Mechanics: Engine modification for Baja Doodlebug

al mc

al mc

Active Member
I purchased a Baja Doodlebug (mini bike) to cover some ground at outside dog/horse event. I knew the engine was underpowered for this use when I bought it...good on flat rough terrain..not enough power to take on a hill.
It has a cheap 2.5hp engine. I have heard that it is 'easy' to replace with a larger engine..say 5hp Honda or Briggs/Stratton. Anyone done this? Thanks
 
mantisman51

mantisman51

Active Member
Yes, it is a simple bolt-on deal. There are 3 issues involved. 1) It has to be a horizontal shaft engine. 2) The bolt pattern on the bottom of the engine has to be the same-to bolt onto the frame. 3) You will have to replace the chain gear, from the old engine to the new. Harbor Freight sells the exact same engines used by Baja manufacturing. The 5 hp is in the $200 range in sale last week's sale.
 
al mc

al mc

Active Member
Originally Posted by mantisman51
http:///forum/post/3089402
Yes, it is a silple bolt-on deal. There are 3 issues involvrd. 1) It has to be a horizontal shaft engine. 2) The bolt pattern on the bottom of the engine has to be the same-to bolt onto the frame. 3) You will have to replace the chain gear, from the old emgine to the new. Harbor Freight sells the exact same engines used by Baja manufacturing. The 5 hp is in the $200 range in sale last week's sale.
Thanks. So basically, as long as I get the correct bolt pattern engine I just have to remove the existing smaller engine and refit the new one with the chain gear!
I do not need speed (15-20mph is plenty) I just want more enough power to go up some rolling hill terrain. In your opinion is 5hp enough? The 2.5 will get me around easily on flat or slight upgrades...
Thanks again. al
 
al mc

al mc

Active Member
Found that Harbor Freight has a store in Newark, DE (my lucky day)
Mantis....the engines on their website are 6.5hp and above. To your knowledge does the 6.5 have the bolt pattern I am looking for? Thanks
 
mantisman51

mantisman51

Active Member
They were selling the 5 hp here at the Tucson store and the 6.5. I would think the pattern would be the same, the problem would come in getting that large an engine in that small a space.
 
reefraff

reefraff

Active Member
When I was a kid the Co mechanic built a mini with a 5 horse BS on it he had modified, that thing was crazy fast even with a grown man on it. 6.5 would have to be at least as fast. Could be fun.
If you can get a stencil of the engine bolt pattern you can check it first to see. Even if the new engine doesn't match up you might be able to re drill your current mount to work.
 
al mc

al mc

Active Member
Thanks for all the comments. I just brought home the 6.5hp from Harbor Freight. This was last day of sale and they had one left so I grabbed it. They threw in a 2 year warranty (I have heard the chinese knock off of the Honda engines are not real sturdy?)for nothing since I was a first time customer?? Total cost $125!
Guys....I am fairly handy but have never done alot with small engines. Is this a pretty easy swap out if bolt pattern/space is sufficient or should I just ask the local garage that services my cars to do the swap?
 
al mc

al mc

Active Member
Originally Posted by ReefForBrains
http:///forum/post/3089495
Upgrading from a 2.5 to a 6.5 .....thats my kind of minibike!!
We demand pictures of the build!
If it is that fast I will send you pictures of me in the hospital after popping the first unintended wheely
 
reefraff

reefraff

Active Member
Originally Posted by Al Mc
http:///forum/post/3089608
Thanks for all the comments. I just brought home the 6.5hp from Harbor Freight. This was last day of sale and they had one left so I grabbed it. They threw in a 2 year warranty (I have heard the chinese knock off of the Honda engines are not real sturdy?)for nothing since I was a first time customer?? Total cost $125!
Guys....I am fairly handy but have never done alot with small engines. Is this a pretty easy swap out if bolt pattern/space is sufficient or should I just ask the local garage that services my cars to do the swap?

It isn't rocket science. I would give it a shot and if you decide you are in over your head then take it in. If your current clutch/sproket assembly will fit on the new engine that will be half the battle.
 
al mc

al mc

Active Member
I found a great web site to get info/help me with this conversion. I think I can post it as in no way does a mini bike site compete with swf.com
oldminibikes.com
I will keep you all posted.
 
ironeagle2006

ironeagle2006

Active Member
Put it to you this way I have a buddy that raced so called OUTLAW Brigs and Stratton 5 horse motors. They would start with a 5HP Briggs motor. Beyond that anything went it was how much you wanted to spend and how crazy you wanted to get. Ever seen a 5HP Briggs turning 7500RPM with 60 HP at the crank while running on 50% Nitro Methane and 40% Ethanol and 10% Turbo Blue for fuel and loving it.
These guys run with the 2 storke carts and sometime will OUT RUN THEM IN THE STRAIGHTS.
 
al mc

al mc

Active Member
Update: I finished the conversion from the 2.5 hp stock engine to a 6.5hp chinese knock off of a honda engine.
The thing screams....I will need to adjust the governer so no one gets killed.
I made the modification so that I could use it on the cross country courses at horse trials. I have yet to find a hill today that it can take with ease.
 
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