Baja Blitz Motor Upgrade

#1
Hi all-

Newbie to mini bikes. I wanted to get something I could take my kids (5, 2, and 10 month) for rides around the neighborhood as well as have something they could learn to ride when they got older. My neighbor had this DB sitting next to the side of his house that I picked up for 20 bucks. The engine runs, but the 97cc is so underpowered. The bike can barely get us up the small hill we live on. I want to do an engine swap, but from everthing I’ve read, going to 212cc like a predator makes me nervous this is overpowered for my uses.

I’m hoping to get some advice/feedback about doing a little smaller engine swap such as a 5 or 5.5 hp engine such as a Briggs, Honda 160cc, or something in that range.I want to keep the budget on the low end and don’t want to do much fabrication if any. Bolt and go would be ideal.

Anyone have experience doing a smaller engine swap? Would the engine swap kits such as the OldMiniBikes work with these engine? What about other 212 parts for smaller engine?

Thanks in advance for your help and patience to the newbie questions!


92AE240E-73C2-4F69-9DC2-00101C5B7AA1.jpeg
 
#2
Hello and welcome! Fantastic deal!

There isn't much available between 2.5-3HP and 6.5HP. You can buy 3 or 4 Predator 212s for the price of some other brands, which is the main reason they are so popular. I would suggest going with a Predator 212 and a Max-Torque SS clutch for the sake of your budget. Flip the clutch (sprocket inboard) to better center the engine, carefully align the chain, and drill the engine plate. With the increased torque, you could install a smaller rear sprocket, depending on your budget. A new high quality chain would be a good investment. Keep the Predator stock, limit the throttle opening if you feel a need.

https://www.bmikarts.com/Max-Torque...-a-34-Bore-for-Go-Kart-or-Minibike_p_721.html

https://www.bmikarts.com/35-RLV-Extreme-Chain-Black-on-Black-Sold-by-the-Foot_p_21523.html

https://www.bmikarts.com/Master-Link-for-Xtreme-Chain_p_647.html

https://www.oldminibikes.com/forum/index.php?media/categories/doodlebug.747/

https://www.oldminibikes.com/forum/index.php?search/328262/&q=doodle+bug&c[title_only]=1&o=date
 

DaddyJohn

Well-Known Member
#3
What a steal for that mini! :D

Anyway, one route is a jackshaft, which simply allows you to lower the gearing without having to resort to a larger rear sprocket (which could get as big as the tire, which is pretty much a non-starter).

What I'd do is a little outside the box I guess... The H50 Tecumseh is a great engine that sorta falls between the Predator 212 and the current engine you have on it. I've done a Tecumseh H50 swap on a couple of those DB's. It makes the DB look like a real vintage mini (basically), and it's no harder than putting on a Predator. The power is much better than the stock unit, but not such that your kids will be doing 12-foot wheelies if they grab a bit too much throttle, lol....:D

Now, realizing you can't go to the store and buy an old Tecumseh engine, they're pretty common on cheap, old snowblowers.
Could be the ticket if you live in an area that might be snow blower friendly.
 
#4
Hello and welcome! Fantastic deal!

There isn't much available between 2.5-3HP and 6.5HP. You can buy 3 or 4 Predator 212s for the price of some other brands, which is the main reason they are so popular. I would suggest going with a Predator 212 and a Max-Torque SS clutch for the sake of your budget. Flip the clutch (sprocket inboard) to better center the engine, carefully align the chain, and drill the engine plate. With the increased torque, you could install a smaller rear sprocket, depending on your budget. A new high quality chain would be a good investment. Keep the Predator stock, limit the throttle opening if you feel a need.

https://www.bmikarts.com/Max-Torque...-a-34-Bore-for-Go-Kart-or-Minibike_p_721.html

https://www.bmikarts.com/35-RLV-Extreme-Chain-Black-on-Black-Sold-by-the-Foot_p_21523.html

https://www.bmikarts.com/Master-Link-for-Xtreme-Chain_p_647.html

https://www.oldminibikes.com/forum/index.php?media/categories/doodlebug.747/

https://www.oldminibikes.com/forum/index.php?search/328262/&q=doodle+bug&c[title_only]=1&o=date
Thanks for the feedback!

That really doesn’t sound too bad. Would I need hardware kit or anything like that in mounting the new engine? Any special fabricating needed? What about throttle linkage connection, does it just link right up, or does it need some fabrication.

