BGF Hongdu/Solex

Have to drill out the mounting bolt first. The Solex exhaust manifold has much more of a ball shape, making it pivot and still seal the muffler joint, all kinds of little nuaunces. Still my Hd runs well and I have no complaints really, its just after watching Brian/Solex on youtube you can tell theres a difference in the engines. Its in the piston/cylinder and or the ignition timing. Im thinking replacing the piston with a BnR piston may be the ticket. If the BnR has the same power as our engines and I paid top dollar for it, Id be pissed! I have run the original Solex carb, no difference except idle speed. can rule the carb out. Any way I am convinced we can get more power. I dont really want a modded motor, just one that puts out its original designed HP.
 
i wonder if the hongdu motors are even all the same. we've definitely noticed small differences in them. maybe some do have the bigger piston and jug and better ports. after all, we have only dealt with a handful of them, and i never did tear mine down to look at the internals. and the chinese change things up like that constantly. look at how many incarnations of the HT engines there are...it's mind boggling. why should these be any different? i'm plenty satisfied with mine as is, but if it could be hopped up with a top end swap i'd be for it. could probably keep the chinese top end as a spare too.

and while we are on that topic, with all else being equal, with the smaller top end i wonder what the actual displacement is. it can't be the 49cc it's supposed to be with a difference like that.
 
I think the displacement is the same the difference is in the piston design The bore on the Hd is roughly.5mm bigger if anything we have slightly more displacement. I just made a vid, will attempt to load on youtube. I dont now how to imbed so maybe some one here can retrieve it. Its not great, first time I tried one while riding single handed. but you will get the idea. I will get back if I can get it posted.
 
for some reason i was thinking the hongdu bore was smaller. i went back and looked at the side by side pic. the hongdu is the one on the left, correct? so it's really just the port size and placement.
 
Colony Five said:
for some reason i was thinking the hongdu bore was smaller. i went back and looked at the side by side pic. the hongdu is the one on the left, correct? so it's really just the port size and placement.
Click to expand...

Yep to all of that. I went ahead and cut the outlet pipe(note the stylish angle). Seemed to notice a difference. While going through the Hd carb when I got it, rememberd the main jet looking funky, so I swapped the jet from the original Solex carb. WOW what a difference! No more 4 stroking and now I could run with the choke fully to the right. The power increase was noticible, Engine sounded more powerful and ran to match. Strange thing is didnt run any better with the original carb. So, the Solex jet in the Hd carb with the pipe cut off really woke it up! I uploaded the vid on youtube maybe some one can embed or link to it, search Hongdu Solex on the rampage Took awhile for me to get comfortable riding with one hand so the first part aint great, but it gets better, listen to the engine. There are some pretty good hills for a little motorbike in the vid. There was no pedaling the motor pulled away from stop and climbed the hills unassisted. Pics of the jets and exhaust.
 

Attachments

  • 002.JPG
    002.JPG
    79.1 KB · Views: 277
  • 003.JPG
    003.JPG
    45.7 KB · Views: 295
  • 004.JPG
    004.JPG
    42.2 KB · Views: 263
  • 006.JPG
    006.JPG
    50.5 KB · Views: 271
wish i could watch it, but i'm still in the stone age with my dial up connection so i don't get along with videos. but it sounds cool.

how much of the exhaust tip did you do away with? was it louder like that or did it change the pitch? i like how mine sounds and how quiet it is.

but the jet, i should have known! it's probably like the chinese scooters...they are always jetted too lean from the factory. was it even marked at all? it sure looks smaller than the solex jet. looks like a replacement jet is in order, not just for the added performance, but also because if it is running as lean as i think it must be it's not good for the engine.
 
i just went out and checked mine, no mark on it, or the air jet under the air filter housing either. might as well put a genuine solex jet in there too.

Cball what size jet is that? i can't make out the number. i have a bunch of them for my aircooled volksie but probably way too big for the HD. stock on the solex is 28 isn't it?
 
