Old Guys Simplex moto-peddle bike

I found some answers to the backfire (actual term "after fire" when occurring on the exhaust side) problem. I will continue to use the term "backfire" from this point on, even though it's incorrect, though most commonly used and understood by most of us, including me.

What follows is my "check list" of what I did to troubleshoot the back fire from the Honda based engine after I sorted the carb to a point of starting and idling the engine.

I ran the engine for 45 minutes and read the plug which looked to be on the lean side. Too lean can lead to a backfire problem. Two factors that I took into account on the intake side of the motor were improper jetting/mixing and air leaking into the carb and intake system. I've found no sign of air leaks on the intake side and decided to not chase carb gobblins off the jump, leaving those to last if required.

Going to the exhaust side I also looked at two factors, since it's the most common cause of backfire in my personal experience; I examined the copper gasket ring and it showed definite signs of a leak. The steel "washer" that I made to compress the copper gasket ring & seal to the manifold was slightly greater than the required diameter and was restricting the "washer" from seating correctly against the gasket. It was actually contacting the casting of the aluminum head just as it began compressing the copper gasket ring at the exhaust port. Bottom line was I had an exhaust leak at that point. A couple of minutes with the file and that was that.

Tested the affair and all was much improved, but with still an occasional pop. Which brought me to the next suspected cause for the engine leaning out. The relatively short, unrestricted free breathing stub exhaust and yet another reason for not buggering with the carb too soon or at all.

Manufacturers of non racing specific carbs, jet for average non modified street engines and moderate altitude operation. Carbs are set up for a mythical average to hopefully work right out of the box. After inspecting the induction system for leaks and finding none I expected to find that the lack of back pressure at the exhaust was leaning the air/fuel mixture (more air than fuel). Remember I'm chasing a quality fuel mixture at this point as the backfiring is just a symptom of the real problem which is to contain the detonation of the fuel/air mix inside the combustion chamber rather than partially igniting in the exhaust manifold.

I'd previously made an exhaust baffle ring (simple 1" long with a 1" hole in it) to install later for lowering the exhaust note a bit. To this I added an 8" section of 1" pipe with quite a few 5/16" holes in it, wrapped some stainless wool around the whole affair and inserted this into the exhaust pipe stub and secured with a C clamp.

No more backfiring! At which point I decided to turn my attention to another area, rather than run the little beast long enough to re read the plug to "see" if it was running richer, but I didn't and that's when the throttle cable decided to pull loose from it's lead keeper in the throttle housing so I'm buggered till a new one gets here next week. At any rate some real progress in the direction of a harmonious outcome...it appears. Alteration of carb setting and or jetting may yet be required. I'll save that for another time.

Rick C.

This photo shows the kayak body shape and small size at work on a leaning wheel design sidecar frame while agressively executing a left hander...sure wish I could find a photo of the same rig taking a similar bend to the right at speed. I really like the shell. Rick C.

I had the opportunity to slow down and remain indoors for the last couple of days, some would say a bit under the weather, and catch up on topics of interest. Thank you all for the wonderful and informative posts with links and photos. They were quite useful in clarifying my thoughts on the Kayak sidecar for the Simplex. I used "Creative staring" at the historical combinations which has been useful...in my mind turning over that which is seen and also the mechanical parts which remain hidden to the camera, but nonetheless exist or could exist under those exterior details which always attempt to obfuscate a fabricator attempting to reverse engineer even the relatively simple design of tools or conveniences of everyday life.

I'm not as yet certain if the sidecar will be partially or fully articulated; as the rigid car is also appealing to me, but my final decision won't be based on lack of knowledge or fear of fabricating a sidecar that is either or both. I may just design both concepts in the same frame with the ability to lock out the wheel and frame transforming the articulating into a rigid platform quickly and safely.

Fun stuff! Hack, cough, sniff & blow...for certain. Rick C.

Ludwig the Brough torsion/leaf spring wheel suspension is interesting, as is your description of the leaping tea tray hack, though I'll not let either influence my sidecar lol.

As to the military version of the Corgi I've seen stranger items dropped to troops by air but none I would judge to be less useful in a war zone... Rick

Throttle cable installed so a ride was in order, short but nothing fell off & everything functioned. Ill' call it a good first effort, I'll need to fab a permanent exhaust baffle before putting in much riding time. Mostly details and fine tuning from here on out, that and completing all the visual details of course. Rick C.

Thanks guys! My statement about falling off was all inclusive as I too remained attached. Although some things remain uncompleted the basics are. The riding experience is a bit different due to the reversal of controls right hand clutch, left throttle and brake, hand shift, but after the first few gear changes it all started to feel better. Shifting is quite leisurely, no need for speed, close throttle, clutch and work the lever. Find a gear you like and just stay there, plenty of torque, even with the 44 tooth sprocket on this one....low is now of some use in riding although second still feels like a good place to start on level ground. It's going to be fun to ride when broken in, just like the Simplex only different! Rick C.

Back fire is back under acceleration. I've new gaskets, larger diameter and thicker as well, on order. Leaking at the top of the seal. So the ring is settling to the lowest point while I'm tightening the whole affair. I reused the old gasket (damaged) as I had no other and knew it probably wouldn't hold up.

I made a tiny little baffle less than 2" long and installed in the stub exhaust and can't believe how much quieter the exhaust note is. It seems much more subdued than the Simplex Copper gator at idle, which has a much "better" muffler design...I thought!

The engine starts and idles well but even with no load in neutral advancing the throttle, quickly or slowly, induces exhaust back fire. It's all just a part of the process...no big deal.

Rick C.

Had 85 degrees and light breeze yesterday and riding was great. Fruit trees and Bradford pears in bloom it seems Spring is approaching Oklahoma "Indian territory" once again. Building is great but riding is the magic that makes it so worthwhile. I encourage everyone to have the tuneups, adjustments and service completed before your "riding season" begins...it's already here and it's coming soon to your neighborhood.

I currently have 5 motorized bikes and 3 mountain bikes and though I ride everyday, except those periods of ice or snow covered roads, which are few in this climate; I still do Spring cleanup and service of them all and actually enjoy the time spent doing so.

I ride my Grubee/Chinagirl board track style more than any other, the frame had over 400 hrs on the clock about a year ago when I pulled the meter to mount on another bike during break in. The 2 stroke has been mounted for most of this time probably 80 percent and has been flawless during all this time and is still running the second plug (NGK) and the original clutch pads. I always use the clutch without pedaling from dead stops with a 48 tooth sprocket so I'm amazed at the longevity of this tiny clutch. I've only tightened it once and that during initial break in. My daily rides seldom exceed 25 mph and I'm probably easier on the motor than most riders but I really think the key is keeping a quality fuel mixture flowing continuously through the engine...no coasting downhill with throttle closed of long idling for any reason, fuel mileage will suffer but cooling and lubrication depend on constant flow of fuel mix through the entire engine. Also the addition of a well finned after market head will dramatically improve the motor cooling, if compression is not dramatically increased as well.

Though my engine has been modified with porting and the addition of a reed valve, balancing, high quality bearings and after market head and carb I'm convinced that understanding how a 2 cycle motor differs in operation from a 4 cycle is the most important part of making them hold together in the long run. Just my point of view and I've been wrong before. Enjoy your rides! Rick C.