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Another Carb thread...(for a 350)

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OK. I have my 91 DR350S looking good now, but to be honest, I used to have a 91 DR250. Ironically, they seem to have about the same amount of get up and go on flat ground. I assume that this is mainly because of the pumper carb in the 250 giving it an edge in acceleration.

That said, I have been thinking. What kind of carbs, new or used, will fit onto a 350? Is there any year carb that would fit off a DRZ400? If it's as simple as finding a 38 or 39mm mikuni flat side TM carb, then what other bikes have these carbs so I can go junkyard and ebay searching?

I guess the easy way to start off is getting the answer to "What carb is this "pumper" carb?" I'm hoping to get a cross reference for swappable carbs out of this. 👍

--ps. please limit the comments about what is wrong with my bike now if it feels so weak. I may be exaggerating to make a point.:worthy:

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People say the DR250 makes good power, especially at higher RPM's. The DR350 will make more power but it comes on early and torque is pretty flat across the RPM range. In other words, the DR250 powerband has a "hit" and the DR350 does not. That may be part of what you feel when you ride both bikes.

Pumper carb on the 350 is a TM33SS (33mm bore). It does not really add any power to the DR350, but changes the character of the power delivery. Throttle response is instant, and it feels like a different bike. It will make a tiny bit more power due to better flow beacuse there is no throttle shaft / butterfly valve in the way. The throttle slide opens up and the entire 33mm bore is un-obstructed at full throttle. Both carbs have an internal 33mm bore.

People have put larger carbs on the DR but you will have no gain in power unless you do serious porting on the head. The stock head and camshaft are the limiting factors for the DR350. Bigger carb on the stock head is a waste of time without it.

Pics of the two carbs, vacuum BST33 on the right, TM33 pumper on the left.

bst33_and_tm33ss_b.jpg

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the dr350 has 9 1/2 to 1 comp the dr250 has 10 1/2 to 1 the rev limiter on the 350 is 9300 rpm 250 is 10,500 rpm. so the 250 makes as much power as the 350 just in diff place in power band as said.

i used a fcr 37mm mx stile on my dr 435 bigbore build and am happy with the carb so far about 150 miles of tuning and breaking in new engine.

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White Bros. sold a flatside TM34 carb as a kit for the DR350's in the past. The carb is a direct fit on the intake / airbox boots and needs a MX style single cable throttle assy. This carb makes good power on the DR (I have ridden a bike with one on it) but it has no accelerator pump. The carb is actually a two-stroke carb modified for four stroke use. Throttle slide, needle jet, jet needle, and jets are all different from stock. Even tuned perfectly, you get a big hesitation if you whack the throttle open quickly. You need to be smooth on the throttle, and the bike responds well. This kit is no longer available and trying to duplicate it will be difficult. You have many variables in tuning a carb not made for this bike that you would be better off with a brand new TM33 to begin with. The carb itself can be bought for about $230 new, and you can source the used airbox / intake boots from a dirt model DR350 yourself. This is what I did on my 1992. I did not need the spacer on the engine intake side (no e-start), so it was easy to do. Only other part needed was the dirt model throttle tube ($14) and use only the "pull" cable from the stock setup. You can get by pretty cheap doing it this way, just find the boots needed on ebay and buy the carb once you have all the parts needed for the conversion.

I would not buy a used TM33, you take a big chance as many have a worn carb body and this cannot be fixed. A carb with this kind of wear is a throw-away part.

Added pic, my friend's 1996 DR350SE with the TM34 carb on it

Image014.jpg

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gotcha. so if you had a cv carb would you not eat lunch for a month to save the money to buy the pumper carb or would you just try to tune the carb you have and make do? (once again, slight exaggeration for dramatic effect).

Oh, and if you found a 38mm carb off a bigger bore bike in decent condition for $20 or $30, would you try to tune it and make that work? Or is that overkill no matter what?

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I would like to say, I would save up for the pumper.....

I modified my CV carb by cutting the spring, drilling the slide, etc before buying the pumper. It helped, but not enough.

I then bought a used carb off ebay, a "good" deal. You guessed it, worn carb body and it would not hold a steady idle because of it. Lots of time and $$ spent for nothing. Finally I bought a new one, jetted it, and it works perfect. I should have done this from the start, but had to try tinkering with everything else first.

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What sort of wear does the carb body suffer from? I just bought a used TM33 on ebay, and am waiting for it to arrive.

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What sort of wear does the carb body suffer from? I just bought a used TM33 on ebay, and am waiting for it to arrive.

the trottle body can wear, and you can get air leakss, in other words, when you start it up the rpm's will be all over the place. TM33 is your best bet, although i've seen a tm38 on a heavly modded dr350.

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Most older pumper carbs will have wear in the throttle slide area of the carb body. Dirt and grit from a poorly maintained airfilter will cause it to wear out faster. When the carb body wears out it allows the throttle slide (when closed) to move back and forth a bit. This will allow enough air around the throttle slide to cause the idle speed to wander all over the place and never be consistent. There is no fix for this problem as the slide area on the carb is not replaceable.

Only solution is to toss it and buy a new one.

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