What rear sprocket would be recommend? Some people also recommend a torque converter, is that necessary?

I’m not sure what you mean by flipping the clutch.

I forgot to introduce myself. I’m Brett
 
#5
What a steal for that mini! :D

Anyway, one route is a jackshaft, which simply allows you to lower the gearing without having to resort to a larger rear sprocket (which could get as big as the tire, which is pretty much a non-starter).

What I'd do is a little outside the box I guess... The H50 Tecumseh is a great engine that sorta falls between the Predator 212 and the current engine you have on it. I've done a Tecumseh H50 swap on a couple of those DB's. It makes the DB look like a real vintage mini (basically), and it's no harder than putting on a Predator. The power is much better than the stock unit, but not such that your kids will be doing 12-foot wheelies if they grab a bit too much throttle, lol....:D

Now, realizing you can't go to the store and buy an old Tecumseh engine, they're pretty common on cheap, old snowblowers.
Could be the ticket if you live in an area that might be snow blower friendly.
I do happen to live in a area that is snow blower friendly. That seems like extra cost of of having to buy a snowblower just for the engine.

What is a jack shaft? Do they make complete kits?
 
#6
Thanks for the feedback!

That really doesn’t sound too bad. Would I need hardware kit or anything like that in mounting the new engine? Any special fabricating needed? What about throttle linkage connection, does it just link right up, or does it need some fabrication.

What rear sprocket would be recommend? Some people also recommend a torque converter, is that necessary?

I’m not sure what you mean by flipping the clutch.

I forgot to introduce myself. I’m Brett
You can buy lots of stuff, adjustable engine mounting plates, throttle kits, etc., but don't really need them.



https://www.youtube.com/results?search_query=predator+throttle

By flipping the clutch, I mean to install it with the sprocket inboard, not outboard. The clutch I linked will work either way. If you use a 212 and mount the clutch with the sprocket outboard, you will have to mount the engine way off-center to align the chain.

https://www.oldminibikes.com/forum/index.php?media/modded-doodlebug.3807/

https://www.oldminibikes.com/forum/index.php?media/minichopper_029.22449/

I didn't mention a torque converter for a few reasons. (1) You are concerned about too much power with a 212, a torque converter would make it seem to have more power. A torque converter (AKA: TAV, CVT) is actually a Continuously Variable Transmission with a range of 2.7:1 to 0.9:1. Just for example, let's say you have a 12 tooth clutch sprocket and a 75 tooth rear sprocket, your fixed ratio is 6.25:1. Replace the clutch with a torque converter, also using a 12 tooth sprocket, and multiply the 6.25:1 ratio by the torque converter's 2.7:1 starting ratio and we get an overall starting (taking off, off the line, whatever you want to call it) ratio of 16.875:1 for tons of torque. The torque converter automatically alters it's ratio as speed increases; if the engine is capable of high enough RPMs, the TC should reach its 0.9:1 (slight overdrive) ratio; multiply that by the 6.25:1 final drive ratio and the overall ratio would be 5.625:1 running flat out. (2) It would be more complicated installing a torque converter, they are a tight fit on a small-frame bike. It can require modifying the torque converter plate to rotate it (raising the driven) and/or raising the engine and/or frame modification. From what you have said, I didn't think you'd want to get into that. (3) Budget. Chinese torque converters were as low as $50-60 on eBay, now they are at least double that; I assume the supply has been interrupted due to COVID-19; a genuine Comet is around $200. As a side note, but not a reason I didn't mention them, they are bulky and heavy, just something one has to accept if one wants the performance they provide.

https://www.oldminibikes.com/forum/index.php?threads/want-to-put-a-tc-on-a-coleman-ct100.141989/

Sprocket: I'd say try it with the stock sprocket and see what you think before spending money on an aftermarket sprocket, it may be fine. Sprocket selection would depend on what you want, a smaller sprocket would reduce torque to the wheel, theoretically increase top speed (depends on whether the engine can reach the same RPM) and lower engine RPM at any given ground speed. Just to simplify things, you might want/need a large sprocket for hilly trails but a smaller sprocket might be better for riding on pavement. The best option, IMO, is a sprocket adapter that accepts split sprockets, makes for easy ratio changes.

https://www.bmikarts.com/Baja-Doodlebug-Sprocket-Adapter-Plate_p_7093.html
 

DaddyJohn

Well-Known Member
#7
I do happen to live in a area that is snow blower friendly. That seems like extra cost of of having to buy a snowblower just for the engine.

