BGF Hongdu/Solex

GoldenMotor.com
cannonball2

cannonball2

Well-Known Member
Oct 28, 2010
3,682
223
63
Colonial Coast USA.
I believe the smaller bikes balance a bit better than say a 26". I am sure the 26 is fine but the 24 seems ideal. The original I have is on 19" wheels and I believe some of the Solexes were on 16". Several members have mounted the unit in the rear. I have enough extra parts to build one more engine, and plan to put it on a 26" aluminum frame MTB in the rear. My 24" Macargi is well balanced at least to me. In the vid I was fimiling while holding the camera and riding with one hand. You see the bike was easy to turn around in the road, with no bad tendencies. Its all a matter of personal preference. At the speeds this things move a good coaster brake is more than sufficent to stop, meaning a simple basic bike can be used. Just some thoughts.
 
wayne z

wayne z

Active Member
Dec 5, 2010
1,743
5
38
louisiana
Best I recall is that the original jet was about .024" I soldered and re drilled to I think .018.
Not sure about the numbers. Just measure the original size with wire drills and calipers to determine it's size. I soldered it up and re drilled with my smallest bit which was .018" then tried it on the road. Can't remember if I had to drill slightly larger again or not.
I just used a standard gun type soldering iron and acid core solder.
I bought my microdrills and hand driver quite cheaply on Amazon.
 
A

ace158

New Member
Jan 30, 2012
27
0
0
Great White North
Hmmm, that's good to know. My original 28cc Solex jets and the Hongdu-jet are the same size. They are a #78 .016. But my plug is telling me its rich. I'm wondering if my fuel return line is too small and the fuel pump is pressurizing the carb and flooding the motor causing zero performance. This seems plausible since a 2-stroke that is too rich causes it to have zero power and it will not rev-out.
 
wayne z

wayne z

Active Member
Dec 5, 2010
1,743
5
38
louisiana
Check that the exhaust is not obstructed. that causes the same symtom. mine had a LOT of weld bead inside the tiny muffler pipe. I ran a snug fitting drill down it to clear it. I also cut the pipe from 4"down to 3/4 " to match the Solex originals. I also drilled a 6mm hole at the lowest point of the muff can, to aid in breathing and drain the muff of oil I also drilled out the 2 air intake holes slightly larger.
 
wayne z

wayne z

Active Member
Dec 5, 2010
1,743
5
38
louisiana
Check your compression. It's supposed to be about 95- 100 lbs or so. Both mine were about 75 psi after break-in. I checked my heads for deck height and I think they were about .100" more than original Solex specs. I cut them down to about .025 or so less than std Solex and they ran right good after that.
 
A

ace158

New Member
Jan 30, 2012
27
0
0
Great White North
I'm using the stock exhaust as benefits in the construction of it are obvious. The exhaust had some sludge needing to be cleaned out. I'm pondering using the original solex head. It starts and idles and runs much better now but I still lack power to propel the bike.
 
wayne z

wayne z

Active Member
Dec 5, 2010
1,743
5
38
louisiana
Have you checked compression with a guage? Checked the flywheel key and timing? Have you had the carb off to check for bad gasket overhang? Carbon buildup in exhaust port/manifold? Measured deck height. Experimented with the jet? Used real fresh gas? Tried running without the muff for the heck of it? Tried blowing with your lungs pressure thru the muff and manifold? If they're any restrictons, you can tell.
Also, you can do a pressure test on the engine and use soapy water to hunt for gasket, seals or casing leaks. Low compression in the crankcase will make it run weak. Even a pinhole in the casting or pump diaphram could have an effect. Don't use more than 5 psi for testing though.

After running it for about an hour steady, to get it hot and give time to leak oil, look for fresh oil residue around the crank seal, all gaskets, fuel pump base, crankcase ect.
Can't think of anything else.
 
A

ace158

New Member
Jan 30, 2012
27
0
0
Great White North
SUCCESS! I took it for a 10km boot today. Not bad considering its -13C outside right now.

I should have known what the issue was. But now it has a Solex head... and it has been throughly taken apart and put back together and taken apart. For $213 shipped, this is by far a great bang for the buck and much much cheaper than the $580+shipping from VeloCruz.

Thanks for the insight guys.
 
A

ace158

New Member
Jan 30, 2012
27
0
0
Great White North
wayne z said:
Have you checked compression with a guage? Checked the flywheel key and timing? Have you had the carb off to check for bad gasket overhang? Carbon buildup in exhaust port/manifold? Measured deck height. Experimented with the jet? Used real fresh gas? Tried running without the muff for the heck of it? Tried blowing with your lungs pressure thru the muff and manifold? If they're any restrictons, you can tell.
Also, you can do a pressure test on the engine and use soapy water to hunt for gasket, seals or casing leaks. Low compression in the crankcase will make it run weak. Even a pinhole in the casting or pump diaphram could have an effect. Don't use more than 5 psi for testing though.

After running it for about an hour steady, to get it hot and give time to leak oil, look for fresh oil residue around the crank seal, all gaskets, fuel pump base, crankcase ect.
Can't think of anything else.
Click to expand...
Compression isn't an issue, and the HD head was actually a decent casting which was very close to the Solex head for cc's. The intake to carb was a bit loose so there was a miniscule leak there, which had no effect on performance what so ever. The old muffler was coked up enough that the engine couldn't exhaust freely. It was barely noticeable but frustrating until now.
 
cannonball2

cannonball2

Well-Known Member
Oct 28, 2010
3,682
223
63
Colonial Coast USA.
ace158 said:
My old muffler was coked up. I'm sure the head if it did have a bump in compression helped a bit too.

CB2, where did you order your front tire from?
Click to expand...
If you are talking tires for my Velosolex(you mentioned 19"), I bought a new set of original Michelins, with tubes off ebay. Seems like it was $60 for the set. These were designed specificly for the Velo with a deep rib tread. They still come up on ebay from time to time.
 
A

ace158

New Member
Jan 30, 2012
27
0
0
Great White North
My Velo has a Chen Shin C109 tire in the back 19-2.00 that luckily still has the tits on it and is in absolutely perfect shape. The front tire is the original ribbed Michellin 19-1.75 that other than dry rot is in okay shape. They can be found quite easily on german ebay. I noticed that the Honda PC50 used the same tire. They were *not* bicycle tires, they are considered moped/light motorcycle tires. Which is one of the reasons they are damn near impossible to find because a bicycle shop won't be the likely place to look. You would have to go to a motorcycle shop.
 
You must log in or register to reply here.
Top Bottom