new guy here with dr70 issues
 

Hey guys been shadowing the site for a while and finally decided to join. You guys really seem to know your stuff about hensims so here goes.

So one of my frequent customers and long time friends brings me this bike he picked up for $100. Its a hensim baja dr70 4speed semiauto. When it runs, it runs amazingly, shifts fine, goes fast as hell for a 70cc. The problem... getting it to run in the first place.

Previous owner beat it pretty bad and said it would only run off 40:1 mix gas. Sure enough that's what it ran on the only 2 times I've gotten it started. I've since cleaned everything up with some seafoam deepcreep and rebuilt the carb. I can't get it to fire on straight 87oct. At all. I've got spark its getting fuel (it backfires every 20 kicks or so) and the most ill get out of it is a put put put puff. I've pulled all the wiring (the enormous 9 wire harness.. ) and cleaned all of the contacts and connections. I've cleaned the mud from the magneto and the magnet. And I got nothing.

Coil is good, cdi (dci?)is good. There's no reed valve to clean or replace. And I get gas out of the carb occasionally. Choke setting or throttle position don't seem to matter.

Anyone who can point me in the right direction I would be grateful!

well, got it running, played with the valves a bit. took the intake valve to .003" and the exhaust to .002" (both were set to .004") runs good in higher rpms but has a slight misfire getting there, also wont stay idling, so now that it runs my question changes.

I've tried every setting imaginable on the carb between the A/F and idle screws. and it'll idle at roughly 2500 rpms (judging by ear) but i know that's pretty high. ive got the a/f set at stock 2 turns out and the throttle stop/idle screw ALL the way in. both needles are clean (throttle and float) and the jets are spotless.

any ideas?

Welcome!

Glad to hear that you made some progress by setting the valves. What posessed the PO to use mixed gas in it? :hmm:

How do you know the CDI is good? My guess is that it's fine, but the only way to know for sure is to swap it.

The carb is likely in need of different jets, but back to that in a moment. Do you have pics of the bike? I have a sneaking suspicion that the exhaust is the same nasty design as Son of Weldangrind's first bike. Show us the bike, and we'll go from there.

Cdi
http://www.sanxin.com.cn/info5/index.asp?id=10 | http://www.sanxin.com.cn/info5/index.asp?id=12
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What's the ohm reading of pickup & source coil
http://www.sanxin.com.cn/exhibit/upl...5233028219.jpg
http://www.sanxin.com.cn/exhibit/upl...5232522204.jpg
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Pickup (tells when to spark) maybe F***ed | Have spark - Sorce coil / EXT maybe OK
IF ohm reading is within limit, check the gap btw pickup & flywheel as CDI maker said. http://www.sanxin.com.cn/Exhibit/exhview.asp?pid=1

I had the 90cc version of this bike and it had the restrictive exhaust. Mine always started on one or two kicks. It too was beat by the PO, but I brought it back to beat it some more.

My guess is that you replaced the plug with a new one. The next thought is that the exhaust may be plugged up with residue from the oil burning.

Ill have to wait till the wife gets home for pics ( her phone is our internet lol) but if you look at a google image search for a baja dr70 its one of the first few pics. Descriptions of the exhaust. Has a 2 bolt slide flange with maybe a 1" mating surface over a 3/4" pipe that makes a direct "u" bend up and a 60*(ish) bend to route it to the back of the pipe. And the gasket is a typical crush style ring gasket that is.. well very.. crushed lol.

Ill take an ohm reading of the cdi tonight when I go get the wife because my ohm meter has since decided to die and I don't have any spare 9v's laying around lol

http://www.purplewaveauction.com/a/2...derby/2434.JPG

Pretty much identical to what I'm working on. Just a lot nicer ( minus that issue with the handlebars lol)

pics of the bike as requested! and more detailed pics of the exhaust itself





http://chinariders.net/picture.php?a...&pictureid=526http://chinariders.net/picture.php?a...&pictureid=527http://chinariders.net/picture.php?a...&pictureid=528http://chinariders.net/picture.php?a...&pictureid=529http://chinariders.net/picture.php?a...&pictureid=530http://chinariders.net/picture.php?a...&pictureid=531

also turns out that the owner gave me the bike because he couldnt pay for the repairs and parts it needs (needs wheels/tires/tubes front and rear, new sprockets, chain and paint... badly along with some other things)

so.. woohoo for free dirtbikes! lol

exhaust
 

yes take the exhaust off... I had a customer and I rebuild the motor because he was using oil like 1 litre every 20 mins... after I got it done it would barley idle and quit... the muffler was plugged from all the oil.... took the exhaust off at the motor ...... just prrrr... replaced muffler... was fine..

