Suzuki Quadracer HQ
LT250R Quadracer => LT250R - Engine => Topic started by: Dimsi on November 12, 2013, 10:11:23 am
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Considering that the inlet diameter for the boyesen reed cage is 35mm, would you see any benefit from having a carburetor that is any bigger (36-39mm)? The way I see it is, you still have a 35mm bottleneck impeding your airflow at high RPM, and a decreased airflow velocity in the wider carb's venturi hurting your low RPM performance. Yet, a lot of ppl go big on the carb size (myself included). What am I missing? Are there other reeds with larger inlets?
Any point between the carburetor and the reeds that is smaller than the carb will make the engine think that the carb is the size of the restricted area. Large carbs on restricted manifolds or reeds can make carburetor tuning difficult or make the carburetor very temperamental to temperature and altitude changes.
The intake manifold is the most common area of neglect by the aftermarket carburetor sellers. The majority of the engines I modify have big carbs with stock intake manifolds. Most stock intake manifolds were made for the stock carbs and restrict the flow of the larger carbs. The transition shape from the carb to the reeds is important. When the shape is not right a larger carb may not make any more power than a stock carb.
Putting the correct exhaust system on your engine will have a much more dramatic effect on you low end power or shape of the power curve than carburetor size.
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Yep, sounds like too much trouble messing with the reeds. I'm confused what you meant by boring the carb to 36mm, mine is 39 and I am thinking of swapping it for a smaller one.
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You are better off staying with the rad valve for that situation. Based on your power range specified, riding requirements and the fact you already have it. Boring your carb to a 36 would be good, if the diameter of the rad valve is a little larger but not necessary. I have one I can measure as I don't remember rite off. I had to do a lot of work on the last rad valve we used to get it to work well with a 39. Pwk to the point I wished I had a 5axis CNC mill. So I could copy it. It s doable to make them run good takes a couple hours of porting and in the end if your looking for mid top still maybe better off with a billet manifold for straight 87-90 setups with airbox or Zilla manifold on a 91-92. The Zilla manifold turns the carb and is fine if you run open filter.
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i have a pwk(or pj.let me check) 36mm if you want to buy it . pm me .
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What is the inside diameter on the zilla reed inlet? And the other reeds you guys suggested?
What I am looking for is more low and mid rpm range power, since I do more trails then anything else. I don't race, this quad is just for fun so I am looking for reliability while also taking advantage of what I currently have. I just resleeved it to stock 67mm; It already has a port job done, according to the shop that resleeved it but have no idea of the specifics; FMF Fatty gold and PWK39mm. I can't make up my mind about whats better - larger reeds or smaller carb :-\
How would the stock TM34 compare with a stock PWK 36mm from a kx125, for example? Would that even come close to being the ideal carb for my set up? Also, can I assume that all PWK carbs are universal as long as the jetting is right?
Thanks for all your help guys, this is my first toy ever so I am pretty new to all of this, and it can get frustrating with all the things I still need to learn. Appreciate all of your help. (Y)
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The stock tm34 works great on most 250's, Once you get into porting, v2 reeds and a SCP pipe, a stock vm34 bored to 37mm works really good.
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i agree with ice with rad reeds peforming well in that rpm range, so if that is what you want then you should be fine. IMO i would ditch the rad reeds and go with vforce but that is because they suit my riding style.
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sounds like you need to change your intake boot to a billet one or one from a zilla
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yeah, I thought the 39mm I have now might be an overkill. Are all 36mm keihin carbs basically the same? If so I might pick one up from ebay and go from there.
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You are correct the carb should be the restriction not the flange. You lose velocity when you are set up like that. They can be ported to work better and have more throttle response. The rad valve is a midrange setup should be used with a 32-36 carb for best results unless worked over then they can be good with a 39.
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Have you noticed any changes as far as performance? Low rpm and high rpm?
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i switch the stock mikuni tm 36 to a tmx 38, the tmx it is not only lager, it also a better carburetor.
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Considering that the inlet diameter for the boyesen reed cage is 35mm, would you see any benefit from having a carburetor that is any bigger (36-39mm)? The way I see it is, you still have a 35mm bottleneck impeding your airflow at high RPM, and a decreased airflow velocity in the wider carb's venturi hurting your low RPM performance. Yet, a lot of ppl go big on the carb size (myself included). What am I missing? Are there other reeds with larger inlets?