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Author Topic: Carb Swaps on LTR450  (Read 1290 times)

Offline PCS

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Carb Swaps on LTR450
« on: October 22, 2012, 10:38:41 pm »
I was going to add some info here on my brain child idea I had about a carb swap to an LTR450. First off why a carb swap at all? if you could try to make as much of the variable the same between the 2, F.I. would perform better for a few reasons. it is less susceptible to changes in weather and elevation. once dial in for your setup it will work well in a much larger range of ambient conditions. 2nd, the angle at which you can mount a FI set up is greater, with carbs, you a limited by the angle the floats are. since LTR's have a down port head similar to a sport bike, typical carbs will not work unless you make a manifold the levels the carb at the expense of chocking the intake port bc you are adding a kink in the intake track. therefore all of the carb swaps up to this point that I could find were all using FCR carbs that came from either a crf 450 dirt bike or from a yfz or yz 450. the make bore is 44mm, but to add all the extra goodies to the carb plus the labor was >$500 plus the price of the carb. on the plus side, carbs are easier to fix in the middle of the desert and dont require a super clean work area and do not require a laptop to make adjustments, not a big deal to me when the atv is at my house but out at the dunes, if something acts up I am most likely done riding. so to me the carb is more reliable. since the ltr has a head similar to a sport bike, I started to look at what that crowd does to increase their performance. I found that the Hayabusa crowd will swap in down draft lectron carbs that can be mounted at a very steep angle so that the motor can still benefit from a down port design of the head. this is done when they have exceeded the flow capacity of the the stock TBs that cant be bored out any larger. so that gave me the idea of running one Hayabusa carb on my LTR suzuki quadracer to my knowledge and according to lectron, no one has attempted this idea. probably since the LTR is the only 4 poke atv with that type of head design and not many people competitively drag race LTRs in the first place.
One of the pics compares a dummy 44mm lectron to a 45mm bored stock LTR tb. the other pics show a 46mm lectron that I am running with other add on to better help with my set up, larger fuel bowl, different floats, adjustable power jet. also, the carb was shorten about 0.500" inchs the engine side and the front lower lip of the bowl was shaven down a bit. I gained about 8 hp to the wheel with the swap over the bored tb before my head gasket popped last time on the Dyno. their were a few obstacles that I had to overcome to get the idea to work that I will cover once I get the pics uploaded to the computer.
1985 Yamaha Tri Z 250
2006 Suzuki LTR 450
2011 Suzuki Hayabusa

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Offline Mitch Keller

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Re: Carb Swaps on LTR450
« Reply #1 on: October 22, 2012, 10:57:07 pm »
 #1> How long have you been running this system?
F Mitch Keller

Offline PCS

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Re: Carb Swaps on LTR450
« Reply #2 on: October 23, 2012, 01:01:47 pm »
had it on completed earlier this spring, however the head gasket popped on jerrys dyno. the ltr has taken a backseat to my hayabusa and other projects around my place.  should have it back together this week.
1985 Yamaha Tri Z 250
2006 Suzuki LTR 450
2011 Suzuki Hayabusa

Offline PCS

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Re: Carb Swaps on LTR450
« Reply #3 on: October 25, 2012, 08:42:57 pm »
Some of the hurdles I had to deal with were the rear shock, the thumb throttle, the manifold, ignition coil, fuel lines, and intake tube.
The rear shock resi normally sits under the throttle body, so that is in the way of the fuel bowl. And I can't turn it 180 degrees because the shock adjuster will then hit the exhaust pipe. It would work if I ran an out of frame pipe. You can run a remote resi or i just switch to a Marvin Shaw shock.
The stock thumb throttle had to be cut and modded to allow the lever to fully open the slide, im running one from my Honda 200x that I cut the inside stop and a small notch on the side to have enough lever pull. Not an issue if you run a small carb.
The stock manifold was shortened and I made the inside diameter about 2mm larger to fit the carb. An FCR carb will just slide in however.
The coil was relocated to the front of the motor instead being mounted on the right side motor mount for clearance.
The last issue was the fuel lines. First, I had to plug all the vents that are used for the fuel pump. The stock systems continuously recirculates fuel through the pump to keep it cool and reduce chance of vapor lock. Also, the shut off valve is built in to the filter housing so i had to use a universal fuel shut off and a pancake style fuel filter.
The KMS intake I was using did not fit the carb so i had to get el diablo help fab one up with mix match parts from cars. I used an intake tube reducer for a Honda Civic that mounts an aftermarket tube to the tb, in my case the tube to the carb. The tube is a shortened intake tube from my 4.6L Mustang GT, the filter is for a 4 cylinder turbo audi K&N intake kit.
1985 Yamaha Tri Z 250
2006 Suzuki LTR 450
2011 Suzuki Hayabusa

Offline El Diablo

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Re: Carb Swaps on LTR450
« Reply #4 on: October 25, 2012, 09:55:26 pm »
I'm glad to see you are making progress with the bike. It definately has come a long way from when you first got it. A lot of guys like the LTR for motorcross but you rarely see them competitive in the sand drags or hillshoot events. It's good to see your bike doing what it does.
Brian
1988 Suzuki LT-250R (The HPR test mule)
1987 Suzuki LT-500R
1990 Suzuki LT-500R
1982 Honda ATC-185S
1982 Honda ATC-250R

Offline PCS

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Re: Carb Swaps on LTR450
« Reply #5 on: October 27, 2012, 07:04:58 pm »
i think we rarely see any quad racers period.  we have to represent.
1985 Yamaha Tri Z 250
2006 Suzuki LTR 450
2011 Suzuki Hayabusa

 

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