What is a jack shaft? Do they make complete kits?
I usually pay $20-$40 for a snowblower, so...;)

You can search the forum for jackshaft threads, but it’s essentially an intermediary shaft between the engine and drive sprocket that allows you to adjust gear ratios or keep the engine centered when trying to get the chain around a wide rear tire (or do both).

Here is a thread with one of my Baja Tecumseh hybrids:

https://oldminibikes.com/forum/inde...g-with-snowblower-engine.165985/#post-1241489
 
#9
You can buy lots of stuff, adjustable engine mounting plates, throttle kits, etc., but don't really need them.



https://www.youtube.com/results?search_query=predator+throttle

By flipping the clutch, I mean to install it with the sprocket inboard, not outboard. The clutch I linked will work either way. If you use a 212 and mount the clutch with the sprocket outboard, you will have to mount the engine way off-center to align the chain.

https://www.oldminibikes.com/forum/index.php?media/modded-doodlebug.3807/

https://www.oldminibikes.com/forum/index.php?media/minichopper_029.22449/

I didn't mention a torque converter for a few reasons. (1) You are concerned about too much power with a 212, a torque converter would make it seem to have more power. A torque converter (AKA: TAV, CVT) is actually a Continuously Variable Transmission with a range of 2.7:1 to 0.9:1. Just for example, let's say you have a 12 tooth clutch sprocket and a 75 tooth rear sprocket, your fixed ratio is 6.25:1. Replace the clutch with a torque converter, also using a 12 tooth sprocket, and multiply the 6.25:1 ratio by the torque converter's 2.7:1 starting ratio and we get an overall starting (taking off, off the line, whatever you want to call it) ratio of 16.875:1 for tons of torque. The torque converter automatically alters it's ratio as speed increases; if the engine is capable of high enough RPMs, the TC should reach its 0.9:1 (slight overdrive) ratio; multiply that by the 6.25:1 final drive ratio and the overall ratio would be 5.625:1 running flat out. (2) It would be more complicated installing a torque converter, they are a tight fit on a small-frame bike. It can require modifying the torque converter plate to rotate it (raising the driven) and/or raising the engine and/or frame modification. From what you have said, I didn't think you'd want to get into that. (3) Budget. Chinese torque converters were as low as $50-60 on eBay, now they are at least double that; I assume the supply has been interrupted due to COVID-19; a genuine Comet is around $200. As a side note, but not a reason I didn't mention them, they are bulky and heavy, just something one has to accept if one wants the performance they provide.

https://www.oldminibikes.com/forum/index.php?threads/want-to-put-a-tc-on-a-coleman-ct100.141989/

Sprocket: I'd say try it with the stock sprocket and see what you think before spending money on an aftermarket sprocket, it may be fine. Sprocket selection would depend on what you want, a smaller sprocket would reduce torque to the wheel, theoretically increase top speed (depends on whether the engine can reach the same RPM) and lower engine RPM at any given ground speed. Just to simplify things, you might want/need a large sprocket for hilly trails but a smaller sprocket might be better for riding on pavement. The best option, IMO, is a sprocket adapter that accepts split sprockets, makes for easy ratio changes.

https://www.bmikarts.com/Baja-Doodlebug-Sprocket-Adapter-Plate_p_7093.html
Super helpful information! Thanks so much! It seems the easiest, cheapest, and most bang for your buck is to do the HF 212 CC predator swap.

To make sure I have the list of parts correct:
- Predator engine swap plate (for easier mounting)
- 12T clutch (Max torque SS recommended)
- #35 chain (how many feet?)
- HF predator engine

Optional parts would be clutch adapter to utilize different size rear sprockets.

Any other recommended or required parts I missed?

I’m also desperately in need of new tires. I probably won’t do much off road riding, at least at this point in time. Any recommendations for tires and where to get them?
 
#10
I usually pay $20-$40 for a snowblower, so...;)

You can search the forum for jackshaft threads, but it’s essentially an intermediary shaft between the engine and drive sprocket that allows you to adjust gear ratios or keep the engine centered when trying to get the chain around a wide rear tire (or do both).

