DR350 Thread

[visovm]

Thanks a lot DR350 people!

To add some comments:
I got this bike from a gentleman in PA who was from somewhere in the area of the Rockeys, so I could see how he could have gotten a CA model bike. Now I have it on the opposite side of the USA.

The original air box was cut open and the carb bad a 130 something main jet in it (but nothing else different like pilot jets, needle, etc.) I think whoever did the work only did half the job and never got the carb really working well with the air box cut. He gave me all the parts which included about 4 other main jets, one of which was the stock main jet.

I have an airbox off a 1999 street model that im changing out. (with the rubber boot from my X model since the carb intake is a different size on the BST33). This way I will have all the stock jets, needles, airbox, filter, exhaust etc. on the bike. I will ride it for a little and make sure its working properly before I decide to do anything. Of course the cap was removed from the idle mixture screw when I got the bike, so i assume it was fiddled with. Thats why i was asking for a base point to start with.

It sounds like 2 turns out from seated is a place to start and than mess with it once the bike has warmed up to operating temp.

As for modifications. I would rather do some cheap mods to the BST33 that I have now...but try to do it the right way.
It sounds like jetting may be the best alternative. I am not too concerned with gas mileage since I only use it in the woods and never go too far from the launch point.

I am waiting on come hardware parts and some carb seals to get the thing back together and working properly (the idle needed seal was torn and may have been part of the problem with poor operation)

So you all have some time to weigh in and discuss.
Thanks again!

[visovm]

Here is the page from the service manual that shows the difference between the two dirt model carbs for 1999



I thought this would be helpful for reference. And notice the idel screw is preset on my carb, thats why i am asking for some settings to start with since I have no idea where it was set from the factory. i have the extended screw so adjustments should not be too hard.

[Zane Neher]

Here's a couple pics of my carb I was asking about earlier.

Hopefully they help.

[motolab]

Originally Posted by jmderyke

Then when the bike is warm adjust it, so if the engine idle goes up it likes it and then turn the idle knob down, ajust the a/f screw to best running conditions.

Usually CA model carbs have the air/fuel screw blocked off so you cant adjust it, nothing a drill cant fix lol

The most proper way to refer to the idle mixture screw (aka pilot screw) on a BST carb is as a fuel screw, as it does not adjust air and fuel simultaneously. There are things called air screws on carbs where you adjust the idle mixture by changing the quantity of air being bled into the pilot circuit. The reason this is important is that a fuel screw makes the idle mixture richer by screwing out and leaner by screwing in, whereas an air screw makes the idle mixture richer by screwing in, and leaner by screwing out. Fuel screws are usually on the downstream side of the slide, and air screws are usually on the upstream side (although I have seen occasional exceptions).

Regards,

Derek

[motolab]

Originally Posted by visovm

Or would it be better to do similar mods at the BST40 (spacer under needle, adjust idle screw, slide drilled) to get better throttle response?

As shimming the needle clip preloads the slide spring beyond standard, it results in lowering the slide rather than raising the needle (except when the slide is against the stops). I would not shim the needle clip unless the goal is actually to lower the slide for a given intersection of throttle angle and rpm. Note that the additional preload from shimming the needle will also make the slide come off the stop at a later point in terms of rpm and throttle position (i.e. more velocity will be required to get it to come up off of the stop).

BST carbs have slide guide, emulsion tube, slide and jet needle wear issues that are exacerbated by the enlargement of slide lift hole area. I'm also not convinced that there is any performance benefit to be had from slide drilling. In fact, dyno testing I did on a BST40 equipped KTM made made the following gains from going from the double lift hole KTM slide to a single lift-hole DR650 slide:

WOT from 4K up, with a max gain of 1.3 HP at 7K rpm.

Across the entire range at 1/4 opening, with a max gain in torque of 1.4 ft-lbs at 3K rpm.

Across the board at 1/8 opening, with a max gain in torque of 2.6 ft-lbs at 2K rpm, along with the usable rev range extended from 3.4K to 5K rpm.

Across the board at 1/16 opening, with a max gain in torque of 1.2 ft-lbs at 2.5K rpm, along with the usable rev range extended from 2.5K to 3K rpm.

Regards,

Derek

[2bold2getold]

Originally Posted by motolab

As shimming the needle clip preloads the slide spring beyond standard, it results in lowering the slide rather than raising the needle (except when the slide is against the stops). I would not shim the needle clip unless the goal is actually to lower the slide for a given intersection of throttle angle and rpm. Note that the additional preload from shimming the needle will also make the slide come off the stop at a later point in terms of rpm and throttle position (i.e. more velocity will be required to get it to come up off of the stop).

