June 3, 2020
I’ve been wanting to try a Lectron carb for a while now on my vintage Honda. After all, the old PJ carb is outdated at this point. While the bike ran great, I knew deep down that it could be better. Also, while I have found Lectron’s generally get positive reviews, every once in a while you read someone’s experience that wasn’t so great. It seems opinions tend to swing between love and hate. This intrigued me to be honest. What was all the fuss about? Are people just drinking the cool aid? Do the people posting negative reviews have other bike issues? A skewed evaluation (not everyone is objective or realistic).
Being as how I am a long time racer and tuner, I have always considered myself a good judge of changes made to the bike. With this in mind I decided to give it a go. After all, my old bike (while heavily modified) could use an upgrade from the original 36mm carb.
To be honest, I expected very little change with the swap. Deep down I felt like most hobbyists struggle to properly jet a standard carb “perfectly”. That most of the time, the positive reviews were because of an improvement over the riders original poor jetting. I figured that by adding the Lectron to my bike that it would run well, but I did not expect anything drastic. Nor did I expect the engine to feel like the peak Hp has increased. To sum it up, I was skeptical.
BIKE SPEC’S – BEFORE
-Bike/Engine – 1993 CR 125
-Cylinder head cut to 0.038” squish, dome reshaped
-Compression ratio set to 18.3:1
-Cylinder has significant porting
-Crankcases have been ported
-Ignition timing advanced 4 degrees
-Custom Hygge Performance pipe – REV pipe
-Running straight 100LL – AvGas
-Maxima 927 Oil, mixed at 36:1
-36mm keihin PJ carb, rebuilt and jetting correctly
How did the bike run before? It ran very strong! The bottom end was soft of course (it is a 125 and I am running a REV pipe), but the midrange and top end were excellent. The bike pulled hard and revved to the moon. It was a little hard to get onto the pipe and felt a little flat between the low to midrange transition. This was attributed to the Rev pipe and porting changes. After all, adding significant top end usually takes away some bottom end. One other issue was that the engine did not idle consistently between being hot/cold. If it was set to idle while cold, it would be idling way too high when hot and on the track. If it was set to idle hot for race conditions, then it would want to stall after a few seconds when cold. My work around was to set correctly when hot, and to stay with the bike and have my hand on the throttle to warm it up.
BIKE SPEC’S AFTER
-Lectron carb was added (ran as shipped other then turning the idle down 1/4 of a turn)
-Addition of a Boyesen Rad valve. This was done to give a better intake transition between the carb and intake boot (reduce the lip from the 38mm carb outlet, to the 36mm reed block opening)RIDE REPORT
At start up, the engine was idling a little high. Turning the idle screw down ¼ of a turn solved this. The bike now idles better and has a much more consistent idle speed between hot and cold (90% better). Once out on the track, I immediately noticed how clean the engine ran in the bottom end and transitioning through to the midrange. It no longer feels flat down low. As the engine gets on the pipe the midrange felt stronger than before. This is noticeable by the butt Dyno. Up top the bike pulls harder then ever, and for longer into the overrev. I was really impressed with the top end. This was something I did not expect. To give some context, there is a few big uphills on the track I was at that are right out of a sweeping corner. With the PJ carb setup, I would start the uphill in 3rd gear and stay there, letting the engine scream. I was unable to shift to 4th and stay on the pipe. If I tried, the engine would fall flat and require clutch to maintain the gear. With the Lectron, I repeatedly hit the same corner in 3rd, I pulled through the gear up the hill and was able to shift to forth about ¾ up. The engine did not fall flat and kept pulling strong, cresting the hill significantly faster then
-More power everywhere
-Metering rod is not adjustable without removing the throttle slide from the carburetor
I am impressed with this carb! For this vintage bike the difference is night and day. I would buy another one in a heart beat. If I can get my hands on a newer 38mm Keihin PWK carb, I would love to test it head to head against the Lectron. I’m curious to see the comparison both on the track and on my dyno. My suspicion is that a newer PWK would fall somewhere between the PJ and Lectron. As far as how the Lectron’s respond to other models, I cannot speak to that. I can say however that my experience was very good on my vintage two stroke.
4.7 out of 5 stars
This is an excellent carb. The engine runs better everywhere and feels like it has more power. The rating was only reduced .3 of a star because there is no external metering rod adjustment. This is something most people may not care about as the carbs are dialed for most models right out of the box, but for testing purposes it would make life a lot easier.