baja minibike engine dies when under load

[gvfc2]

I have recently obtained a baja minibike with a 97cc 2.8hp hensin?(think I spelt it right) engine. It sounds like its have a compression leak. I can easily turn it by hand and I hear an air leak or something. When I do get it started(takes a while without a recoil starter) it idles fine. With tire in the air I can rev all I want. But I put it on the ground and give it throttle it dies. Could this be because of the compression leak?

 

[gvfc2]

Just realized I posted in wrong section. Instead of making extra work for the mods. I'm turning this into a well here's my project

 

[Nodroz]

I've ever read something on some website:
Remove the spark plug.
Put your finger on the hole where the spark plug goes.
Crank a few times. The compression should be strong enough to lift you finger out the hole.

Anyhow, you said you're hear the air leaking out of it. Try to search the source of the leak, and see if you can repair it. Maybe it's just a worn head gasket.

 

[gvfc2]

Yea I'm hoping is just that. It sounds likes its coming from around the carb area tho. And if its doing that I think maybe a stuck valve

 

[r_chez_08]

These engines make good boat anchors. I have heard so many bad things about them. Pretty sure they are a Honda g100 clone. I had a g100 genuine on a minibike. Didn't go well.

The carbs are really hard to get set up right as far as I have heard. But check the compression first if you think that's what it is. May be a combination of things. Valves not seating, rings gone or head gasket gone most likely. Could be stuck valve or damaged valve seats, check compression with the thumb method first though.

IMO if it is going to cost you much to sort it out, get a predator clone for $99 if you can afford it, since you are missing a recoil anyway. Best upgrade you could ever do. I hear they are pretty fun bikes then.

JMO.

 

[gvfc2]

Well I will look into the predator. How strong are they? Might just junk the engine. Its worth 200 from what I've quoted and it would cost more to fix it.

How strong and what size are the predators your talking about?

 

[Nodroz]

Well I will look into the predator. How strong are they? Might just junk the engine. Its worth 200 from what I've quoted and it would cost more to fix it.

How strong and what size are the predators your talking about?

The Predator 206cc engine should be more than enough. They cost you about $100.

 

[r_chez_08]

Well I will look into the predator. How strong are they? Might just junk the engine. Its worth 200 from what I've quoted and it would cost more to fix it.

How strong and what size are the predators your talking about?

I would never pay $200 for the doodleug motor. Don't think anyone would, they are really not great. Fine for kids under 12 but other than that...
No offense! The doodlebugs are awesome apart from that!

The Predator 206cc engine should be more than enough. They cost you about $100.

*212cc. Yeah they can be had for as little as $99 with the correct coupon. I have heard the quality is better than most 'clones'. The predators are bored and stroked 196cc honda gx200 clones with a few other differences. They are meant to be pretty torquie at low RPM compared to the 196cc's because of the extra 16cc.

Fix the motor if you wish, but for $125 you can have that predator on your bike (you need a new centrifugal clutch, or torque converter).

It will have over double the take off, and because it can actually get to it's maximum RPM, speed will increase too.
JMO. I usually reccomend fixing motors for the learning experience and cost, but I would not bother.

 

[Doc Sprocket]

Those G100 knockoffs ARE a pain in the @$$. I have two Baja Dirt Bugs (same thing) for my kids. The carbs are especially twitchy. I have both of them running well, but they were bloody awful when I got them. I did not get them new, but nearly new. From the factory, they are jetted too lean. I drilled both of them.

They other problem is that they are geared too high for the amount of power they (don't) have. They are advertised as 2.8hp. Not bloody likely.

If you weigh more than about 100lbs, forget it. You either need to upgrade the engine, or install a jackshaft kit.

If you want to re-jet, gimme a bit of time and I will try to remember the jet size I finally settled with...

 

[gvfc2]

Ill just go get a predator. The clones that's on it do seem kinda crappy. And the people that had it before me I could tell they didn't know jack about. Oil is super black. Never cleaned and just overall looks crappy. Either they stole it or they just don't care about stuff like that. The guys son seemed like a pot head too. Came with a flat tire that's bald and has a giant hole in it. Also has no throttle. Surprised the engine started at all

When I get my electricty back on I will post some pics of it

 

[r_chez_08]

Wow. Sound like great people! If you don't mind, how much did you pay?
No throttle? Are you talking twist throttle?
I am getting a new twist throttle for my mini bike. Looking at the metal one on ombwarehouse.com. They seem pretty good. Don't get a plastic one, IMO they are crap. Had 3, all 3 broke.

Check eBay or gokartsupply for a new tire. Or ask bluethunder where he got his, I can't remember, but it was reasonable. It was for a Baja warrior but the site had good deals.

 

[Doc Sprocket]

I've been racking my brain trying to remember which numbered drill I used. It was somewhere in the #72-#74 range but I forget which one worked best. I was thinking tonight I'd pull a jet out to gauge it, but if you're going to replace the engine, I won't bother.

One point worth noting- If you change the engine, you'll need a new clutch- the stock one is metric.

EDIT- I just found the pin vise I used to drill my doodlebugs' jets, and the bit was still in it. Although you may no longer need this, I will post it for future reference.

I used a #74 drill, 0.0225", which equates to a #60 jet.

 

[robbie]

Not that this is an important post, but I just thought I'd throw in an endorsement for the Predator 212 cc engine. I put one on a cement mixer, and the only complaint I have is that the rope is a piece of crap. Put a real rope on it, and it's a great engine.

 

[gvfc2]

I paid 90$ for it. Seemed like a good deal so I went for it. Yea there's no twist grip. Yea figured I get a knew clutch. Since I will why not just upgrade to a tc instead of a cent. Clutch. Make it even better

 

[gvfc2]

Well I got the engine started and took it for a ride. Wow the engine is weak but fun. It wasn't starting due to the throttle linkage wasn't hooked up from the gov. Arm the the valve on the carb. Got the rear tire patched with some rtv silicone and now it has alot more speed and can climb the hill on my road with more speed. Will post pics when I get electricity back

 

[Doc Sprocket]

You fixed the tire with silicone?

 

[gvfc2]

Yes I did. Took the tire off the rim and had an inner tube I was able to cut up and used some rtv silicon and sandwiched the rtv between the inner tube and the tire where the hole was and it stopped leaking

 

[r_chez_08]

Wow. And I thought I was bodge.
How big was the hole?

 

[gvfc2]

Eh not that big but big enough and small enough. If that makes sense.

Edit: its actually been holding up to. Got at about 10psi as the wheel is onky rated for 5psi and its not leaking. I didnt think it woukd hold up this long

 

[Bluethunder3320]

did you put the predator on it yet?

i did an engine swap in one of these. get the PMR engine mount, and a 3/4 bore clutch. thats all you need!

the difference between the 2.5 and the 6.5 is a huge upgrade. it pulls wheelies on its own!