BST carbs have slide guide, emulsion tube, slide and jet needle wear issues that are exacerbated by the enlargement of slide lift hole area. I'm also not convinced that there is any performance benefit to be had from slide drilling. In fact, dyno testing I did on a BST40 equipped KTM made made the following gains from going from the double lift hole KTM slide to a single lift-hole DR650 slide:

WOT from 4K up, with a max gain of 1.3 HP at 7K rpm.

Across the entire range at 1/4 opening, with a max gain in torque of 1.4 ft-lbs at 3K rpm.

Across the board at 1/8 opening, with a max gain in torque of 2.6 ft-lbs at 2K rpm, along with the usable rev range extended from 3.4K to 5K rpm.

Across the board at 1/16 opening, with a max gain in torque of 1.2 ft-lbs at 2.5K rpm, along with the usable rev range extended from 2.5K to 3K rpm.

Regards,

Derek

Wow, guess I'm really confused. It appears to me there is a small, brass, removable air jet in the throat of the carb on the air cleaner side. It's drilling traces back to a junction with the fuel from the idle fuel jet in the bowl where air and the fuel mix and then their volume is controlled by the air fuel screw. So it looks like there is at least some air fuel mix before the idle air/fuel adjustment screw. Had a friends DRZ run me around in circles for half a day before I found that stopped up idle air jet. He let it set up for a while. Ran really bad. And the tiny (#10 I think) washers that are used to space the needles up are of a small enough outside diameter (same as that little plastic spacer thingy) to not effect the diaphram spring preload. They raise the needle just like moving the clip down on an adjustable needle. At least not the ones that come in those jet kits you can buy. Don't know why anyone would spend $70+ for one of those jet kits for $20 or $30 worth of jets and a couple of washers. As far as drilling the slides and cutting the springs goes, it looks like you might want to be real carefull there. Lots of variables involved there. My FZ1 came with one of those "Jet Kits" when I bought it from the PO. They had it all screwed up. Main jets in the choke/start jet spots, etc. Had to take it all apart and redo everything. When I asked the PO about it he said he took it to the dealer to have the jet kit installed. Hard to believe a real mechanic could mess up like that.

[jmderyke]

Originally Posted by motolab

The most proper way to refer to the idle mixture screw (aka pilot screw) on a BST carb is as a fuel screw, as it does not adjust air and fuel simultaneously. There are things called air screws on carbs where you adjust the idle mixture by changing the quantity of air being bled into the pilot circuit. The reason this is important is that a fuel screw makes the idle mixture richer by screwing out and leaner by screwing in, whereas an air screw makes the idle mixture richer by screwing in, and leaner by screwing out. Fuel screws are usually on the downstream side of the slide, and air screws are usually on the upstream side (although I have seen occasional exceptions).

Regards,

Derek

Didnt know anyone could be so picky about idle mixture screws names

[motolab]

Originally Posted by 2bold2getold

It appears to me there is a small, brass, removable air jet in the throat of the carb on the air cleaner side. It's drilling traces back to a junction with the fuel from the idle fuel jet in the bowl where air and the fuel mix and then their volume is controlled by the air fuel screw. So it looks like there is at least some air fuel mix before the idle air/fuel adjustment screw.

It does not matter whether there is some air mixed with the fuel before it reaches the fuel screw. It still controls the mixture by adding or subtracting fuel.

And the tiny (#10 I think) washers that are used to space the needles up are of a small enough outside diameter (same as that little plastic spacer thingy) to not effect the diaphram spring preload. They raise the needle just like moving the clip down on an adjustable needle.

Since the parts order is slide, small white spacer, clip, spring seat, and then spring, and the spring seat bottoms on the clip and not on the slide, a small washer will indeed increase the preload. To prove it, I took a .020" thick by .195" OD washer and put it under the clip, and then measured the distance from the top of the slide's spring well to the spring seat, and that distance was .020" less than without the washer installed.

Regards,

Derek

[2bold2getold]

You may be right about the slide spring preload, but not sure how much .020" more compression makes on these 20+ year old springs. I see what you're saying about throttle rotation and slide height. Maybe thats why all these jet kits say to cut off some of the spring after shimming the needles. Still seems kind of hit or miss to me. It would take a lot of equipment to determine if those kind of changes made significant improvements. I think it's hard to beat the factory guys with their budget and testing. I wouldn't do any of it on my DR350. Mine is bone stock and runs great. ..... And just wanted to illustrate idle concerns can be connected to the idle air jet as well as the fuel jet.

