaust leaks, but I think I did that several months ago and didn't find anything...won't hurt to check again though.

Thanks for the tips everyone.

 

Okay...seems nothing was working, so I got some new intake manifold gaskets (blue James Gaskets), new James Gasket carb seal to intake gasket, and tried all over from the beginning.

It seems that the cheap-o intake to head gaskets I had on it weren't sealing very well at all and I had a humongous intake leak of air. Adjusting the rich/lean screw was literally making no difference. I could screw it all the way to seated and the bike would idle like nothing was wrong, no change in the idle whatsoever. Same out, no change in idle.

Now, with the new gaskets, the rich/lean screw actually is working! Only needed to turn it out 1 3/4 to get the bike to idle right and then another 1/8 turn just for a little richer kick.

If one thing I would advise when doing this, have some kind of light grease or oil to coat the gaskets going on the heads, so that it makes adjusting the intake manifold *MUCH* easier up or down to fit the carb on correctly.

Goping to make tiny adjustments here and there during the next few days probably, and will let everyone know if things are working as they're supposed to be still.

 

Glad to hear.... Sometimes getting the right AFR can be a real pita. Lots of influences.... Enjoy...

 

After getting all that sorted out, I have in the past experienced the boom on a hot start. So what I did was just "bump" the start button to release compression and gasses, then try to start it. Helps eliminate the boom.

 

Surely that 'boom' has got to be something to do with too rich/too lean. It's trying to figure out which it is. That little bump will work, as I did it today also, but I don't like to do that to the starter.

I've got the air mixture screw at 2 turns out. I still got one boom today after a 40 mile ride, ate, then came out and it happened when startig the bike.

At the stoplight 2 minutes away from where I ate, I had to sit for several minutes to get my green, and as I twisted the throttle I got a small 'chuff' out of the carb. <sigh>

I figure that's just something to do with the idle (I hope), and I'll experiment with that up and down along with air mixture from 950 rpm's up to 1050 rpm's.

Good from this intake air leak fix - it seems I've got my mpg's back, at least so far on an 85 mile test ride. Looks like it will be going from an average of 45 mpg to maybe 48 or 49 mpg, and rode nice at 70 mph.

Bad from this intake air leak fix - now I'm back to the weak stock cam. I have the 'fix' for that waiting too, I just need the scratch for some new lifters and I'll throw the new cam, adjustable pushrods, cam bearing, lifters (when I get them) in and see if that gets me some more power down the road and for passing.