I've cooked a few two stroke mufflers to get the oil out, and you should be able to do the same thing. I place the muffler vertically in a vise on my welding table (outside), and slowly heat it with a propane torch. On an old two-stroke muffler, expect that process to take about an hour, but it should be much less for you. Keep heating it until the smoke stops billowing out.

You could just buy a new exhaust, but propane is cheap.

i have a spare muffler i can throw on if needed, would it make that much of a difference with the way it runs? thats crazy. guess it would make sense though.. kind of the equivalent of a clogged catalytic converter?

anything else i should do while im hacking up the exhaust? would replacing it entirely and upgrading it be a bad idea for something this small? say go from that stock 1" pipe to 1 1/4"? would make for more even and unrestricted flow straight out of the head.

not meant to sound stupid but my specialty is cars (primarily japanese sports cars 300zx, supra, rx7/8) ive worked on a few quads and bikes but nothing as extensive as what ive had to put into this one.

Your logic is certainly correct. More air out = more air in, assuming the intake side is up to the job.

You wouldn't believe what some of these mufflers look like inside. There's plenty of opportunity for oil to be trapped.

what are your suggestions for the carb? is there a way to enlarge the jets i have without having to buy a "performance" carb?

i actually have plans for this motor if i can get it to start and run reliably, was thinking of converting it to electric start and putting it on a flat cart (solid frame single pan go-kart with the sprockets from a honda cbr 600 (14&41 tooth combo) to have some fun with at car shows etc

There are tons of parts available for these.

$46 shipped. http://www.ebay.com/itm/EXHAUST-PIPE...3bc4d5&vxp=mtr

For sure. With a numbered drill bit index, you can enlarge the jets as much as you wish. What size main jet is in there now?

Another motor that already has electric start is not too expensive, and that would allow you to keep this bike in one piece as well.

I like your idea of building a kart for car shows. The most creative kart I saw (at the local track) was built using the body of a wheelbarrow, and it formed a tub like an early Model T hot rod. Awesome!

If you head in that direction, please start a new thread on it. :tup:

So i looked down inside the muffler just a minute ago and its literally just a can welded to the pipe and has a removable baffle (which is beat all to hell but very open and clog free). So im now baffled (haha see what i did there? Lol) as to why its not running right. Im going to order a new cdi and coil tonight and see if that makes a difference when they arrive.


I honestly have no idea what the sizes of the jets are, though i could probably measure them with my calipers.

As for the cart, im on an extremely tight budget because business is really slow right now thats why i was looking at an electric start conversion. I have a line on a cart frame for $50 and i can make the mounts , shifter, etc myself. Was actually looking at the parts on the bike and i can use the foot brake arm and pedal for the shifter and it already has spots for linkage to mount to... lol. Another reason i want use this motor is for the 4speed. Most of the elec. Start motors ive looked at were 3spd with reverse which would be nice but i can live without reverse lol.

I genuinely laughed out loud when I read that. :D

The jets should be stamped with the size. You can't measure them with calipers, since it's the ID in question. You can get a rough idea by inserting bits from a numbered drill bit index and then converting the decimal to metric.

Have you actually removed the jets and cleaned them? Have you blasted the jet passages with carb cleaner? That might be the fix.

I bought a brand new China 110 with electric start and a four speed for $110. You should certainly be able to find a used one for less. That said, three speeds plus reverse would be a good thing.

Keep an eye on the free section of CL; you never know what you might find for kart materials. You might even find the perfect rusted wheelbarrow for a body. A dead lawn tractor would also be a good donor.

I recently installed a new muffler and header on a Baja Dirt Runner 50, and it was very simple. The cost of a new muffler is about the same as a complete system. Here's an example: http://www.ebay.com/itm/Muffler-Exha...171caa&vxp=mtr

The plastics are removed in the pic, so it's easy to see how it's mounted.

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