[mustangwagz]

Got them there DR350 Crash bars i ordered via ebay, Imma see if my buddy can replicate them just for the heck of it. Ill let yinz know. THEN ill get pictures n stuff! man they look awesome, and will fit flawlessly! Someone put some time into them!

[motolab]

Originally Posted by 2bold2getold

You may be right about the slide spring preload, but not sure how much .020" more compression makes on these 20+ year old springs.

How old the spring is makes no difference to the fact that shimming the needle will increase the preload on the spring, and, except when the slide is at either stop, will richen the mixture by lowering the slide rather than by raising the needle.

I see what you're saying about throttle rotation and slide height. Maybe thats why all these jet kits say to cut off some of the spring after shimming the needles.

Doubtful for two reasons. One, most jet kits include an adjustable needle (otherwise, why buy one at all?). Two, while clipping the spring does reduce the preload, it also increases the rate.

It would take a lot of equipment to determine if those kind of changes made significant improvements.

I use a 5-gas EGA equipped eddy current brake dynamometer for this purpose.

I think it's hard to beat the factory guys with their budget and testing.

It depends on how you define "beat".

I wouldn't do any of it on my DR350.

Definitely understandable.

Mine is bone stock and runs great.

Not to say that it doesn't, and I might well agree with you, but in my experience, there seem to be varying definitions of the word "great".

And just wanted to illustrate idle concerns can be connected to the idle air jet as well as the fuel jet.

10-4.

Regards,

Derek

[TopDeadCenter]

Got my 350 fired for the first time today. Started pretty easy after the carb got fuel and the rings got a little oil.

One thing really troubles me. I did an oil and filter change. I added one quart and a majority of the second. Fired it up and let it get warmish then checked the level. No oil on the dipstick. Added the remaining oil in the second quart. Repeated the level check proceedure and there is still nothing on the dipstick. I've got two quarts in and it's not registering anything. I never even had to wipe the dipstick. Bone dry.

What am I missing?

TDC

[visovm]

Wow, lots of great carb information here, I think I have digested most of it.

With regards to the "pilot screw" I will call it that from now on since that is what its called in the service manual. The consensus seems to be to start with 2-turns out and than adjust from there once the bike is warmed up.

As for the carb mods:
If you look back at my previous pictures you can see that the slide is already drilled with one hole on either side of the needle. I believe this is how the carb came stock, but for reference the top of the slide looks like this:



If anyone thinks otherwise than please let me know.

As far as I can tell it does not look like the needle was ever shimmed with washers and the spring does not appear to be trimmed. Judging from the responses I should leave it this way.

Likewise, the best way to improve performance and throttle response would be to get a jet kit or spring for the TM33 carb, instead of fiddling with shims, and trimming of the spring.

Thanks again for the explanations of the BST carb mods. I think I am finally beginning to understand how all the components work together.

[plugeye]

Originally Posted by TopDeadCenter

Got my 350 fired for the first time today. Started pretty easy after the carb got fuel and the rings got a little oil.

One thing really troubles me. I did an oil and filter change. I added one quart and a majority of the second. Fired it up and let it get warmish then checked the level. No oil on the dipstick. Added the remaining oil in the second quart. Repeated the level check proceedure and there is still nothing on the dipstick. I've got two quarts in and it's not registering anything. I never even had to wipe the dipstick. Bone dry.

What am I missing?

TDC

you need to ride it with some rpms for a bit.
in my exp, this motor sumps like crazy

[markk900]

Originally Posted by visovm

As far as I can tell it does not look like the needle was ever shimmed with washers and the spring does not appear to be trimmed. Judging from the responses I should leave it this way.

Likewise, the best way to improve performance and throttle response would be to get a jet kit or spring for the TM33 carb, instead of fiddling with shims, and trimming of the spring.

I think it seems pretty clear the carb you have is stock and unaltered, so now the question really is "what problem are you trying to solve"? If things are running well now then why change anything?

The discussion about the spring and needle was interesting, but instead of shimming the needle why not just order a stock one with the adjustable clip and not worry about that aspect? I'd assume that the adjustable clip will eliminate any concern over spring preload.....

Or use your already modded airbox and add the kit from Jesse @ Kientech (I have been happy with that mod, though it lowers fuel economy).

I assume that was a typo about getting a jet kit for the TM33 since you have a BST?