Here is a thread with one of my Baja Tecumseh hybrids:

https://oldminibikes.com/forum/inde...g-with-snowblower-engine.165985/#post-1241489
That is a sweet little setup. I like how the engine doesn’t take up every inch of the internal frame. I may have to check some local listings to see if anything is hiding out there
 
#11
Someone local to me is selling this pressure washer for 50 bucks that has a tecumseh motor, but I can’t tell what size it is and if this would work on my DB

1588141345624.jpeg
 

DaddyJohn

Well-Known Member
#13
Someone local to me is selling this pressure washer for 50 bucks that has a tecumseh motor, but I can’t tell what size it is and if this would work on my DB
That's probably not optimal, as it's likely only 3hp or so (it's what's called a side-popper), and the shaft on it may not be proper for mounting a clutch to. You will need a 3/4" keyed shaft of about 2.5" or so in length.
 
#15
It seems the easiest, cheapest, and most bang for your buck is to do the HF 212 CC predator swap.

To make sure I have the list of parts correct:
- Predator engine swap plate (for easier mounting)
- 12T clutch (Max torque SS recommended)
- #35 chain (how many feet?)
- HF predator engine

Optional parts would be clutch adapter to utilize different size rear sprockets. (Would need to then buy split sprockets, yes?)

Any other recommended or required parts I missed?

I’m also desperately in need of new tires. I probably won’t do much off-road riding, at least at this point in time. Any recommendations for tires and where to get them?
 
#17
I would say you made the right choice by going with the Hf 212cc. Plenty of power, parts are cheap, and HF will replace it if something goes wrong. You can't beat that!

Something I will add about the predator 212 is how the governor can be easily adjusted. There is a screw that acts as the stop for the throttle arm. Adjusting it in will limit the engine speed, and adjusting it out will obviously allow the engine to rev higher. You can just play with that adjustment until you are comfortable with it.

As far as upgrades for the mini bike you have there, I highly recommend a hydraulic brake conversion. The mechanical caliper will get the job done, but the hydro setup is night and day. It stops much quicker, with much less effort. OldMiniBikes stocks them for under $50 -> https://www.OldMiniBikes.com/upgraded-baja-doodlebug-db30-hydraulic-brake.html
 
#18
Thought of more stuff lol.

For the chain, I always buy in 10ft rolls of #35, around $15 off ebay and they typically come with a couple master links. A trick I learned for installing fresh chain on these bikes is to remove the tensioner roller, tension the chain by pushing the engine forward and locking it down. Then ride it a bit with the tensioner roller still removed. New chain always stretches after the first couple rides. Once it stretches, install your tensioner roller. That way you start out with the tensioner in the forward most position and have plenty of room for adjustment down the road.

Something else I don't see mentioned is a clutch guard. The 97cc chain guard will not bolt on to the predator. You will want one that covers both the top and side of the clutch so someone's foot or calf doesn't get into the clutch. I run this one from gopowersports and have been happy with it. It doesn't interfere with the rear chainguard either. -> https://www.gopowersports.com/mini-bike-chain-guard/
 
#19
Thought of more stuff lol.

For the chain, I always buy in 10ft rolls of #35, around $15 off ebay and they typically come with a couple master links. A trick I learned for installing fresh chain on these bikes is to remove the tensioner roller, tension the chain by pushing the engine forward and locking it down. Then ride it a bit with the tensioner roller still removed. New chain always stretches after the first couple rides. Once it stretches, install your tensioner roller. That way you start out with the tensioner in the forward most position and have plenty of room for adjustment down the road.

Something else I don't see mentioned is a clutch guard. The 97cc chain guard will not bolt on to the predator. You will want one that covers both the top and side of the clutch so someone's foot or calf doesn't get into the clutch. I run this one from gopowersports and have been happy with it. It doesn't interfere with the rear chainguard either. -> https://www.gopowersports.com/mini-bike-chain-guard/
Thank you so much! Everyone has been so helpful. I’m getting pumped to swap this thing into a little beast.
 
#20
I’ve been emailing the guys at OldMiniBikes and they suggested this “Everyone focuses on the rear sprocket, where if we just get a larger tooth count clutch, it is easier to install and less expensive!
The standard clutch has 12 teeth...that is the wheelie popper clutch! If we go to a 14 tooth clutch we still have an acceptable 5 to 1 ratio with the stock rear sprocket and it won't always wheelie!”

Thoughts? Not that I don’t trust them, they obviously know what their doing and the fact they offered a cheaper and easier route is pretty cool. Would like to the ⚙️ heads thoughts.
 

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