Stoppin' tha Poppin'

Wish you had posted the weekend here as an Event earlier - it's 5-7 Oct.  Birmingham is not too far from me (FT Walton Beach, FL).  Let me check the weather!

https://alabama.travel/upcomin...r-vintage-festival-3

https://www.barbermuseum.org/e...er-vintage-festival/

WOLFGANG posted:

Wish you had posted the weekend here as an Event earlier - it's 5-7 Oct.  Birmingham is not too far from me (FT Walton Beach, FL).  Let me check the weather!

 

Woflgang,

Come on! The weather's going to be great.

I'm taking two bikes to sell. 1950 Moto Guzzi Airone. Previous owner was Milan Telephone & Telegraph and 1999 BMW R1100S.

any backfiring ive encountered has been a burnt exhaust valve:{

Popping can be lean idle mix setting. Or exhaust leak, or intake leak. Not usually accelerator pump. I usually get the pumps set rich enough for it to run right, then lean it until it stumbles. Richen it just enough to remove the stumble.

No kidding

A burnt exhaust valve or loose head will show up in a compression test.  I'd pursue the intake leaks - using starting fluid.

Guess I didn't make myself clear...It was UNBURNED GAS

Better change the oil then. Probably high gasoline content if it was that bad. Plugs too.

Can't figure out why you asked the question if you already have all the answers.

I must be slow this evening.  I didn’t read that Jim asked a question.  He just posted to show others a problem and his competent fix.  

And you’re right, Jim.....There is precious little written info on how to adjust the accelerator pump stroke, other than to stick a small vial down the carb throat to measure the amount of gas squirted out of the accelerator jet on a throttle stroke.  Whether that is more or less versus the exposed threads on the pump actuator is never mentioned.

Thanks for the info, Jim.  I’m sure some others on here will have the same problem and might stumble upon your post.  

Now get out there and drive it!

I think he was just sharing his experience so if others have the same problem they could look here for a possible solution. And if we’re being snippy, he didn’t ask any questions. He merely posted his findings. 

DannyP posted:

Better change the oil then. Probably high gasoline content if it was that bad. Plugs too.

Can't figure out why you asked the question if you already have all the answers.

DannyP posted:

Better change the oil then. Probably high gasoline content if it was that bad. Plugs too.

Can't figure out why you asked the question if you already have all the answers.

Danny. I thought you had all the answers! I asked no question.

Your help, as always, is very much appreciated when I do.

Jim Gilbert - Madison, Mississippi posted:

There is very little information I could find on the adjustment of the accelerator pumps. You would think that this would be important enough that it would be addressed...maybe it is somewhere.

My mistake. I thought the above was kind of a question.

I tried adjusting my pumps to .3cc or .4cc per stroke. This didn't work for me it was WAY too much. I think I read somewhere that that was the recommended setting for this. I did the whole vial thing under the jet. I got them dead even side to side, but that much just about killed the motor.

Turning the nut inward, exposing more threads on the end of the accel pump rod, gives more throw and more squirt. 

Good luck with your adjustments. 

Which carbs do you have, Jim? Mine are Dell 40's, and I'm still getting a wee bit of stumbling off idle, even after I installed a new Pertronix distributor with vacuum advance. I suspect the accelerator pumps may need to be a tad richer.

As you turn the accelerator pump actuator nuts in, the pulse volume increases.  Try turning them in a turn or two and see what happens.  You can always return them to where they were.  If that doesn’t work, a slightly larger accelerator pump jet might work (available from CB Performance ) and you’ll then have to tune them in again.  It’s an iterative process........

For what it's worth, the only WEBER accel pump jets available now are zero bypass. The older ones were labelled "50" meaning 50 percent bypass. That means half the fuel for each accelerator pump "shot" is bypassed back to the float well. These jets are specified in the CB Weber book for 2 liter or so VW motors with dual Webers.

I tried to use the newer zero bypass jets, but couldn't get them to work properly. They either were too much or not nearly enough. I couldn't get them to a happy medium that worked for my engine. So back to the "50s" and easy to dial in. There is a small amount of info on all this in CB's Weber carb book.

There is a check ball in the accelerator pump valve/jet. If this is gunked up it may never close fully or open. Ultrasonic cleaning works for me on this.

Jim Gilbert - Madison, Mississippi posted:

I've had a difficulty with some backfiring on my Speedster since I returned from Florida in July. On the trip home the car ran fine no popping at all. After returning home the popping developed quickly. I was fairly sure that the carburetors were set up too rich and re-balanced and adjusted them after "Turning the carburetors around" and making changes to the linkage.

Still had the poppin'.

I realized when on a road trip it seemed to stop. I had suspected the accelerator pumps might be at fault and that was the case.

My Spyder had a 150hp engine. Many of the Speedsters have a smaller engine, less HP. That's the case with my car. The engine is pretty and has plenty of go, but it's not the same engine that was in the Spyder.

There is very little information I could find on the adjustment of the accelerator pumps. You would think that this would be important enough that it would be addressed...maybe it is somewhere.

On the Spyder the accelerator pump adjustment nut was turned in with 1/2" of rod sticking out past the nut. Except for the endless cleaning of the idle jets the carburetors worked flawlessly. The pumps on the Speedster were turned in just as far.

Well... after turning out the adjustment nut to about 3/16" each, I took a turn up the Natchez Trace. I ran the engine at a number of loads from slow lug to full power and the poppin' is gone.

There may be  more tweaking in the future, but for now this feels good.

Getting ready for Barber's Vintage Motorcycle weekend. If you haven't been there, it's the finest motorcycle museum in the country, possibly the world. No question about the track. Porsche uses it for development and Porsche Driving School. Located in Leeds, Alabama, just outside of Birmingham off the I-459/ I-20 exit.

This is my 14th and last year. The bureaucrats have ruined it for the swap meet vendors. I'm in space A29.

Ya'll come.

Jim--I know you posted this a while back ---maybe you have fixed it already but I wanted to add my recent. experience .  Danny mentioned idle settings as a possible culprit and that was sort of what I went through with my Dells.

My engine was delivered with .65 idle jets and at sometime in the past for some reason I don't remember, I switched them for .60 idles. I usually log everything I do to my car but didn't in this instance.  Anyway at the Maggie Valley event I was having awful popping and backfiring.  also the idle wasn't like it has been, which was right at 900 whenever it was idling. I Backfiring seemed to stop at over 50 mph which a smarter guy than me would recognize as an idle jet issue.  I still got some backfiring even at that speed sometimes.  I just received the Thomlinson Dellorto Tech Manual Damned hard to find)  and read that "backfiring and popping can be caused by too small idle jets" and so I switched back to the .65 size and it was a total miracle. Zero popping at any speed and perfect idle.  VOILA!  

I have some extra jet sizes and would be happy to send them to you if you could use them and haven't solved your popping issue yet.  Danny called it too--he recognized that popping means LEAN, not rich, as I had thought.