It is a 28cc(flow/minute). There are 2 jets I believe, one is the 28cc the other is a 32cc. I believe the 28 is the most common. These are specfic to the Velo designed carb. These are calibrated in flow/minute, not hole size. The problem with mine I believe is that is was miss drilled(off center). Check yours to see if its centered or not.
 
see vid here<iframe title="YouTube video player" width="480" height="390" src="http://www.youtube.com/embed/cc5n_FORkAs" frameborder="0" allowfullscreen></iframe>
 
I .recieved my second HD today. Fit and finish is real good. No dents and smooth, glossy paint.

Got the Chinese stickers, and a bright orange fuel tube. The plastic fan housing was cracked from poor packing. Gonna try one of those plastic welding kits from HF.

Also got the standard tank with the free coating of slightly scaly rust inside.
Best EZ way I've found is to treat it with
phosphoric acid solution from Hdw store. This neutralizes the oxidation and it turns from red to dark.

This is done after rattling some pea gravel with water and detergent in it for a while. Beware of the delicate in-tank filter, and donT let the gravel damage it. Rinse well, let dry, them add some of the rust neutralizer and shake, rinse dry,and it's ready.

Yahoo! This one has a light coil!

I might pull the jug for inspection if it has the easily reusable copper base gasket.
Wont hafta tamper with the head gasket to get to the piston.

I ordered new rings for my other HD from Steve's. not sure which engine type he's sending .

gonna try to have this one running tomorrow.
 
Thanks for the link to the vid C5, you are right I missed it. I cut about 1.75" off the outlet, actually leaving 3/4" is the object. The sound did increase, but only slightly. I also ran a corresponding size drill through it. I am going to pull the jet out of the #2 hd this morning to see wht it is like.

Waynez, watch the vid it should leave you with a new perspective of the Hd. I am well pleased with its power now, and there may be a little more to be had!
 
Checked the jet in the 2nd carb and it is drilled on center and looks ok. So I guess the 1st jet might be somewhat defective. I have the remains of a jet drill set I have had forever, but did not have a bit small enough to check the sizes. Visably they look the same, but who knows. Cutting the exhaust might be something to entertain. Since I have an exrea carb, I might consider the bore out to 7mm, but will have to find the recommend let drill to enlarge the jet first.

Also remember my muffler is modded also with the 5.5mm hole in the bottom. It may take that plus the cut to show the difference-who knows!
 
ok, I just pulled the jug off my new #2 HD. Guess what? All 3 ring gaps were perfecty aligned on the intake port.
Could there be some vague reason for doing this?

Like maybe they think that the incoming rush of mix keeps the ring ends from catching on the port?

Is that also why they round off the rings at the gaps?

Have they had probs with rings catching with these and their tryin to put band-aids on it?

I'm gonna set the rings at the 10-2-5 ring positons and button it up.

The piston ports aren't round. They have a sorta flat spot at the top. I thought this was flash, but there is a substantial fillet behind them.

Later
 
my main jet isn't off center, but i have no way to determine the size. i'm confused about what exactly the parts from steve's are...if i order a jet from steve's, am i getting a quality jet or just another chinese jet that may or may not be right? i want a genuine solex jet.
 
Colony Five said:
my main jet isn't off center, but i have no way to determine the size. i'm confused about what exactly the parts from steve's are...if i order a jet from steve's, am i getting a quality jet or just another chinese jet that may or may not be right? i want a genuine solex jet.
Click to expand...

I think Steves is selling Chinese based stuff, however I think it is from the upgraded engine. The piston I keep referring to is not whats in our engine, so that stuff is different and probably better quality.

I corresponded with Jeff Mathews of Velocruze, the parts he sells are European in origin. You might try a jet from him if you feel you need one. At this point I am going to use the jet that came with my #2 engine.
 
Waynez, the original solex rings are cut at an angle at their gaps to help seal them, the Hds are straight. There is no reason to have the gaps aligned, set em like you said. Have you checked the gaps?

That flat at the top of the piston ports is supposed to improve low end. It was a mod that could be done to the original piston, mentioned in BrianSolexes mod page.
 
You must log in or register to reply here.
Back
Top