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lets talk about the dr350 engine.

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I have a 91 dr350s.

 

Just scanning through the forum folks complain it has a weak top end prone to oil starvation.  

 

Is there a way to improve that? Have a machinist widen oil channels? Are later years an improvement?

 

Are there any other questionable attributes to the engine? weak valves or springs? chains?

 

Is the rod tough, forged? 

 

I see stock replacement pistons from wiseco and they seem to be higher compression. Do you get enough of a performance boost to make changing worthwhile? Does the added compression make it harder to kick start? If one went to the bigger piston kit what are the downside of that besides expense?  

 

Any aftermarket cam or from a similar suzuki that offers an upgrade?

 

I am a bit of a tinker that loves to improve my motor machines.

 

 

 

 

 

 

 

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I have a 91 dr350s.

 

Just scanning through the forum folks complain it has a weak top end prone to oil starvation.  

 

Is there a way to improve that?

yes, check the oil level after every ride & keep it near full

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I I think the old starvation problems are primarily due to operator negligence. Because the oil level is a p.i.t.a to check I think many people don't keep the oil tank full. Also, the small interior o-ring under the oil filter tends to get lost. It will sometimes stick to the old filter and gets thrown away. If the new filter is installed without that o-ring, it is simply bypassed by the oil potentially resulting in bearing damage.

I have run Wiseco pistons in two of my DR engines. Not because I wanted the higher compression but because their pistons are about one-third the price of the Suzuki parts. I have no complaints about the Wiseco piston but also see very little advantage to the higher compression ratio in this engine. The DR350 engine is in a fairly high state of tune already. I think it would be difficult to extract significantly more power from it without sacrificing reliability or drivability. However, you can easily improve the throttle response of the street model by replacing it's carburetor with the Mikuni TM33 that is standard on the off-road model. I emphasize throttle response because I don't think you'll actually get any more horsepower. The engine will just respond more quickly to throttle opening giving the perception of more power. However, because the TM33 has an accelerator pump you will likely use more fuel than with the constant velocity BST33 that is standard on the S & SE models.

Jesse Keintz (keintech.com) is the "go to" guy for DR350 performance mods. He probably knows as much as anyone outside of Suzuki about these engines and can help you if that's the route you want to go.

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Could just be me but ive never heard of the DR 350s having top end lubrication problems

Every engine has an Achilles heel. In my opinion the early failure point on the DR350 tends to be the camshaft "bearings". Actually there are no real bearings as the camshaft runs in machined races in the aluminum head. I see ruined cam races more than anything else on these motors. Just finding a used head is pretty challenging and if you do find one, it's likely to be expensive because breakers know what they are worth.

As I said above I don't think it's a design deficiency. It's standard engineering practice on Japanese engines with aluminum heads. I believe it's primarily because people that the oil run low these bikes.

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TN2Wheeler you have the wiseco pistons just because you had to have replacement pistons? 

 

I think you are right this isn't an engine that has much monkey room to modifying.  If I want a more powerful bike I should buy a more powerful bike. I believe the DR350 is more than adequate for my level of daring doing and need for speed. 

 

I am going another direction with fuel injection. I got it all together but there was just something stopping it from going vroom. Got frustrated and dropped the project. Going to give it another go cuz it solves so many tuning issues and is easier to start and I got too much money and pride invested to FAIL!!!!  If I fail then back to carb.

 

This is a new carb on ebay. Thought it was interesting

 

http://www.ebay.com/itm/261390120304?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

 

My motor has 16K on it and afaik besides a small oil leak is good to go. Looking around not a lot of options like you said. All I saw was pistons, valves, valve springs ($$$$$$), gaskets, cam chain and a manual cam chain tensioner. 

 

If I wanted to freshen up what would be best to replace? 

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I chose the Wiseco piston because I needed a 1mm overbore and it was far cheaper than the Suzuki parts.

I like the reliability and field repairability of a carburetor on my off road bikes. However there is a DR650 owner who has done fuel injection on his bike. If are going to do that with the 350 you might find some useful information on his website (mxrob.com)

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I already have the fuel injection done and everything on the bike. Just need to figure out where that one (or two) gremlin is hiding.  

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I agree that you shouldnt try and push too much out of these engines.  They are reliable, but the head is the biggest problem.  Cam bearings tend to get scarred up from oil starvation.  Also, id make sure you frequently check valve clearances.  The dirt model carb is a common replacement from the stock street version carb.  If you do any work to the head, be careful to not over-trque the oil line that connect to the head on the left side, it will Crack (i know this from experience).

The dr350 is a great bike and alot of fun.

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Just picked up a 1992 Dr350 a couple weeks ago for $400. PO said he could not get it started an when he did it ran really rough. I got it running pretty quickly by going thorugh the carb and putting a new filter and the cover back on teh air box. However it sounded like either the valves were really our of adjustment or teh cam chain was loose.

 

Come to find out the exhaust rocker was worn pretty bad as part of it had gaulded to the camshaft. The cam did clean up pretty good but as I am unable to find a used rocker I am going to go ahead and replace both the cam and the rocker new.

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Mr Rocket what would cause a rocker to do that? Low oil? 

 

so far I haven't the bravery to go into this little engine. I did change the intake, heads, cams in my mustang though so maybe I will get that brave. No guts, no glory. Almost no gory either. Toss up.

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Mr Rocket what would cause a rocker to do that? Low oil? 

 

so far I haven't the bravery to go into this little engine. I did change the intake, heads, cams in my mustang though so maybe I will get that brave. No guts, no glory. Almost no gory either. Toss up.

I am uncertain as to the cause.

From what I can glean form Interweb research......

  1. oil starvaion could be one culprit.
  2. Or maybe a bad valve adjustment.
  3. And possibly an out of adjusment decopmresion lever.

All due to poor maintenance. Either way the rocker is toasted.

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I just took off the valve cover assembly to find the exact same thing. The exhaust valve worn right down on the pad. I'm debating what to replace, the single rocker at approx $50 or both rockers and a cam for around $300....

If I do end up doing the cam, does anyone know where I can get a higher performance cam?? Is the dirt model the same cam shaft??

What can we do to prevent this in the future? I've only owned the bike about 2-3 months so I don't think it was my doing that caused that. I check valves and everything as soon as I got it. I should maybe take all the oil lines of and give all them a good cleaning and reseal them cause they all seem to weep a bit around the bolts.

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